Digitized by the Internet Archive in 2015 https://archive.org/details/chemistryforengi02blou \ CHEMISTRY ENGINEERS AND MANUFACTURERS. A PRACTICAL TEXT-BOOK. BERTRAM BLOUNT, F.I.C., F.C.S., ASSOC.INST.C.E., CONSULTING CHEMIST TO THE CROWN AGENTS FOR THE COLONIES. A. G. BLOXAM, F.I.O., F.C.S., CONSULTING CHEMIST, HEAD OP THE CHEMISTRY DEPARTMENT, GOLDSMITHS' INSTITUTE, NEW CROSS. TKlUtb illustrations Volume II— Chemistry of Manufacturing Processes, LONDON: CHARLES GRIFFIN AND COMPANY, LIMITED; EXETER STREET, STRAND. 1896. [All Bights Reserved.] ul PKEF ACE. The sole object of the chapters comprising this volume is to give the reader a general view of the principles which underlie the several manufactures described. It is in no way intended to present such an account of details as will suffice for the student of any particular industry, as indeed must be obvious from the size of the book. The usefulness with which the authors venture to accredit their work is to be found in the fact that it seeks to expound those dominant principles which are too often hidden beneath masses of mere detail, and are consequently apt to be overlooked by the specialist in any one branch, to his detriment, in that he frequently fails to apply to his own work principles which are matters of common knowledge elsewhere. These remarks are rendered necessary by the fact that the scope and intention of the first volume of this book appear to have been occasionally misunderstood. The Bibliography, which will be found at the end of the work, will serve to indicate the sources of information which are at hand for those who desire further details on any particular subject. In this volume the authors have had the able advice of Mr. Geo. H. Hurst concerning the technique of Bleaching and Dyeing, and they take this opportunity of thanking him for his valuable assistance. London, October, 1896. 36169 CONTENTS. Sulphuric Aeid PAGE I Raw Materials for Vitriol Making— j Sulphur, . . . . 1 ' Pyrites and other Raw Materials, ... 2 Skeleton of Process of Vitriol Making, .... 2 Processes and Plant — Pyrites Burners, . . 3 Production of Sulphur Di- oxide, .... 5 ER I. Manufacture. PAGE Vitriol Chambers, . . 7 Manufacture of Nitric Acid, 8 Conversion of Sulphur Di- oxide into Sulphuric Acid, .... 11 Concentration, ... 15 Purification, ... 16 Nordhausen or Fuming Sulphuric Acid, . . 17 CHAPTER II. Manufacture of Alkali Leblanc Process — Raw Materials, . . 19 Manufacture of Salt Cake, 22 Hydrochloric Acid, . . 24 Manufacture of Black Ash, 25 Lixiviation of Black Ash, . 27 Evaporation of Tank Liquor, 28 Finishing the Soda Ash, . 29 Caustic Soda, . . .30 Commercial Standards for Trading in Alkali, . .31 Treatment of Tank Waste, 32 Chlorine and Bleaching Powder — Production of Chlorine, . 35 Manganese Recovery Pro- cess, . . . .37 and its Bye-Products. Deacon's Chlorine Process, 39 Production of Bleaching Powder, . . .40 Potassium Chlorate, . . 42 Ammonia-Soda Process — Principles and Plant, > . 43 Production and Recovery of Ammonia, ... 47 Recovery of Chlorine, . 49 Other Chemical Processes for Making Alkali- Cryolite Process, . . 51 Electrolytic Processes, . 51 Review of Alkali Manu- facture, .... 53 CHAPTER III. Destructive Distillation. General Principles, . . . 55 Destructive Distillation of Coal — Kinds of Coal, ... 56 Carbonising in Retorts for Gas Production, . . 58 The Process of Distillation, 60 Plant and Purification, . 62 Products— Gas, . . 66 Valuation and Utilisation of Coal Gas, ... 67 viii CONTENTS. PAGE Enrichment of Coal Gas, . 71 Oil Gas, .... 74 Gas Liquor, ... 75 Coal Tar, .... 76 Carbonising in Ovens for Coke Production, . . 83 Carbonising Peat, . . 87 Destructive Distillation of Wood — Burning in heaps or "meilers," ... 83 Charring in Kilns and Re- torts, .... 90 PAGE Products — Charcoal, Tar, Wood Spirit, Gas, . 91 Destructive Distillation of Shale — Pvetorts, .... 97 Products — Crude Oil or Tar, Amnion iacal Liquor, Gas, . . . .100 Destructive Distillation of Bones — Bone Charcoal, Oil, Am- monia, Gas, . . . 104 CHAPTER IV. Artificial Manure Manufacture. Phosphatic Manures — Mineral Phosphates, Super- phosphate, . . .107 Precipitated Phosphates, Basic Slag, Bones, . 109 Nitrogenous Manures — Ammonium Sulphate, Nitrate, Organic Nitro- genous Manures, . .112 Potash Manures, . . .114 General Manures — Farmyard Manure, Sewage, Guano, . . . .114 CHAPTER V. Petroleum. Origin and Distribution, . 117 Refining — Wmning of Petroleum, Trans- Products of Fractionation, 120 mission, .... 118 Ozokerite, 123 Asphaltum, 124 CHAPTER VI. Lime and Cement. Lime-burning — Portland Cement, 134 Forms of Calcium Car- Burning and Grinding bonate, .... 126 Cement Clinker, . 134 Kilns for Lime-burning, . 128 Composition and Properties Cements — of Portland Cement, 137 Mortar, Plaster of Paris, . 130 Puzzuolanic Cements, 140 Hydraulic Cements, Hy- Artificial Stone, Water draulic Lime, 132 Glass, .... 141 Roman Cement, Septaria Nodules, 133 CONTENTS. ix CHAPTER Clay Industries PAGE Clay Industries — Clays, . . . .143 Bricks and Tiles, . . 144 Porcelain,. . . . 146 Stoneware and Earthenware, 149 Glass — Raw Materials, . .150 VII. and Glass. PAGE Fusion of Raw Materials to Glass, . . . 152 Annealing and Hardening Glass, .... 156 Coloured and Opal Glass, . 158 Properties of Glass, . . 160 CHAPTER VIII. Sugar and Starch. Sucroses — Cane Sugar, Concentration, 162 Beet Sugar, Extraction and Concentration, . 165 Utilisation of Uncrystal- lised Sugar, . . .172 Osmose Process, Elution Process, Strontia Process, 173 Minor Sources of Sugar, . 176 Refining Raw Sugar, , 177 Lactose and Maltose, . 180 Glucoses — Dextrose, Starch Sugar, . 181 Lsevulose, Invert Sugar, . 182 Starch — Manufacture of Starch, . 184 Wheat Starch, Rice Starch, 185 Maize Starch, Dextrine, . 186 CHAPTER IX. Brewing* and Distilling. Fermentation — General Principles, . 189 Beer — Malt, . . . .190 Malt Adjuncts, . . 193 Hops and Bitter Principles, 194 Water for Brewing, Yeast, 194 Mashing, . . . .196 Boiling and Cooling, . 197 Fermentation of Wort. , . 199 Cleansing of the Beer, . 203 Racking and Finishing Processes, . . . 204 Wine — Grapes, .... 205 Fermentation of Grape Juice, . . . .206 Fortification of Wines, . 207 Minor Fermented Liquors, . 208 Spirit — Brandy, Whiskey, Gin, Rum, 209 Alcohol, Silent Spirit, . 215 Alcoholometry, Methylated Spirit, . . . .218 Vinegar — Slow and Quick Vinegar Processes, . . . 219 Factitious Vinegar, . . 222 X CONTENTS. CHAPTER X. Oils, Resins and Varnishes. Fats, Liquid and Solid — Constitution of Fats and Oils, Saponification, . 223 Classification of the Chief Fats and Oils, . . 226 Winning and Refining of Fats and Oils, . . 228 Properties and Uses of Fats and Oils, . . . 231 Turpentines, Resins, Caoutchouc — Turpentine, Essential Oils, 240 Resins, .... 241 Caoutchouc, Vulcanised Rubber, . . . 243 Varnishes — Oil Varnishes, . . . 245 Spirit Varnishes, . . 246 Soap- CHAPTER XL Soap and Candles. Candles — 24^ Raw Materials, Manufacture, Fitted Soap, Soft Soap, Toilet Soap, . 248 Tallow, Wax and Sperm Candles, . . . 250' Hydrolysis of Fats for Stearin Candles, . . 252 Glycerin, . . . .255 CHAPTER XII. Textiles and Bleaching". Textile Fibres — Wool, Wool Fat, York- shire Grease, . . 257 Silk, Artificial Silk, . . 259 Cotton, . . . .260 Flax, Hemp, Jute, . .261 Wood Wool and Mineral Fibres, .... Bleaching — Wool and Silk Bleaching, . Cotton, Linen, and Jute Bleaching, . . . 265 CHAPTER XIII. Colouring Matters, Dyeing and Printing. General Principles — Dyestuffs defined, Theory of Dyeing, . Colouring Matters — Organic Synthetic Dyestuffs — Nitro-compounds, Azo-compounds, Quinone Derivatives, Ali- 270 273 273 278 262 264 Triphenyl methane deriva- tives, Nitrobenzene, Ani- line, Magenta, . . "203 Phthalein Dyestuffs, . 292 Azine Compounds, Mag- dala Red, Mauveine, Quinonoximcs, Indamincs, 302 Dyestuffs containing Sul- phur, Methylene Blue, . 3 V 1 CONTENTS. XI PAGE Oxazine Colouring Matters — Auramine, Tartrazines, 307 Aniline Black, Indulines, Safranines, . . .311 Quinoline Derivatives, . 316 Natural Organic Dyes tuffs — Indigo, Artificial Indigo, . 319 Dyewoods, Logwood, Brazil Wood, Fustic, . 324 Lichen Colouring Matters, Litmus, . . .326 Cochineal, Lac Dye, . 327 Mineral Dyes — Chrome Yellow, Man- ganese Brown, Prussian Blue, . . . .328 l'AOK Dyeing and Mordants — General Principles, . . 329 Mordants, Basic Mordants, Acid Mordants, . . 330 Cotton Dyeing, . . 333 Wool Dyeing, . . . 335 Silk Dyeing, . . . 338 Jute Dyeing, . . . 339 Printing — Cotton Printing ; Steam, Pigment, Dyeing, Dis- charge and Resist Styles, 340 Wool Printing, . . 342 Water for Dyeing, . . 343 CHAPTER XIV. Paper and Pasteboard. Raw Materials — Rags, Esparto, Wood, . 344 Manufacture of Paper Pulp — Esparto Boiling, Recovery of Alkali, . . . 345 Mechanical and Chemical W^oodPulp, . 347 Mineral Pigment ments — White Lead, Dutch, Ger- man and Precipitation Processes of Manufacture Zinc White, Barytes, CHAPTER XV Pigments White Pig- 149 Whiting, 353 Blue Pigments — Ultramarine, 354 Prussian Blue, . 356 Smalt, Cobalt Blue, . 357 Green Pigments — Brunswick Green, 358 Chromium Greens, Copper Greens, Rinmann's Green, 359 and Paints. Yellow Pigments- Chrome Yellow, Cadmium Yellow, King's Yellow, Red Pigments — Red Lead, Vermilion, Antimony Ver- milion, .... Iron Pigments — Red Oxide, Ochres, Siennas, Umbers, . Organic Pigments — Lampblack, Boneand Ivory Black, .... Cochineal Carmine, Sepia, Paints and Vehicles, 360 361 361 362 303 364 365 366 xii CONTENTS. CHAPTER XVI. Manufacture of Leather, Glue and Size. PAGE Leather — Raw Materials — Hides and Skins, . . 367 Water, . . . .372 Tanstuffs, Tannic Acid, . 373 Preparatory Processes — Cleansing and Softening, . 3S1 Unhairing, . . . 382 Softening Processes, . 384 Tanning Processes — Tanning with Tanstuffs, Sole Leather, Dressing Leather, Dyeing Leather, 386 Acids— Hydrofluoric Acid, . .413 Boric Acid and Borax, . 414 Arsenic Acid, . . .415 Oxalic and Lactic Acids, . 416 Tartaric and Citric Acids, 418 Benzoic Acid, Salicylic Acid, Saccharine, . 419 Salts— Chromates and Bichromates, 420 Manganates and Perman- ganates, . . . 422 Sulphates, Copper Sulphate, Copperas, Alum, . . 423 PAGE Tanning with Mineral Salts, Alum Tanning, Chrome Tanning, Iron Tanning, . . . 3S9 Tanning with Oils, Wash Leather, . . .391 Finishing Processes — Finishing Sole Leather, . 392 Currying, Russia Leather, Patent Leather, . . 393 Theory of Tanning, . . . 394 Gelatine, Glue and Size, . . 395 405 407 408 410 411 Potash Salts, . . . 426 Strontium Salts, . .429 Halogens — Bromine, Iodine, Potas- sium Iodide, . . .43 Cyanogen Compounds — Potassium Cyanide, Prussiate of Potash, Sulphocyanides, . . 432 Solvents — Carbon Bisulphide, Carbon Tetrachloride, . . 434 CHAPTER XVII. Explosives — General Principles, . Gunpowder, Kitre, . Nitro-Explosives (High Explosives), Gun-cotton Nitroglycerin Explosives, Manufacture of Nitro- glycerin, Dynamite, Explosives and Matches. Blasting Gelatine, 398 Cordite, 400 Other Nitro-explosives, Matches — 403 Phosphorus Manufacture, Red Phosphorus, Match Compositions, CHAPTER XVIII. Minor Chemical Manufactures. CHEMISTET FOR ENGINEERS AND MANUFACTURERS. VOL. II. THE CHEMISTRY OF MANUFACTURING PROCESSES. CHAPTER I. SULPHURIC ACID MANUFACTURE. RAW MATERIALS FOR VITRIOL MAKING. Sulphur. — Native sulphur occurs in rocky deposits of volcanic districts, notably in Sicily; it averages 20 per cent, of the total rock, but may reach as high a proportion as 80 per cent. It is obtained (1) either by a crude liquation process, consisting in igniting a heap of the rock (calcarone), and collecting that portion of sulphur which escapes combustion and flows out, or by melting out the sulphur (in the case of rich materials) by heating it in closed vessels by extraneous fuel ; (2) by distilling the ore in iron retorts set obliquely ; (3) by systematic extraction with carbon bisulphide, and subsequent distillation of the solvent. The nature of the apparatus for the third method may be gathered from the figure of an oil extractor (see Oils, Yol. II., Chap. X.); the pro- cess is also used for obtaining sulphur from gas-purifying masses (see Destructive distillation, Yol. II., Chap. III.). Sulphur is obtained in small quantity by the distillation of pyrites, FeS 2 , which gives up rather less than half its content of sulphur. Recovered sulphur from alkali waste and gas liquor is dealt with under the corresponding heads. Sulphur is put upon the market in the refined state, the refining being simply a process of distillation ; the rapidly cooled 1 2 SULPHURIC ACID MANUFACTURE. vapour (yielding the insoluble modification) is sold as flowers of sulphur. When cast into sticks, it is known as " roll brimstone." Pyrites is by far the most important source of sulphur for vitriol making ; commercial grades contain about 50 per cent, of sulphur. Smalls are simply the broken fragments of pyrites, and need no separate comment. Gas purifier mass [spent oxide) may contain 40 to 50 per cent, of sulphur, and thus ranks with pyrites smalls. Nitrate of soda is sufficiently dealt with under Artificial manures (Vol. II., Chap. IY. ). Air and water are the other raw materials for vitriol manu- facture. SKELETON OF PROCESS OF VITRIOL MAKING. In order to make clear the details of manufacture described below, the following outline of the process of vitriol making, as usually carried out, may be here given. The sulphur in either of the forms used in practice (viz., pyrites, spent oxide, or elementary sulphur) is burnt in a kiln by the heat of its own combustion, and the sulphur dioxide, mixed with air, and nitrogen corresponding with the oxygen used in the combustion of the sulphur, meets nitric acid vapour, generated as described below, and immediately reacts with it, liberating oxides of nitrogen. This mixture of gases passes into leaden chambers where it meets with steam ; a re- action resulting in the formation of dilute sulphuric acid occurs, in which all the constituents, save the nitrogen, are concerned. The latter gas has to be removed from the chambers by a draught, and in order to avoid the carrying away of the oxides of nitrogen, which, although taking part in the reaction, are regenerated in the course of it, a column — the Gay-Lussac tower — down which strong sulphuric acid trickles, is interposed between the chambers and the chimney. The oxides of nitrogen are absorbed by this sulphuric acid, and are re-introduced into the sphere of reaction in the leaden chambers by being expelled from the sulphuric acid by the heat of the gases from the pyrites kiln, which gases are caused to ascend the tower — the Glover tower — placed between the pyrites kiln and the leaden chambers ; the sulphuric acid, containing oxides of nitrogen, from the Gay- Lussac tower, is allowed to trickle down this column, the oxides of nitrogen being driven off and carried into the first chamber. PROCESSES AND PLANT. — For the production of the sulphur dioxide some furnace is necessary for burning the pyrites, sulphur, or other sulphur-containing material. The con- struction of this differs somewhat with the nature of the material to be burnt. Pyrites burners are of two forms — (1) burners for lump pyrites, and (2) burners for " smalls." These two are re- PYRITES BUHNERS. 3 quired, because in the crushing of pyrites, as mined, both lumps and dust ("smalls") are produced, which, if burnt together, would form an impervious layer, greatly impeding the proper admission of air. Burners for lump pyrites consist of fire- brick chambers, A (Fig. 1), about 6 ft. x 5 x 4 ft., with slightly sloping sides, set in pairs, and provided with a grate, B, made of iron bars of square section which can be rotated at will. The pyrites rests on this grate to a depth of 2 to 3 feet, and as it burns the iron bars are rotated, allowing the burnt ore to drop out. The burners are fitted with two doors, one at the top for charging the pyrites, and a smaller one lower down for adjusting the burning charge. In burning, not only has enough air to be introduced to oxidise both sulphur and iron of the pyrites, according to the equation — 2FeS 2 + O n = Fe 3 0 3 + 4S0 2 , but also sufficient to convert S0 2 into H 2 S0 4 by the aid of the nitrous gases that act as carriers of oxygen (see p. 11). In the actual management of the burners, the two main objects to be attained are the conversion of as much of the sulphur as possible into sulphur dioxide, and the avoidance of the formation of clinker (" scars ") due to the fact that defect of air allows of the production of the fusible sulphide, FeS. This latter object is achieved by stirring the charge through the lower door. As the complete combustion of the sulphur of the pyrites in prac- tice cannot be effected without an excess of air more than enough to serve for the subsequent oxidation of S0 2 to H 2 S0 4 , the efforts of the manufacturer are directed to keeping the air supply as small as is consistent with the above conditions. It is found that the flue gases from burners using pyrites contain about 7 per cent, of S0 2 , together with some SO s resulting from the formation and subsequent decomposition of sulphates of iron in the oxidation of the pyrites, and about 10 per cent, of oxygen, which serves for the conversion of the S0 2 into H 2 S0 4 . It is not practicable to roast out the whole of the sulphur from the pyrites, the burnt residuum usually containing from 2 to 3 per cent, as basic ferric sulphate, and the sulphates of metals such as zinc and copper, the oxides of which are stronger bases than is ferric oxide. In the case of cupreous pyrites, which are burnt and returned to the copper smelter, it is not desirable to burn the whole of the sulphur, as for the extraction of copper there should be present 1 to 1 J times its weight of sulphur, unless the ore be poor in copper and intended to be extracted by the wet way, in which case roasting as completely as possible is sure to leave enough sulphur in the ore (see Copper, Vol. I., p. 165). Not only do the smaller fragments of crushed pyrites need to be burnt in furnaces different from those used for lump pyrites, but spent purifier from gas works (see Destructive distillation, Vol. 4 SULPHURIC ACID MANUFACTURE. BURNERS FOR SULPHUR. 5 II., Chap. III.) has also to be treated in a similar manner. The burner for smalls must be so arranged that the material is spread in a fairly thin layer, inasmuch as the kiln form, described above, would be speedily choked. The smalls burner is shown at C in Fig. 1. It consists of a rectangular firebrick box provided with horizontal fireclay shelves, so disposed that the smalls can be raked from one to the next below by a rake inserted through the opening. The smalls are fed in through the hopper, D, and when they have been distributed on the shelves the combustion is started by the fire on the grate, E. The smalls, when once ignited, evolve sufficient heat to maintain the combustion. When the burner is working normally, the whole of the neces- sary air is admitted through the lowest door, and the smalls are only completely burnt on reaching the lowest shelf, at which stage the burnt material contains from 1 to 2*5 per cent, of sulphur. Various mechanical burners for pyrites smalls have been devised, the object in view being to keep the pyrites stirred, and thus constantly expose fresh surfaces to oxidation, but they have not met with extended application, as they tend to clog with the fine dust. When vitriol is made from sulphur, the simplest form of burner consists of an iron tray, on which sulphur is thrown from time to time, and there volatilised and burnt. In better forms of burner, provision has to be made for the complete com- bustion of such sulphur as is sublimed. This is effected by the addition of firebrick towers into which a subsidiary supply of air is introduced to cause complete combustion. When sulphur instead of pyrites is used, the air is required to oxidise S only, and not Fe as in the latter case, whence it results that the exit gases are richer in S0 2 and poorer in N than those from pyrites burners. The difference is indicated by the fact that gases from sulphur burners contain 11 per cent, of S0 2 as compared with 7 per cent, from pyrites burners. The amount of free oxygen is about 10 per cent., the balance being of course nitrogen. Another source of S0 2 , for the manufacture of sulphuric acid, is zinc blende (see Zinc, Vol. I., p. 181), which is roasted in muffle furnaces heated by generator gases and provided with heating channels for warming the in-coming air so as to insure the com- plete oxidation of the S of the blende. In order the better to attain this end, the roasting is done systematically, the ore being transferred from one muffle to the next through a series. Sulphuretted hydrogen, such as is produced from alkali waste (see Alkali, Vol. II.) or by the neutralisation of crude ammoniacal liquor from gas works, can be burnt to S0 2 and water, and used as a raw material in the production of sulphuric acid. Sulphur dioxide is frequently made by the methods described above for producing sulphurous acid and sulphites, which are much used in paper-pulp making (q.v. Vol. II.). Where a solution of 6 SULPHURIC ACID MANUFACTURE. sulphurous acid is alone required, the kiln gases are scrubbed with a small amount of water (which soon becomes saturated), and are absorbed in cold water flowing down a coke tower. To prepare liquid S0 2 , however, it is necessary to obtain the gas free from admixed nitrogen, in order that its partial pressure may be as high as possible. For this purpose the solution of sulphurous acid in water is heated in leaden retorts, and the S0 2 thus expelled is dried by scrubbing with vitriol, and is compressed in an ordinary gas compressor, about 2*5 atmospheres being required. The liquid S0 2 is collected in iron and copper cylinders and drums, and, for small quantities, in stout glass bottles. The liquid has a specific gravity of about 1 -4, and boils under atmospheric pressure at - 10° C. = 14° F. It is used as a convenient and compact source of the gas in many industries. The chief sulphites commercially used are sodium bisulphite, NaHSOg, prepared by saturating soda crystals with S0 2 , and normal sodium sulphite, Na 2 S0 3 ,7H 2 0, which is prepared by adding sodium carbonate solution to a solution of the bisulphite. The bisulphite is the less soluble, and finds application as an antichlor. Calcium bisulphite, CaH 2 (S0 3 ) 2 , prepared similarly, is sold in solution for brewers' use as a disinfectant. In the manufacture of sulphuric acid, however the S0 2 may have been produced, it is led by a flue, F (Fig. 1), common to a set of burners, to the Glover tower (v.i.). In this flue one or more (usually two) nitre pots, G, are set. These consist of cast-iron vessels, generally cylindrical, placed in the flue beneath hoppers through which the nitre (sodium nitrate) is charged in quantities of about half a cwt., sulphuric acid being introduced through S-shaped syphon tubes, which serve as traps, to decompose the nitrate and liberate nitric acid. The pots are fitted with a waste pipe, running through the wall of the flue, whereby the liquid nitre-cake (NaHS0 4 ) can be drawn off when the charge is ex- hausted. The heat of the burner gases, which have a temperature of about 300° C. = 572° F., is also sometimes utilised for con- centrating chamber acid (v.i.). Much dust is liable to be deposited in the flue, particularly when pyrites smalls and arsenical ores are burnt. Where this deposit is large, it is needful to lead the flue into a dust chamber before it enters the Glover tower. This chamber is an enlargement of the flue, provided with baffle plates, in which the rate of the current of gases is diminished, and the s stream mechanically broken up so that the dust is thrown down. In works where chamber acid alone is made, and the Glover tower dispensed with (v.i.), it is necessary to cool the burner gases before they enter the lead chambers, which is effected by greatly pro- longing the burner flue, in which case the dust deposits in this prolongation. The flue dust consists mainly of burnt ore me- chanically carried over, mixed with volatile impurities, chief among these being arsenious oxide and sulphuric acid (from the decomposition of sulphates of iron formed in roasting the pyrites). VITRIOL CHAMBERS. 7 The Glover tower, H (see Fig. 1)— the function of which, in the reactions involved in the manufacture of vitriol, will be dealt with later — is a strong structure, square or circular in section, with leaden walls lined with refractory and acid-proof firebrick, and filled with some acid- and heat-resisting material, such as flint or firebrick, arranged so as to distribute evenly liquid trickling down the tower ; it is supported on brick arches, underneath which the pyrites flue enters the tower. The upper part of the tower, where the temperature is lower, may consist, as shown in the figure, of a plate column such as that described under the head Chambers. At the top of the Glover tower is a tank containing the chamber acid and the nitrous vitriol from the Gay-Lussac tower (v.i.); this tank supplies a distributing arrangement, such as a lead or glass wheel, K, worked by the reaction of the acid flowing from its radial arms. The exit pipe, L, for the gases which ascend the tower is at the top, and is connected with the first chamber. Vitriol chambers are invariably made of lead — generally of a thickness corresponding with a weight of about 6 lbs. per square foot— and consist of rectangular " curtains" standing in "saucers " which are large, flat trays, the edges of which are turned up to a height of 1 2 to 15 inches. The sheets of lead composing the curtain, and those of which the saucers are made, are autogenously soldered (" burnt ") by means of a hydrogen flame fed with a blast of air (see Yol. I., p. 34), and are fastened to the framework of wood which supports them by lead straps — themselves "burnt" on to the lead — attached to the wood by nails coated with lead. The whole arrangement resembles a box with a loosely-fitting lid turned upside down, and is shown in section across the longer axis of each at M. The whole is gas tight, on account of the saucer containing enough acid to seal the edges of the curtain. The chamber is carried on piers to allow of inspection and repair on all sides. The space below is utilised for the pyrites burners. The number of chambers and their size vary with the practice of different works. Usually, from two to four are used, and the size varies from 100 to 130 feet x 25 to 30 feet x 16 to 20 feet in height ; it generally being supposed that about 20 to 25 cubic feet of space are required for each pound of sulphur burnt per day. The chambers are connected by lead tunnels, and the last of the series communicates with the bottom of the Gay-Lussac tower. Instead of relying on mere chamber space for the mixing and reaction of the gases, it has been proposed to use smaller chambers, and to interpose plate columns, up which the gases must pass in going from one chamber* to the next, whereby an economy of chamber space is possible. These columns consist of a lead- lined tower fitted with horizontal stoneware plates, which are perforated, each perforation having raised edges and being surrounded by ridges, so that there may be always a little pool of liquid ready to overflow and drop through the perforation on to the plate next below, which is so placed that 8 SULPHURIC ACID MANUFACTURE. the drop does not fall through a hole, but on to the surface of the plate ; the arrangement is made clear by Fig. 2. Fig. 2. — Perforated stoneware plate for plate columns. Much liquid condenses in this column, and this aids the occurrence of the reactions necessary for the preparation of sul- phuric acid, which are described below. These Lunge-Rohrmann plate columns, as they are termed, are occasionally substituted for ordinary Glover and Gay-Lussac towers. The Gay-Lussac tower, N, is arranged like the Glover tower, and is of similar dimensions, but usually somewhat higher — e.g., about 35 to 40 feet in height. A cistern at the top contains vitriol of specific gravity 1*75, which is raised to this position from the " acid egg" shown at O in Fig. 1. The method by which it is raised involves the use of no moving parts, compressed air being forced into the egg, and driving the acid up the pipe leading therefrom to the tank at the top of the Gay-Lussac tower. The acid flows from the cistern into a distributor similar to that used for the Glover tower, and already described. Where two Gay- Lussac towers are employed, the gases pass from the top of the first into the bottom of the second. In either case, a proper draught is secured by a pipe, P, running from the top of the Gay- Lussac tower to a chimney shaft. Inasmuch as the acid which has passed down the Gay-Lussac tower has to be raised to the top of the Glover tower by an acid egg like that already described, it is customary to build the towers side by side. Manufacture of Nitric Acid. — In those vitriol works in which nitric acid is used as such (v.i.), instead of being generated on the spot in nitre pots as described above, an apparatus for its produc- tion necessarily forms a part of the plant. As this is similar to the plant employed by makers of this acid for other purposes, it will be described here. In all cases, it is made by heating sodium nitrate with strong sulphuric acid in cast-iron retorts. In English works these are generally horizontal cylinders, 5 feet x 2 feet, closed at each end by a sandstone slab (Yorkshire flags), one end being permanently affixed and provided with an exit pipe for the acid vapours, the other end serving as a charging door. Nitric acid has but little action on the iron, provided it be strong ; if weak, a considerable action occurs. For this reason the whole of the retort should be kept hot to prevent the aqueous acid condensing on its upper part, a proceeding preferable to lining the upper part with firebrick, as is sometimes practised. The high temperature of the upper part of this still is secured by an appropriate setting of the cylinder in its furnace. The quantity of nitric acid obtainable MANUFACTURE OF NITRIC ACID. 9 from any given weight of sulphuric acid depends primarily upon the temperature employed. Thus, if the temperature be com- paratively low, the reaction takes place between equal molecular proportions of sodium nitrate and sulphuric acid. Thus — NaX0 3 + H 2 S0 4 = HN0 3 + NaHS0 4 , whereas when it is higher two molecules of nitric acid are liberated by one of sulphuric, 2NaN0 3 + H 2 S0 4 = 2HN0 3 + Na 2 S0 4 . In practice it is not economical to use proportions complying with either of these equations. For the first, an undue amount of sulphuric acid is needed,* and in the second case the high temperature decom- poses much of the nitric acid as soon as it is formed, and, moreover, the resulting sodium sulphate is solid, and even at high tempera- tures is difficult to remove from the retort. Furthermore, it is not customary to use the strongest commercial vitriol (specific gravity 1'84) because this has a tendency to dehydrate the nitric acid, resulting in the production of oxides of nitrogen. The sulphuric acid actually employed is often of specific gravity 1*72, and is used to the extent of about 25 per cent, in excess of that required by the second equation, given above. In this case the residue in the retort ("nitre-cake") is a mixture of Na 2 S0 4 and NaHS0 4 , and is sufficiently liquid to run out when the charge is worked off. The charge consists of one and a-half cwt. of sodium nitrate (95 per cent. NaNG 3 ) and about an equal weight of sulphuric acid of specific gravity 1 '72. The form of retort most in vogue on the Continent, is a cast-iron cylindrical pot 5 ft. by 5 ft., with a wide neck fitted with a cover, the whole being enclosed in a furnace so that condensation may not take place at any part. A tube at the bottom of the retort serves for running off the nitre-cake, and another at the shoulder as an exit for the acid vapours. The apparatus employed for condensing the acid usually consists of a number of two-necked stoneware Woulfe's bottles. The acid which condenses in the first of these is the strongest, but the most impure, containing splashings from the retort and oxides of nitrogen. That at the far end of the series contains chlorine (from the chloride present in commercial sodium nitrate), and is com- paratively weak. Any acid still uncondensed is caught in a tower or plate column, which, in the case of a plant attached to a vitriol works, is fed with sulphuric acid (specific gravity 1*75), and the resulting nitrous vitriol used in the Glover tower. Otherwise the tower is fed with water. The crude nitric acid when first con- densed is red from the presence of oxides of nitrogen. For some industries this is an advantage, and indeed a so-called "nitrous * In soda works ample vitriol can be used with economy, for the residue of the nitric acid still goes to the salt-cake furnace, and is there utilised to the full. 10 SULPHURIC ACID MANUFACTURE. acid" is made by the addition of reducing substances— e.g., starch and sulphur — to the charge. Where a colourless acid is required, however, the red acid is " bleached " by warming and blowing air through it, the gases evolved being caught in the tower mentioned above. When the acid is used in vitriol works, this refining is unnecessary. The condensing process just described has several defects — e.g., the liability to fracture of the condensing pots, and the contamina- tion of a great part of the acid with oxides of nitrogen. Moreover, the distillation takes place slowly, and the yield of strong acid falls considerably below the theoretical limit, owing to Fig. 3. — Nitric acid still and condensers. the fact that the acid is not collected fractionally. These difficulties are said to be overcome by Guttmann's method of condensation. His condensers (see Fig. 3) consist of pairs of stoneware pipes, A, A, A, very thin in the walls, to aid condensation, and connected at the top by Q bends, and inserted at the bottom into a receiving pipe, B, with diaphragms between the legs of each bend, so that the condensed acid collects and can be drawn off out of contact with the still uncondensed gases. The final exit gases are caught in a plate tower. The system is said to be particularly adapted for the manufacture of the strongest nitric acid, free from oxides of nitrogen, such as that required for the manufacture of explosives. REACTIONS IN THE VITRIOL CHAMBERS. 11 Several grades of nitric acid are prepared for industrial use. Common aqua fortis is a dilute acid, and of specific gravity 1'3 ; it contains about 45 per cent, of HN0 3 . It is used for parting gold and silver, for preparing silver nitrate and for pickling metal goods. A stronger acid, of specific gravity 142, containing 69 per cent. HN0 3 , is also employed for similar purposes. This corre- sponds with the hydrate 2HN0 3 ,3H 2 0, and distils unchanged at 120° C. = 248° F. at ordinary atmospheric pressure. A stronger acid of specific gravity 1*5, containing 92 per cent, of HN0 3 , is also prepared, and is employed lor nitration (see Explosives^ ol. II., Chap. XVII.). This acid boils at 86° C. = 187° F. with partial decomposition into water, oxygen, and oxides of nitrogen, so that it cannot be distilled unchanged at the ordinary pressure. The chief impurities in nitric acid, as commonly made, are sulphuric acid and sodium sulphate, chlorine, oxides of nitrogen, iodic acid and perchloric acid (from iodate and perchlorate in the sodium nitrate), and iron. Conversion of S0 2 into H 2 S0 4 . — The S0 2 , produced as already described in the pyrites burners, passes into the Glover tower in company with nitric acid vapour from the nitre pots, and sufficient oxygen (derived from the excess of air necessary to burn the pyrites). The reaction of S0 2 with nitric acid takes place according to the following equation : — 2S0 2 + 2HN0 3 + H 2 0 - 2H 2 S0 4 + N 3 0 3 .* The reactions that occur in the Glover tower will be appreciated later, and will be referred to again. As soon as the gases, consisting of S0 2 , air, and N 2 0 3 , reach the chambers, they come in contact with steam, which is injected by the jets (R, Fig. 1) supplied from a boiler. When fuel is dear, water-sprays forced under pressure through platinum nozzles on to a platinum button, so as to " pulverise " the jet, have been used, but are liable to the objections that they cool the chambers below 40° C. = 104° F. — the minimum temperature for satisfactory working — and neither aid the draught nor promote the mixing of the chamber gases. The most probable explanation of the formation of sulphuric acid from these gases, and of the way in which the oxide of nitrogen serves as a carrier of atmospheric oxygen to the S0 2 is, that the S0 2 , N 2 0 3 , O, and H 2 0 combine to form nitrosyl- sulphuric acid, according to the equation — 2S0 2 + N 2 0 3 + 0 2 + H 2 0 =2S0 2 {g^ 0) . * It is stated by Ramsay that N 2 0 3 can only exist in the liquid state, and becomes NO + N0 2 on evaporation. In this case, it could not be liberated under the conditions obtaining in vitriol making ; the equation must, therefore, be modified thus — 3S0 2 + 2HN0 3 + 2H 2 0 = 3H 2 S0 4 + 2NO. Corresponding alternative equations will be quoted for the reactions taking place at other stages of the process. 12 SULPHURIC ACID MANUFACTURE. The substance thus produced may be regarded as sulphuric acid in which an atom of hydrogen of one of the hydroxyl groups has been replaced by the radicle (NO). In the event of the atmosphere of the chambers being unduly dry, nitrosyl-sulphuric acid may be actually deposited as a white mass (" chamber crystals "). In contact with more water, however, it splits up thus — 2S0 2 (OH)(N0 2 ) + H 2 0 = 2H 2 S0 4 + N 2 0 3 , the cycle of changes being then repeated. * It must not be supposed that the reactions in the vitriol chamber constitute such a regular cycle as has been indicated. Variations depending upon alteration of conditions, such as the relative mass of one or other of the reacting gases at any particular part of the chamber, and the temperature prevailing in different parts (portions near the wall being lower in temperature than those in the centre of the chamber) undoubtedly occur. The main point to be comprehended is, that one or more of the intermediate oxides of nitrogen serve, by diut of their chemical mobility, as carriers of oxygen from the air to S0 2 . The equations formerly supposed to represent these changes illustrate this fact in its simplest form — NO + 0 = N0 2 , S0 2 + N0 2 + H 2 0 = H 2 S0 4 + NO, the cycle being then repeated. However the sulphuric acid may be generated, it forms as a mist, which gradually rains down upon the bottom of the chamber, constituting the chamber acid referred to hereafter. On account of the need for thorough intermixture of the reacting gases, and of the condensing influence of a considerable surface upon them and upon the mist of sulphuric acid formed, it is found inexpedient to use one large chamber, two or more of moderate size being preferable, and, recently, small lead chambers, or even plate columns between larger chambers, as referred to above, have been tried with satisfactory results. In any case, the cubic content of the chambers must be great (v.s.), because a large volume of inert nitrogen from the air has to be handled, and a rapid current of the gases is undesirable, as prohibiting the proper fulfilment of their interactions. In the last chamber, an excess of air and * Adopting the view that N 2 0 3 does not exist at the temperature of the chamber (above 40° C. = 104° P.), the equation would be — 2S0 2 + 2N0 2 + 0 + H 2 0 = 2S0 2 (OH)(N0 2 ). The decomposition of this substance then takes place, by its reacting with a further quantity of S0 2 and water, thus — 2S0 2 (OH)(N0 2 ) + S0 2 + 2H 2 0 = 3H 2 S0 4 + 2NO. The nitrogen dioxide is then regenerated by combination with oxygen — NO + 0 = N0 2 . THE GAY-LUSSAC TOWER. 13 nitrous gases and but little S0 2 should be present. The excess of air used to burn the pyrites (v.s.) should suffice for the complete final conversion of NO into N 2 0 3 or ^^2> as otherwise the re- covery of this gas cannot be effected in the Gay-Lussac tower, into which the exit gases from the chambers pass. The only permanent gas necessarily remaining after the forma- tion of H 2 S0 4 , is the nitrogen of the air. But for the presence of this gas, the manufacture of vitriol might almost be conducted in a closed space. Failing pure oxygen cheap enough to be used instead of air, it is necessary to provide some means of collecting the nitrogen oxides, which would otherwise be carried away with the nitrogen which escapes up the chimney stack. This is the more requisite as the nitrate employed is the most costly reagent used by the vitriol maker. In good practice, 3 to 4 parts of sodium nitrate are needed per 100 parts of sulphur burnt, this being entirely owing to the unavoidable loss, even when a Gay- Lussac tower is used. It will be understood that in an ideal plant working with a perfect cycle of reactions, no nitrate after the first batch would be needed, but this state of things is never approached, not only on account of the mechanical loss by escape at the exit flue, and by dissolution in the chamber acid (in works where chamber acid is used without concentration in the Glover tower), but also by reduction of a portion of the higher oxides of nitrogen to nitrous oxide and nitrogen, which are unabsorbed in the Gay-Lussac, and still further by some nitric oxide escaping conversion into higher oxides in the last chamber, and being, therefore, unabsorbed in the Gay-Lussac. The Gay-Lussac tower has been already described. The vitriol flowing down it meets the exit gases, and absorbs therefrom the N 2 0 3 * found in the last chamber, combination ensuing with the production of nitrosyl- sulphuric acid, according to the equation — 2H 2 S0 4 + N 2 0 3 = 2S0 2 (OH)(N0 2 ) + H 2 0. The quantity of vitriol required for this purpose is considerable, amounting to about half the make of the chambers, because, if it be allowed to absorb too much N 2 0 3 , giving a product unduly rich in N 2 0 3 , a portion of the latter is likely to escape. It must have a specific gravity of at least 1*72, weaker acid absorbing badly. The saturated acid (" nitrous vitriol ") running out at the foot of the Gay-Lussac is pumped by means of an " acid egg " to the top of the Glover, and is there distributed and allowed to flow down the tower in the manner already described. The nitrous vitriol, mixed with the chamber acid, meets the ascending burner gases and gives up its N 2 0 3 , which is carried into the first chamber, reacting with S0 2 and H 2 0 in the way previously mentioned. The vitriol flowing down the Glover is thus denitrified, * Compare footnote, p. 11, for the doubts cast on the existence of N 2 O a at the temperature of a vitriol chamber. 14 SULPHURIC ACID MANUFACTURE. and at the same time concentrated by the heat of the burner gases. A portion is cooled in leaden worms, and returned to the Gay-Lussac to act as an absorbent of N 2 0 3 , and the remainder is concentrated, or used without concentration, as may be required. It is usual on the Continent to substitute nitric acid which has been made by a separate plant (v.s.) for that evolved from the nitre pots used in English practice. Where a Glover tower is employed, nitric acid is passed down the tower, together with the chamber acid, and is there decomposed according to the equations given on p. 1 1 . In the absence of a Glover tower, the nitric acid is run into the first chamber, but to avoid the corrosion of the lead it is received on a cascade of glass or stoneware, on which it is spread out in a thin layer, becoming entirely decomposed by the entering burner gases before it reaches the floor of the chamber. The advantage of the use of nitric acid in place of nitre pots is that the regulation of the quantity of oxides of nitrogen in the chambers can be more easily effected according to the exigencies of working. Another plan for making good the loss of nitrate consists in introducing sodium nitrate into the Glover, but in this case the resulting vitriol is contaminated with sodium sulphate. The acid which collects on the floors of the chambers (chamber acid) must be continually tested during the working of the process, to ascertain its specific gravity. Should this exceed 1*625, the lead is unduly attacked, and the acid retains consider- able quantities of the oxides of nitrogen. The collection of the samples for the test is performed by means of leaden rain-gauges (see S, Fig. 1) situated in different parts of each chamber, and connected with the outside by means of a lead siphon pipe. Each of these " drips " is provided with an hydrometer, whereby the specific gravity of the acid is determined, and the amount of steam to be admitted ascertained. Usually 1 part by weight of sulphur burnt requires 2^ parts of water as steam. The acid from the drips is generally stronger than that from the bottom of the chambers ("bottom acid"), chiefly because it is taken from the centre of the chamber where the steam supply is smaller than at the sides. It is customary to connect the saucers of the various chambers by pipes, and to draw off the chamber acid by means of a lead box connected by a wide pipe with one of the chambers, and provided with an exit pipe which can be opened or closed by a plug operated by a suitable handle. In order to control the production of S0 2 in the burners, and the consumption of sodium nitrate, the chambers are provided with sights, through which their working can be judged by observing the colour of the gases they contain. The gas in the last chamber should be fully red from the presence of an ample excess of nitrogen oxides and of oxygen. The Gay-Lussac tower is also provided with sights, and as a further check the exit gases are systematically collected and analysed. According to the regulations of the Alkali Act, the CONCENTRATION. 15 exit gases must not have an acidity greater than that corresponding with the presence of 4 grains of S0 3 per cubic foot, but in good practice the amount escaping is considerably below this limit, being, viz., about 1*5 grains per cubic foot. CONCENTRATION". — The chamber acid is strong enough for some purposes, but concentration must generally be carried out. The passage of the chamber acid down the Glover tower, concen- trates it to a specific gravity of 1"72, but usually contaminates it with iron salts (derived from the dust from the pyrites burners), so that its further concentration in retorts (v.i.) cannot be econo- mically effected on account of the separation of such impurities. However, for alkali making by the Leblanc process, Glover acid is suitable. Where a Glover tower is not used, or in cases where it is desired to avoid the contamination referred to above, concentra- tion to the same specific gravity is performed in lead pans, which are either heated by furnace gases passing over the surface of the liquid (in which case the acid is contaminated with flue dust, thus acquiring a brown colour to which the acid owes its name, " brown oil of vitriol," "B.O.V."), or by bottom heating which produces a purer acid. On account of the tendency of the lead pans to buckle, by unequal expansion, it has been recently proposed by Carulla to insert a sheet of copper between them and their iron setting, the difference between the coefficient of expansion of lead and copper being smaller than that between the coefficient of ex- pansion of lead and iron ; at the same time the high conductivity of copper for heat contributes to a more even heating. High- pressure steam in lead coils is also used. The concentration in lead pans cannot be carried further than that corresponding with a specific gravity of 1*72, as the lead is seriously attacked when this strength is exceeded. With regard to the quality of the lead of which these pans and the leaden chambers should be con- structed, it may be said that the purest lead is the best. The greater the content of the nitrogen oxides in the acid, the more the pans are attacked. When a higher degree of concentration is needed, the acid is boiled down in glass or platinum stills. The former are large glass retorts, about 3 feet in height and 21 inches in diameter, set in sand baths and heated from below. Though their first cost is small, frequent breakages make the system an expensive one. A better method is that of concentrating in very shallow flat-bottomed platinum stills which are provided with internal partitions so that the acid traverses a considerable distance in- side each still, and can be run through the stills continuously. The platinum is considerably attacked during concentration, to an extent largely dependent upon the impurities present in the vitriol, nitrous vitriol being particularly active. As much as 3 grammes of platinum per ton of acid of specific gravity 1*84, con- taining 93 per cent. H 2 S0 4 , is dissolved when a little nitrous acid 16 SULPHURIC ACID MANUFACTURE. is present. To diminish this loss, stills of a 10 per cent, iridio- platinum alloy have been tried, but abandoned as being too brittle. Better success has attended the use of a plan devised by Heraeus, in which a thin layer of gold is alloyed with and rolled hot into a sheet with platinum, the gold lining of retorts made of this material resisting well. To economise platinum, the heads of the stills are made of lead, double walled, and cooled with water, by which means they resist the attack of the weaker acid distilled off during concentration. Recently, various methods of systematic concen- tration have been introduced, consisting essentially in a series of vessels, of glass or refractory stoneware, or of shallow platinum troughs, arranged terrace-wise so that the acid to be concentrated flows down the series, and is either heated by a flue below the vessels, or by furnace gases passing over them, in a direction the reverse of that of the flow of the acid. Acid already concentrated to a specific gravity of 1-84 can be further evaporated in cast-iron vessels (as obtains in American practice) without attacking them. There is a limit to the concentration of sulphuric acid by boiling, for when a strength of 98 per cent. H 2 S0 4 is reached, the acid dis- sociates considerably into H 2 0 and S0 3 . Acid of higher strength, approximating to what is commercially known as " monohydrate " — i.e., pure H 2 S0 4 — can be prepared by freezing ordinary concen- trated acid of 96 to 97 per cent, strength, by exposing the acid in sheet iron cells immersed in a solution of calcium chloride cooled to - 20° C. - - 4° F., superfusion being averted by the addition of fragments of frozen sulphuric acid. The blocks of frozen acid are removed by immersing the cells for a few seconds in hot water, and are broken up, drained in a hydro-extractor, packed and melted in iron drums, in which the acid can be transported. So-called " solidified sulphuric acid " consists either of kieselguhr saturated with vitriol or a semi-solid mass made by heating mix- tures of sulphuric acid with sodium sulphate, containing more available sulphuric acid than does sodium bisulphate. These pre- parations are used for convenience of transit, and are made ready for use by addition of water, in which case the kieselguhr mixture has to be allowed to settle, to deposit the silica that has been used as an absorbent. PURIFICATION. — Chamber acid contains oxides of nitrogen, lead sulphate, and arsenic (when pyrites has been used). During its passage down the Glover tower it takes up iron (v.s.). The most objectionable of these impurities is the arsenic, which passes into the hydrochloric acid produced in the manufacture of salt cake, and unfits it for many applications. Arsenic is eliminated by passing H 2 S through the chamber acid and allowing the preci- pitated As 2 S 3 to settle. Arsenic-free vitriol is, however, best made from brimstone, native or recovered (see Sulphur, Vol. II., p. 1). Oxides of nitrogen are got rid of by heating the acid with am- monium sulphate before it goes into the platinum stills, where this NORDHAUSEN OR FUMING SULPHURIC ACID. 17 impurity would cause corrosion (v.s.). The equation representing the reaction is N 2 0 3 + (NH 4 ) 2 S0 4 = N 4 + H 2 S0 4 + 3H 2 0. Iron and lead are allowed to remain in ordinary vitriol. When a less impure acid is required, the comparatively weak distillate from the platinum stills is concentrated and utilised, or, for labora- tory use, distillation in glass is adopted. The specific gravity of sulphuric acid reaches a maximum at a strength of 977 per cent., when it has the value of 1*8415 (15° C. = 59° F.). It follows, therefore, that the statement of the specific gravity of a sample of vitriol (even disregarding the influence of impurities such as lead sulphate) does not define its strength when this is between 95 and 100 per cent. On account of this, highly concentrated sulphuric acid should be bought on analysis and not according to its specific gravity. NORDHAUSEN OR FUMING SULPHURIC ACID. — The first form in which sulphuric acid was commercially manu- factured was as fuming sulphuric acid at Nordhausen in Saxony, and the manufacture has continued but little changed to the present day. Ordinary vitriol is still called in Germany English sul- phuric acid, in contradistinction to the fuming acid. The production of fuming sulphuric acid depends on the fact that the sulphates of all but the strongest bases — e.g., the alkalies and alkaline earths — are decomposed by heat, many of them yielding sulphuric anhydride (S0 3 ) as the main product of the decom- position. The sulphates actually employed are, as yet, only those of iron and aluminium, which are dissociated at a moderate tem- perature. The simplest typical case of the decomposition of a sulphate, by heat, with the production of IS0 3 is that afforded by ferric sulphate, thus — Fe 2 (S0 4 ) 3 = Fe 2 O s + 3S0 3 . In practice, however, ferrous sulphate is the raw material of the manufacture. The salt is dried to expel its water of crystallisation, during which process it becomes partially oxidised by air, with the formation of basic ferric sulphate. The basic ferric sulphate splits up according to the equation given above, save that the Fe 2 O a bears a larger proportion to the S0 3 , and the FeS0 4 decomposes in the following manner : — 2FeS0 4 = Fe 2 0 3 + S0 3 + S0 2 . Formerly, when dehydration was not carried out, both sulphuric acid and S0 3 were distilled over, the product being common Nordhausen acid. Nowadays the raw material is obtained by weathering " vitriol shales," such as are found in Bohemia. They already contain some sulphates, together with about 15 per cent, of pyrites, with 2 to 3 per cent, of alumina, most of the remainder consisting of silica. When this mineral is exposed to the air, the 2 18 SULPHURIC ACID MANUFACTURE. iron pyrites oxidises to ferrous sulphate and sulphuric acid, which latter combines with the alumina and other bases; the ferrous sulphate further oxidises to basic ferric sulphate. The weathered mineral is lixiviated, and the liquor is concentrated to a syrup, which solidifies on cooling to a yellowish-green mass, which is finally calcined and known as " vitriol stone." In whatever way the sul- phates of iron or aluminium are obtained, they are heated in small clay retorts to redness, the distillate being received in long stone- ware flasks containing a small quantity of water or a weaker fuming acid from a previous operation. By redistilling the distillate at a low temperature, the sulphuric anhydride passes over first, and by condensing the vapour in already fuming acid, or by itself,' a Is ordhausen acid of any desired strength can be obtained. The best commercial product contains 98 per cent, of free S0 3 . The residue in the retort (caput mortuum) constitutes the colcothar or rouge of commerce (see Pigments, Vol. II., Chapter XV.). Its content of Fe 2 0 3 depends on the nature of the raw material. H 2 S0 4 and S0 3 mix in all proportions, but also form a fairly definite solid compound, corresponding with the formula H 2 S 2 O r (i.e., H 2 S0 4 S0 3 ), commercially known as solidified oil of vitriol. Sodium bisulphate, NaHS0 4 , gives off water when heated, and forms Na 2 S 2 0 7 , which, at a temperature of 600° C. = 1,112° F., breaks up into Na 2 S0 4 and S0 3 , a reaction which has been used for the pro- duction of the latter substance, nitre cake serving as the raw material. Numerous attempts have been made to take advantage of the combination which occurs between sulphur dioxide and oxygen when heated in contact with such substances as finely- divided platinum and the oxides of iron, chromium and copper, but they have not proved commercially successful. It is stated, however, that the S0 3 present in burner gases (v.s.) can be econo- mically collected. S0 3 and fuming sulphuric acid (anhydro- sulphuric acid) find application in the dissolution of indigo as indigo sulphonic acids (see Colouring Matters and Dyes, Vol. II., Chapter XIII.), for purifying ozokerite, and in the manufacture of synthetic dyes. For some other purposes it is preferable to oil of vitriol by reason of its smaller content of water, and con- sequently greater sulphonating action (see Dyes, Vol. II., Chapter XIII.). SALT. 19 CHAPTER II. MANUFACTURE OF ALKALI AND ITS BYE-PRODUCTS. L LEBLANC PROCESS. HAW MATERIALS. — The raw materials used in the manu- facture of soda by the Leblanc process, which dates from 1791, are salt, vitriol, calcium carbonate, and small coal, the process consisting essentially in converting salt into sodium sulphate and heating this with limestone and small coal, whereby it is converted into sodium carbonate. Salt. — This substance occurs as a mineral in beds of rock salt in widely-scattered districts, and in solution as brine in sea-water and salt springs. The most importaut deposits of rock salt in England are those in Cheshire and Worcester, though recently considerable quantities have been found at Middlesbrough in Durham. In Cheshire and in Ireland (Carrickfergus) the rock salt is mined. The rock salt is dark red to bright yellow in colour (owing to the presence of the ferruginous marl associated with it). The purest specimens are colourless, and approximate in composition to pure sodium chloride — a characteristic Cheshire sample containing 98*3 per cent. NaCl together with 0*05 percent. MgCl 2 and 165 per cent. CaS0 4 . The presence of calcium sulphate is usually explained by the supposition that the salt is the product of the evaporation of inland, seas, from which calcium sulphate and sodium chloride, as respectively the most insoluble and the most abundant salt present in sea water, would be thrown down, the mother liquor containing more soluble and less abundant salts (see Stassfurt salts, Vol. II., Chap. XVIII.). Where natural waters have accumulated in strata adjoining those of rock salt, a boring made through the superincumbent strata will bring the water in contact with the salt and produce a saturated solution, which can be pumped up and evaporated. Where no water is naturally present, the wells may be artificially supplied therewith, and the brine pumped as mentioned above. Water is naturally available for the Cheshire deposits, while it is artificially supplied in the Middles- brough district. The method of pumping brine (although this 20 MANUFACTURE OF ALKALI AND ITS BYE-PRODUCTS. necessitates subsequent evaporation) is cheaper than mining solid salt, where the depth of the salt bed is great. The composition of the brine may be gathered from the following analyses : — Cheshire. Worcester. NaCl, . . 25-222 per cent., 22-452 per cent. CaS0 4 , . . 0-391 „ 0-387 Na 2 S0 4 , . . 0-146 „ 0*390 MgC0 3 , . . 0-107 „ 0-034 The degree of concentration of these brines may be gathered from the fact that a saturated solution of salt in water contains 26*5 per cent, of NaCl. The brine, however obtained, is evaporated in salt-pans made of boiler-plate and set over the flues of a series of furnaces which vary somewhat in size, according to the quality of salt to be produced. For the manufacture of fine-grained or lump salt, the pans are from 25 to 35 feet long, 20 to 24 feet wide, and 15 to 18 inches deep. The brine is boiled, the temperature reaching 107 "5° 0. = 225° F. The salt which separates is raked to the sides of the pan, and is lifted out from time to time on perforated skimmers. The crystals are thrown into wooden boxes, where they agglomerate on account of the crystallisation of the brine adhering to them. The blocks in which salt is commonly sold as table salt are obtained in this way. They receive a final stoving before they are sent into the market. Common salt is a coarser grade used for manufacturing purposes, and is made at a lower temperature (in somewhat larger pans), so that the crystals are larger and more impure. The temperature of evaporation varies from 60° to 80° C. = 140° to 176° F. The crystals are treated as in the preceding case, but are merely drained on the shelves (hurdles) surrounding the pans. "Fishing salt " is made at a still lower temperature, and in still larger pans. The temperature is from 35° to 60° C. = 95° to 140° F., and the drawing of the salt takes place at less frequent intervals. "Bay salt" is made in the largest pans, sometimes over 130 feet long by 28 feet broad, and at a temperature of 35° to 50° C. = 95° to 122° F. The grain of the salt depends not only on the temperature of evaporation, and on the time allowed for crystallisation, but also on the influence of impurities in the mother liquor. So marked is this influence that it is customary to add some colloid substance — e.g., gelatine or glue — to the pan when the smallest crystals are required, the process being known as "poisoning the pan." "Hopper salt" is an accumulation of crystals resembling a four- sided hopper, and is produced by the addition of a little alum to the pan. The calcium sulphate and magnesium carbonate in the brine, deposit in the salt pans, causing a scale which has to be occasionally picked out and frequently causes the pan to leak by overheating. Thus it nearly always happens that brine from one or other of the pans finds its way into the fire beneath, where EXTRACTION OF SALT FROM SEA-WATER. 21 the sulphurous gases from the coal cause an evolution of HC1. This frequently becomes a nuisance, and the chimney gases are, therefore, under the supervision of the Inspectors under the Alkali Act. Brine is also concentrated on the Continent by being allowed to trickle over stacks of brushwood ("graduation towers") whereby water is evaporated by wind and sun, and fuel is saved; the evapora- tion of the saturated brine is completed in salt-pans as described above. Sea-water is used as a source of salt, both in hot and cold countries, where its evaporation may be effected without the use of fuel, the expense of which is too great to allow its employment to be remunerative on account of the large quantity of water to be evaporated. The following is the percentage composition of ordinary sea-water : — Per cent. NaCl, 2-64 KC1, 0 07 MgCl 2 , 0-31 MgBr 2 , 0-01 MgS0 4 , 020 CaS0 4 , 013 The "salts gardens" on the shores of the Mediterranean consist of shallow pits into which sea-water is allowed to flow after it has been clarified by subsidence in a deep tank. The heat of the sun evaporates the water, and the crystals are raked out at intervals. The mother liquor (" bittern ") contains magnesium salts, and is worked up for bromine and sometimes also for Glauber's salt (Na 2 SO 4 ,10H 2 O) (see Minor Chemical Industries, Vol. II., Chap. XVIII.) and occasionally for potassium chloride, though the latter industry has been nearly superseded by the production of potash salts at Stassfurt. In cold climates (as in Russia) advantage is taken of the fact that when a saline solution is exposed to a tem- perature below 0° C. sa 32° F., nearly pure ice separates first. Sea-water is allowed to freeze in shallow pits, the ice is fished out and the freezing repeated ; a mother liquor is ultimately obtained which will pay for evaporation. In many countries salt for eating is taxed, but allowed free for industrial purposes, provided it be denatured so as to be unfit for human consumption. Thus in Germany, cattle salt is denatured with \ per cent, of ferric oxide and \ per cent, of wormwood ; salt for manure with \ to 1 per cent, of soot or 2 per cent, of powdered lignite ; salt for soda manufacture with sodium carbonate, sodium sulphate, sulphuric acid or ammonia ; appropriate admixtures are used for other industries, the object in all cases being to render the salt not edible, while still fit for its particular industrial use. Vitriol, the next raw material used in the manufacture of soda, has been dealt with already. Calcium carbonate is used both as chalk and limestone, and any other available form — e.g., recovered alkali waste (v.i.). The 22 MANUFACTURE OF ALKALI AND ITS BYE-PRODUCTS. limestone and chalk should be as free from silica as possible, and not dolomitic, the material containing the former impurity causing waste of soda as silicate, while dolomitic limestone contains mag- nesia, which is too feeble a base to do the work required of it. The calcium carbonate must be dried and crushed to fragments the size of a pea. Small Coal. — The small coal, or " slack," used should be as free as possible from ash, which causes waste of soda by the silica it contains. Lump coal would be better, as containing a smaller proportion of ash, but it is too costly. Washed slack is poorer in ash, but often as much as 5 per cent, is commonly present ; 8 per cent, of ash is still considered good by the alkali maker. . The nitrogen in the coal causes waste of soda by the production of sodium cyanide. Wood charcoal — the best form of carbon for the process — is too dear for use now. MANUFACTURE OF SALT-CAKE. — The reaction in- volved in the manufacture of salt-cake by the ordinary method is represented by the equation — 2NaCl + H 2 S0 4 = Na 2 S0 4 + 2HC1. The apparatus in which the reaction is carried out is called the salt-cake furnace, and may have one of two forms. In either case Fig. 4. — Salt-cake furnace. A, Pan; G, cover; B, pan flue; D, muffle; E, muffle flue; C, furnace; H, flues ; F, damper. the first part of the decomposition, resulting in the formation of NaHS0 4 as well as Na 2 S0 4 , takes place in a circular or elliptical cast-iron pan, A (Fig. 4), varying in size from about 9 feet in diameter and 18 inches deep to 6 feet by 4 feet by 12 inches (in the case of one of elliptical shape). An arched cover, G, usually of acid-proof fireclay, suffices to collect the hydrochloric acid from the pan ; the acid gas escapes by the fireclay flue, B. In order to complete the expulsion of hydrochloric acid, the con- tents of the pan is shifted into a fireclay muffle, D, also provided MANUFACTURE OF SALT-CAKE. 23 with an exit flue, E, both pan and muffle being heated by the furnace, C, and the flues, H. To avoid any escape of gas from the muffle into the furnace flue, a higher pressure is maintained in the latter than that which prevails in the muffle, so that the leakage, if any, is in the other direction. In this country the muffle is frequently dispensed with, in which case the direct flame of the fire is allowed to play over the salt-cake spread on the hearth of a kind of reverberatory furnace, the hydrochloric acid escaping to- gether with the furnace gases. Under these conditions the pan is heated by a separate furnace. The charge is about 6 to 16 cwts., the smaller quantity being used for furnaces without muffles (open roasters), which can be worked off in about one hour, and the larger for muffle furnaces (close or blind roasters), in which the time for each batch is about two hours. The acid used is generally of the strength of that coming from the Glover tower, having a specific gravity of 1*72. The weight required of acid of this strength is rather more than that of the salt charged. The action is at first violent, and as it slackens is aided by stirring ; when the mass becomes pasty, the damper, F, is raised and the charge pushed over by a " shoving-rake " into the roaster, where its decomposition is completed at a bright red heat. The yield is 116 to 120 parts of salt-cake for 100 parts of salt charged. Various mechanical furnaces for preparing salt-cake have been devised, but that originated by Mactear alone appears to be in use. It consists essentially of a circular firebrick hearth which rotates beneath a furnace dome that carries the exit flues. In the centre of the dome there is a hopper, through which salt and acid are fed into a central pot, which serves as the pan, the rest of the bed of the furnace acting as the roaster. The process is continuous, and the contents of the pot overflows on to the rotat- ing bed, where the charge is gradually worked towards the cir- cumference by fixed rakes, and, being heated by the flame of the furnace, is completely decomposed by the time it has reached the circumference, where it drops into an annular delivery trough, the salt-cake therein serving as a lute to the edge of the rotating bed. In this case the whole of the HC1 is mixed with all the furnace gas. Instead of using sulphuric acid to decompose salt, potential sulphuric acid — i.e., S0 2 , 0 and H 2 0 — can be employed, as in the Hargreaves and Robinson process. The reaction that occurs is — 2NaCl + S0 3 + 0 + H 2 0 = Na 2 S0 4 + 2HC1. In order that the reaction may be complete, the salt must be in a sufficiently porous state to allow the gases to penetrate it thoroughly, an object which is attained by moistening it, moulding it into cakes, and drying it. These cakes are charged into vertical cast- iron cylinders holding about 40 tons each, heated by external vertical flues. Gases from a pyrites burner are mixed with super- 24 MANUFACTURE OF ALKALI AND ITS BYE-PRODUCTS. heated steam, and caused to traverse the cylinders seriatim, entering at the top and passing out at the bottom. The passage of the gases is systematic — i.e., the fresh gas always meets nearly converted salt, and exhausted gas passes away through fresh salt. The tem- perature at which the reaction obtains is about 500° 0. = 932° F., and is partly maintained by the heat evolved in the course of the reaction, which is exothermic. The movement of the gas is pro- duced by a Roots blower placed at the end of the cylinders, and likewise serving to pass the HC1 on to the condensers. Good commercial salt-cake will contain not less than 97 to 98 per cent, of Na 2 S0 4 . About two-thirds of the salt-cake made is used for the production of soda, for which purpose it should be as free as possible from chlorides. A large proportion of the remainder is employed in glass making, for which it is required free from iron, an object attained by dissolving it in water, making the solution alkaline with lime, whereby ferric hydroxide is precipitated, and recrystallising. As sodium sulphate normally crystallises as Ka. 2 SO 4 ,10H 2 O, the cost of freight is considerable, and it is, there- fore, sometimes prepared as the anhydrous salt, the formation of which can be induced by adding various substances— e.g., a crystal of Na 9 S0 4 itself — to a solution of the salt at a temperature above 40° C. = 104° F. Hydrochloric Acid. — In whatever way the conversion of sodium chloride into sulphate may have been effected, the gas HC1 has to be condensed by absorption in water, save in the rare cases where it is used as such (Deacon's process, q.v.). This is the more important inasmuch as it is illegal to allow more than 0*2 grain of HC1 per cubic foot of chimney gases to escape into the air. The gases from the pan are usually collected separately from those evolved in the roaster, being purer, and in cases where open roasters are used, more concentrated. In all cases the gases from the furnace are cooled by passing through a length of earthenware pipes or sandstone flues, or even through iron pipes, provided the temperature of these be not allowed to fall to the condensation point. An alternative plan of cooling consists in injecting a spray of water into stone tanks through which the gases pass, or the gases are led up a small tower fed with a limited amount of water, which suffices to cool the gas and condense sulphuric acid and stop flue dust (both the latter impurities being derived from the roaster). The gas is then passed through a series of stone tanks or, on the Continent, " bombonnes " (Woulfe's bottles) half filled with water, and exposing sufficient surface to the air to allow the HC1 to be absorbed by the water. They are provided with side pipes, and are connected together so that a stream of HC1 proceeds in one direction and is met by a flow of water in the opposite direction. The strongest acid is obtained in these con- densers, but all the gas is not absorbed, so that it must finally be passed through a coke tower supplied with water. The tower is MANUFACTURE OF BLACK ASH. 25 built of acid-proof bricks and varies from 40 to 100 feet in height. The yield of acid is about 130 to 148 parts of aqueous acid of 1*17 to 1 *18 specific gravity (containing 34 to 36 per cent. HC1) per 100 parts of salt-cake made. By far the greater portion of this acid (muriatic acid) is used for making chlorine (Vol. II., p. 35), the remainder being employed in many minor industries. Crude muriatic acid contains as im- purities ferric chloride and organic matter (which give it a yellow- colour), arsenic and sulphuric acid. Arsenic is derived from the vitriol made from pyrites, which is commonly used. Most of the impurities in hydrochloric acid can be removed by distillation, except arsenic, which comes over with the first fraction as AsCl 3 ; the later portions may, however, be obtained free from this im- purity. An alternative plan for removing the arsenic consists in precipitating it as As 2 S 3 , by means of H 2 S, allowing the precipitate to settle, and distilling the acid. MANUFACTURE OF BLACK ASH.— This is the next step in the process of making sodium carbonate by the Leblanc method. It is effected by heating a mixture of sodium sulphate (salt-cake) with calcium carbonate and small coal. The reaction may be assumed to take place in two stages — (1) Na 2 S0 4 + C 2 = Na 2 S + 2C0 2 . (2) Na 2 S + CaC0 3 = Na 2 C0 3 + CaS. The resulting black ash is thus essentially a mixture of sodium carbonate and calcium sulphide. The sulphate should contain not more than 0*5 per cent, of NaCl nor more than 1 *5 per cent, of free acid, calculated as S0 3 . The proportions adopted in practice are — 100 parts of salt-cake, 100 of limestone or dry chalk, of the size of a pea, and 40 to 60 parts of coal. The proportion of calcium carbonate and coal is greater than is indicated by the above equations, because, inasmuch as black ash is only clinkered and not fused, an excess of these reagents must be present to ensure each particle of salt-cake coming into contact with them. The excess is also useful as promoting the porosity of the black ash and favouring lixiviation, and, further, by generating CO in the interior of the mass when this is plastic at the last stage of the process, thus— CaC0 3 + C = CaO + 2CO. The CO renders the black ash porous like dough, and the subsequent hydration of the lime, simultaneously produced, disintegrates the masses of black ash during lixiviation. The operation is con- ducted in a species of reverberatory furnace, closely resembling the roaster of the salt-cake furnace, but with a hearth in place of the muffle. The half of the hearth nearer the grate is about 3 inches lower than that near the flue ; the charge is introduced through a hopper on to the upper or back half, where it is dried and subjected to a preliminary heating, after which it is raked over to the lower part of the hearth, which has a temperature 26 MANUFACTURE OF ALKALI AND ITS BYE-PRODUCTS. of from 700° to 1,000° C. = 1,292° to 1,832° F. Here the charge is heated until the sodium sulphide, which at first forms (v.s.), is fused, and the mass becomes a thick paste, which is then thoroughly mixed by means of a rake and gradually drawn towards the door of the furnace, situated at the side of the lower hearth. There is a copious evolution of C0 2 , and the mass becomes more pasty; the reaction evolving CO (v.s.) now sets in, this stage being recog- nised by the bursting of small jets of burning CO from the charge. The mass is then raked into a "ball" and withdrawn into an iron truck, where its quality can be judged by the continued evolution of CO and the expansion of the ball. It is usual to utilise the waste heat from the black-ash furnace to concentrate the liquor obtained by lixiviating the black ash ; for this purpose a boiler pan is placed in a prolongation of the flue, so that the hot products of combustion pass over the surface of the liquor. Fig. 5. — Revolving black-ash furnace. A, Cylinder; B, B, rings; C, furnace; D, flue. Mechanical furnaces for the production of black ash are known as revolvers. Inasmuch as the chief function of the workman in making black ash consists in turning and mixing the charge, it is obvious that if this mixing be effected mechanically, larger charges can be handled in a given time, and better intermixture can be secured. An ordinary revolving black-ash furnace consists of a cylinder, A (Fig. 5), made of boiler plate and lined with firebrick, resting on rollers on which work rings, B, B, concentric with the cylinder. The central part of each end of the cylinder is open, and is so placed that the hot gases from the furnace, C, can pass through it, supplying the heat necessary to convert the charge, and escaping by the flue, D, in which boiling- down pans may be set. Usually, ordinary large furnace grates LIXIVIATION OF BLACK ASH. 27 are used as the source of heat, but a producer would probably be better. The charge is introduced and removed through a manhole in the side of the cylinder. The revolver is driven by suitable gearing so that it can be rotated slowly at the beginning of the process (1 revolution in four minutes) and afterwards at a quicker rate (5 revolutions per minute). The charge is much larger than with the roaster furnaces, and need not be mixed before it is introduced, mixture being effected by the rotation of the cylinder, aided by the agitation produced by two fixed projections on the lining, called "breakers." The calcium car- bonate and two-thirds of the coal are first put in and the cylinder revolved until some caustic lime has been formed ; the salt-cake and the remaining coal are then added, and the revolution continued at a higher speed until the operation is complete. The object of this preliminary "liming" is to ensure the presence of enough caustic lime in the black ash to allow of its easy lixiviation. Properly made black ash has a blackish-brown surface with a grey porous fracture ; its composition may be gathered from the following analysis (Kolb) : — Sodium carbonate, silicate, . ,, aluminate, ,, sulphate, . ,, chloride, . Calcium oxide, sulphide, . ,, carbonate, Ferric oxide, Coal, . 79 per cent. 52 „ 44 „ 92 „ 85 68 96 „ 92 „ 21 20 „ 98-49 Traces of cyanide, ferrocyanide, soda in an insoluble form, and Na 2 S are also generally present. Black ash absorbs moisture and C0 2 from the air, the lime being thus slaked, causing the disintegration of the mass ; long exposure is undesirable, lest a reverse reaction between the CaS and Na 2 C0 3 occur, involving waste. Lixiviation of Black Ash. — Well-made black ash is suffi- ciently porous to be easily extracted even when in comparatively large pieces, but if ill-made, and therefore dense, it must be crushed to a coarse powder before lixiviation. The method of extraction consists in exposing the fragments in tanks, provided with false bottoms, to systematic treatment with water, in such a way that fresh water comes in contact with nearly exhausted ash and strong liquors with fresh ash. Contact of the ash with air is avoided as much as possible, as a rapid oxidation of calcium sulphide, and consequent loss of soda by double decomposition 28 MANUFACTURE OF ALKALI AND ITS BYE-PRODUCTS. of the calcium sulphate thus formed with the sodium carbonate, occurs. Inasmuch as the black ash is anhydrous, and contains a considerable quantity of caustic lime, it causes a rise of tem- perature when first brought into contact with water; thus the temperature of the strong liquor may be 60° C. = 140° F., while that of the weak liquor should not exceed 37° C. = 99° F., as otherwise the reverse reaction between CaS and Na 2 C0 3 tends to take place; for the same reason the liquor must not be allowed to become stronger than is indicated by a specific gravity of 1 *28. Besides being inevitably associated with loss of soda, Na 2 S? the product of the reverse reaction, is objectionable on account of its solvent action on FeS (derived from the iron of the tank), which colours the liquor green. The calcium sulphide and other in- soluble substances left in the tank are periodically removed, and constitute tank waste (q.v.). The constitution of the tank liquor obtained in this way is given below : — Na 2 C0 3 + NaOH, .... 23 '60 per cent. NaCl, 0-50 Na 2 S, 0-13 Na 2 S 2 0 3 , 0-30 Na 2 S0 4 , 0-23 „ 24-76 Small quantities of sodium sulphite, cyanide, ferrocyanide, thio- cyanate and silicate, and ferrous sulphide are also present. As much as 20 per cent, of the alkali will generally be in the form of caustic soda, which results from the action on the sodium carbonate of the surplus lime, used in the black ash process for indirectly imparting porosity as described above. The tank liquor is allowed to settle, and when clear is submitted to the action of 0O 2 (in order to carbonate the caustic soda) by being run down a tower filled with broken stoneware, or, preferably, containing chains or wire rope, down which the liquor trickles ; lime kiln gases are passed up the tower. During the carbonation, sodium sulphide, as well as the hydrate, is converted into car- bonate, and ferrous sulphide is thrown out of solution ; at the same time sodium silicate and aluminate are decomposed, the acid radicles being precipitated and the quantity of useful soda, Na 2 C0 3 , increased. Sodium ferrocyanide is an objectionable impurity in tank liquor, inasmuch as it appears in the calcined soda ash as Fe 2 0 3 and impairs its colour. It can be removed by heating the tank liquor to 180° C. = 356° F. under pressure, when it reacts with another impurity, sodium thiosulphate, to form sodium thiocyanate and sulphite, the iron being separated as ferrous oxide ; it may also be removed by precipitation with a sine salt as zinc ferrocyanide. Evaporation of Tank Liquor for Soda Ash (Anhydrous COMMERCIAL FORMS OF ALKALI. 29 Na 2 C0 3 ). — The clear settled tank liquor, carbonated and freed from ferrocyanide, is evaporated, at near its boiling point, for the production of black salt, impure Na 2 C0 3 .H 2 0. The evaporation may be performed, as already mentioned, by the waste heat of the black-ash furnaces, but the product is then contaminated by flue dust and S0 9 from the fuel. Pans heated from the bottom, and mechanical evaporators, such as Thelen's, in which the salt is mechanically scraped out as fast as formed, are also used. The black salt is drained from the mother liquor (red liquor), which is boiled down separately for a less pure alkali, or is converted into caustic soda (v.i.). Evaporation by multiple effect under diminished pressure (see Sugar, Vol. II., Chap. VIII.) has not proved successful. Finishing the Soda Ash. — To drive off the molecule of H 2 0 in the black salt, calcination at a red heat in an ordinary rever- beratory furnace is necessary. When carbonation of the tank liquor has been omitted, the black salt is mixed with sawdust before calcination, in order that the combustion of this may supply C0 2 for the conversion of NaOH and Na 2 S into Na 2 C0 3 ; the product is, at best, less pure than that from carbonated tank liquor. Various mechanical carbonating furnaces have been devised, the chief advantage of which lies rather in the saving of labour than of fuel. The best commercial soda ash is white, and contains not more than a trace of caustic soda and 98 to 99 per cent, of Na 2 C0 3 . That carbonated with sawdust still contains at least 2 per cent, of caustic soda, and has to be refined by dissolution in water, removing Fe.,0 3 by settlement and re-evaporation in pans heated by coke fires, followed by calcination. The product is known as refined alkali. For purposes, such as soap making, where caustic soda is prepared from soda ash, a grade known as "caustic ash," containing as much as 20 per cent, of caustic soda, is used. Soda crystals, &a 2 CO 3 ,10H 2 O (washing soda), though containing only 37 per cent, of Na 2 C0 3 , is preferred for scouring wool and for domestic use, largely because of its freedom from caustic soda. It is usually prepared by recrystallising the solution of soda ash, which should be freed from sulphide and should contain not more than 2 per cent, of caustic soda. The solution for crystal- lisation is made with water above 34° C. = 93° F. (the tem- perature at which Na 2 CO 3 ,10H 2 O is most soluble), and is saturated; it is allowed to cool in shallow crystallising pans. The formation of good crystals is said to be promoted by the presence of 1 per cent, of sodium sulphate. The mother liquors are boiled down and calcined. Crystal carbonate, Na 2 C0 3 .H 2 0 (83 per cent, of Na 2 C0 3 ), is a proprietary name given to the product obtained by crystallising from a boiling saturated solution of carbonated and thoroughly purified tank liquor. It is applicable to the same purposes as 30 MANUFACTURE OF ALKALI AND ITS BYE-PRODUCTS. those for which soda crystals are used, and costs less for trans- port per unit of Na 2 C0 3 . Bicarbonate of Soda, NaHC0 3 . — This is prepared by car- bonating the normal carbonate with any concentrated form of 00 2 . Volcanic gases and C0 2 from fermentation are used, other- wise C0 2 evolved by the action of HC1 on limestone is employed. Soda crystals, as such, are generally used as the raw material, though a saturated solution of soda ash may be substituted. (Bicarbonate is now chiefly made by the ammonia-soda process — q.v. Vol. II., p. 43.) In the former case the crystals, placed on a drainer, are exposed to the action of the gas for six to nine days; much water comes away, in accordance with the equation — Na 2 CO 3 .10H 2 O + C0 2 = 2NaHC0 3 + 9H 2 0. This forms a liquor which is boiled down and yields an impure weak soda ash. In the second case the bicarbonate separates from the solution. Drying at a temperature not exceeding 45° 0. = 113° F. is necessary to avoid loss of C0 2 . Sodium sesquicarbonate, Na 2 C0 3 .NaHC0 3 .2H 2 0, is also prepared from mixed solutions of sodium carbonate and bicarbonate, crystallised not below 35° 0. = 95° F. ; it is used for wool washing. Sodium bicarbonate is a milder alkali than the normal carbonate, and on this account is used when the action of the latter is too drastic. Caustic Soda. — The reaction involved in the production of caustic soda (NaOH) from sodium carbonate is expressed by the equation — Na 2 C0 3 + Ca(0H) 2 = CaC0 3 + 2NaOH. In practice, caustic soda is prepared by causticising purified tank liquor; this must be well settled, and have a specific gravity of 1*08 to 1*10. The purification of the tank liquor by exposure to C0 2 is omitted in the case of that which is to be causticised, inasmuch as a portion of the soda is already present as caustic soda, and the carbonation of this would involve waste of lime in subsequently decarbonating. The tank liquor must, however, be freed from sulphide ; this is effected either by blowing in air, the oxidising action of which may be enhanced by the addition of Weldon mud (v.i.), or by precipitating the sulphide as ZnS or PbS, which process is preferable for high-grade (77 per cent.) caustic. The strength of the liquor to be causticised is limited to that corresponding with a specific gravity of I'll), because stronger liquors prevent the completion of the reaction, inasmuch as strong caustic soda is capable of removing C0 2 from CaC0 3 , the above equation becoming reversed. In order further to prevent this back action, the proportion of lime employed is in excess of that indicated by the equation, advantage being thus taken of the principle of mass action. The process consists in placing slaked lime (11 cwts. to 1 ton of caustic lime per 10 tons of tank liquor) in an iron cage and COMMERCIAL STANDARDS FOR TRADING IN ALKALI. 31 immersing it in the boiling tank liquor, purified, and of the concentration indicated above. The liquor is kept agitated by steam injection or by paddles. When the liquor is completely causticised the clear solution is drawn off. It has approximately the following composition : — NaOH, 10-25 per cent. Na 2 C0 3 , ...... 3*29 NaCl, 0 14 Na 2 8 2 03, 0-29 Na 2 S0 4 , 0-25 The calcium carbonate sludge, left at the bottom of the causti- cising pan, is filtered and washed, and the washings used for diluting the tank liquor for the next causticisation. The washed lime mud will serve, instead of bought calcium carbonate, for preparing a further quantity of black ash. Red liquor, the mother liquor from black salts (v.s.) was origin- ally largely used for the production of caustic soda as already containing much caustic. The product is less pure than that from tank liquor. It sufficed to boil down this red liquor, when the sodium carbonate and other salts contained in it separated and left an impure concentrated caustic liquor. The production of solid caustic soda from the causticised liquor takes place in two stages. The liquor is boiled down in pans to specific gravity 1 *4 and the sodium carbonate and other salts are fished out ; the liquor is settled and the evaporation completed in caustic pots. The salts separated during concentration are worked up with a fresh batch of black ash. Towards the end of the concentration in caustic pots, any residual sulphide is oxidised by the addition of about 1 per cent, of sodium nitrate. This converts the sulphide into sulphate, and is at the same time reduced to nitrite, which remains in the caustic. The material in the pot is allowed to settle, and ladled out into drums, in which it solidifies. Various grades of caustic soda are made, known commercially as " 60 per cent.," " 70 per cent.," " 77 per cent." (Na 2 0) (v.i.) and " caustic bottoms." These contain respectively about 80 per cent., 90 per cent., 96 per cent., and 59 per cent, of NaOH, the remaining salts present being chiefly sodium chloride and sodium sulphate, save in the case of bottoms, when as much as 20 per cent, of insoluble matter may be present. Caustic soda is largely used by soap and paper makers, and in the purification of petroleum and tar oils ; there are various minor applications of this alkali. Commercial standards for Trading in Alkali. — The only rational way of stating the strength of soda ash and caustic is in terms of the percentage of Na 2 C0 3 and NaOH, respectively. This method is not generally adopted. The German plan for both substances consists in reckoning 32 MANUFACTURE OF ALKALI AND ITS BYE-PRODUCTS. the total alkali as Na 2 C0 3 , a process indefensible for caustic soda. In this country the total alkalinity is stated in percentage of Na 2 0, each per cent, being 1°; this would be a suitable method but for the custom of taking the atomic weight of sodium as 24, which causes the stated percentage to be higher than the real. Nowadays the valuation is made correctly and translated by various fraudulent methods of calculation into a higher alleged content of soda, the method varying with the district. Stated by the English method (Na = 24) pure sodium carbonate is 59-26° strength, the real value (Na = 23) being 58-49°. Pure caustic soda on the same standard is 78 05°, the real value (Na = 23) being 77'5° TREATMENT OE TANK WASTE (ALKALI WASTE). — It will be realised from the foregoing, that practically the whole of the sulphur of the sulphuric acid used in the manufacture of salt-cake remains in the tank waste from the extraction of black ash. The dry waste thus produced amounts to 1| tons per ton of soda ash made. Formerly the whole of this had either to be heaped outside the works, or carted out to sea, if the nuisance, arising from the sulphuretted hydrogen evolved from it, became intolerable. Its composition is given below : — Na 2 C0 3 , 1 -63 per cent. CaC0 3 , 38-81 Ca(OH) 2 , 9-53 CaS, 35-12 CaSoOs, 1-49 Coal, 6-27 A1 2 0 3 , 0-13 FeS, 2-76 Si0 2 , 1-21 Sand, 2-61 99-56 The action of air and moisture on this substance produces hydro- sulphides, polysulphides, sulphites, and thiosulphates. These being washed out by the rain, drain away from the heap, the drainage giving up H 2 S by the further action of C0 2 of the air, and also itself contaminating adjacent water supplies. Inasmuch as sulphur is, with the exception of nitrate, the most expensive raw material used in the production of soda, the only rational way of dealing with alkali waste consists in recover- ing the sulphur as such. The sole method successfully effecting this is the Chance-Olaus recovery process, which is worked as follows: — Fresh alkali waste is made into a cream with water and subjected to the action of lime-kiln gases in a set of vertical cylinders, 16 feet by 5 feet. The C0 2 of the lime-kiln gases first attacks CaS of the alkali waste, producing CaC0 3 and H.,S: CaS + H 2 0 + C0 2 = CaCO :{ + H 2 S. The H 2 S passes into the RECOVERY OF SULPHUR PROM TANK WASTE. 33 next cylinder containing alkali waste and is absorbed, forming calcium hydrosulphide Ca(SH) 2 , approximately pure nitrogen, from the lime-kiln gases, escaping. After the waste has been completely decomposed in the first cylinder, C0 2 will pass on to the next and react with Ca(SH) 2 , thus — Ca(SH) 2 + C0 2 + H 2 0 = CaC0 3 + 2H 2 S. The sulphuretted hydrogen is collected in a gasholder. It will be seen that the rationale of the process consists in ob- taining a fairly concentrated sulphuretted hydrogen by first enriching a portion of the waste to be treated and then de- composing this enriched waste. In practice, a set of seven decomposing cylinders is found requisite for this purpose. The average strength of the sulphuretted hydrogen produced is 32 per cent, of H 2 S, the remainder being nitrogen with a little C0 2 . The residue from the tank waste, thus treated, consists of CaC0 3 , containing a little alkali, and may be used for making black ash, and has been tried for the manufacture of Portland cement (q.v.), but is not well fitted for this purpose on account of the sulphur which it contains.* The sulphuretted hydrogen stored from this process may be burnt, instead of pyrites, for vitriol making, but this method of utilisation is not remunerative ; it is, therefore, used to produce recovered sulphur in a Claus kiln. The Claus kiln, which serves for the recovery of sulphur from H 2 S however obtained (see Gas Manufacture, Vol. II., p. 76), is an apparatus devised for the smooth carrying-out of the reaction H 2 S + O = H 2 0 + S, when the sulphuretted hydrogen is diluted with inert gas, such as nitrogen. The kiln consists of an iron cylinder, A (Fig. G), liued with fire- brick, and having a grate, B, at its lower part, upon which a layer of ferric oxide, C, about 18 inches thick, rests. The dilute sulphuretted hydrogen constituting the Chance gases is mixed with about four-filths of its volume of air, and the mixture is passed into the kiln below the grate. The ferric oxide which has already been heated is now kept hot by the heat of the combustion of the hydrogen in the H 2 S, the combustion being induced by the presence of this hot oxide. The resulting steam and sulphur vapour pass into a series of chambers, in the first of which, D, the temperature is sufficiently high for liqujd sulphur to be deposited, while in the succeeding chambers, E, flowers of sulphur are condensed. The combustion of the H 2 S is not * Another method of utilising tank waste is the Parnell and Simpson process, in which the waste liquors of the ammonia-soda process {v.i.) are worked up. The reactions involved are — (1) 2NH 4 C1 + CaS = CaCl 2 + (NH 4 ) 2 S. (2) (NH 4 ) 2 S + 2C0 2 + 2H 2 0 = 2NH 4 tiC0 3 + H 2 S. The H 2 S is collected in a gasholder, and the ammonium bicarbonate used for making ammonia-soda. 3 34 MANUFACTURE OF ALKALI AND ITS BYE-PRODUCTS. generally complete in the Claus kiln, so that the exit gases must be passed through a furnace and washed, to avoid nuisance. The Chance process for recovering sulphur from alkali waste is rapidly displacing other processes for effecting a similar object. The only one of these which needs notice here is that of Mactear 171 S3 O CD o S a u PQ T3 J modified by Pechiney, which is designed for treating drainage from tank- waste heaps, thus avoiding the worst nuisance. Air is blown through the drainage until sufficient of the sulphide which it contains has been oxidised to thiosulphate, so that it reacts completely with the remaining sulphide when hydrochloric acid is added, according to the equations — CHLORINE AND BLEACHING POWDER. 35 (1) CaSo0 3 + 2HC1 = CaCl 2 + H 2 0 + S0 2 + S. (2) Ca(SH) 2 + 2HC1 = CaCl 2 + 2HoS. (3) S0 2 + 2H 2 S = S 3 + 2H 2 0. The sulphur is thus recovered. CHLORINE AND BLEACHING POWDER. — The manu- facture of chlorine for conversion into bleaching powder is always a part of the Leblanc process, because nearly all the chlorine of the salt appears as hydrochloric acid, which has fewer applications than has chloride of lime. In order to prepare chlorine from hydrochloric acid, the hy- drogen of the latter must be oxidised to water. While many oxidising agents will effect this, the cheapest is manganese di- oxide, which reacts as follows : — Mn0 2 + 4HC1 = MnCl 4 + 2H 2 0 ; MnCl 4 = MnCl 2 + Cl 2 . Manganese tetrachloride (MnCl 4 ) exists in the brown solution of manganese dioxide in cold strong HC1. It is very unstable, and splits up on warming into manganous chloride (MnCl 2 ) and free chlorine. For manufacturing purposes, where the liquor is heated, the reaction may be considered to proceed thus — Mn0 2 + 4HC1 = MnCl 2 + Cl 2 + 2H 2 0. Such other oxidising agents as may be practically substituted for manganese dioxide will be dealt with later. The hydrochloric acid, condensed as described above (p. 24), is used for making chlorine ; it should contain at least 20 per cent. HC1 (specific gravity 1*10), and is better when stronger; it should be as free as possible from sulphuric acid, for removing which in the form of barium sulphate, barium chloride has been used. The manganese dioxide is always originally used as a man- ganese ore (an impure natural manganese dioxide), though nearly all of it is recovered as an artificial oxide (v.i.) after each distil- lation of chlorine, and used repeatedly. The manganese ore now comes chiefly from Huelva, and should contain at least 65 per cent, of Mn0 9 and be free from calcium carbonate, because this wastes acid and yields C0 2 , which contaminates the chlorine. The technical valuation of " manganese " for chlorine making consists in estimating the "available oxygen" — that is, the per- centage of oxygen in the ore above that necessary to form the base MnO, and therefore available for oxidation of HC1. Chlorine stills are stoneware, carboy-shaped vessels, filled with an inner perforated cylinder holding the manganese, and pro- vided with an inlet neck for the acid and an outlet pipe for the chlorine ; the still is heated by a steam jacket. Another form consists of a stoneware cylinder with a false bottom for holding the manganese, covered by a leaden bell, the 36 MANUFACTURE OF ALKALI AND ITS BYE-PRODUCTS. lower edge of which is trapped by water in an outer vessel, which also serves as a water jacket for heating the still. Both the above forms are fit only for small installations. In large works the stills are made on the pattern shown in Fig. 7 ; they consist of siliceous stone slabs, tongued and grooved, and made tight by caoutchouc or a lute of tar and fireclay. The walls are held in their place by iron clamps. A sandstone slab fitted in the same manner serves as a lid, and is provided with a manhole for charging the still, while a discharging hole is situated in one of the side slabs. The manganese rests on a Fig. 7.— Chlorine still. false bottom, to prevent caking; the charge is 6 to 10 cwts. The acid (25 to 35 cwts.) is run in through a lead pipe which terminates in an acid seal, and steam is supplied through another lead pipe, continued within the still as a stoneware column, which passes below the false bottom, where it has several open- ings for the distribution of the steam. The acid is run in quickly at first, chlorine being spontaneously evolved, and more acid added from time to time, until the evolution of chlorine slackens, when steam is slowly injected, the temperature of the still reaching 90° 0. = 194° F. as a maximum. The charge is worked off in 24 to 48 hours. The chlorine, which escapes RECOVERY OF MANGANESE. 37 through a leaden pipe in the lid, is passed into the bleaching- powder chambers, described below. Even should the reaction between Mn0 2 and HC1 for the production of chlorine, given above, be capable of realisation in practice, half of the chlorine of the hydrochloric acid would be retained in the still as manganous chloride. On account of the presence in native manganese of other oxides than that of manganese, and of the impossibility of pushing the saturation of the hydrochloric acid to the point of neutrality, considerably more than half the acid is wasted, as far as the production of chlorine is concerned. Thus of the total hydrochloric acid used, it generally happeDS that one-third appears as chlorine, rather more than one-third as manganous chloride, and nearly the whole of the remainder as free hydrochloric acid, a comparatively small proportion being accounted for as ferric chloride, aluminium chloride, barium chloride, &c. The comparative costliness of manganese has made its recovery, in order that it may again serve as an oxygen carrier, essential. The only method which successfully attains this object is the Weldon recovery process. The still liquor, consisting of man- ganous chloride, acid with hydrochloric acid, and containing some ferric chloride, is agitated in "neutralising wells" with ground chalk or limestone; here the free acid is neutralised, calcium chloride being formed, and the iron is precipitated as ferric hydroxide, the manganous chloride not being precipitated by this reagent except so far as the still liquor contains free chlorine (always the case), which causes a precipitation of an equivalent quantity of manganese as dioxide. The neutralised liquor is pumped into settlers of wrought or cast iron, and, after settling, is run off into iron cylinders, the "oxidisers" ; the mud is washed, and the washings used for making milk of lime for the next operation. This consists in adding milk of lime in the proportion of 1 molecule of lime to 2 molecules of manganous oxide, the quantity generally amounting to 12 to 14 cwts. of lime per ton of bleaching powder niade.* The lime must be free from magnesia, inasmuch as this is too feeble a base to decompose manganous chloride with the requisite rapidity, and, therefore, remains in the mud as MgO, ready to consume a portion of the hydrochloric acid in the mud-still. The oxidisers are placed vertically, and are supplied with air, and are fitted with a steampipe which main- tains the temperature at 55° C. = 131° F. The reaction taking place in the oxidisers consists first in the precipitation of manganous oxide, and the formation of calcium chloride, by the action of the lime on the manganous chloride. This is oxidised by the stream of air with the formation, in the presence of lime, of calcium manganite (CaO.Mn0 2 ) and manganous manganite (MnO.Mn0 2 ). *It is convenient, on account of commercial considerations, to calculate items of cost per unit of the finished product. 38 MANUFACTURE OF ALKALI AND ITS BYE-PRODUCTS. For further elucidation of the chemistry of this process it may be stated that when air is blown through a precipitate of manganous oxide, manganous manganite is formed, the oxida- tion only proceeding sufficiently far to provide an acid oxide (Mn0 2 ) to combine with the basic oxide (MnO). The rapidity of absorption of oxygen is enhanced by the presence of a more powerful base than MnO — e.g., CaO — when calcium manganite is formed ; but it is impracticable to produce a calcium manganite in this way, unmixed with manganous manganite. It will be seen from what has been said, that the oxidised liquor consists of a solution of calcium chloride containing in suspension calcium manganite and manganous manganite ; the proportions of the lime, and of manganese as manganous oxide and manganese dioxide, being in accordance with the following analysis : — Mn0 2 , 66 per cent. MnO, 17 CaO, 16 99 The necessity for the use of lime has been indicated above ; its quantity is reduced as far as possible in order to avoid a greater loss of acid in the still than is absolutely necessary, by adding still liquor containing manganous chloride ("final liquor") to the mud after the first stage of blowing ; a portion of the lime in the calcium manganite is thus removed, leaving a more acid calcium manganite, and forming calcium chloride and manganous hydroxide, the latter being then converted into manganous manganite by the further action of air. The calcium chloride in the liquor plays an important part in assisting the oxidation, by reason, it is believed, of its solvent action on calcium man- ganite, which appears to act as a carrier of oxygen. The precipitated manganites thrown down in the oxidisers are known as "Weldon mud." When the process is properly conducted,, about 80 per cent, of the total manganese in the mud is in the form of Mn0 2 , so that its value for producing chlorine is equal to that of a high grade native manganese, and is enhanced by its- finely-divided condition. The contents of the oxidisers are run into settlers, the calcium chloride solution is drawn off, and the Weldon mud, still fluid enough to pass through a pipe, trans- ferred to the mud-stills, which are similar in design to those used for the native manganese, but larger, generally octagonal and not provided with a false bottom, because the mud is completely soluble in the hydrochloric acid. The waste liquor from the still is worked up again in the same way. « The recovery of manganese by Weldon's process is so complete that the amount of fresh manganese ore requisite to replace that lost, is about 1 per cent, of the bleaching powder made. It will be seen that only one-third of the chlorine in the salt,, deacon's chlorine process. 39 the original raw material, appears as gaseous chlorine, the re- mainder being run to waste as calcium chloride. The improve- ments which have been suggested in the preparation of chlorine by the use of manganese dioxide as an oxidising agent, have been in the direction of reducing this waste of two-thirds of the chlorine. In the most hopeful of these, magnesium carbonate is substituted for calcium carbonate for neutralising the still liquors, in order that advantage may be taken of the fact that magnesium chloride decomposes when heated with the evolution of a part of its chlorine as hydrochloric acid. The neutralised still liquor is evaporated to dryness, and the residue roasted in air, so that chlorine is evolved and magnesium manganite, which can be used as an oxidiser in the chlorine stills, remains. By this means a larger proportion of chlorine can be obtained, amounting to 60 per cent, or more of that in the salt. This process is not at present in extended use. Numerous oxidising agents, other than Mn0 2 , have been suggested for the production of chlorine, but that which has alone proved moderately successful is atmospheric oxygen, em- ployed as in the Deacon process. The principle of this process is expressed by the equation 2HC1 4- O = H 2 0 + Cl 2 , which can only be realised — and then partially — when both the HC1 and H 2 0 are gaseous, as the decomposition of 2 mols. of HC1 (gaseous) involves the absorption of 44 Cal., and the formation of 1 mol. of H 2 0 (gaseous) evolves 58*7 Cal. ; this leaves a balance of 14*7 Cal., so that the reaction is exothermic, whereas, when both substances are liquid the reaction is endothermic, and, therefore, cannot take place spontaneously. The oxidation of HC1 by atmospheric oxygen can be effected by supplying energy from without in the form of heat ; but the process is slow and incomplete. In the presence of cupric chloride, however, the reaction takes place more readily, inasmuch as cupric chloride, by dint of its facility for dissociating into cuprous chloride and chlorine at 400° C. = 752° F., acts as a carrier of oxygen from the air to the hydrogen of the HC1. The stages of the reaction may be represented thus (according to Hurter) : — (1) 2CuCl 2 = Cu 2 Cl 2 + Cl 2 . The oxygen of the air then reacts with cuprous chloride thus — (2) Cu 2 Cl 2 + 0 2 ^ 2CuO + Cl 2 . The cupric oxide is regenerated to cupric chloride by the action of the HC1— (3) CuO + 2HC1 = CuCl 2 + H 2 0. The same cycle of changes is then repeated. In practice, the gaseous HC1 from the decomposing pans of salt-cake furnaces (that from the roasters is too dilute) is cooled 40 MANUFACTURE OF ALKALI AND ITS BYE-PRODUCTS. by passage through long pipes and a scrubber, and thus freed from the bulk of the steam which accompanies it ; it is then heated by traversing a stove similar to those used for hot-blast furnaces (Vol. I., p. 131) to a temperature of 500° C. = 932° F. The acid gas is pulled through the whole apparatus by a Roots blower at the exit end, enough air being drawn in through the doors and flues of the furnace which heats the decomposing pan. About 4 vols, of air to 1 vol. of HC1 are required. This mixture of gases, having passed through the stove already referred to, enters the decomposer, which consists of a vertical cast-iron cylinder, shown in horizontal section in Fig. 8. The mixture of gases passes into the outer annular space, A, then through the annular layer of active material, B, and escapes into the cylindrical centre space, 0, whence it is drawn off by a pipe, D. The active material con- sists of burnt clay broken into lumps and saturated with a solution of cupric chloride, the mass containing 0*6 to 0'7 per cent, of copper. After having been used for a time, corresponding with an output of 10 to 12 cwts. of bleaching powder, the material ceases to be active and must be re- newed. The decomposer is not externally heated, the temperature of the incoming gases sufficing to carry on the reaction. The exit gases from the decomposer contain from one- half to one-third of the chlorine which is present, in the free state, the remainder being still as HC1, which is condensed in the usual way. If the gas is to be used for making bleaching powder, it is dried by passing up a tower fed with vitriol. When properly worked the process yields a gas containing as much as 10 per cent, of chlorine, but this strength is much below that of the gas obtained from manganese stills, and on account of this com- parative dilution the bleaching-powder chambers in which it is absorbed differ in detail from those described below for stronger chlorine. Production of Bleaching Powder. — The process for manu- facturing bleaching powder, or chloride of lime, consists in passing chlorine over slaked lime, which absorbs the gas, forming " chloride of lime." The reaction which occurs is still a subject Fig. 8. — Decomposer for Deacon's chlorine process. A, Annular space ; B, active material C, centre space ; D, pipe. PRODUCTION OF BLEACHING POWDER. 41 •of discussion, but, whatever its course, it appears to result in the production of a compound CaCl.OCl, which, on contact with water, decomposes according to the equation — 2(CaC1.0Cl) = Ca(OCl) 2 + CaCl 2 . The calcium hypochlorite [Ca(OCl).J and chloride (CaCl 2 ), formed in this way, dissolve in the water, leaving a residue of unaltered slaked lime. The slaked lime must be prepared from "fat" quicklime by sprinkling with water, in order that no excess of the latter may be present, and must be sifted from unslaked lumps. It is spread on shelves in large leaden chambers, about 100 feet long, 7 feet high, and 10 to 20 feet in width, the floor being made of stone slabs. The chlorine is admitted into these systematically, and the progress of absorption is judged by the colour of the gas as observed through windows in the walls. When the yellow colour has disappeared, the lime is turned over by spades and fresh chlorine is admitted, after the absorption of which the process is complete. When the chambers are not worked in sets, the excess of chlorine is drawn off and absorbed in milk of lime, to make bleach liquor. The bleach maker is not allowed to let gases containing more than 2J grains of chlorine per cubic foot escape into the air. When dilute chlorine, such as is obtained in the Deacon process, is used, systematic working is a necessity, and the chambers are much larger than usual. The average yield of bleach is about one and a-half times the weight of the slaked lime used. When properly made, it is a nearly pure white powder, which becomes slightly damp when exposed to air, and decomposes in the presence of moisture and C0 2 , which cause it to give off hypochlorous acid ; it is the presence of this body which gives chloride of lime its character- istic smell. It should contain at least 35 per cent, of " available chlorine" — i.e., chlorine in a condition to effect oxidation, and, therefore, bleaching action. Where a local market exists for bleach, "bleach liquor" is sometimes prepared by passing chlorine into milk of lime, con- taining 1 to lbs. of slaked lime per gallon of water, and mechanically agitated. It contains calcium hypochlorite and calcium chloride, and the available chlorine, per unit of lime, is higher than in bleaching powder, because lime is more thoroughly attacked when in an emulsion than when in the solid state. The eau de Javelle and eau de Labarraque first made in France are " chloride of potash " and soda respectively, and are pre- pared by passing chlorine into solutions of the corresponding carbonates, whereby the chlorides and hypochlorous acid are produced — Na 2 C0 3 + 4C1 + H 2 0 = 2NaCl + C0 2 + 2HOC1. 42 MANUFACTURE OF ALKALI AND ITS BYE-PRODUCTS. They contain more available chlorine than bleach, but are less stable. Liquid chlorine, contained in steel cylinders at a pres- sure of 8 atmospheres, is now a commercial product. It boils at - 33-6° C. = - 28° F., and its specific gravity is 133. Potassium Chlorate. — This salt is also a bye-product of the manufacture of alkali by the Leblanc process, free chlorine being essential for its production. While hypochlorites are formed when chlorine is passed into cold alkaline liquids, chlorates are produced when the temperature is near 100° C. = 212° F. In the manufacture of potassium chlorate, calcium chlorate is first prepared, thus — 6Ca(OH) 2 + CI] 2 = 5CaCl 2 + Ca(C10 3 ) 2 + 6H 2 0. This is decomposed by the addition of potassium chloride, thus — Ca(C10 3 ) 2 + 2KC1 = CaCl 2 + 2KC10 3 . It is cheaper to form calcium chlorate as an intermediate product, because five-sixths of the potash in caustic potash, if that were used directly, would be converted into chloride, a comparatively low-priced salt. The first stage in the process consists in passing chlorine into cast-iron cylinders containing milk of lime and provided with agitators, several such vessels being worked systematically. The heat evolved during the reaction raises the temperature suffi- ciently to induce the production of calcium chlorate instead of calcium hypochlorite. Even in careful work a certain amount of oxygen is evolved from the decomposition of calcium hypo- chlorite, representing a corresponding loss of chlorate, this loss being smaller when an excess of chlorine is present. The finished liquor, which is pink from the presence of calcium permanganate, is run into settlers, and potassium chloride is added. The clear liquor, containing potassium chlorate and calcium chloride, is run off, and the mud, containing impurities in the slaked lime, is washed, the washings being used in making the next batch of milk of lime. The chlorate liquor is boiled down in iron pans until its specific gravity is 1 *35, when potassium chlorate crystallises ; the salt is recrystallised before it is marketed. The mother liquor contains at least 12 per cent, of the total chlorate, part of which may be recovered by cooling the liquor to — 20° C. = - 4° F., when more potassium chlorate crystallises. It is economical of chlorate to substitute magnesia for lime, as a portion of the magnesium chloride produced can be crystallised before adding the potassium chloride, and the final mother liquors are less bulky and hold less potassium chlorate in solution. Potassium chlorate is anhydrous, and is used in the manufac- ture of matches, fireworks and explosives, and generally as an oxidant. Sodium chlorate, which is preferable for some purposes to potassium chlorate, on account of its greater solubility, is THE AMMONIA-SODA PROCESS. 4a made by removing a part of the calcium chloride from calcium chlorate liquor at a temperature of 10° to 12° C. = 50° to 54° F., and adding sodium sulphate ; the precipitated calcium sulphate is filtered off, and the solution of sodium chlorate is evaporated to crystallisation. The salt is anhydrous. II. THE AMMONIA-SODA PROCESS. This process — which was first put into practical shape by Solvay (1863), although the knowledge of its fundamental reaction is of much older date — depends on the fact that when solutions of sodium chloride and ammonium bicarbonate are mixed, double decomposition occurs, resulting in the formation of ammonium chloride and sodium bicarbonate, the latter being precipitated on account of its sparing solubility in solutions of the former. In practice, the ammonium bicarbonate is formed in situ by passing carbon dioxide into a brine saturated with ammonia, the reaction proceeding thus — NaCl + NH 3 + C0 2 + H 2 0 = NaHC0 3 + NH 4 C1. The ammonia is recovered by treatment of the NH 4 C1 solution with lime, according to the equation — 2NH 4 C1 + Ca(OH) 2 = 2NH 3 + CaCl 2 + 2H 2 0. The carbon dioxide is also partly recovered in the process of con- verting the sodium bicarbonate into the normal salt, ISTa^Og — 2NaHC0 3 = Na 2 C0 3 + H 2 0 + C0 2 . As the fundamental reaction belongs to the reversible class, the conversion of the sodium chloride is incomplete, only about two- thirds being obtained as carbonate. The manufacture consists of two essential operations, the one being the preparation of a pure brine saturated with ammonia, the other the carbonation of this brine with lime-kiln gases and with the C0 2 recovered as indicated above. The purification of the brine from magnesia, iron oxide, and silica, and its saturation with ammonia, are effected in the same operation in an apparatus which is typified by Fig. 9. The vessel, A, is filled with brine, and receives a charge of lime which is to precipitate the impurities above mentioned. The brine is then allowed to flow into B, where ammonia, from the still to be subsequently described, is introduced through the distributor, 0, the liquor being kept cool by the water coil, D. To ensure saturation of the brine, which may have been diluted by the water accompanying the ammonia blown in, salt may be introduced through the pipe, E. 44 MANUFACTURE OF ALKALI AND ITS BYE-PRODUCTS. By circulation of the liquor between A and B, thorough mixture is obtained, and when saturation, as indicated by the alkalinity of test samples, is complete, the sludge is removed, mainly by decantation, in a separate vessel provided with an overflow pipe and a sludge cock. The clarification is then completed by passage through a filtering cloth before the brine E u i Fig. 9. — Brine saturator for ammonia-soda process. A, Vessel for purifying brine ; B, saturator ; C, false-bottom distributor ; D, water coil ; E, salt injector. is passed through the cooler, which consists of a series of pipes constructed on the principle of a Liebig's condenser. These movements of the ammoniacal brine are actuated by a force pump, which serves at the same time to raise it to the top of the carbonating tower. This apparatus, represented in Fig. 10, is a cast-iron cylinder, THE AMMONIA-SODA PROCESS. 4& A, some 40 to 50 feet high, containing a number of fixed diaphragms, B, about 3 feet apart, each with a central hole through which a rod, C, passes down the whole length of the tower. To this rod are attached perforated, saucer-like plates, D, D, at such distances that they rest upon the fixed diaphragms, B. The ammonia- cal brine is introduced at the middle of the tower by the pipe, E, from the storage tank, situated at the level of the main, F, about 12 feet from the top of the tower. The pipe, G, serves to equalise pres- sure between the main, F, and the top of the tower. It will be seen that the column is kept filled up to the level of F with ammoniacal brine, and it will be understood that by this arrangement of introducing the ammoniacal liquor at the middle of the column of liquid, the ammonia carried upwards by the ascending current will be fixed by the C0 2 which the top part of the column has already absorbed ; the advantage of having ammonium bicarbonate at this part of the column arises from its being less vola- tile than ammonia itself, so that a smaller quantity of this valuable reagent is carried away with the waste gases through the pipe, H, than would be the case if the liquor were let into the top of the column. The introduction of A, Cylinder ; B, diaphragms ; C, rod ; D, D, perforated plates ; E, liquor injection pipe ; F, main ; G, pipe for equalising pressure ; H, exit pipe ; K, gas injection pipe. Fig. 10. — Carbon ating tower for ammonia-soda process. 46 MANUFACTURE OF ALKALI AND ITS BYE-PRODUCTS. the lime kiln gases, containing about 30 per cent, by volume of C0 2 , is effected by pressure through the pipe, K, at the base of the tower. A certain amount of systematic working is attained by forcing gases rich in C0 2 {e.g., from the ignition of the NaHC0 3 ) into the cylinder, through this lower pipe, where they act upon nearly spent ammoniacal brine, and passing gases poorer in C0 2 through a pipe in the upper part, where they meet a richer brine. The lime kiln gases used must be cool and free from flue dust and S0 2 ; these objects are attained by washing with water both before and after compression. The C0 2 is generally so far used that the exit gases contain about 10 per cent., besides some ammonia which is absorbed by passage through a new batch of brine, followed by a scrubbing with sulphuric acid. The most favourable temperature for the realisation of the double decomposition between the sodium chloride and am- monium bicarbonate is 15° C. = 59° F., and in order to maintain this as nearly as practicable, the heat of the reaction is removed by external cooling of the carbonating towers by a stream of water. It is claimed that the expansion of the compressed lime kiln gases, as they pass through the column of liquid, contributes to this cooling effect. As the crystals of sodium bicarbonate form, they collect on the perforated diaphragms down which they slide, passing through nicks in the circumference of these, and through the central holes of the fixed diaphragms, forming a sludge at the bottom of the cylinder ; a certain amount of agitation can be imparted to the diaphragms to promote the subsidence of the crystals. The sludge of crystals flows from the bottom of the cylinder on to a vacuum filter, is washed with a small quantity of water, and is then ready for conversion into soda ash. The mother liquor and washings from the vacuum filter contain, on account of the imperfection of the reaction and the solubility of sodium bicarbonate, sodium chloride (frequently amounting to one-third of that present in the original brine), sodium bicarbonate, ammonium bicarbonate, and ammonium chloride. The mother liquor is run into the ammonia recovery apparatus (v.i.), and yields as final products ammonia and ammonium carbonate —which are returned to the brine satura- tors — and sodium chloride, which is run away. Thus, that portion of the sodium bicarbonate which remains dissolved in the mother liquor is reconverted into sodium chloride, and is run to waste. On account of the comparatively small demand for sodium bicarbonate, the bulk of the first product of the ammonia-soda process is converted into soda ash, but a portion of it is recrystallised, to eliminate adhering ammonia, in an atmosphere of C0 2 under pressure, and sold for making baking powder, &c. The conversion into soda ash is carried out by heating the PRODUCTION AND RECOVERY OF AMMONIA. 47 bicarbonate in a horizontal cylinder provided with an agitator, or in retorts. The carbon dioxide, carrying the small quantity of ammonia, is returned to the lower portion of the carbonating tower. The apparent density of ammonia soda-ash is about 0 - 8, while that of Leblanc soda-ash is 1*2. When a dense form of soda-ash is required, a second furnacing is adopted. By reason of its mode of preparation, ammonia soda-ash is free from caustic soda, and may contain a little bicarbonate. Caustic soda can be produced in the ammonia-soda works by causticising the ash with lime in the ordinary way (see Vol. IT., p. 30), but the process is more costly than with Leblanc soda, because in the latter case, as has been shown, the crude soda- ash contains a considerable amount of caustic soda ; this finds its way into mother liquors which have no analogue in the ammonia-soda process,, where what mother liquor there is (from the carbonating towers) must be used for the recovery of ammonia, in the course of which operation the sodium bicar- bonate contained in the liquor is decomposed. A method of causticising dry soda-ash is, therefore, of special value for the ammonia-soda process. The most promising consists in heating soda ash with ferric oxide, whereby C0 2 is expelled and a loose compound of Na 2 0 and Fe 2 0 3 , sodium ferrite, is formed. This is decomposed on treatment with water, giving a concentrated soda- lye and ferric oxide which can be used over again. The evapora- tion of the concentrated soda-lye is a comparatively economical process. Production and Recovery of Ammonia. — The process for the recovery of ammonia in the ammonia-soda process does not essentially differ from that adopted for the preparation or recovery of ammonia in other industries — e.g., the preparation of ammonium sulphate at the gas works. The following general description of the apparatus employed will, therefore, apply to all cases where this gas is produced or recovered : — Most sources of crude ammonia contain ammonia as such, ammonium carbonate, frequently sulphide, and non-volatile ammoniacal salts. The first three of these constituents are sufficiently volatile to be expelled when the liquor is heated, therefore the fraction of ammonia thus obtained is known as " free ammonia," while the non-volatile salts must be heated with some base stronger than ammonia — e.g., lime — the fraction liberated in this manner being known as "fixed ammonia." A still adapted for general use consists of two portions, the one arranged for the expulsion of " free ammonia," the other for the liberation of " fixed ammonia." The separation of a more from a less volatile substance, such as ammonia from water, is best effected by the process of fractional distillation, which is always aided by some kind of dephlegmator ; in ammonia stills, as in alcohol stills, this takes the form of a fractionating column. 48 MANUFACTURE OF ALKALI AND ITS BYE-PRODUCTS. The liquor containing free and fixed ammonia is run through the pipe, A (Fig. 11), into the fractionating column, B, the internal construction of which is similar to that used for dis- tilling spirit, and is described in the section dealing with this subject. During its passage down this tower, the liquor en- c F Fig. 11. — Ammonia still. A, Liquor inlet ; B, dephlegmator ; C, gas exit pipe ; D, D, stills ; E, E, sludge cocks ; F, lime inlet. counters a current of steam, and, becoming heated, parts with its volatile ammonia together with other gases, the products of the dissociation of volatile ammonium salts, such as H 2 S and C0 2 . These gases pass away by the pipe, C, and if the ammonia is to be converted directly into ammonium sulphate, as is the RECOVERY OF CHLORINE IN THE AMMONIA-SODA PROCESS. 49 case at a gas works, it is sent into the saturator containing sulphuric acid, as described in the section on gas manufacture. When the ammonia is used to saturate brine in the ammonia- soda process (v.s.) it needs no further treatment, inasmuch as only ammonia and carbon dioxide are present. From the bottom of the fractionating column, the liquor, con- taining the fixed ammonia, enters the still proper, D, D. For continuous working several such stills are used, so that one may be in operation while another is being emptied, a system of dis- tributing-pipes and cocks serving to connect each at will with the column. The lime necessary for freeing the ammonia is introduced into the stills, either as milk of lime through a pipe, F, or as lumps contained in an iron cage. The whole apparatus is heated by the injection of steam, the heat necessary to liberate the fixed ammonia and to work the rectifying column, being thus obtained. The spent sludge is run off from D by a sludge cock, E, at the bottom of the still ; in the case of the ammonia-soda process the " sludge " consists chiefly of calcium chloride, together with some sodium chloride derived from the decomposition of the sodium bicarbonate remaining in solution after the bulk of this salt has separated in the carbonating towers. This decomposition occurs thus — NaHC0 3 + NH 4 C1 = NaCl + NH 3 + H 2 0 + C0 2 . Such sodium chloride as has escaped conversion in the carbon- ating towers (v.s.) will also be in this sludge liquor. Recovery of Chlorine in the Ammonia- Soda Process. — Whereas in the Leblanc method of making soda, one-third of the chlorine in the original salt is recovered as an essential part of the working cycle, in the ammonia-soda process none is obtained by the ordinary manner of working. Various suggestions have been made to remove this drawback. According to the method of working described above, the chlorine appears finally as cal- cium chloride, this plan being obligatory from the necessity of recovering ammonia. An obvious economy consists in the direct recovery of both the constituents of ammonium chloride — - viz., NH 3 and HC1 — which is rendered the more feasible on account of the ease with which ammonium chloride is disso- ciated on volatilisation. No practicable method of separating the NH 3 and HC1 in the dissociated ammonium chloride having yet been devised, it is, therefore, necessary to employ some base capable of combining with the HC1. The base chosen for this purpose must be sufficiently feeble to allow of decomposition of the corresponding chloride on heating in air. Most of the basic oxides, save the alkalies and alkaline earths, fulfil this condition, but magnesia presents many advantages over others that could be used. One of the best methods of this class is that devised by 4 50 MANUFACTURE OF ALKALI AND ITS BYE-PRODUCTS. Mond. The liquors from the ammonia-soda process are cooled considerably below 0° C. = 32° F., and the ammonium chloride which separates, together with some salt and sodium bicarbo- nate which do not interfere, is volatilised in antimony-lined vessels (which resist its attack), and passed over heated (400° C. = 752° F.) magnesia, whereby magnesium chloride and ammonia are formed. The latter is returned to the ammonia-soda plant, and the former is heated at 800° to 1,000° 0. = 1,472° to 1,832° F. in air supplied from a Cowper's hot-blast stove (see Iron, Vol. I., p. 131), whereby it is decomposed into magnesia and chlorine. It is claimed that gases containing 7 to 10 per cent, of chlorine are thus obtained. The magnesia serves for repetition of the process. The ease with which magnesium chloride (and in a smaller degree calcium chloride) is decomposed by being heated in air, may be utilised for the recovery of chlorine from the still liquor of the ammonia recovery process. In the case of calcium chloride, the comparative stability of this substance militates against success.* By substituting magnesia for lime in the ammonia stills, magnesium chloride appears in place of calcium chloride and can be treated by the Weldon-Pechiney method. This process, which may also be applied both to obtaining chlorine from aqueous hydrochloric acid by previously converting it into magnesium chloride, and for the manufacture of chlorine from the waste magnesium chloride obtained in working up Stassfurt salts (see Potash, Vol. II., Chap. XVIIL), consists essentially of three stages. In the first, magnesium oxychloride is synthesised by grinding magnesia with a strong solution of magnesium chloride, the composition of the moist mass approxi- mating to the formula 5Mg0.4MgCl 2 . This oxychloride is reduced to pieces of the size of a walnut, and dried by passage on waggons through a heated chamber at 300° C. = 572° F. The dried oxy- chloride, which has lost half its water and some 5 to 8 per cent, of its chlorine as HC1 during the drying, is filled into narrow firebrick chambers previously heated by a locomotive regenerative furnace to a temperature of about 1,000° C. = 1,832° F., and heated air is passed over it. 45 per cent, of the chlorine is thus evolved free, 40 per cent, as HC1 (derived by the action of the residual water in the dried oxychloride), and the balance remains in the residue, which is cooled and returned to the process. The escaping gases, containing some 6 to 8 per cent, of chlorine, the remainder being HC1, N, and surplus air, pass into a condenser consisting of a stone tower filled with a number of cross tubes of glass, through which water is circulated. Here the water is * The decomposition of calcium chloride is aided by the presence of an acid oxide, the cheapest that can be applied being silica, thus : — CaC] 2 + Si0 2 + H,0 = CaO.Si0 2 + 2HC1. ALKALI, BLEACH, AND CHLORATES PRODUCED BY ELECTROLYSIS. 51 •condensed, and the gases next pass through a series of bom- bonnes, and finally through a coke scrubber, in order to condense fully the HC1. The chlorine is utilised for making bleach and •chlorates. III. OTHER CHEMICAL PROCESSES FOR MAKING ALKALI. Several other processes for making alkali have been devised, l>ut their application has been limited. They depend upon the following general principles: — (1) The decomposition of a sodium salt by means of a base capable of forming an insoluble pre- cipitate with the acid of the sodium salt, such as is expressed by the equation — Na 2 S0 4 + Ba(OH) 2 = 2NaOH + BaS0 4 . (2) The treatment of a sodium salt at a high temperature with an acid radicle capable of displacing the radicle in the sodium salt at that temperature, and of forming a new sodium salt, decomposable by water or C0 2 , thus — (1) 2NaCl + SiOo + H 2 0 = Na 2 SiO s + 2HC1. (2) Na 2 Si0 3 + C0 2 = Na 2 C0 3 + Si0 2 . A process of this class, which has been put into actual work, is the Cryolite Process, in which sodium carbonate is produced •as a bye-product in the manufacture of aluminium sulphate — 3NaF.AlF 3 + 3CaC0 3 = Na 3 A10 3 + 3CaF 2 + 3C0 2 . In this case the alumina functions as an acid oxide, yielding sodium aluminate, which can be decomposed in aqueous solution by C0 2 — 2Na 3 A10 3 + 3C0 2 = 3Na 2 C0 3 + A1 2 0 3 , the alumina being subsequently converted into aluminium sul- phate. The principles of methods (1) and (2) may be combined, as in the Staveley process, in which sodium sulphate is treated with calcium carbolate, (C 6 H 5 0).,Ca, made by agitating crude carbolic acid with milk of lime ; the reaction proceeds thus — Na 2 S0 4 + (C 6 H 5 0) 2 Ca = 2C c H 5 ONa + CaS0 4 . The sodium carbolate thus obtained is decomposed by C0 2 , crude carbolic acid being regenerated — 2C 6 H fi ONa + C0 2 + H 2 0 = Na 2 C0 3 + 2C 6 H 5 OH. Alkali, Bleach, and Chlorates produced by Electrolysis. — When fused sodium chloride is submitted to electrolysis, chlorine is evolved at the anode and metallic sodium at the •cathode ; in the presence of water the sodium is never liberated 52 MANUFACTURE OP ALKALI AND ITS BYE-PRODUCTS. as such, because of the immediate formation, in its place, of caustic soda and hydrogen, HOH + Na = NaOH + H. In an open cell the hydrogen thus evolved tends to combine with the chlorine by diffusion through the liquid, and HC1 (and finally NaCl) is regenerated; a similar contact of the anode and cathode products — namely, chlorine and caustic soda — gives rise to the formation of sodium hypochlorite and sodium chlorate (see Elec- trolytic bleaching, Vol. II., Chap. XII.). It follows that when caustic soda and chlorine are to be produced, the anode and the cathode products must be separated — e.g., by a porous septum. The decomposition of sodium chloride under these conditions may be represented by the equation — NaCl + HOH = NaOH + H + CI. Cathode. Anode. The voltage of the current, and, therefore, the total electrical energy needed to decompose a solution of salt, is necessarily greater when hydrogen is liberated, and chemical work thus done, than when the evolution of hydrogen is prevented ; in some systems the hydrogen is oxidised by the use of an oxidant, such as copper oxide, which can be readily regenerated by heating in air ; in this case the super- fluous work done is represented finally by the reduction of CuO to Cu, instead of by the more energetic reduction of H 2 0 to H 2 . In practice, too, it is advantageous to suppress this hydrogen, for mechanical reasons. The simplicity of the production of alkali and chlorine by electrolytic methods is largely discounted by the difficulty of finding a material capable of withstanding Fig. 12.— Diaphragm for the action of nascent chlorine, and of con- electrolytic process of structing a diaphragm efficient to prevent making alkali. mixture of the liquids on each side, and A, V-shaped slats; B, yet of low electrical resistance, asbestos. These difficulties are met, in the Green- wood process, by the use of an anode of plates of retort-scurf (gas carbon) coppered on one side and cast to a core of type-metal, in order that a large plate 01 this refractory form of carbon may be made. The diaphragm consists of a series of V-shaped slats (A, Fig. 12) packed with asbestos (B). An iron plate can be used as the cathode where there is no corrosive action. The process is continuous, separate supplies of brine being circulated through the anode and the cathode compartments, chlorine being given off in the REVIEW OF THE PROCESS OF ALKALI MANUFACTURE. 53 former, while the liquor in the latter becomes enriched with caustic soda, until a concentration is attained at which the liquid can be economically evaporated, the salt being fished out and the caustic soda finished in the usual way. The chlorine, which is of full strength, can be used for making bleach by the methods already described. No attempt is made to utilise the hydrogen. Other systems are similar in arrangement, but differ in mechanical details (see Sodium, Yol. I., p. 226). The direct production of chlorates by electrolysis becomes possible if the electrolyte be hot and the chlorine and alkali allowed to commingle. The method of suppressing hydrogen with copper oxide is here convenient, as the use of a diaphragm may be then dispensed with and intermixture facilitated. The reaction takes place on the following lines : — 6KC1 + 3H 2 0 = KCIO3 + 5KC1 + H 6 . The advantage of this method is that a cheap potassium salt (the chloride) can be directly converted into chlorate. REVIEW OF THE PROCESS OF ALKALI MANU- FACTURE. — The keen competition between makers of alkali by the Leblanc and the ammonia-soda process lends special interest to the consideration of the chemical reasons for their relative success. In both cases NaCl, the only practicable source of soda, has to be converted into Na 2 C0 3 , a process involving the absorption of energy, some idea of the amount of which may be gathered from our knowledge that the quantity of energy in terms of heat which would be required to produce Na 2 C0 3 from NaCl by the simplest conceivable process, expressed by the equation — 2NaCl + 0 + C0 2 = Na 2 C0 3 + Cl 2 is 19 '6 Cals. The only known method of doing this amount of chemical work directly, is by the use of electrical energy. Electrolysis has not hitherto been remuneratively applied for the manufacture of alkali and chlorine, not only because of the practical difficulties mentioned on p. 52, but on account of the fact that the energy requisite has to be obtained circuitously by the combustion of coal beneath a boiler, and by engine and dynamo as intermediaries (see Vol. I., p. 93); this process of conversion of heat into electricity is of low efficiency. Another difficulty, at present encountered, is the large and costly plant required for a comparatively small output. Failing electrolysis, the requisite energy must be supplied by stages. The energy changes of these stages may be briefly considered. In the Leblanc process, the formation of salt-cake is an exothermic reaction, the energy for which is derived from the sulphuric acid (itself containing the energy evolved by the com- bustion of sulphur, which has been imparted to it during the 54 MANUFACTURE OF ALKALI AND ITS BYE-PRODUCTS. concentration in the Glover tower). In the black ash furnace the- energy absorbed in the reduction of Na 2 S0 4 to Na 2 S is furnished by the fuel. There is but little energy involved in the double decomposition between CaC0 3 and Na 2 S. Thus, in the Leblanc process the chemical energy of the sulphur has been utilised in the process, and restored in the black ash furnace, for the sulphur can be recovered from calcium sulphide without the expenditure of any considerable quantity of fresh energy. In the ammonia-soda process the main reaction, involving the conversion of sodium chloride into sodium bicarbonate, does not require the application of external energy, but the conversion of sodium bicarbonate into sodium carbonate — that is, the same end-product as in the Leblanc process — requires the application of energy in the form of heat. The only other cause of the- expenditure of energy occurs in the liberation of ammonia from' ammonium chloride, which is brought about by the action of lime prepared by the dissociation of CaC0 3 into CaO and C0 2 , the energy having its origin in the consumption of fuel. The fact that the C0 2 produced during the burning of the limestone- is necessary in the process, contributes to economy of energy, as. well as of material. It will be clear from this, that the expenditure of energy, in the form of fuel, is considerably less than that needed for the Leblanc process. The balance against the Leblanc process is, however, not all waste, as a portion appears in the form of the chemical energy of HC1, whereas calcium chloride is the corre- sponding product in the ammonia-soda process; the difference in the chemical energy of these two compounds is well illustrated by the relative ease with which chlorine can be obtained from them. It is this difference which enables the Leblanc process to retain its footing, in spite of the cheaper production of alkali by the ammonia-soda process. The improvement of such methods as the Weldon-Pechiney for the treatment of the residual chloride of the ammonia-soda process, tends to nullify this advantage. Before the successful recovery of sulphur (Chance process) was practised, the Leblanc process was at a still greater disadvantage, for at that time energy was expended nearly sufficient to recover the sulphur, which was nevertheless thrown to waste as calcium sulphide. Attention has already been called to the greater ease with which caustic soda is produced from Leblanc soda-ash than from ammonia soda. The reason why caustic soda and bleach are best prepared by the Leblanc method, and pure soda-ash by the ammonia-soda process, will be evident from contemplation of the above considerations. GENERAL PRINCIPLES. 55 CHAPTER III. DESTRUCTIVE DISTILLATION. General Principles. — The term destructive distillation is applied to the process of heating a complex substance to its point of decomposition. This is generally accomplished by per- forming the operation in a closed retort, as in coal-gas manufac- ture, but may be effected by the limited combustion of the sub- stance to be distilled, so that the heat generated destructively distils the remainder, as in charcoal burning and the manufac- ture of blast-furnace coke. The class of substances usually treated are such carbon compounds as are split up at a high temperature with the evolution of gaseous and liquid products, a residue relatively richer in carbon being left — a change which is indicated by the term " carbonisation." Such bodies are coal, shale, and wood. It will be understood that the essential difference between the process of destructive distillation and that of ordinary distillation (such as that of alcohol), consists in the fact that the substances collected in the receiver in the former operation do not pre-exist in the retort — they are products of the process, not educts. The nature of the products obtained is dependent on tem- perature, and, in a minor degree, on pressure. E. J. Mills has drawn attention to the fact that at high temperatures aromatic hydrocarbons — e.g., those of the benzene and homo- logous series — predominate in the liquid products, while at low temperatures hydrocarbons of the fatty or paraffin series are present in greater amount. To the kind of change caused by destructive distillation, the same author applies the term "cumulative resolution," by which he means the polymerisa- tion of the substance distilled in conjunction with the removal of water from it ; thus cellulose, w(C 6 H 10 O 5 ), (the typical con- stituent of wood), may be viewed as suffering decomposition by the following steps : — He considers that the organic matter in coal and shale contains C r) H 10 O 5 C6H 8 0 4 CgH 6 0 3 C 6 H 4 0 2 C 6 H 2 0 H 2 0 = C 6 H 8 0 4 . H 2 0 = C 6 H 6 03- H 2 0 = C 6 H 4 0 2 . H 2 0 = C 6 H 2 0. H 2 0 = C 6 . 56 DESTRUCTIVE DISTILLATION. carbon which may be represented as existing in groups of C 3 , so that its ultimate composition, as far as the carbon is concerned, is expressed by wC 3 . This group, he states, can be traced in the products of destructive distillation. It has to be noted, however, that it has been shown by Ramsay that pure cellulose yields acetic acid and methyl alcohol among its products of destructive distillation, and that their formation can scarcely be explained by the example of cumulative resolution given above. The whole question in its theoretical bearings is complicated by the fact that the substances which it is customary to distil destruc- tively are mixtures, and that numerous interdependent reactions no doubt take place. Thus, in the destructive distillation of wood, an exothermic change occurs at one point of the reaction, while with pure cellulose no such effect has been observed. A change of this kind may be attributed to the oxidation of a portion of the hydrogen or carbon of the material distilled, at the expense of another portion richer in oxygen, the reaction being induced by the attainment of a particular temperament. "Whatever be the precise mechanism of the changes involved in destructive distillation, the products usually include hydrogen, water, carbon monoxide and carbon dioxide; gaseous, liquid and solid hydrocarbons of several series and their oxygen derivatives; ammonia, organic bases, and cyanides (if the substance contain nitrogen); and sulphuretted hydrogen, carbon bisulphide, sulpho- cyanides, and bodies of which thiophen is a type (should sulphur be present). It is to be noted that the oxygen derivatives generally precede hydrocarbons in the order of distillation. The characteristic products for those classes of substances which are destructively distilled on an industrial scale, and the con- ditions governing their formation, will be dealt with under separate headings. It suffices to state here that when wood, brown coal, and bituminous shale are distilled, the products are chiefly of the paraffin series, and that when coal is distilled they are mainly aromatic. L DESTRUCTIVE DISTILLATION OF COAL. Kinds of Coal. — The various kinds of coal have been already classified in Vol. I., p. 49, and repetition is unnecessary. The class of coal used for destructive distillation is known, according to Griiner's classification, as "caking coal burning with a long flame." The average composition ranges from carbon 80 to 85 per cent., hydrogen 5 to 5*8 per cent., oxygen and nitrogen 10 to 14-2 per cent. These numbers are calculated on the coal free from ash, which averages 5 per cent. Coals of this character are hard, tough, dark, and lustrous, and have a specific gravity of 1-28 to 1-30. Various English gas coals exhibit considerable GAS-MAKING COALS. 57 deviations from these values, and could hardly be classed under Griiner's system. The following may be quoted : — Sp. Gr. C. H. S. N. O. Ash. H 2 0. Newcastle gas coal, . 1-26-1-33 80-2-84-3 4-6-5-3 0-8-1-3 0-9-1-7 4-3-9-2 1-4-5-6 11-1-7 South York silkstone, 1-26 80-3-82-0 5-0-5-7 1-2-1-6 1-7-1-9 5-2-7-2 2-3-3-3 0-9-1-3 Derbyshire silkstone, 75-7-76-9 5-0-5-8 2 3-2 4 1-6-1-7 5 6-7-5 3-0-4-4 3-6-3-9 Barnsley gas coal, . 75-6-76-6 4-8-5-0 1-3-2-8 1-6-1-7 6-9-7-5 3-9-4-6 0-8-3 5 Cannel, 69-0 8-8 1-3 1-9 8-9 10-1 The mere analysis of a coal does not suffice to determine its value for gas making, and it is, therefore, customary in gas works to put a small quantity through the whole process of distillation, in an apparatus similar to that used on the large scale, when both the quantity and quality of the gas and coke are determined. The yield and quality of both are dealt with in two subsequent sections. Cannel yields a gas of higher illuminating power than does gas coal, and it is used for enriching coal gas obtained from the latter. It should be added, however, that Deville has shown that there is a certain connection between the composition of gas coals and the nature and quality of the products of their destruc- tive distillation. The following table exhibits the composition of typical gas-making coals, calculated for the pure coal substance, free from ash and water : — t H. III. IV. 1 V. Carbon, 88-38 86-97 85-89 83-37 81-66 Hydrogen, . 5-06 537 5-40 5-53 5-64 Oxygen, 5-56 6 66 7-71 10-10 11-70 Nitrogen,* . 1-00 100' 1-00 TOO 100 Of these coals, that represented in column III. has the com- position typical of the best gas coal ; it yields a large quantity of gas and coke of good quality. Coals I. and II. give much coke, but poor gas. Coals IY. and Y. give gas of high illumi- nating power, but a small quantity of coke, and that of poor quality. The yield of coke decreases with the increase of oxygen in the coal, whereas the quantity of tar and liquor increases. * Assumed value. 58 DESTRUCTIYL DISTILLATION. The amount of aromatic hydrocarbons in the products appears to be independent of the content of the coal in oxygen, sulphur, and ash. (A.) CARBONISING IN RETORTS FOR GAS PRO- DUCTION. — The system essentially consists in heating the coal in a fireclay retort of elliptical or of O section, set in a furnace heated by producer gas. Formerly a furnace burning solid fuel — part of the gas coke — was used, but greater economy is obtained by using the coke in a producer, 10 to 15 per cent. Fig. 13. — Gas retort furnace. P, Producer ; W, water pan ; C, primary air channel ; T, secondary air channel ; F, F, exit flues ; U, chimney ; A. A, A, A, combustion channels. of coke, reckoned on the weight of coal carbonised, sufficing, instead of 25 to 40 per cent. The temperature of carbonisation is also higher ; this, however, contributes to the production of a less valuable tar, which being, moreover, more viscid, causes obstructions more readily. For the use of coke in a producer, see Vol. I., p. 65. A section of a typical retort of modern design is shown above. Its average dimensions are 9 to 10 feet long, 16 to 22 inches wide, 13 to 16 inches in height, and the walls have a thickness of 3 inches in the middle and 4 inches at the mouth. It is closed by a cast-iron mouthpiece projecting about 16 inches from the furnace (Fig. 13), bolted on to the thick fire- CARBONISING IN RETORTS FOR GAS PRODUCTION. 59 clay end, and provided with an "ascension pipe," 6 to 7 inches in diameter, and with a cast-iron door fitting on a bedplate, made air- tight by a lever hinge. Nowadays, retorts of double this length, with two mouths ("through retorts"), each with its appropriate fittings, are used, and are charged from each end. The mode of setting is shown in the illustration. In the case of the through retorts, separate furnaces and flues are used for each half. The method of heating is as follows : — An ordinary producer, P (Fig. 13), fed with the coke as it is drawn from the retorts {v.i.), is built close to the bench of retorts, the distance being the least possible to prevent loss of heat from the producer gas in passing. Fig. 14. — Setting for gas retorts. A, A, Section through retorts ; B, B, section through regenerator channels. to the space surrounding the retorts. A primary supply of air is drawn over a pan of water, W, placed beneath the fire-bars of the producer, but separated from these by a plate. It then passes through a firebrick channel, C, heated by contact with the flues conveying the products of combustion from the chamber containing the retorts, and is thereby heated to about 500° C. CO DESTRUCTIVE DISTILLATION. = 932° F. ; from this channel it enters the producer, where it forms gas of the average composition — CO 20*6, H 15*0, C0 2 8*6, N 55-8. This gas at the temperature of 1,150° C. = 2,102° F. passes up the channel, S, where it mixes with the " secondary " air (which is at a temperature of 1,000° C. = 1,832 3 F.), drawn in through the channel, T, heated by the exit gases passing through the neighbouring flues, F, F. In contact with this second supply of air the CO and H burn to C0 2 and H 2 0, and the flame plays round the retorts through the channels, A, A, A, A, the exit gases going to the chimney, U, by way of the flues, F, F, the walls of which are used for heating the secondary air supply, at a temperature of 1,400° C. = 2,552° F. A cross section through both retorts and regenerator is shown in Fig. 14, the former being represented at A, whilst the latter is shown at B. Charging and Drawing.— This is still generally effected by hand, the coal in quantities of 2 to 3 cwts. being introduced into the retort by means of a long scoop, the operation taking about forty seconds. At the end of the distillation the coke is drawn by long iron rakes, and, where the gaseous system of heating is in use, a portion falls directly into the producer, and the rest is quenched, while the retort is immediately recharged. Mechanical charging and drawing are, however, largely used. West's system involves the use of an automatic scoop ; to this the objection that it damages the retorts has been made. Other systems require the use of inclined retorts set at such an angle (about 30°) that the charge will fall out (after exhaustion) when dislodged by a slight push. The charging is effected from the top through a hopper, the angle of incline favouring the even distribution of the charge. The Process of Distillation. — The quantity and quality of volatile products obtained, and the time occupied by the distilla- tion, are largely dependent upon temperature. This generally ranges from 616° C. to 980° C. = 1,141° to 1,796° F., and even to 2,000° F. = 1,093° C, in a six-hour charge. The quantity of gas varies from 10,000 to 12,000 cubic feet per ton. The in- fluence of temperature upon the quantities of gas and tar pro- duced is generally seen in the larger volume of gas evolved at high temperatures, and the smaller amount of tar. The following table exhibits the yield of coke obtained from the coals mentioned on p. 57 ; it varies but slightly with the temperature : — Newcastle gas coal, South Yorkshire silkstone, Derbyshire silkstone, Barnsley gas coal, . Cannel, .... Percentage Coke. 67 66 64 64 50 Besides the carbon left as coke, there is a portion, constituting, THE PROCESS OF DISTILLATION. 61 however, but an insignificant fraction of the whole, left as a dense coherent coating (retort scurf, retort carbon, or gas carbon) on the interior of the retorts. This is produced by the decom- position of a part of the gaseous hydrocarbons evolved from the coal, and is useful as rendering the retort impervious to the gas, even though it crack, and harmful as reducing the capacity of the retort and hindering the access of heat to the coal from without. Chemically, a disadvantage accrues from this decomposition ("cracking," see Petroleum, Yol. II., Chap. Y.) of illuminating hydrocarbons to a point at which they deposit carbon — a decomposition which should be delayed until the hydrocarbons are burnt in an illuminating flame • per contra, heavy hydrocarbons that would otherwise condense in the tar are cracked with the formation of less condensible gaseous illuminants. As an example of this disadvantageous cracking, the following figures, which show the percentage of hydrocarbons and of hydrogen in the gas at different periods of the distillation, may be quoted : — Lapse of Time after Charging. Hydrocarbons. Hydrogen. 10 minutes. \ \ hours. H „ 5* » Per cent. 68 50 36 24 Per cent. 20 38 52 67 Experiments on a large scale have been made on the effect of the addition of slaked lime to the coal before its introduction into the retort; the amount added is 2*5 per cent.; it is claimed that the yield of gas is thereby increased to the extent of 5 per cent., but it is of 5 per cent, smaller illuminating power; the proportion of ammonia obtained with the tar is also increased in many cases from 20 to 50 per cent, of the amount ordinarily obtained, but this depends largely on the nature of the coal, no increase being sometimes observed. One of the principal objects of liming the coal is to increase the yield of ammonia ; that there is a large margin for improvement in this respect is shown by the following table giving the proportion of nitrogen usually appearing as ammonia and in other forms : — Per cent, of Total Nitrogen. Evolved as ammonia, ...... 14*50 cyanogeD, ...... 1'56 uncombined nitrogen, . . . . 35*26 Remaining in coke, . . . . . . . 48*68 100*00 G2 DESTRUCTIVE DISTILLATION. In spite of the multiplicity of the substances obtained during the process of destructive distillation, as already enumerated, they are commercially divisible into gas, tar (together with ammoniacal liquor), and coke. It follows from the general statements which have been made in the introductory section, that these products represent stages characterised by an increase in the content of carbon. Thus the gas contains as typical con- stituents, hydrogen and hydrocarbons of the paraffin series ; the tar is characterised by hydrocarbons of the benzene and still further condensed series ; while the coke approximates in com- position to carbon free from hydrogen. Their formation is, however, not successive but simultaneous, so that arrangements are necessary for separating them as they are produced. At the same time it is necessary to remove from the gas various con- stituents which would be objectionable in its use for lighting and heating. Both objects are attained by plant whose arrangement is typified in Fig. 15, and which will be described before con- sidering the products themselves in detail. Plant. — The volatile products are drawn from the retorts, A, by the exhausters, B (see below), through the ascension pipes, C, and the water contained in the hydraulic main, D, which is common to all the retorts, and whose function is to remove the less volatile portions of the tar and any solid matter, such as already condensed naphthalene and solid carbonaceous material carried over mechanically. A further use of this main is to serve as an hydraulic seal for the dip pipes, E, as the downward portions of the ascension, pipes are termed ; these are immersed to the depth of 1 to 1^ inches. This seal prevents the gas finding its way back into the retort when the latter is opened for charging. The products condensed in the hydraulic main are conveyed away by a pipe called the foul main (leading from the end of the hydraulic main), and are treated together with the rest of the tar. Another pipe, F, at the upper part of the hydraulic main conveys the gas to the condenser, which may be an air condenser, G, consisting in older plants of a series of vertical cast-iron pipes connected by D -shaped heads at the top, and set into a horizontal box with partitions between each adjacent pair, so that the liquid products are collected and the gaseous are free to pass throughout the system. This arrangement has the objection that the air warmed by contact with the lower part of each pipe rises, and by displacing the cold air hinders condensation : in modern practice this is met by arranging the pipes horizontally (see Fig. 15). Water-cooled condensers differ from the above in that the gas passes up a tower containing a number of vertical iron pipes through which water circulates in a direction contrary to that of the gas. In most English works the air condensers are still preferred. In English practice the exhauster (Beale's rotatory exhauster, B) 64 DESTRUCTIVE DISTILLATION. is a drum in which a second drum revolves, set eccentrically to the outer drum, and carrying a slide traversing the inner surface of the outer drum, thus pulling the gas from the retorts and pushing it to the succeeding portions of the plant, and is placed directly after the condensers. Other systems (e.g., the Korting) which are much used on the Continent involve contact with water in the exhausters ; these are, therefore, placed after the scrubber in order that the valuable ammonia may not be absorbed by the water they contain. The scrubber, or washer, H, is designed to extract the ammonia from the gas ; at the same time it removes a portion of the C0 2 , H 2 S, cyanogen, and sulphocyanogen. In its older form it consists of towers filled with wooden chequer-work or packed with coke, or provided with perforated horizontal plates, over which water is sprayed by a distributor at the top.* The gas ascends and is washed by the descending water. The clogging of the towers and the formation of channels among the packing thereof cause a loss of efficiency, so that other forms (such as that shown in the figure) are used, in which water is continually agitated with the gas in a cylinder by means of parallel metal discs attached to an axial shaft, which revolves at the surface of the water, so that one-half of each plate is continually exposing a freshly wetted surface to the gas. All methods of washing should be systematic — i.e., the water should travel through the washers in a direction the reverse of that of the gas. Much of the H 2 S, CS 2 , HON, HSCN, and C0 2 still remains in the washed gas, and has to be removed by passage through the purifiers, K. Two purifying materials are in common use — namely, slaked lime and hydrated ferric oxide. Neither of these is perfectly efficient alone nor capable of completely removing CS 2 ; but this latter object can be effected by lime which has been partially saturated with H 2 S, and thus converted into calcium hydrosulphides (Ca(SH)(OH) and Ca(SH) 2 ). The hydrated ferric oxide removes H 2 S thus — (1) Fe 2 O s . H 2 0 + 3H 2 S = Fe 2 S 3 + 4H„0. (2) Fe 2 0 3 . H 2 0 + 3H 2 S = 2FeS + S +"4H 2 0. The first is the chief reaction. The advantage of the hydrated ferric oxide over lime, which would also remove H 2 S, is that the mixture of Fe 2 S 3 and FeS can be taken out of the purifier and exposed to the air whereby it is "revivified" in accordance with the following equations, in which the water is not expressed : — (1) Fe 2 S 3 + 0 3 = Fe 2 0 3 + S 3 . (2) FeS + 0 = FeO + S. The FeO becomes converted into Fe 2 0 3 upon further exposure. *In large works the gas is generally "roughed" in some such washer as the Livesey, which consists of a tank with baffle plates to divide up the gas, and is finished in tower scrubbers. The washer-scrubbers described above are sometimes used alone. GAS PURIFYING VESSELS. 65 The oxide can be used repeatedly until it is "spent" — i.e., until it contains so much sulphur (50 per cent.) and other impurities as to be inoperative. The revivification can be effected simul- taneously with the purification, and the labour of removal from the purifier avoided, by the admission of 2 per cent, of air into the gas before it enters the purifiers; this, however, is objection- able as introducing the diluent nitrogen; Yalon's process sub- stitutes oxygen (0-5 per cent.) for the air. The spent oxide is valued in this country for its sulphur, which is recovered by burning it in the manner of pyrites "smalls" (see Sulphuric acid, Yol. II., p. 5). As the hydrated ferric oxide also removes HON and HSCN it is, when spent, valued chiefly on the Continent for the Prussian blue and sulpho- cyanides which it is capable of yielding (see Cyanide, Yol. II., Chap. XYIII.). The lime also removes the C0 2 , together with a portion of the H 2 S and the CS 2 , in the following manner : — Ca(OH) 2 + C0 2 = CaC0 3 + H 2 0 Ca(OH) 2 + 2H 2 S = Ca(SH) 2 + 2H 2 0 Ca(OH) 2 + H 2 S = Ca(SH)(OH) + HoO Ca(SH) 2 + Ci> 2 = CaCS 3 + H 2 S The sulphur is not recovered from the spent lime, which is sometimes reburnt with the elimination of most of the sulphur as S0 2 , and of all the C0 2 , but with the simultaneous forma- tion of a good deal of calcium sulphate, the accumulation of which soon renders fresh lime necessary. The best arrangement for combining the advantages of these three purifying materials is as follows : — Each is disposed on wooden trays arranged in tiers in an iron box, L, provided with a cover, having a water seal to allow of its ready removal. The gas is forced by the above-mentioned exhausters through a series of these in the following order : — The first ("carbonate vessel") contains moist slaked lime, and chiefly removes C0 2 ; it is incapable of removing much of the H 2 S, because of the decom- posing effect of the C0 2 on the calcium hydrosulphide which would be formed. The second (" oxide vessel") is filled with the hydrated ferric oxide, generally Irish bog ore containing about 32 per cent, of Fe 2 0 3 .H 2 0, finely ground and mixed with an equal bulk of sawdust ; this removes most of the H 0 S. The third ("sulphide vessel") contains the slaked lime from an earlier purifier which has become saturated with H 2 S, and is rich in calcium hydrosulphide ; this removes most of the CS 2 , and the sulphur content of the gas is thereby lowered to a point such as that adopted as a standard by the Metropolitan Gas Referees. The last (" check vessel ") contains moist slaked lime or ferric oxide, and removes the remaining trace of H 2 S which has been expelled from the calcium hydrosulphide by the CS 2 . These purifiers are generally worked in pairs. 5 66 DESTRUCTIVE DISTILLATION. The use of Weldon mud (see Alkali, Vol. II., p. 38) lias been recently adopted. The chemistry of its action on the H 2 S is similar to that of the action of Fe 2 0 3 (v.s.), but traces of H 2 S are more easily removed by it than by ferric oxide. Weldon mud is easily revivified in situ by the admission, together with the coal gas, of a volume of air appropriate to the percentage of H 0 S to be removed ; about 1 per cent, of the volume of the gas is generally sufficient, if the vessel be periodically blown through with pure air. The gas issuing from the purifiers is measured by passing through the station metre, M, and is collected in the gasholder, N. The pressure of the gasholder is usually sufficient to effect the distribution of the gas through the mains unless the consumers be at considerable distances, when additional pumps on the prin- ciple of the Beale's exhauster are necessary for this purpose. Products — Gas. — According to Mills the average yield of the chief products for large works per 100 parts of coal is — gas (specific gravity 0*48, 17 candle power) 16*6 per cent., ammoniacal liquor 14*1 per cent, (yielding (NH 4 ) 2 S0 4 , 0*87 per cent.), tar 5*3 per cent., coke 66 per cent. The following table gives the average composition of the gas before and after purification : — Unpurified. Purified. By vol. By vol. H, 47 per cent. 51 per cent. CH 4 , 34 „ 36 CO, 5 » 5 „ Heavy hydrocarbons (C„H TO ), . 4 „ 4 H 2 S, 1 „ NH 8 , co 2 , 4 N, 4 „ 4 per cent. The constituents of the crude gas, which are commonly called impurities, are generally quoted in terms of grains per 100 cubic feet. Thus, Butterfield * gives the following table as expressing the limits for Durham coal carbonised at moderately high tem- perature : — Grains per 10O cubic feet. Ammonia, . . . 0 65 to 0*95 per cent, by vol. or 200 to 300 Carbonic acid, . . 1-2 „ 1*8 „ ,, 980 ,, 1,470 Sulphuretted hydrogen, 09 ,, 1-5 „ „ 570,, 950 Carbon bisulphide, . 0*020 „ 0*035 „ „ 28,, 50 Other sulphur compounds, ... ... 5 ,, 8 Cyanogen, . . . 0"05 „ 0*10 ,, „ 50,, 100 * Gas Manufacture (Chas. Griffin & Co., Ltd.). VALUATION AND UTILISATION OF COAL GAS. G7 The manner in which the composition and quality of the gas are influenced by the temperature of distillation is illustrated below (L. T. Wright). Newcastle coal yielded at the tempera- tures named : — Dark red Bright red Bright orange heat. heat. heat.* Cubic feet of gas per ton, Illuminating power of equal vols, of gas (candles), . 20-5 17'8 15-6 Illuminating power (candles) of gas from equal weights coal, ..... 34 35 37 Hydrogen (H) per cent., 38-1 43-8 48-0 Methane (CH 4 ), . 42 7 34-5 30-7 Carbon monoxide (CO), . 8-7 12-5 14-0 Heavy hydrocarbons (C M H m ), 7-6 5-8 4-5 Nitrogen (N), 2-9 3 4 2-8 The gas in these experiments was lime-purified. It will be seen that although the gas made at the higher temperatures is poorer in illuminating power when equal volumes are com- pared, yet that the total illuminating power obtained from the greater volume of gas given off at high temperatures of carboni- sation is in excess of that yielded by the gas produced at low temperatures. In modern practice the greatest possible yield of gas is obtained by carbonising at high temperatures, and the illuminating power is brought up to the standard (v.i.) by enrichment, which is dealt with in later paragraphs. It is to be noted that a high tempera- ture of distillation increases the quantity of the chief impurities, C0 2 , H 2 S, CS 2 , and CIS". Thus, in certain results it was found that the C0 2 varied between 16 and 18 grains per cubic foot; the H 2 S between 8*4 and 10*6 grains per cubic foot; the CS 2 , 0-27 and 0-40, and the ON, 0-13 and 0*56 grain per cubic foot. Valuation and Utilisation of Coal Gas. — The valuation of gas for commercial purposes generally consists in the determina- tion of its illuminating power and the estimation of its objec- tionable impurities. The illuminating power is measured by a photometer, the standard instrument prescribed by the Gas Referees being the "Evans." Its principle consists in illumi- nating a paper which is greased, save for a central spot ; one side of this paper is illuminated by the gas to be tested, burnt at the rate of 5 cubic feet per hour from a standard burner, and on the other by the standard light which is obtained from one or two sperm candles (six to the pound), each burning at the rate of 120 grs. per hour. The position of * For the temperatures roughly equivalent to these technical phrases see Vol. L, p. 83. G8 DESTRUCTIVE DISTILLATION. the screen between the two lights, when the non-greased spot appears similar to the greased part of the paper on viewing it from both sides, serves to measure the illuminating effect of the two lights, their intensities varying directly as the square of their distance from the screen. (A more accurate standard light has been devised by Vernon Harcourt, and consists of a burner consuming a mixture of air and the vapour of the hydrocarbon pentane, C 5 H ]2 , giving the light of one sperm candle. At present the instrument has been considered too delicate for practical use.*) The illuminating value, however obtained, is expressed as the number of standard candles to which it is equivalent. This value is roughly judged at the gas works by ascertaining what pressure is required to yield a flame 7 inches in height, from a standard jet (jet photometer) ; this depends on the fact that the amount of gas issuing from a constant orifice, at constant pressure, is dependent upon its specific gravity, which is roughly related to its illuminating power; thus, 16-candle gas is about specific gravity 0*36 to 0*38; 19-candle gas, 0'42 to 0*43; 20-candle gas, 0-45 to 0-46 ; gas from Boghead cannel (36-candle), 0*75. The lower the specific gravity of the gas, and the lower its illuminat- ing power, the higher the pressure needed to give a 7-inch flame. With regard to the objectionable impurities in gas, the sul- phur compounds are injurious in that S0 2 is produced by their combustion, and some sulphuric acid is ultimately formed. The ammonia is objectionable from its tendency to form cyanogen and oxides of nitrogen during combustion. H 2 S is tested for, separately from the other sulphur compounds, by exposure of paper soaked in lead acetate to a stream of the gas (10 cubic feet in all, per test) ; it should be entirely absent, as shown by the paper remaining undarkened. An ingenious instrument has been devised for obtaining a continuous record of the freedom, or otherwise, of the gas from H 2 S, and consists of a strip of lead paper caused to traverse a bell jar through which the gas is passed, the paper being driven by clockwork at a known rate, and entering and leaving the jar by mercury traps. The ammonia is next determined by passing the gas through a glass cylinder filled with beads moistened with a solution con- taining a known quantity of sulphuric acid ; from the amount of this remaining unneutralised after the experiment, the quantity of ammonia is calculated. In the Metropolis its amount must not exceed 4 grains per 100 cubic feet. For determining the sulphur compounds, other than H 2 S, the gas is finally burnt in a Bunsen burner and the products of combustion caused to pass up a tower filled with glass marbles. The air in which the gas burns is drawn through lumps of ammonium carbonate, the vapour of which fixes the S0 2 , ammonium sulphite and sulphate * Another instrument (the Dibdin lamp) on the same principle has been devised, which is free from this objection. ILLUMINATING POWER OF COAL GAS. 69 being produced ; these are caught by the water of combustion and condensed by the cold glass marbles. The water is collected, and the sulphur in it determined as barium sulphate. The sulphur must not exceed 17 grains per 100 cubic feet in summer, and 22 in winter. The illuminating power of coal gas doubtless depends on the nature and quantities of its constituents, but the relation between the two is not yet thoroughly ascertained. It is customary to consider the constituents as falling into three classes : — (1) The illuminants ; (2) the non-illuminant combustible gases ; (3) the diluents which contribute neither to the luminous nor to the heating effect. The illuminating effect is generally agreed to be ultimately due to the separation of solid carbon in the flame, though the reactions by which this is brought about are still under discussion. Formerly it was supposed that the unsaturated hydrocarbons, which consist mainly of members of the olefine, acetylene, and benzene series, were alone concerned in the production of light, inasmuch as these bodies are known to burn with luminous flames. At the present time there is reason to believe that the chief saturated hydrocarbon present — viz., CH 4 — which by itself has a non- luminous flame, yet when heated to the temperature of a coal gas flame will also contribute to the luminosity by its decomposition, so that the former criterion known as "carbon density," by which term was implied the ratio of carbon to hydrogen in the unsaturated hydro- carbons, is of doubtful value. Hydrogen and carbon monoxide are the chief non-illuminant combustible gases, and serve to raise the temperature of the flame, upon which the incandescence of the carbon depends. Nitrogen and carbon dioxide are the main diluents, and diminish the luminosity of the flame by absorbing heat, and by increasing the volume of the flame. The proximate composition of an average sample of coal gas (South Metropolitan) is, according to Y. B. Lewes, Per cent. Hydrogen, 57 'OS *Unsaturated hydrocarbons, . . 4*38 Saturated ,, ... 33*99 Carbon monoxide, .... 2*63 ,, dioxide, . . . . . 0'79 Nitrogen, 0'96 Oxygen, ...... 0*15 Carbon bisulphide, . ... . 0'02 Inasmuch as the illuminating power of gas depends largely upon the conditions of combustion, as distinct from the composition of the gas itself, much attention has been paid to the form of burner which shall combine the highest illuminating effect with the smallest consumption of gas. There are four types of burners in general use :— (1) The simple jet so arranged as to spread the * Containing acetylene,, 0 035. 70 DESTRUCTIVE DISTILLATION. flame in a broad thin sheet, with or without a regulating valve for governing pressure — e.g., the common "batswing" and " fishtail." (2) The argand, in which a greater supply of air is obtained by means of a glass chimney surrounding an annular flame, the temperature of which is raised by the heat radiated from one side of the ring to the other. (3) The regenerative burner, in which the gas is burnt in a ring and the products of combustion are caused to circulate round the air supply, and thus heat it ; such are the Wenham, Siemens, and Fourners. (4) The incandescent burner, such as the Welsbach, in which an air-gas flame (v. i.) plays upon refractory material, in the form of a cap or mantle, and heats it to incandescence. The air-gas flame is produced by allowing the gas to stream from a small orifice, whereby it produces a lowering of pressure in its immediate neighbourhood, and draws in a supply of air (about two and a-half times its volume), with which it mixes as it passes up a wide tube, burning at the end of this tube with a flame which is rendered non-luminous, partly by the diluting action of the air, and partly by the presence of sufficient oxygen to burn the hydrocarbons without the intermediate liberation of carbon. The advantages of this flame are that it is hotter in certain portions than a similar luminous flame, and that it does not deposit soot. If arrangements be made to admit more air than two and a-half times the volume of the gas, the flame becomes smaller and burns with a greenish inner cone, and is much hotter, inasmuch as the action of excess of oxygen over- comes the diluting effect of the air. Such burners are known as "solid flame burners," and must be provided with a metal gauze cap to prevent the explosive mixture of gas and air taking fire down the tube. The action of the gauze is similar to that in a Davy safety-lamp, and depends upon the fact that if the heat of a flame be rapidly conducted away, the flame is extinguished. A quiescent mixture of gas and air is only explosive when the quantity of gas lies between 5 and 30 per cent, of the total volume of the mixture. Burners of this description are used for gas fires and cooking stoves. The relative illuminating power of gas burnt under different conditions is shown by the following table (A. Wilson) : — Candle Power per Cubic Foot per Hour. British Thermal Units per Candle Power per Hour. Flat flame, o 347 Argand, .... 2-2 315 Siemens regenerative, 2-G 26G Wenham, .... 4-5 154 Welsbach, 7-0 ENRICHMENT OF COAL GAS. 71 From this it is seen that, apart from other considerations, such as first cost and cost of maintenance, the incandescent system is the most economical. The conversion of the chemical energy of coal gas into light is extremely imperfect, only about 0*5 per cent, of the total energy appearing as luminous vibrations in the case of a common argand. Regenerative burners have about double this efficiency — viz., 1 per cent. The quantity of energy appearing as luminous radiation from an incandescent electric lamp supplied by a gas engine and dynamo is about 0*75 per cent, of the chemical energy of the gas consumed in the engine, while if an arc light be used the efficiency rises to 3*5 per cent. For the utilisation of coal gas for domestic heating and as a source of mechanical power, see Vol. I., p. 61. Enrichment of the Gas. — This was, until recently, wholly effected (when done at all) by carbonising sufficient cannel coal to bring the illuminating power to the required standard. The quantity generally used is about 10 to 15 per cent, of the coal carbonised. The cannel is mixed with the ordinary gas coal, and the two carbonised together. The name " cannel " is from the word " candle," the analogy arising from the fact that a splinter of the coal burns brilliantly when ignited. Cannel is of the nature of a shale rather than of a true coal, and its composition (p. 57) indicates the divergence, which is also illustrated by the quality of the tar obtained during the dis- tillation. This contains so much paraffin that it is of little value to the tar distiller. (Compare Shale, Yol. II., p. 100). The candle power of cannel gas varies according to the quality of the cannel and the temperature of distillation, but is usually as high as 30 c.p. The following analyses of gas supplied to Scotch towns are given by P. Frankland : — Illumin- ating Power. Un- saturated Hydro- carbons. Saturated Hydro- carbons. H. CO. co 2 . 0. N. Edinburgh, 30 12-23 42-93 33 24 661 0-35 1-00 3-64 Glasgow, 27 10-00 40-20 39-18 714 0-29 0-06 3 07 St. Andrews, 27 10-04 42-13 33-63 5-10 273 0-48 2-83 From these it will be seen that the unsaturated hydrocarbons, or " illuminants," are present in more than twice the quantity found in ordinary coal gas, and that the saturated hydrocarbons are also considerably higher, while the hydrogen shows a cor- responding decrease. The difference of illuminating power is dependent upon these facts. The increasing dearness and badness of cannel have led to the 72 DESTRUCTIVE DISTILLATION. use of other methods of enriching gas. That at present most in use consists in adding a regulated amount of water gas, charged with the vapours of comparatively heavy hydrocarbons, to the gas produced in the retorts from common gas coal. Water gas is the product of the action of steam upon heated carbonaceous fuel, the fundamental reaction governing its forma- tion being H 2 0 + C = CO + H 2 . This reaction is endothermic — i.e., it requires the application of extraneous heat to maintain it. The amount of heat that has to be supplied is 38,770 gram-units per 18 grams of liquid water decomposed. The heat necessary to produce the decom- position may be supplied by heating the vessel containing the carbonaceous matter (generally coke) in a furnace, but such procedure is uneconomical and the usual practice is to bring the coke to a white heat by means of the exothermic reaction — C + O + N 4 = CO + N 4 + 29,690 gram-units per 12 grams of C burnt. The method adopted for taking advantage of both these reactions is as follows : — The fuel is contained in a firebrick chamber (the producer or generator), at the bottom of which a blast of air is delivered at 12 to 15 inches water pressure. The resulting producer gas (CO and N) is led into another fire- brick vessel or "stack" packed with brickwork where it meets a fresh supply of air and is partially burnt, heating the brickwork to whiteness; the partially burnt gas then passes into another similar stack where it meets a second supply of air and is completely burnt, thus furnishing a second hot chamber. At the end of about five minutes the blast of air is shut off and steam, at about 130 lbs. per square inch, let in through the heated coke producing water gas, an example of the average composition of which is— H 49-17, CH 4 0-31, CO 43 55, C0 2 2-71, N 4-06, H 2 S 0-2. After it has left the coke, the water gas passes into the first brickwork chamber (carburettor) where petroleum oil (which may be fairly crude, but must be free from cokey residue when distilled), such as " solar oil" — a product from the distillation of Russian petroleum, intermediate between the burning and lubricating oils (see Petroleum, p. 122), of specific gravity 0*87 — is sprayed in, and then into the second chamber (superheater) where the oil which has been already vaporised and partly decomposed or "cracked" is "fixed"— i.e., resolved into more nearly permanent gases. This enriched water gas is then scrubbed, passed through purifiers, and mixed with the purified coal gas from the carbonising retorts. The benefit to the coal gas will be gathered from the following analysis of a sample of New York oil-water gas : — H 26*25, saturated hydrocarbons; 28-91, CO 27-12, N 1-92, unsaturated hydrocarbons 15-80, candle power 29-68. The character of the unsaturated hydrocarbons produced during the cracking and fixing is but little known; ENRICHMENT OF COAL GAS BY OIL VAPOUR. 73 there seems reason to suppose, however, that they are relatively rich in benzene. If the gas coke be used for making water gas, 1 ton of coal could first be made to yield 12,000 cubic feet of coal gas, and the resulting coke (about 60 per cent, of the weight of the coal) could produce about 18,000 cubic feet of water gas and 66,000 cubic feet of producer gas. The respective fractions of the total energy of the coal thus represented are best compared as follows : — Cu. ft. x Cal. . Cal. Coal gas, ..... Water gas, ..... Producer gas, .... 12,000 x 170 18,000 x 74 66,000 x 28 2,040,000 1,332,000 1,848,000 5,220,000 Taking the coal as having a calorific value of 8,300 Cal. — i.e. 7 yielding 8,300,000 Cal. per ton of 1,000 kilos. — this is equivalent to an efficiency of 63 per cent. It will be noted that the heat required to distil the coal destructively must be deducted if the net efficiency of the process has to be reckoned. The cost of carburetted water gas is not very different from that of coal gas, its advantages lying less in cheapness that in ease of control and adaptation to the maintaining of the illuminating value of the coal gas with which it is mixed. It has a special value in countries containing anthracite but little bituminous coal, as by this means the former can be used for the production of lighting gas by conversion into water gas and subsequent enrichment of the product. Other methods of enriching gas, depending on the intro- duction of the vapour of hydrocarbons less costly than benzene, into the coal gas, have proved more difficult of application owing to the tendency of the vapours to deposit in the delivery pipes. Nevertheless, considerable success has attended the use of the system in which a light petroleum oil (carburine, specific gravity 0*68) is passed through steam-heated pipes, and the vapour is admixed with the gas. One gallon of such oil will impart 1 candle power to 8,000 cubic feet of gas. The cheapening of benzene by its recovery from coke ovens (q-v.) has led to its- proposed use for enrichment. Another system of the same class is that known as the "albo- carbon," in which the gas passes over melted naphthalene heated by the burner itself. All these methods of enrichment, entail the consumption of the gas immediately after the en- riching vapour has been introduced. It has recently been found possible to manufacture calcium carbide (CaC 2 ) by heating a mixture of chalk and coke in an DESTRUCTIVE DISTILLATION. electric furnace. This compound evolves acetylene (C 2 H 2 ) when brought in contact with water — CaC 2 + 2H 2 0 = Ca(OH), + C 2 H,. Acetylene, being an endothermic compound (0 2 , H 2 = -47,750 gram-units), and capable of easy decomposition with separation of carbon, burns with a flame which is of high temperature and high illuminating value (240 candles per 5 cubic feet per hour). It appears, however, that the value of this gas as an illuminant is much depreciated when the gas is mixed with coal gas, so that the " enrichment value " of acetylene is comparatively poor. Acetylene will probably come into use as an illuminant on a small scale; it is liquefied by a pressure of about 80 atmospheres at 18° C. = 64° F. ; the liquid is colourless, and has a specific gravity of 0*4. Water at 18° C. = G4° F. dissolves about its own volume of the gas. Commercial calcium carbide contains about 80 per cent, of CaC 2 , and yields some 10,000 cubic feet of acetylene per ton. The gas has a considerable action on copper 221 0-27 , , 3, 2-27 0-47 Parkgate, 2-40 0-70 Cannel, .... 1-60 0-46 The liquor from small works, in agricultural districts, is some- 76 DESTRUCTIVE DISTILLATION. times applied directly as a manure, but in large works it is used for the production of ammonium sulphate, which, is also chiefly used for manurial purposes (manure salts), see Artificial Manures, Vol. II., Chapter IV. Incidentally, the sulphur present as ammonium hydrosulphide is evolved as H 2 S, which is burnt in Claus kilns (see Alkali, Vol. II., p. 33) for the re- covery of the sulphur. The working up of the gas liquor for ammonium sulphate is carried out in the following manner : — The liquor is heated to drive off the free ammonia, and the vapour is absorbed in sul- phuric acid, forming ammonium sulphate, which crystallises and is periodically fished out. It is the common practice in England to use only that part of the ammonia which is liberated on distilling the liquor alone, but sometimes, especially on the Continent, the fixed ammonia is liberated by the addition of lime. A typical apparatus is described in the section dealing with the recovery of ammonia (see Ammonia-Soda Process, Vol. II., p. 47). Commercially, ammoniacal liquor is evaluated by the number of ounces (avd.) of pure oil of vitriol required to saturate 1 gallon of the liquor. The common strength is about 8 ounces. Coal Tar. — Coal tar may be considered as those products of the distillation which distil at a temperature above the boiling point of benzene (80° C. = 176° F.), containing in solution small A proportions of more volatile products, of the same classes as those ' which occur in the gas itself. The condensation occurs in the hydraulic main, the condensers, and to a smaller extent in the ;? ; scrubbers. The specific gravity of tar varies between 1*1 and 1*2, and is usually between 1*12 and 1-15. The influence of the temperature of distillation on the specific gravity and yield of coal tar for different kinds of coal is shown by the following table : — Class of Coal. Temperature of Distillation. Specific Gravity of Tar. Percentage Yield on Coal. Derbyshire black shale, No. 1, Derbyshire black shale, No. 2, Notts top hard cannel, . ( Very high, < Normal, ( Very low, Very high, < Normal, ( Very low, \ Normal, \ Very low, 1-210 1-185 1-145 1-207 1-185 1*136 1-147 1-116 5-74 5- 88 6- 47 7 29 10- 92 11- 86 Tar is a very complex mixture, and contains the following classes of substances : — (1) Hydrocarbons of the paraffin and benzene series, the former in small quantities; naphthalene,, anthracene, and their homologues. (2) Phenols and their con- DISTILLATION OF COAL TAR. 77 geners. (3) Sulphur compounds, including H 2 S, CS 2 , mercaptan and thiophen, present in small amount. (4) Nitrogen compounds, such as ammonia, aniline, and other organic bases. (5) Com- pounds of uncertain character, rich in carbon, constituting the pitch. Of these the benzene hydrocarbons, the phenols, the naphthalene, anthracene and pitch are present in largest quantity, and are separated by distillation in the following manner : — The tar is always wet with gas liquor, and is separated from this as far as possible by subsidence, as the presence of water causes frothing in the stills. The retort is a vertical cylindrical vessel with an inwardly curved bottom and a dome- shaped top through which a thermometer passes ; it holds about 25 tons. It is heated by direct firing, and is fitted with steam jets at its lower part for blowing in steam towards the end of the distillation. Occasionally horizontal cylindrical stills with mechanical stirrers are used. The vapours pass from the still head to the condensers which are usually cast-iron worms cooled with water in the usual way. The products are collected in closed tanks which are changed as the different fractions, best indicated by the temperature of their distillation, come over ; an outlet must be provided for permanent gases such as H 2 S, CS 2 , and paraffin hydrocarbons, which are evolved at various stages of the distillation, and is either connected with a chimney shaft, or, if nuisance must be avoided, with a set of scrubbers and purifiers. The distillate is collected in the following fractions : — (1) First runnings, up to 105° C. = 221° F. (2) Light oil, up to 210° C. = 410° F. (3) Carbolic oil, up to 240° C. = 464° F. (4) Creosote oils, up to 270° C. = 518° F. (5) Anthracene oil, from 270° C. to the " pitching point," which varies according to whether hard or soft pitch is to be made. In modern practice the first two fractions are frequently collected together. Although the re- ceiver is changed at the above-mentioned temperatures, it must he remembered that the fractions will contain compounds which boil at higher temperatures than those named, on account of the tendency of one vapour to carry over others at its boiling point, even though their boiling points be higher. The proportions of the five fractions vary greatly. The following is the typical com- position of Beckton tar : — ( consisting of ammoniacal liquor, First runnings, . . 3'66 per cent., < 2 - 00 per cent. ; crude naphtha, ( 1 *66 per cent. Light oils, . . . 1*62 Carbolic and creosote oils, 15*70 ,, ( containing crude anthracene (30 Anthracene oils, . . 20'73 ,, < per cent, real anthracene), 1*90 ( per cent. Pitch, . . . .56*29 Loss, .... 2-00 100-00 78 DESTEUCTIVE DISTILLATION. The first runnings consist of ammoniacal liquor — which is added to, and worked up with, the main quantity previously separated by subsidence — and crude naphtha, which consists of hydro- carbons of the benzene series, mainly benzene and toluene, accompanied by the more volatile impurities of coal tar, such as CS 9 , thiophens, &c. This is generally worked up with the light oils. The light oil (specific gravity about 0*9) derives its name from its being lighter than water ; it consists of a large number of hydrocarbons of the benzene series, among which benzene is present in minor quantity ; toluene and the three xylenes occur in somewhat greater amount, together with heavier hydrocarbons. Bases of the pyridine series and tar acids or phenols are also pre- sent. The first step in working up the light oil is redistillation, which takes place in a still similar to that used in distilling the tar; the distillate is then divided into first runnings, which are similar to those obtained from tar itself and are worked up with them as described below for crude naphtha, and last runnings, which contain the phenols and are added to the carbolic oil. The crude naphtha is first agitated successively with strong sul- phuric acid and caustic soda; the former combines with the bases, dissolves part of the thiophens and olefines, and chars other impurities; the latter removes the tar acids (phenols) and neutral- ises residual sulphuric acid. Inasmuch as the acid also converts phenols into sulphonic acids, from which the phenols are not easily recoverable, it is preferable to treat first with caustic soda (specific gravity 1*15) to remove these, and then with sulphuric acid, finishing by washing with a weaker solution of soda. The "acid tar," as the spent acid is termed, is used for making am- monium sulphate after the separation of the coarser impurities, and as a source of pyridine bases used to denature alcohol for industrial purposes in Germany. The spent soda is acidified with sulphuric acid, and the liberated tar acids worked up with the carbolic oil. The naphtha thus purified is fractionated in a still of the same pattern as that used for the tar itself, the dis- tillate being collected up to 140° C. = 284° F. for benzols, and from 140° to 170° C. = 338° F. for solvent naphtha. The dis- tillate up to 140° C. is about 50 per cent, of the total, and that between 140° and 170° C. 25 per cent., the remaining 25 per cent, being heavy oil, which goes to be worked up with the carbolic oils. The fractionation of the crude benzol is effected in a still heated by a steam coil, and provided with means for injecting steam towards the end of the distillation. In this and the subsequent rectifications the still is fitted with a dephlegmator — that is to say, an arrangement for condensing the less volatile products and returning them to the still ; it is generally either a coil surrounded by water kept at a constant temperature, or a CARBOLIC OILS. 7£ tower similar to that used in the Coffey still (see Brewing and Distilling, Vol. II., Chap. IX.). The benzol is mainly required by the aniline colour maker who uses two qualities — one containing some 70 per cent, of benzene and about 25 per cent, of toluene, and known in the trade as " 90 per cent, benzol," meaning that this proportion of it distils below 100° C. ;* the other containing about 44 to 48 per cent, of benzene and much toluene, and known as " 50 per cent, benzol/' meaning that this proportion of it distils below 100° C. By regulating the temperature of the dephlegmator, either quality may be obtained, or the hydrocarbons themselves may be isolated ; benzene (boiling point, 80° C. = 176° F.), toluene (boiling point, 111° C. = 232° F.), and xylene (boiling point, 138° to 141° C. = 280° to 286° F.)— a mixture of the three isomeric hydrocarbons thus known — are now articles of com- merce. The purest benzene is obtained by freezing the com- mercial product; its melting point is 5-5° C. = 42° F. Beside these products from the crude benzol, a portion boiling up to 170° C. = 338° F. (compare p. 78) is marketed as " sol- vent naphtha this is similar to the fraction boiling between 140° to 170° C. from the distillation already referred to, of the washed crude naphtha. Solvent naphtha consists largely of xylenes and cumenes, and is so called from its application as- a solvent for indiarubber. It should be free from naphthalene, which is often present in a similar fraction used for burning in street lamps, and known, therefore, as " burning naphtha." The carbolic oils, which are included with the creosote oils mentioned in the analysis of tar quoted above, amount to 4 to 5 per cent, of the original tar. The point at which the receiver of the tar still is changed, is fixed not only by the temperature, but by the appearance of solid naphthalene in the distillate, an indication that the bulk of the " tar acids " f (phenol and its homologues, commercially known as carbolic and cresylic acids) has come over. The oil is filtered from such naphthalene as separates on cooling, and is extracted with a solution of caustic soda which dissolves out the tar acids. A cheaper method is that known as the West-Knight and Gall pro- cess, which consists in treating the oil with a mixture of lime and sulphate of soda, whereby sulphate of lime and the sodium salts of the tar acids, " sodium carbolate," are formed. The un- *In this and all other cases, "benzol" is used to signify the commercial product, while "benzene" indicates CgH 6 . Both are absolutely distinct from "benzine," which is a petroleum product. Toluol and xylol are com- mercially used for toluene and xylene. + These are now sold as disinfectants, being dissolved in a soap solution for this purpose : trade names such as creolin and lysol are used for such solutions. 80 DESTRUCTIVE DISTILLATION. attacked neutral oil is sometimes worked up for naphthalene (q.v.), or if this be not wanted the oil is returned to the light oils, inasmuch as it contains benzene homologues. The alkaline solu- tion of sodium carbolate is generally mixed with the alkaline washings of the light oil (v.s.), and treated with sulphuric acid, which sets free the tar acids, these floating upon the aqueous liquid as an oily layer. The sodium sulphate formed is practi- cally valueless where caustic soda has been used for extracting the tar acids, but can be used over again when a mixture of sodium sulphate and lime has been employed. In any case the aqueous liquor is drawn off, the crude tar acids allowed to settle for a •day or two, and sold as " crude carbolic acid " of specific gravity 1*05 to 1*065. The "crude carbolic acid" is worked up for "pure carbolic acid "—i.e., phenol, C 6 H 5 (OH). The crude acid contains, besides phenol, cresol, water and some neutral oils. The separation of phenol and cresol is effected either by fractional distillation or fractional precipitation of their solution in caustic soda with sulphuric acid. When an insufficient quantity of acid is added to a solution containing the sodium salts of phenol and cresol, the latter, as the weaker acid, is first precipitated, and thus can be separated from the undecomposed sodium salt of phenol, which is then similarly acidified, and the phenol got out. However obtained, the frac- tion richest in phenol solidifies on cooling to about 10° C. = 50° F. The crystals (melting point 42° C. = 108° F., boiling point 182° C. = 360° F.) are freed from the still liquid portion by treat- ment in a centrifugal machine, and generally again distilled with an addition of 0-2 to 0*3 per cent, of potassium bichromate, and a little sulphuric acid ; the object of the addition of this oxidising agent being to destroy the impurity that hastens the change by which even pure phenol becomes red on exposure to air and moisture ; this discoloration takes place especially easily when the acid has been distilled from a metal still, so that the phar- maceutical product is finally distilled in glass. The commercial grades of carbolic acid comprise those containing water — which in consequence melt at a lower temperature than the anhydrous acid — and mixtures of phenol and cresol. In consequence, the term "carbolic acid" is objectionable because necessarily vague. The chief uses of all the grades are for disinfecting purposes, the production of salicylic acid, colouring matters, and explosives (q.v.). The creosote oils are chiefly valuable on account of the naphthalene they contain, and for their use as a preservative for timber (see Vol. I., p. 46). They consist of a solution of naph- thalene, anthracene, and similar solid hydrocarbons, in liquid hydrocarbons, the composition and nature of which have not yet .been fully ascertained. When the creosote oils, as they come from the tar still, cool, ANTHRACENE OIL OR GREEN OIL. 81 much naphthalene is deposited, amounting to about 5 to 10 per cent, of the tar, and is separated by draining, and then pressed in hot presses like those used for stearic acid ("stearin") and anthracene (q.v.). It is further purified from acid and basic impurities by successive treatment with caustic soda and sul- phuric acid. In the latter process 5 per cent, of manganese dioxide (Weldon mud; see Alkali Manufacture, Yol. II., p. 38) is added, in order that the final product may remain white on keeping. Some naphthalene is also obtained from the carbolic oils, as has been already mentioned. The washed naphthalene is either sublimed or distilled, preferably the latter. Iron stills heated by direct fire and provided with dephlegmators are used ; a safety-valve is provided in case the worm should block, although in the best practice the "worm" is a straight pipe through the centre of which runs a small steam pipe, and round which the condensing water circulates. The portion coming over between 210° and 235° C. = 410° and 455° F. (indicated by a thermometer in the vapour) consists of nearly pure naphthalene ; the object of the steam pipe in the condensing tube is to keep the naphtha- lene in the liquid state, and allow it to run into a receiver fitted with a partition reaching nearly, but not quite, to the bottom ; through this space the naphthalene (specific gravity 1-1517, melting point 79° C. - 174° F., boiling point 218° C. = 424° F.) which sinks in the water, passes, and is collected free from water in the other division. The molten naphthalene is cast into cakes, candles or marbles, according to its intended use. The cakes are used in place of camphor as an insecticide. The candles and marbles are employed for the "albo-carbon light" — i.e., for enriching coal gas with naphthalene vapour the moment before its combustion (see p. 73). Naphthalene is also converted into naphthols, nitro-naphthalenes and naphthylamines, which are used for the production of synthetic colouring matters. Nitro- naphthalene is also used for " deblooming " mineral oils — i.e., removing their fluorescence — the object being to allow of their being used as adulterants without immediate detection. The creosotes themselves after separation of naphthalene are not usually further treated, but go for creosoting timber as already described (Vol. I., p. 46). A small portion, however, is employed for the manufacture of lubricants, and also for burning in blast lamps used for outdoor illumination — e.g., the Lucigen or Wells light — for which purpose it is filtered and fetches a higher price. The anthracene oil or green oil is the last fraction of the distillate from tar, and comes over between 270° C. = 518° F. and the pitching point. The crude oil has a greenish colour, and partially sets on cooling to a buttery mass containing about 30 per cent, of solid constituents — one-third of which is anthracene, the rest being other solid hydrocarbons — e.g., phenanthrene and chrysene — the remaining liquid consisting of oils of high boiling 6 82 DESTRUCTIVE DISTILLATION. point, of which but little exact knowledge exists. The pure anthracene does not usually amount to more than 07 per cent, reckoned on the original tar. Anthracene oil is worked up by allowing it to cool for a few days so that crystallisation may be as perfect as possible, and the solids are separated by means of nitration under pressure through convas bags, or by a filter press, or by a centrifugal machine. A portion of the solids remaining in the oil is recovered by redistilling and filtering again. The crude anthracene is subjected to hydraulic pressure at a tem- perature of about 40° C. = 104° F. The expressed oils from both operations are returned to the creosote oil tank. The pressed anthracene contains about 30 to 33 per cent, of actual anthracene, and is ground and washed with solvents, generally solvent naphtha (v.s.) or sometimes petroleum spirit (see Petro- leum, Vol. II., Chap. Y.), the operation being conducted in closed vessels provided with stirrers, and the solvent, after having been run off, recovered by distillation. This raises the percentage of anthracene to upwards of 50 per cent. A further purification must be effected before the anthracene can be converted into anthraquinone (its chief commercial derivative ; see Colouring: Matters, Vol. II., Chap. XIII.), by sublimation in a current of superheated steam, which gives a product containing about 60 per cent, of anthracene in a state of division sufficiently fine to allow of its subsequent oxidation to anthraquinone. j The tar dis- tiller generally puts 30 per cent, anthracene on the market, and it is valued by the "unit" — that is, at so much per cwt. for every per cent, of anthracene present. Pure anthracene is a white crystalline substance with a bluish fluorescence; it melts at 213° C. = 415° F., and boils slightly above 360° C. = 680° F. Pitch.— The "pitching point" varies from 360° to 400° C. = 680° to 752° F., according to the amount of anthracene oil distilled off and the quality of the pitch left. As anthracene is a valuable product, it is now customary to push the distillation so as to obtain as much of this as possible, and consequently "hard pitch" is produced. When the distillation is not carried so far, "soft pitch" results. It is blacker and more lustrous than hard pitch, and, containing a large proportion of oil, softens at 40° C. - 104° F., and melts at 60° C. = 140° F., as against 80° C. = 176° F., and 120° C. = 248° F. for hard pitch. Nowadays, hard pitch is generally softened by the addition of creosote oil, and is substituted for the old "asphalt" which was produced by stopping the distillation of tar when only light oil had been distilled off. Hard pitch contains, per cent., C, 75 ; H, 8 ; O, 16, and a trace of ash. It is used for making patent fuel (coal-dust briquettes), rough varnishes, and for adulterating natural mineral asphalt. It is sometimes distilled for a further portion of an- thracene which is much contaminated with chrysene. Gas Coke. — As already stated, a portion of this is used for COKING IN HEAPS. 83 heating the retorts; the remainder finds application in the neighbourhood for such industries as cement making and lime burning, and for domestic heating. Good gas coke should not contain more than 10 per cent, of ash. (B.) CARBONISING IN OVENS FOB COKE PRO- DUCTION. — In orderto overcome objections that exist to theuse of coal in many metallurgical processes (see Iron, Vol. I., p. 133), coke is prepared, coal being carbonised for this purpose in much larger quantities than for gas making; the essential difference in the two methods is that in the first the coke is the main product, while in the second (gas making) it is the bye-product. Gas coke cannot be substituted for oven coke on account of its lighter and more porous structure, due in great measure to the rapidity of the carbonisation. Caking coals are those best fitted for coking, because they leave a compact, coherent coke, but mixtures of caking and non-caking coals can also be successfully carbonised. As sulphur and ash are objectionable for the metallurgical use of coke, it is advantageous to use as pure a coal as possible. To this end the mineral matter (shale and " brasses " — iron pyrites) is removed by "washing." Coal-washing machinery, such as the Luhrig-Coppee plant, consists essentially of sizing and levigating apparatus like that used for concentrating ores (see Metallurgy, Vol. I., p. 210), and by its means pure small coal can be prepared which yields good coke, which, notwithstanding that the coal used was small, will be in large pieces owing to the fusion and agglo- meration that coking coal undergoes. A typical coke of good quality has the composition — C, 93-15 per cent.; H, 0*72 per cent.; N, 1*28 per cent.; 0, 0-90 per cent.; ash, 3-95 per cent. The chief variation in the composition of coke is due to its content of ash, which is obviously dependent on that in the coal. For the discussion of the influence of the physical properties of coke on its suitability for metallurgical use, see Iron, Vol. I., p. 133. (1) Coking in Heaps. — The earliest method of coking, and one which is still used to some extent, consists in carbonising coal in meilers or heaps similar to those used for carbonising wood in charcoal burning. The process is one of destructive distillation, the combustion of a portion of the coal sufficing to distil the rest, and is, therefore, analogous to coking in an oven, although there are no confining walls. The methods most in use may be reduced to three types : — (a) The coal is made into heaps of 20 feet diameter and 4 feet in height, or into ridges about 200 feet in length and 12 feet across and about 2 feet high, which are ignited at numerous points on the outside by driving in stakes and inserting live coal in the holes thus formed. On the cessation of the evolution of thick smoke and flame at any point, the heap at that spot is covered with coal dust and the combus- tion checked, and this process is pursued until the whole heap is carbonised. The main objection to this process is that the outer 84 DESTRUCTIVE DISTILLATION. part of the heap is apt to be burnt before the inner is completely carbonised. This has given rise to the use of type (b), which consists of a heap covered with small coal and provided with a conical brick chimney having numerous apertures. The heap is lighted by throwing burning coal down the chimney, and the combustion thus extends from the centre towards the circum- ference, the products of combustion escaping through the chimney, which is closed when they cease to be evolved. Type (c) is of similar construction, but is not covered, and the chimney is closed immediately after ignition, so that the flames proceed outwards. A variation of coking in heaps consists of coking in kilns, which are large rectangular enclosures of firebrick, with openings in the walls for the exit of gases. In coking in heaps the operation takes from two to three days, while a similar period must elapse to allow the coke to cool. (2) Coking in Beehive Ovens by Partial Combustion. — This method is similar in principle to coking in heaps, in that Tig. 16. — Beehive coke oven. C, Opening for charge ; 0, H, air holes ; C H, flue ; D, damper ; C K, coke ; E, false door. sufficient air is admitted into the oven to burn part of the coal and produce heat enough to carbonise the rest. As its name implies, this form of oven (one variety of which is shown in Pig. 16) consists of a dome-shaped chamber which is about 10 feet in diameter and 4 feet to the springing of the dome. The floor of the oven is traversed by a winding flue designed to keep the floor cool by the circulation of air through it, and thus prevent the rapid distillation of the fresh charge and consequent formation of bad coke. Similar flues are sometimes used for the walls. The charge for each oven is about 3 tons, which is intro- COKING IN OVENS WITH RECOVERY OF PRODUCTS. 85 duced either through a door in the side of the oven or through an opening in the top, C. It is held in place by a false door, E. The door is provided with holes for the admission of air, O, H. These are gradually closed after about three hours, and after some twenty-four hours are completely closed, the oven being eventually drawn forty-eight hours after charging. The smoke is led off by a flue, C H, common to a group of ovens ; each oven is provided with a damper, D. If the oven be made with the whole of one side serving as a door, the coke, K, can be removed by an " anchor," which is an iron framework to which a chain can be attached, and which is inserted before the charge. In this type of oven, as in the heaps, no use is made of any of the pro- ducts of distillation, the only valuable material obtained being coke. (3) Coking in Ovens by the Combustion of the whole of the evolved Gases. — Ovens other than the beehive may be looked upon as enlarged gas retorts, which in most cases are set horizontally, but sometimes — e.g., in the Appolt — are placed verti- cally. The analogy is imperfect in the present class, as the pro- ducts of distillation are allowed to escape by the pressure of their evolution through holes in the walls of the retort, so that they can be mixed with the air in the surrounding flues and there burnt to supply the heat necessary for distillation. In class (4), to be described below, the analogy is stronger, as the gases are led away from the coke, and may even be used for lighting purposes. This third type is best represented in the Coppee and the Appolt ovens, which depend upon the same principle of heating, but are somewhat different in construction. The Coppee ovens are about 2 feet wide, 30 to 35 feet long, and 4 to 5 feet to the springing of the roof. They are slightly tapered in the direction of the length for convenience of removing the coke by the thrust of an hydraulic ram. They are charged from the top, and hold from 3 to 6 tons. They are built in stacks side by side, one side of the oven being perforated, the openings leading into flues, the other side of which is in contact with the unperforated wall of the next oven. There is no recovery of products from this type of oven. The other example to be mentioned is the Appolt coke oven, in which the retort is vertical, and is about 13 feet in height, and tapering from the top 3 feet 8 inches by 13 inches to the base which is 4 feet by 18 inches. It is loaded from the top, and at the end of the run the coke withdrawn through a door at the bottom. (4) Coking in Ovens with Recovery of Products. — An ideal coke oven would have the whole of the tar and ammonia recovered, and be heated exclusively by its own combustible gases. It is found, however, that as the evolution of gas slackens towards the end of the operation, the coke is insufficiently heated 86 DESTRUCTIVE DISTILLATION. and suffers in quality. It is, therefore, customary to allow either access of air to the coke towards the end of carbonisation, or to use a supplementary mode of heating by solid fuel or producer gas. The removal of the tar and ammonia is aided by drawing CARBONISING PEAT. 87 them off by means of an exhauster, such as Beale's (see Gas Manufacture, Vol. II., p. 62), or by a steam injector. A well- known example of an oven for the recovery of products is the Simon-Carves, which is very similar in construction to the Coppee oven. Fig. 17 shows the arrangement of the Simon-Carves oven. The oven, A, is fed through the openings, b, b, from the trucks, B, B, the gases evolved being drawn off through the ascension pipe, M, into an hydraulic main. A portion of the gas passes through the pipe, P, into the flue, S, where it meets a supply of air drawn through the regenerating flues, d, d, d, the products of combustion escaping through the flues, e, e, to the stack, H, which serves for a number of ovens. The coke is expelled from the oven en masse by the ram, G, and is quenched as shown at K. The tar and ammonia are separated in a manner similar to that in use for the corresponding products obtained in the distillation of coal for gas production. The tar is, however, different in character from ordinary coal tar, if air be admitted to the coke. In that case it is poor in hydrocarbons of the benzene series, and consists largely of paraffins. If on the contrary no air be admitted the tar is similar to London gas tar, but poorer in light oils and phenols than are country tars. The admission of air also causes loss of ammonia by oxidation, and, in short, the improvement of the quality of the coke is effected at the expense of the other products. In the Simon- Carves plant the yield of coke may be taken at about 77 per cent., the tar 6*12 gallons, and the ammoniacal liquor (6*7° Twaddle) 27*7 gallons per ton of coal carbonised, corresponding with 11 to 14 per cent, of the nitrogen in the coal. The tar is gener- ally sent to the distiller, but the ammonia is worked up on the spot, in a manner similar to that used for the ammoniacal liquor of gas works. Notwithstanding the many improvements in coke ovens fitted for the recovery of the tar and ammonia, and the undoubted value of these products, and in spite of the greater yield of coke (77 per cent, as against 65 per cent.), many ironmasters prefer the coke from the old-fashioned beehive oven. The hardness and density of the coke are increased the narrower the oven — i.e., the greater the opposition to the expansion of the coal while in the plastic state. Carbonising Peat. — Attempts have been made to carbonise peat profitably in order to obtain peat charcoal, acetic acid, ammonia, and paraffin wax and oils. The process has been con- ducted in retorts of the modern type used for shale distillation (q.v.). Recent experiments show a yield from the air- dried peat of about 37 per cent, of charcoal containing about 5 per cent, of ash,* 41 per cent, of liquor containing nearly 6 per cent, of tar and a little ammonia and acetic acid, and 22 per cent, of gas * The average from unselected samples is probably considerably higher. 88 DESTRUCTIVE DISTILLATION. containing combustible constituents. The difficulty in utilising peat in this manner arises from the fact that it occurs in a very- moist and bulky condition, associated with much earthy matter, its composition being very irregular. Some preliminary process of compression and desiccation is necessary before distillation is practicable. At the present price of other carbonaceous materials (coal and petroleum) the prospect of the remunerative distil- lation of peat is remote. II. DESTRUCTIVE DISTILLATION OF WOOD. The essential constituent of wood is ligno-cellulose, which is a carbohydrate of the formula 0 12 H 1S 0 9 . With it are associated incrusting substances consisting of resins and tannins peculiar to each species of wood. Air-dried wood contains 15 to 25 per cent, of water, while the amount of water in growing wood Fig. 18. — Charcoal burning in heaps. A, Covering ; M, annular gap. varies greatly with the species, ranging from 18 to 50 per cent. The ash or mineral constituents of wood amount to 1 to 1*6 per cent. The chief substances present in the ash are potassium and sodium carbonates — one or other preponderating, according to the species — lime and magnesia. The composition of the ash varies to some extent with the soil on which the trees are grown. The ultimate composition of wood (deducting the ash and moisture) averages — C, 50*5 per cent. ; H, 6*3 per cent. ; O, 42 per cent. ; N, 1 *2 per cent. When wood is heated out of contact with air, it suffers decomposition in accordance with the principles of destructive distillation detailed at the beginning of this chapter. (A.) BURNING IN HEAPS OR " MEILERS."— This process is similar to that already described for coal, being indeed its prototype. The whole arrangement is shown in Fig. 18. A stake or " quandel " is driven into the ground, and around it logs of wood are carefully packed, sometimes horizontally, some- times vertically disposed. In the latter case, three or four CHARCOAL BURNING IN HEAPS OR " MEILERS." SO stakes are used for the centre to form a sort of rough chimney. The diameter of the mound varies from 10 to 60 feet. The interstices of the logs are filled with small wood, and a covering, A, of turf or " charcoal breeze " — i.e., powdered charcoal from a previous operation — is made, and is thickest at the top of the mound. The foot of the heap is not covered at the beginning of the burning, an annular gap, M, being left, the covering being supported by twigs pegged down by forks of wood, the whole arrangement being called the " armour." A channel, left during building, from the circumference to the centre of the heap, serves for the introduction of live charcoal for igniting the heap. If a chimney has been made in the middle, this serves the same pur- pose. The faggots immediately around the stake have been par- tially charred in a previous operation, so that the ignition of the heap may be ensured. When the heap is lighted, the holes are closed, and "sweating" — i.e., the escape of moisture from the- annular space at the base — sets in. The supply of air is regu- lated by partially closing the uncovered space, to avoid danger of explosion of mixtures of air and the inflammable gases that are given off. When the smoke, which is at first yellow, changes to grey, charring proper is known to have set in, and all openings are closed. During carbonisation the cover has to be renewed as it falls in. After some days a stake is driven through the covering in several places near the ground, to form passages for the escape of the tar. More perforations are made in the upper part of the heap as the charring proceeds — the judgment of the burner being guided by the appearance of the smoke — in order to create an up-draught, and insure the charring of the wood on the outside of the heap. Small piles take six to fourteen days to carbonise, large ones one month. Rectangular heaps are sometimes used, the walls being made of stakes and rough boards. By conversion into charcoal by burning in heaps, wood loses on an average some 25 per cent, of its bulk, and 75 to 80 per cent, of its weight. Its apparent specific gravity — i.e., including pores — varies Irom 0*2 to 0-5, according to the wood from which it is derived. The real specific gravity is from 1*5 to 2*0. Beechwood charcoal produced by this method has the following composition : — Water, 7 0 per cent. ; carbon, 86-2 per cent. ; H, 2*3 per cent. ; O and N, 1*5 per cent. ; ash, 3*0 per cent. On keeping, the moisture may increase to about 12 per cent., which diminishes the value of the charcoal as a fuel (Vol. I., p. 56). In general, the products of the destructive distillation, other than charcoal, escape or are burnt, but by building the meiler on a concave brick floor, a portion of the tar is caught and re- covered. The difficulty of generally adopting this plan, is that the brick floor necessitates that the heap should be kept to one place and the wood brought to it. The rectangular heaps am 90 DESTRUCTIVE DISTILLATION". better adapted for the recovery of tar, as they are worked from one end to the other and the draught carries the tar con- tinuously in the direction of the length of the heap. Lime has been proposed as a covering, for fixing the acetic acid (one of the products), and other coverings sufficiently rigid to admit of the introduction of pipes have been tried. The objections to both arrangements is that unless the cover be flexible it will not fall in as the wood shrinks. (B) CHARRING IN KILNS.— The kilns, which are chiefly used in America, are rectangular brick structures with an arched roof, some 40 to 50 feet long and 12 to 18 feet wide, and about 12 to 18 feet to the spring of the roof, holding 100 to 180 tons, or cylindrical structures 28 feet in diameter, 12 feet high, and covered with a dome. In either case vent-holes are left in the walls, and are opened and closed according to the supply of air required. The charring takes 6 to 10 days, and 4 to 6 days are needed for cooling. The products are not recovered in these kilns; those forms designed for the recovery of products are of beehive shape, and the air has access to the charge through a grate. The entry of air is stopped as soon as the walls are hot enough to complete the charring. The kiln is filled partly through the door and partly through a hole in the top which is closed before ignition. A pipe in the upper part of the kilns leads the products through a condenser. (C) CHARRING IN RETORTS.— Many forms of retorts are used ; they are generally made of boiler plate and set hori- zontally, although cast iron is also used as a material and the setting is vertical in many cases. The size varies considerably, but 3 feet diameter by 8 feet long is not unusual. The charge for a retort of this size is about 6 cwts. The retorts are heated by the flame of the gas evolved from the distillation, supple- mented by a little wood or charcoal. The general arrangement for the distillation of wood in retorts is shown in Fig. 19, in which A is the retort, set in the furnace, B, in which the fire from the grate, C, circulates round the retort, the furnace gases finally passing away by the flue, D. The products of distillation pass through the condensing pipe, E, set in the water jacket, F. The liquid products flow through the small pipe, G, into the trough, H. The uncondensed gas passes through the pipe, K, into the main, L, which is common to several retorts, and whence the gas finally passes through the pipe, M, into the grate, C. The door, N, of the retort is removed when the distillation is complete, and the contents of the retort are pulled out bodily by a windlass attached to the bar and frame, O. The quantity of charcoal obtained by distillation in retorts is about 27 per cent, of the weight of the wood, but of this some 5 per cent, is necessary for heating the retort, so that the net PRODUCTS OF CHARCOAL BURNING. 91 result is no better than when burning in heaps is used. The value of the distillate constitutes the chief advantage of dis- tillation in retorts. PRODUCTS. — These are charcoal, tar, crude acetic acid, spirit and gas. 92 DESTRUCTIVE DISTILLATION. (a) Charcoal. — The average yield from the wood of two typical trees is : — * Crude pro- ligneous acid (watery distillate). Acetic acid (glacial) in watery distillate. Tar. Charcoal. Gas. Oak, . Scotch fir, . 47-6 45-0 5-4 2-7 6-4 10 0 24 9 28-0 22-1 27 0 In each case the watery distillate contains about 1 per cent, of wood spirit, reckoned on the wood. With regard to the quality of the charcoal produced by these several methods, it depends on (1) the nature of the wood, and (2) the temperature of distillation. The hard close-grained woods, such as oak and beech, give a hard dense charcoal, while woods of lighter and looser" texture, particularly woods of conifers, give a correspondingly soft charcoal. The higher the temperature of distillation the blacker the charcoal, and the more nearly it approaches pure carbon (Vol. L, p. 56). Char- coal is also made at very low temperatures (360° to 520° C. = 680° to 968° F.) for gunpowder making, superheated steam being sometimes used for charring. The qualities prepared at the lowest temperatures are brown in colour, and are known as red charcoal (charbon roux). It is less porous and hygroscopic, and more inflammable than black charcoal, and has, when freshly made, the average composition, 74 per cent. 0., 24*5 per cent. O and H, and 1*5 per cent. ash. After a time it will be found to have taken up as much as 10 per cent, of water. For further information concerning low temperature charcoal see Explosives , Vol. II., Chapter XYII. Besides its use as a fuel, which has already been dealt with in Yol. I., p. 56, charcoal is applied as a deodoriser on account of its property of absorbing, and to some extent oxidising, objection - able gases. This oxidation is effected by the atmospheric oxygen which the charcoal has absorbed during cooling and storage. 1 vol. of charcoal can occlude 9-25 vols, of O, and similarly large quantities of other gases. High temperature charcoal takes up less gas than a low temperature product. The application for filtering water depends upon the same principles. Being a non- conductor, charcoal is used as a packing to hinder the trans- mission of heat. (b) Wood Tar.— The yield of tar varies from 7 to 10 per cent, of the wood, rising to 14 per cent, in the case of pine wood. Wood tar is characterised by the large proportion of oxygenated bodies it contains. Tar condensed from the distillate from wood * Fawsitt, Journ. Soc. Chem. Ind., 1885, p. 319. WOOD SPIRIT. 93 distilled in closed retorts varies according to the nature of the wood, that from the conifers being rich in terpenes, due to the decomposition of the resinous constituents of the wood ; that from other woods, such as beech, contains hydrocarbons of the paraffin and benzene series, together with various phenols and their derivatives. Stockholm tar is that which is most commonly used as a pre- servative for wood, and is produced from coniferous woods by a process of distillation in which it is the most valuable product ; the process consists in filling the wood into large holes, shaped like inverted cones, in the ground. The wood is ignited at the top, and allowed to burn slowly, access of air being hindered by partially covering the pile with earth ; the tar collects in a trench at the bottom. Russian tar is characterised by being specially rich in pyro- catechol (see Leather, Yol. II., Chap. XVI.). In America, crude wood-tar creosote oil from coniferous wood is substituted for coal-tar creosote in creosoting sleepers and piles (Vol. L, p. 47). Purified Wood-tar creosote is obtained by separating the tar into two fractions by distillation, and washing the heavier fraction with caustic soda, whereby creosote is dissolved. The alkaline solution is boiled in air to oxidise impurities, and precipitated with sulphuric acid ; these two processes are repeated, and the product distilled; the fraction from 200° to 220° 0. = 392° to 428° F. constitutes commercial wood-tar creosote, which contains 50 to GO per cent, of guaiacol, C 6 H 4 (OH) (OCH 3 ), and creosol, C 6 H 3 CH 3 (OH) (OCH 3 ), together with small quantities of many other phenolic derivatives. It is a powerful antiseptic, and much used in medicine. (c) Wood Spirit The distillate from wood consists of a mix- ture of tar and watery liquid, the latter containing acetic acid and wood naphtha or wood spirit. The tar is separated by sub- sidence and used for the purposes already mentioned, and the watery liquid is drawn off from the top, and worked up for acetic acid, acetone and methyl alcohol. The method of working up varies according to what grade of acetate of lime is to be pre- pared. If brown acetate of lime (v.i.) be required, the crude watery distillate (pyroligneous acid) is neutralised at once with lime and distilled in an iron still until the spirit has come over, and the distillate (about 20 per cent, of the whole) is too weak in inflammable constituents to flash when thrown on to glowing cinders (a preferable test is the specific gravity of the liquid). The acetate of lime remains in the retort. If grey acetate of lime be needed, the pyroligneous acid is distilled, to remove tarry matter, in copper retorts — iron being attacked by the acid — heated by coils conveying superheated steam, and the distillate either collected in two fractions, the first being the spirit, and 94 DESTRUCTIVE DISTILLATION. the second the acetic acid, or neutralised with lime and redistilled until the spirit has come over. Crude wood spirit is a complex liquid containing methyl alcohol, acetone, methyl acetate, alde- hyde, allyl alcohol, and dimethyl acetal, with small quantities of the three methylamines, ammonium acetate, oils of the aromatic series, and tarry matter. It is distilled with excess of lime, which retains water, hydrolyses methyl acetate into methyl alcohol and calcium acetate, and to some extent decomposes the amines. The distillate consists of methyl alcohol and acetone, together with ammonia and small quantities of amines ; for the complete retention of these and of the ammonia, subse- quent distillation over a small quantity of sulphuric acid may be adopted. The most important point in the purification is the hydrolysis of the methyl acetate, as the presence of this body makes it difficult to get the specific gravity of the finished product down to the limit set by the Excise (see Brewing and Distilling, Vol. II., Chap. IX.). The oils must be elimin- ated as completely as possible, as they cause the spirit not to be "miscible" — i.e., capable of mixing with water without pro- ducing a turbidity. This separation is sometimes effected by diluting with water until precipitation of the oils occurs, shaking with melted paraflin wax, filtering, and distilling. The finished wood naphtha (wood spirit) is nearly colourless ; its specific gravity is 0*827, corresponding with a strength of 61° over proof. It contains 80 per cent, of methyl alcohol, 6 per cent, of acetone, and 12 per cent, of water, besides traces of empyreu- matic products that give it a disagreeable taste and smell, and fit it for denaturing alcohol (see Brewing and Distilling, Vol. II., Chap. IX.), which is its main use. The rest goes for aniline colour making (q.v.), as a solvent in varnish making, and for burning in lamps. Acetone, (CH 3 ) 2 CO, which is also an article of commerce, can be made by distilling the wood spirit over calcium chloride, which retains the methyl alcohol, but it is generally prepared (for making chloroform) by the distillation of acetate of lime. Pure methyl alcohol, CH 3 OH, may be recovered from its calcium chloride compound (CaCl 2 . 4CH 3 OH) by distillation with water and subsequent dehydration with lime. The method generally used, however, consists in passing dry chlorine through boiling wood spirit, whereby the acetone is converted into chlorinated products of high boiling point, and fractionally distilling the methyl alcohol from these. The pure alcohol boils, according to the latest authorities, at 65° C. = 149° F.; its specific gravity, when anhydrous and also when diluted with water, is nearly identical with the value for ethyl alcohol of the same strength. (d) Acetic Acid and Acetates. — The yield of acetic acid varies greatly ; the following are some figures illustrating this : — WOOD GAS. 95 Lime, Aspen, . Pine, Birch bark, . For further information concerning acetic acid see Vinegar, Yol. II., Chap. IX. The chief commercial acetates include brown and grey acetate of lime, brown sugar of lead, and acetates of iron (pyrolignite of iron, iron liquor or black liquor). For the brown acetate of lime the crude pyroligneous acid is neutralised with powdered chalk or lime, and sometimes distilled to recover the wood spirit (v.s.), and sometimes evaporated directly to dryness, preferably by steam heat, the salt fished out as it separates and dried in kilns at a temperature of about 125° C. = 257° F. Its colour is due to tarry matter. It contains 70 to 75 per cent, of real acetate of lime, (C 2 H 3 0 2 ) 2 Ca, the balance being water, tarry matter, and excess of lime as carbonate. The grey acetate is similarly pre- pared from the pyroligneous acid that has been once distilled to free it from tarry matter. Acetate of lime is used for the manufacture of acetic acid (by distillation with sulphuric acid), and other acetates, and for calico-printing. Brown sugar of lead (crude lead acetate) is the product of the neutralisation of once-distilled pyroligneous acid with litharge. The mixture is boiled and well stirred, skimmed, and crystallised. It is used in the preparation of alum mordants (see Dyeing, Vol. II., Chap. XIII.). Pyrolignite of iron is a solution of crude ferroso-ferric acetate, containing a little pyrocatechol, which gives it its black colour. It is made by dissolving scrap iron at a temperature of 65° C. = 149° F. in crude pyroligneous acid of specific gravity 1*04. The liquor is evaporated to a specific gravity of 1*13, when it contains about 10 per cent, of iron. It is used in Dyeing and Calico -Printing, Yol. II., Chap. XIII. (e) Gas. — Crude wood gas contains about 53 per cent, of C0 2 ; when freed from C0 2 , the gas contains CO, 82 per cent.; CH 4 , 14 per cent.; C 2 H 4 , 0-75 per cent., and the balance nitrogen. Gas of this composition is of little illuminating value, and only serves for heating the retorts. That produced by the distillation of resinous wood — e.g., pine — may, on the other hand, be rich in illuminants, but is of no value till freed from C0 2 by lime puri- fiers (see Coal Gas, Yol. II., p. 65). The relative quantities of the products of the destructive dis- tillation of wood at varying temperatures have been determined by laboratory experiments made by Ramsay and Chorley * on wood, on pure jute fibre, and on cotton wool (cellulose). They have incidentally noticed that when the wood or jute fibre is * Journ. Soc. Chem. hid., 1892, pp. 395 and 872. Glacial Acetic Acid. 10'24 per cent., reckoned on the wood. 8-06 ,, 5-65 ,, 2-20 DESTRUCTIVE DISTILLATION. heated in a flask, surrounded by an air bath, a sudden rise of temperature in the interior of the flask to a point some 50° C. above that of the air bath, takes place at a temperature of about 300° C. = 572° F. They consider this to be evidence that the destructive distillation of wood is accompanied by an exothermic reaction. They have observed that at this temperature the pro- ducts, which are similar in the main to those obtained on the large scale, are formed in largest quantity. At 500° 0. = 932° F. the percentage of charcoal is considerably lower than at 360° C. = 680° F., and the percentage of gas a good deal higher. The yield of acetic acid is little influenced. Different woods gave a fairly constant yield of acetic acid but no experiments with resinous woods were made. III. DESTRUCTIVE DISTILLATION OF SHALE. Shale is a carbonaceous mineral which appears to have been formed from the remains of marine animals and plants, mixed with argillaceous mud, consolidated into a slaty mass. The Scottish shales, which may be taken as typical of their class, are below the coal measures, and accompany strata of marl, limestone and sandstone. The nature of the carbonaceous matter in the shale is unknown, but, inasmuch as none of the substances obtained by the destructive distillation of the shale can be directly extracted from it by solvents, it may be certainly stated that such substances do not pre-exist in the shale. The average composition of Broxburn shale is C, 20 per cent. ; H, 3 per cent.; 0,0*5 per cent.; N, 0*7 per cent.; S, 1*5 percent.; ash, 69*8 per cent. I The ash consists of silicates approximating in composition to a ferruginous impure clay, and is often tolerably fusible. The main difference between shale and cannel coal consists in the percentage of ash, rich shales approximating to cannel in their composition ; this is well illustrated by the New South Wales "kerosene shale," which contains only 8 per cent, of ash, and a splinter of which will burn like cannel. The winning of the shale is conducted similarly to the winning of coal ; at Broxburn it crops out at the surface, but nowadays has to be mined. The process of distillation differs from those previously considered in that it is conducted at a much lower temperature, and is, in most cases, aided by the injection of superheated steam. It must be noted that the object of this distillation is the production of paraflinoid hydrocarbons, for the obtainment of which the shale is particularly adapted, doubtless both on account of the specific nature of the bituminous matter present, and because of its being spread over a larger surface of inert matter (the ash) tending to prevent condensation into benzene hydrocarbons ; should the temperature be allowed to DESTRUCTIVE DISTILLATION OF SHALE. 97 rise, such condensation would tend to occur even as it does in the high temperature distillation of oils conducted for the manu- facture of oil gas (Yol. II., p. 74). The nature of the products may be gathered from the average yield at Broxburn : — Per cent. Volatile matters. Crude oil or tar, . . . . . . 12 Ammoniacal liquor, ..... 8 Gas, 4 Total, — 24 Non-volatile (spent shale). Combustible, ....... 9 Ash, 67 Total, — 76 100 The apparent discrepancy between these figures and those given above for the ultimate composition of the shale is to be accounted for by the fact that the injected steam is condensed with the ammoniacal liquor, and increases the total amount of products obtained. In modern practice two types of retorts are used for the distil- lation, the improvements on the older forms consisting in affording facilities for consuming the "fixed carbon" of the spent shale (cor- responding with coke from coal) as fuel for heating the retorts. Both types are on this account set vertically. In the older of the two, of which the Henderson retort (Fig. 20) may be taken as an example, the retorts are closed vessels heated by a separate furnace into which the spent shale can be dropped by with- drawing the bottom plate of the retort when the charge is worked out. In the more modern type, such as the Young and Beilby (Fig. 21), the lower part of the retort serves as a com- bustion chamber for heating the material in the upper, so that no hard and fast distinction can be drawn between the retort and its furnace. The details of construction will be readily comprehended from the accompanying figures. Fig. 20 represents the Henderson plant. Four cast-iron re- torts, of which a pair is shown in the figure, A, A, 15 feet long and of elliptical section (2 J feet by 1 foot), with walls 1J inches thick, are set in a firebrick casing over a furnace, B, divided by a vertical partition. They are charged from the top, and one of the set is discharged into the furnace every four hours by drawing back the bottom plate, C. The products of distillation are led off at the lower part of the retort by a pipe, D. The retorts are protected from direct contact with the flame by the firebrick arch, E, the furnace gases passing up the flue, F, and finally escaping by the pipe, G, which is at the bottom of the furnace, and of small sectional area in order that the draught may be 7 98 DESTRUCTIVE DISTILLATION. sufficiently gentle for the combustion of the spent shale. The non- condensable gases from the distillation (v.i.) are also turned into the furnace through the pipe, H. Superheated steam is admitted to the retorts by the pipe, K, to aid the process of distillation. Fig. 20.— Henderson shale retort. A, A, Retorts; B, furnace ; C, bottom plate; D, products pipe ; E, firebrick arch ; F, flue ; G, flue gas pipe. Fig. 21 shows the Young and Beilby retort, which, like the Henderson, is set in groups of four, and consists of an upper part, A, of cast iron, some 9 feet long, circular or elliptical in section, placed above a firebrick portion, B, about 8 feet long, of oblong section— 1 foot 11 inches by 10 inches at the upper end, and 2 feet 5 inches by 12 inches at its widest point. The ends SHALE RETORTS. 99 are curved outwards to admit of the discharge of the consumed spent shale at the side. The destructive distillation of the shale takes place in the upper cast iron part of the retort, and by the time the material reaches the lower firebrick portion it contains nothing but " fixed carbon," which is there consumed by a current of air injected at C. Steam is also blown in at these Fig. 21. — Young and Beilby's shale retort. A, Upper part (iron) ; B, lower part (firebrick) ; C, place where air current is injected ; D, flues ; E, hopper ; F, mains. points to aid in the production of ammonia (v.i.), and, in some forms of plant, supplementary external heating is adopted by burning producer gas in flues (D) surrounding the retorts; The admission of air without steam into the retort would be more effective as far as producing heat for the oil distillation, which takes place in the upper part of the retort, is concerned, 100 DESTRUCTIVE DISTILLATION. but the use of steam is necessary to favour the production of ammonia. A multiple hopper, E, serves for feeding the retorts, which are worked continuously; the products of the distillation pass through the green shale in the hopper, serving to raise its temperature, and into the mains, F. It will be noted that modern practice in shale distillation is tending to the use of retorts analogous to the common gas producer worked for the production of oil and ammonia as the main products, and, therefore, driven at as low a temperature as possible, so as to confine the combustion to its lower part, and carry on distillation in its upper part. The general system of plant for the recovery of the products of distillation of shale resembles that used in the manufacture of coal gas, particular care being taken to recover the oil (equivalent to gas tar), which is the main product of the process, rather than the gas, which is of subsidiary importance being merely burned under the retorts. PRODUCTS. — The nature of these has been already indicated (v.s.) ; the oil being the most important may be considered first : — (a) Crude Oil or Tar. — This is collected from the condensers (which are air condensers ; see p. 62), and amounts to some 30 gallons per ton in the case of the Broxburn shale. It is of greenish colour, and semi-solid from the presence of paraffin wax. Its quality depends on the class of retort used; that from the old vertical retorts and the Henderson has a specific gravity of 0-89, and is more tarry — that is, contains a larger proportion of overheated and coked products ; this is shown by its leaving 5*10 per cent, of coke on distillation, which is, however, valuable as being free from ash and sulphur. The tar from the newer forms of retort (Young and Beilby) has a specific gravity of 0*87, and is so free from tarry matter that it may be worked as once-run oil (v.i.). It is separated from ammoniacal liquor in settling tanks, and is pumped into cast-iron stills holding up to 2,000 gallons, and resembling tar stills (p. 77). From these it is distilled as far as possible, when it is known as once-run oil ; but in modern practice the crude tar is distilled continuously in sets of three oblong stills with arched roofs and concave bottoms. In the first still the distillation is carried to the point when the fraction known as "green naphtha" (specific gravity 0*753) has come over, the residual oil being passed into the second still where the distillation is carried to the point when heavier oils, of specific gravity about 0-835, come over ; after this the remaining oil goes into the third or coking still where the distillation is carried to the coking point, the distillate ranging in specific gravity from 0-860 to 0 9 65. By this method the first two stills do not have to be stopped for clearing, as all the coke is deposited in still OIL FROM SHALE DISTILLATION. 101 No. 3, which is used in duplicate so that one may be running while the other is being cleared. The fraction from the first still (green naphtha, specific gravity 0-753) corresponds with the first fraction (naphtha) from the redistillation of the once-run oil when the old intermittent process, similar to tar-distilling (p. 77), is used. This fraction is purified by successive treatment with caustic soda and sulphuric acid, and is marketed as solvent naphtha (benzine or benzolene), or is used on the works for purifying paraffin wax. The description of the further operations applies to the continuous process, the older intermittent process being similar in principle. The heavier fractions from stills 2 and 3 (green oil) are mixed and redistilled to obtain two fractions, light and heavy oils. The light oil is obtained by distilling until a specific gravity of about 0*850 is attained; this oil yields the illuminating oil, of which there are several grades, distinguished by their specific gravity, and for the obtainment of these the light oil is redistilled. The bulk of Scotch illuminating paraffin oil ranges in specific gravity from 0*800 to 0*820, and is similar to American kerosene as an illuminant (q.v.), but has usually a higher specific gravity and flashing point (see Petroleum, Yol. II., Chap. V.). Chemically, the two differ on account of the larger proportion of olefines in shale oil, as indeed is indicated by its odour. The heavy oil contains the paraffin wax, and is cooled until the "crude scale" separates ; this is removed by a filter press, and the still liquid portion, " blue oil," cooled again for a further yield. The blue oil is then redistilled, and the fraction treated with caustic soda and sulphuric acid to obtain the different grades of lubricating oil, ranging in specific gravity from 0*865 to 0*900. The treat- ment of the blue oil (this applies also to the lighter illuminating oils) consists in agitating it in wrought-iron tanks first with the strongest vitriol (the concentrated acid not acting on the iron) for a few hours at a temperature as low as practicable, to avoid acting on the olefines, and allowing it to settle ; the acid combines with basic impurities, and the quantity must be regulated to remove these without attacking the olefines, which are more easily attacked than are hydrocarbons of the paraffin series. The settled matter is known as "black tar" or "vitriol tar," and is run off from below and used again, should the system of distil- lation adopted involve the production of a cruder oil at an earlier stage; in the contrary case it is washed with hot water to remove the sulphuric acid, and injected, together with steam, into the furnaces, serving as a fuel. Another plan, suggested by Rave, consists in treating the tar with iron borings, and obtaining as a final product a bituminous substance useful for coating battery tanks and for making varnish. The acid-washed oil is treated with caustic soda (specific gravity 1*3), which removes acid im- purities. It is black when the treatment has been properly 102 DESTRUCTIVE DISTILLATION. conducted, but otherwise may be a white gelatinous mass (see Petroleum, Solidification of, Vol. I., p. 58). As the impurities removed by soda are phenolic bodies, they may be recovered by precipitating the soda solution with C0 2 , the resulting sodium carbonate being causticisecl and used again. The finished lubri- cating oils appear to owe their properties to the presence of iso-paraflins, the normal compounds being poor lubricants. Paraffin scale or crude paraffin wax is the most valuable and characteristic constituent of shale oil. The solid portion of the heavy oil, separated by filtration, is submitted to one of three processes. One of these consists in heating it with vitriol at a temperature not exceeding 60° C. = 140° F., then with caustic soda, and finally thoroughly washing with water, the object of the process being to attack the oily products and leave the crystalline wax. Another, which is more often em- ployed, is that in which the scale is crystallised several times from shale naphtha (v.s.), the solution being filtered through animal charcoal or similar decolorising agent, and the crystalline mass pressed to get rid of the last of the solvent. The rationale of this process rests on the fact that the paraffins of low melting point are more soluble than those of high melting point. The third is a process of liquation, or " sweating," and is effected by casting the crude scale into thin cakes and compressing it be- tween mats of cocoa-nut fibre in hot presses, the more fusible substances being thereby expressed. The chief use of paraffin wax is in candle manufacture (q.v.), but it is also used as a waterproofing material for matches, paper, &c, and as an elec- trical insulator. When put on the market it should be white and well crystallised ; its price is greater the higher the melting point, which ranges from 45° to 60° C. = 113° to 140° R The average yield from crude shale oil is as follows : — (b) Ammoniacal Liquor. — This mainly differs from gas liquor in containing a smaller quantity of sulphur compounds. It amounts on the average to 65 gallons per ton of shale, which quantity may be increased to 120 gallons per ton when much steam is used in the distillation. The amount of ammonium sulphate obtained from the liquor varies with the type of retort used, the Henderson yielding from 16 to 20 lbs. per ton of shale, and the Young and Beilby twice as much, the quantity being further increased by the ammonia recovered from the producer Naphtha, Illuminating oils, Lubricating oils, Paraffin wax, . Loss, 37 17 13 28 5 per cent. 100 DESTRUCTIVE DISTILLATION OF BONES. 103 gas used as an auxiliary source of heat. The distribution of the nitrogen of the shale is about 20 per cent, as ammonia, 50 per cent, in the spent shale, and the remainder in the tar and gas. In processes like that of Young and Beilby, where the spent shale is treated with steam, a portion of the nitrogen is removed and increases the yield of ammonia. The bulk of the ammonia in the liquor is as carbonate ; the liquor is distilled in a column still (see Brewing and Distilling, Vol. II., Chap. IX.), and the ammonia passed into sulphuric acid, which may be that which has been recovered from the acid tar. The general process of making ammonium sulphate is similar to that adopted for gas liquor (p. 76). (c) Gas. — The gas evolved in distillation contains hydrocarbons of the paraffin and olefine series. About 2,000 cubic feet per ton of shale are obtained at Broxburn. By passing the gas through scrubbers, kept moist with heavy oil, nearly 3 gallons of gasolene (a mixture of light hydrocarbons) can be obtained per ton of shale. The gasolene is recovered, by heating the oil used to collect it, and is employed for carburetting air for illuminating purposes. The rest of the gas is used for firing the retorts and lighting the works. IV. DESTRUCTIVE DISTILLATION OF BONES. The main object of bone distillation is the production of animal charcoal (bone-black), valuable bye-products being oils and ammonia. It will be seen below that the organic portion of the bone is comparatively small in amount, so that the coke is rich in mineral matter, containing only about 10 per cent, of carbon. Bone appears to be a cartilaginous tissue which has become impregnated with calcium phosphate and carbonate, removable by treatment with dilute hydrochloric acid, the original skeletal mass of organic matter being left. The com- position of bone varies with the kind of animal — and its condition and age — from which the bone has been obtained. The following is a representative analysis of dry bone : — Per cent. Fat, 6 Nitrogenous matter (Osseine), 28 consisting of calcium phosphate, 56 per cent. ; calcium carbonate, 8 per cent. ; magnesium phoshate, 1 per cent. ; calcium fluoride, 1 per cent. 100 The water varies, about 20 to 25 per cent, being an average amount. The fat is extracted either by melting it by heating with steam, with subsequent addition of cold water (which removes 4 to 5 per cent, of fat), or by dissolving it in volatile Mineral matter, . . 66 104 DESTRUCTIVE DISTILLATION. solvents (which extract 6 to 8 per cent, of fat), such as light petroleum, carbon bisulphide, &c; it is used for soap making (q.v.). The fat-free bone is either used as manure (p. Ill) or boiled for glue, which process converts the osseine into gelatine and extracts it, the boiled bones being used as manure. The fat-free bones from which the osseine has not been extracted are those used for bone-black manufacture, for which purpose they are carbonised, according to Continental practice, in covered iron or fireclay pots, the products being allowed to escape, partly on account of the difficulty of separating them from the furnace gases, and partly because the most volatile constituent (ammonia) is decomposed by the high temperature employed. In this country, the distillation is usually carried out in iron or fireclay retorts similar in most respects to coal- gas retorts, the charge varying from 2\ to cwts. ; the products are collected in condensers similar to those used in gas works, and may be considered under the following heads : — (a) Charcoal. — This contains a very small quantity of carbon spread over a large surface of mineral matter. The following analysis is due to Newlands Bros. : — "Carbon," .... Calcium and magnesium phos- phates, calcium fluoride, &c. , Calcium carbonate, Calcium sulphate, . Ferric oxide, .... Silica, Alkali salts, .... 100-00 Moisture originally present, 8*00 per cent. The yield of "char" should be about 65 per cent, of the original bones. It is cooled in covered vessels, and passed through a magnetic separator, which removes metallic iron accidentally present, this being objectionable to the sugar refiner. The higher temperature in the pot method of carbonisation causes the charcoal to be of better quality than that produced in retorts. Besides its appli- cation in sugar refining, the charcoal is used for filtering and decolorising water, oil, paraffin wax and glycerine. The pigment called "ivory black" is generally finely-divided bone black. When once exhausted in these various uses, bone black can be revivified by burning, and this process can be repeated several times (see Sugar, Vol. II., Chap. VIII.), but the char eventually becomes spent, when it is sold to the manure maker. (b) Oil. — Bone oil (Bippel's oil, animal oil) is derived from the osseine and any residual fat there may be in the bone. Per cent. 10*51 ^ con taining 10 per cent, of \ its weight of nitrogen. 80-21 8-30 0-17 0-12 0 34 0-35 PRODUCTS OF DISTILLATION OF BONES. 105 The former is highly nitrogenous, as shown by the following figures : — C, ...... 50*4 per cent. H, 6-5 „ N, 169 0, 26-0 S, 0-2 100-00 Bone oil is, therefore, richer in nitrogenous derivatives than is the tar from coal, wood or shale. It is a dark-brown liquid (specific gravity 0-914 to 0*970) of offensive smell, and amounts to 3 to 5 per cent, of the bones carbonised ; it contains fatty nitriles, pyrrol and its methyl derivatives, hydrocarbons of the series C n H2n-4, various compound ammonias and pyridine bases. It is redistilled, when much ammonia in the form of carbonate and cyanide comes off, together with the oil, and a black resinous tar remains and is used for making Brunswick black. The oil is now used, on the Continent, for denaturing spirit, and a small quantity is worked up for the pyrrol, C 4 H 4 NH, it contains, which is converted into tetraiodopyrrol, C 4 I 4 NH, employed as an anti- septic in place of iodoform. The richness of the oil in pyridine, C 5 H 5 N, and similar bodies, to which the vegetable alkaloids are closely allied, opens up the prospect of synthesising these latter from bone oil. Coniine (the alkaloid of hemlock) has been already prepared from picoline (methyl pyridine), obtained from bone oil. At present, on account of the foetid odour of the oil, it is mostly burnt under the retorts. (c) Ammonia. — At one time the distillation of bones was the chief source of ammonia, but its importance has decreased since the birth of coal-gas manufacture. The proportion of ammonia, reckoned as ammonium sulphate, is about 6 to 7 per cent, of the weight of the bones distilled. The resulting ammonium sulphate is usually highly coloured, from the presence of pyrrol red. (d) Gas. — A good deal of gas of high illuminating power is given off during distillation, but it contains too much sulphur to be readily purified, and is, therefore, burnt at the works either for lighting or for heating retorts and boilers. 10G ARTIFICIAL MANURE MANUFACTURE. CHAPTER IV. ARTIFICIAL MANURE MANUFACTURE. A manure is a substance designed to supply one or more of the essential constituents of plant food, and, where necessary, to improve the physical condition of the soil to which it is applied. The essential constituents of plant food must contain the elements C, H, O, N, P, S, K, Ca, Mg, Fe, and probably Si, CI, and Na. Of these, C, H, O, and some of the N are derived from air and rain ; most of the nitrogen and the remaining elements being obtained from the soil. Almost every soil will contain enough Ca, Mg, S, Fe, Si, CI, and Na for the growth of a full crop, but N, P, and K are often present in but small quantity, and become exhausted by the removal of farm produce. A general manure is usually understood to be one which can supply these three constituents, but inasmuch as some crops either contain an excess of one or other of these, or are better able to obtain some one or other of them from the soil, than are other crops, it is frequently economical to apply a special manure to meet the needs of such crops. For what is known as to the requirements of individual crops, a work on agricultural chemistry must be consulted. It thus happens that special manures are divided into phosphatic, nitrogenous, and potash manures. It is necessary, in order for a manure to be efficient, that it shall not only contain the requisite constituent or constituents of plant food, but that the nutriment shall be in an assimilable form, and it has been ascertained that in whatever condition the plant food may be actually absorbed, the absorp- tion takes place the more rapidly the more soluble the food constituents. (A.) PHOSPHATIC MANURES.— The only abundant form in which phosphorus is found, is as the various forms of cal- cium phosphate (phosphate of lime), and, to a smaller extent, as aluminium and iron phosphates. Of these, the calcium phos- phates are better capable of supplying phosphorus to the plant than are iron and aluminium phosphates, probably because of the greater ease with which this compound is dissolved by feeble acids — i.e., carbonic acid — and by saline solutions. Deposits of calcium phosphate are widely distributed. The most definite mineral containing calcium phosphate is apatite, PHOSPHATIC MANURES. 107 3Ca 3 (P0 4 ) 2 . CaCl 2 or 3Ca 3 (P0 4 ) 2 . CaF 2 , both varieties being known. It contains 70 to 80 per cent, of calcium phosphate. The less nearly pure apatites, known as phosphorites, are obtained chiefly from Estramadura (containing 50 to 70 per cent, of Ca 3 (P0 4 ) 2 ), and from Canada (containing 70 to 80 per cent, of Ca 3 (P0 4 ) 2 ). They are associated with quartz and calcium carbonate. Other deposits of calcium phosphate, less distinctly characterised as minerals, are found in Carolina, the West Indian Islands, France, Germany, and Belgium, and in Cambridge and Suffolk. The form known as coprolites, sup- posed to be fossilised animal excreta, occurs in England and France, the Cambridge deposits being the best (55 to 60 per cent. Ca 3 (P0 4 ) 2 ). The South Carolina phosphate is known as "land phosphate" and "river phosphate," the latter being obtained by dredging. West Indian phosphates, or Caribbean phosphates, are not all available for superphosphate manufac- ture (v.i.), as some of them contain much iron and aluminium, the variety known as Redonda phosphate being mainly alumi- nium phosphate. Their use is consequently limited. Florida phosphates exist in the form of pebbles, and massive as rock. They vary considerably in richness — e.g., 60 to 70 per cent. Ca 3 (P0 4 ) 2 for pebbles, and 75 to 80 per cent, for rock. These phosphates, even when very finely ground, are but slowly assimilated by plants, and are, therefore, almost ex- clusively used for making superphosphate, the process consisting in treating them with sulphuric acid in order to realise the equation — Ca 3 (P0 4 ) 2 + 2H 2 S0 4 = 2CaS0 4 + CaH 4 (P0 4 ) 2 , Superphosphate as nearly as is practicable, CaH 4 (P0 4 ) 2 being soluble in water. Calcium carbonate, a common impurity in phosphates, consumes sulphuric acid in this treatment. Other objectionable impurities in phosphates are the ferric oxide and alumina, because both oxides form insoluble phosphates, so that the proportion of soluble phosphate in the prepared superphosphate is dimin- ished by their presence. Various plans have been proposed for removing calcium carbonate — e.g., treatment with an aqueous solution of C0 2 or S0 2 , in which calcium carbonate is soluble ; or by causticising the lime by heat, and acting upon it with an ammonium salt — e.g., the chloride — the ammonia being re- covered. Redonda phosphate (essentially A1P0 4 ) has been converted into an available form by treatment with sulphuric acid, yielding aluminium sulphate and phosphoric acid, or by heating with sodium chloride and superheated steam, whereby a portion of the phosphoric acid is converted into sodium phosphate. The variation in the composition of commercial phosphates may be gathered from the following analyses ( Warington) : — 108 ARTIFICIAL MANURE MANUFACTURE. Canadian (Apatitic). S. Carolina (River Phosphate). Coprolite (Cambridge). Water, 0-4 23 4-0 Ca 3 (P0 4 ) 2 , . S6'9 56-3 5S-1 CI and F, . 3 2 3 4 8i0 2 , . 10 140 8-2 CaO, . 76 10*5 11*9 MgO, . 0-6 10 Fe 2 0 3 + FeO, 2 2 2-2 A1 2 0 3 , . 1-3 20 S0 8 , • . 10 0-9 co 2 , . . 4-6 6-8 Small quantities of minor impurities are also generally present. "Superphosphate" is a mixture of calcium sulphate as gypsum with the acid phosphate of lime, CaH 4 (P0 4 ) 2 , which is the essential manurial constituent. The crude calcium phosphate to be converted into superphosphate should be, as stated above, as free as possible from iron and aluminium compounds (not more than 3 per cent, of Fe 2 0 3 + A1 2 0 3 ) aud from calcium car- bonate. The material is ground very finely — e.g., to pass a sieve having 80 meshes per linear inch — and is charged intermittently in 4 to 5 cwt. lots into a mixer consisting of a lead-lined wooden tank, provided with an agitator, where it is mixed with chamber acid (vitriol of specific gravity 1*53 to 1*61), run in as required from an adjacent tank. The quantity of acid needed varies with the composition of the phosphate, 13 to 18 cwts. per ton of phos- phate being the usual limits. The mixer is built above a brick chamber known as the " pit" or "den," and into this the semi- fluid mass, after it has been agitated for a few minutes, is dis- charged through a shoot. The temperature of the mass in the pit rapidly rises to 110° C. = 230° F. Much gas is evolved (C0 2 , HC1, and HF), and solidification sets in. The gases are drawn off through flues, and pass through a scrubber, necessary on account of the objectionable character of HC1, and still more of HF. When the pit is nearly full, one of the sides, which is of wood and removable, is taken down and the product dug out and passed through a disintegrator, whereby it is reduced to powder. When mixed manures, such as "grass manures," are being made, potash salts and nitrogenous materials are mixed during passage through the disintegrator. The proportion, of sulphuric acid used in making a superphosphate is generally as great as possible without impairing the dryness of the finished manure. It is usually more than sufficient for the realisation of the equation given above. It is now supposed that the re- action which occurs takes place in two stages, the sulphuric acid first liberating an equivalent of phospheric acid, which then PRECIPITATED PHOSPHATE. 109 reacts with the remaining Ca 3 (P0 4 ) 2 . The presence of calcium sulphate tends to solidify the mass by combining with 2 mole- cules of H 2 0 and setting like plaster of Paris. The value of a superphosphate depends on its content of phos- phoric acid soluble in water, which is commercially called "soluble phosphate" — i.e., the amount of phosphoric acid found, on analysis, to be soluble, is calculated back to Ca 3 (P0 4 ) 2 . An ordinary super- phosphate will contain 24 to 30 per cent, of soluble phosphate, 40 to 45 per cent, of calcium sulphate, and 2 to 3 per cent, of insoluble phosphate. Attempts have been made to produce superphosphates containing more soluble phosphoric acid than the quantity mentioned above, in order to save carriage ; thus " double superphosphate " is made by extracting an ordinary superphosphate with water, removing the calcium sulphate by means of a filter press, and evaporating the liquor with untreated phosphate of a quality easily attacked by phosphoric acid. Such preparations may contain 80 to 90 per cent, of soluble phosphate. When superphosphate is kept, a portion of the soluble phos- phate becomes insoluble in water owing, it is supposed, to the interaction of calcium superphosphate, CaH 4 (P0 4 ) 2 , and normal calcium phosphate, Ca 3 (P0 4 ) 0 , thus — CaH 4 (P0 4 ) 2 + Ca 3 (P0 4 ) 2 = 4CaHP0 4 . A further action, which has been already mentioned, occurs between the ferric oxide and alumina contained in crude phos- phate and a portion of the phosphoric acid, insoluble ferric phosphate (FeP0 4 ) and aluminium phosphate (A1P0 4 ) being- formed. Although such "reverted phosphate" is insoluble in water, it is more soluble in saline solutions — e.g., ammonium citrate solution — than is the natural phosphate, Ca 3 (P0 4 ) 2 , and is reckoned as possessing a certain manurial value. These points have to be taken into consideration in the analytical examination of superphosphate. Precipitated Phosphate. — When a mineral phosphate will not pay for conversion into superphosphate it may be used for the production of precipitated phosphate, which consists mainly of " dicalcium phosphate," CaHP0 4 . The preparation is conducted by dissolving the phosphate in hydrochloric acid, sufficiently dilute to leave siliceous matter and much of the oxides of iron and aluminium undissolved. The solution is neutralised by lime or chalk, when the precipitated phosphate is thrown down. It has been proposed to utilise alkali waste (calcium sulphide) for this precipitation, the point of neutrality being discernable by the formation of FeS ; the H 2 S evolved is collected for use as a source of sulphur (see Alkali, Yol. II., p. 33). As already stated, this form of calcium phosphate is more valuable than Ca 3 (P0 4 ) 2 , and, being precipitated, is very finely divided ; it contains up to 40 per cent, of P 2 0 5 , and is much used abroad. 110 ARTIFICIAL MANURE MANUFACTURE. Basic Slag. — It has been found within recent years that the phosphatic slag from the basic process of steel-making possesses considerable value as a fertiliser. The content of P 2 0 5 varies from 10 to 25 per cent., and the average composition of the slag is — P 2 0 6 , CaO, MgO, FeO, Fe 2 0 3: Per cent. 175 49-6 4-7 9-8 4-1 A1 2 0 3 , MnO, S, . so 3 , Si0 2 , Per cent. 20 40 0 5 02 8-0 According to Hilgenstock, the P 2 0 5 exists as a calcium phos- phate, of the composition indicated by the formula 4CaO.P 2 0 5 . Fig. 22. — Ball grinding mill. A, Drum ; B, steel balls ; C, sieves ; D, iron plates. This substance is more readily soluble in saline solutions — e.g., ammonium citrate — than is Ca 3 (P0 4 ) 2 , to which the fact that basic slag is more efficient as a manure than mineral phosphate is, may be attributed. The slag is, however, of little value as a manure DISSOLVED BONES. Ill unless it be very finely ground — e.g., 80 per cent, of it should pass a sieve having 100 meshes per linear inch. The attainment of this condition constitutes the preparation of the slag for the market, and is expensive on account of the hardness of the material. Grinding is commonly performed by a ball mill shown in Tig. 22, which consists essentially of a drum, A, the inner surface of which is polygonal ; the drum contains a number of balls of cast steel, B, of various sizes. Rotation of the drum breaks up the slag by the rolling and percussive action of the balls, and the comminuted material is systematically separated by sieves, C, in the sides of the drum. The sieves which effect the final separation are protected from direct contact with the balls by the perforated iron plates shown at D. Bones. — These are of manurial value mainly on account of their phosphates, but they also contain nitrogenous matter unless a previous extraction has taken place. The average composition of dry bones is — Per cent. Fat, ... 6 Nitrogenous matter, 28 ( consisting of Ca 3 (P0 4 ) 2 , 56 per cent. ; Mineral matter, . 66 \ CaC0 3 , 8 per cent. ; Mg 3 (P0 4 ) 2 , 1 per ( cent. ; CaF 2 , 1 per cent. = 66. 100 Fresh bones contain about 37 per cent, of nitrogen; they de- compose very slowly when used as manure. When the bones are previously fermented in heaps, the nitrogenous matter becomes more readily assimilable. Bone Meal. — Bones are also more available as manure when they have been steamed for the removal of fat (see Destructive distillation, Yol. II., p. 103). Boiled bones which have passed through the glue-makers' hands (see Glue, Yol. II., Chap. XYI.) contain a smaller proportion of nitrogen (14 per cent. N) than do raw bones. The boiled bones can be more finely divided than is represented by the condition of bone meal ; the fine product is known as bone flour. Dissolved bones is the product of the treatment of bones with sulphuric acid. Bone ash is much imported from South America, and is used for making high-grade superphosphates, which contain about 75 per cent, of soluble phosphate. Com- parisons made between the four phosphatic manures which have been described, show that they are available in the first year according to the following ratio : — Superphosphate, 100 Finely-ground basic slag, ..... 61 Steamed bone meal, . . . . . . 10 Ground coprolite, ....... 9 112 ARTIFICIAL MANURE MANUFACTURE. It must be remembered that such portion of phosphatic manures as is not used in the first year is available subsequently. (B.) NITROGENOUS MANURES.— Ammonium Sul- phate. — This is obtained as a bye-product in the destructive distillation of coal. Its preparation has been described in the section on gas manufacture, p. 76. Pure ammonium sulphate contains 21-21 per cent. N, corresponding with 2575 per cent. NH 0) , and is a colourless salt. The commercial product varies in colour from grey to brown, owing to the presence of tarry matter, and is sometimes yellowish from the presence of As 2 S 3 ; this body is formed by the action of the H 2 S from the gas liquor on the arsenic present in the sulphuric acid in which the am- monia was absorbed. Commercial ammonium sulphate usually contains about 24*5 per cent, of ammonia. It should be free from ammonium sulphocyanide, which is a plant poison. This impurity is rarely present, save when the ammonium sulphate has been made by the direct saturation of gas liquor with sul- phuric acid. Soot, which contains ammonium sulphate from the nitrogen and sulphur of coal, is also used as a manure. It contains on an average 4-2 per cent. NH 3 . Nitrate. — Sodium nitrate is obtained from the deposits of crude nitrate in Chili and Peru. The deposits, which lie about 6 to 10 feet below the surface, are known as caliche, and form a layer 4 to 6 feet deep. It is associated with clayey substances, and is stated to contain the following constituents : — Sodium nitrate, Sodium chloride, . Sodium sulphate, . Calcium chloride, . Potassium iodide,* Aluminium sulphate, Magnesium sulphate, Insoluble matter, . 21*01 per cent. 55-27 4- 74 0-33 0-87 981 5- 93 2-04 100-00 The composition is, however, very various, and the content of sodium nitrate may reach 50 per cent. The caliche is broken in a stone breaker, and systematically lixiviated in tanks heated by closed steam. (Water being a rare commodity in nitrate districts, it has to be used for repeated extractions.) When the liquid reaches a specific gravity of 1*55, it is run into crystallising vats, in which it remains from four to six days ; the mother liquor is then run off, and used for the obtainment of iodine (see Vol. II., Chap. XVIII. ). The nitrate deposited, after having been sun-dried, has the following com- position (Buchanan) : — * The iodine characteristically present in crude nitrate probably exists as iodate ; some of the chlorine is also present as perchlorate. ORGANIC NITROGENOUS MANURES. 113 NaN03, . 96 - 75 per cent. NaCl, 0-75 Na 2 S0 4 , 0-30 Insoluble matter, ..... 0*10 Water, 210 100-00 Organic Nitrogenous Manures. — Dried blood obtained from slaughter-bouses is a type of these. It contains from 9 to 12 per- cent. N. Ground hoofs and horns form another manure of this class, as also waste woollen material — e.g., shoddy (5 to 8 per cent. N) for manuring hops. Before nitrogen in ammonium sulphate or organic substances can be taken up by a plant, it must be converted into a nitrate. The nitrogen in organic substances is chiefly in an albuminoid form. The first decomposition which such substances undergo results in the production of ammonia. The oxidation necessary for the. conversion of ammonia into nitric acid is dependent upon the presence of a so-called "nitrifying" organism, which is a bacillus to which the name nitromonas has been provisionally assigned. The organism requires the usual mineral constituents — e.g., phosphates — for its growth, and free access of air, on which account it is not active in the ground at a greater depth than 6 feet. Nitrites, instead of nitrates, are produced by it when its activity is sufficiently impaired. In order that all the ammonia may be converted into nitric acid, a fixed base must be present, otherwise ammonium nitrate is the final product. The temperatures between which the organism can act are 3° and 55° C. = 37° and 131° R, 37° C. = 99 J F. being that at which it is most active. Darkness is favourable to its development. The process of nitrification is but one phase of the general oxidising action which is associated with the growth of this bacillus. Thus it is capable of converting iodides into iodates. "De- nitrifying" organisms appear also to exist in the soil, capable of reducing nitrate even to free nitrogen. These become active when the soil is water-logged, and are inimical to plant life. The process of nitrification is so rapid that ammonium sulphate is scarcely less readily assimilated than is sodium nitrate. There is, however, a certain amount of difference in the quality of certain crops when manured with nitrate and ammonium sul- phate respectively, which will be found set forth in books on the subject. Another difference in their action is on the soil itself;- before the nitrification of ammonium sulphate can be completed, the sulphuric acid must be removed by a base — -e.g., lime — in the soil, and a further quantity of base will be required by the nitric acid when formed. The comparative slowness with which nitrogenous organic manures are taken up, is due to the necessity for their previous 8 114 ARTIFICIAL MANURE MANUFACTURE. conversion into ammonia during the process of decomposition. An advantageous effect of nitrate is its stimulating action upon growth, enabling plants to resist conditions unfavourable to the healthy attainment of maturity. It has become questionable whether crops cannot obtain the nitrogen which they require from the free nitrogen of the air. This certainly occurs with leguminous plants, upon the roots of which nodules containing micro-organisms are developed, which appear to be capable of converting nitrogen from the air in the pores of the soil into an assimilable form. The nitrogen in ammonium sulphate, and that in nitrate, has about the same commercial value, which is not much higher than that for the most easily decomposable organic nitrogenous sub- stances. The nitrogen in bones is of considerably lower value. (C.) POTASH MANURES.— Potash, a necessary constituent of plant food, is supplied as one or other of the products obtained in the Stassfurt industry (see Potash, Vol. II., Chap. XVIII.). The chief salts used are kainit (K 2 S0 4 . MgS0 4 . MgCl 2 . 6H 2 0), which contains some 70 per cent, of the pure mineral, corre- sponding with 13 to 14 per cent. K 2 0 ; the double sulphate of potassium and magnesium (27 to 28 per cent. K 2 0) obtained from kainit; canallite (KC1 . MgCl 2 . 6H 2 0, with about 11 per cent. K 2 0 in the crude mineral) ; and crude potassium chloride of strength corresponding with about 50 per cent. K 2 0. Mag- nesium salts and chlorides detract to some extent from the manurial value of these substances. Where timber is abundant, wood ashes are used containing 5 to 10 per cent. K 2 0. (D.) GENERAL MANURES are valued for their content of nitrogen, potash, and phosphates. Earm-yard manure, the excrement of cattle, mixed with straw, may be regarded as the natural general manure, for it serves to return to the soil much of the plant food removed by the crop on which the cattle are fed. Since immature animals utilise more of the ash constituents of fodder than do full-grown animals, the composition of the manure depends upon the age of the stock; it also varies with the character of the food. Farm- yard manure is generally heaped, when it undergoes fermenta- tion and much carbonaceous matter is dissipated as C0 2 , CH 4 , &c, and on that account the manure becomes concentrated to some extent. Rotten farm-yard manure will contain 65 to 80 per cent. H 2 0 and 2*5 to 3 per cent, of true ash — i.e., exclusive of earth and sand. It contains from 0 4 to 0-65 per cent. N, 0*4 to 0*7 per cent. K 2 0, and 0*2 to 04 per cent. P 2 ^5- ^he nutritive consti- tuents of the animal excrement and that in the litter (straw) are both included in the above figures. The nitrogen of the urine being in the form of urea, uric acid, &c, is more readily available than that in the solid excreta. GUANO. 115 Sewage and Products therefrom. — The application of human excrement as a manure is largely practised, particularly where it is customary to keep the excrement concentrated or merely diluted with an absorbent and deodorant — e.g., earth or peat. Where the system of water-carriage is in use, the extreme dilution of the excrement renders it possible only to apply the sewage by the process of irrigation. The composition of human excrement is not essentially different from that of farm-yard manure ; its amount may be gathered from the following table, which gives the average quantities per head per year : — Dung. Urine. Total quantity, . Dry matter, Nitrogen, . P 2 0 5 , . . . K 2 0, 107 lbs. 24£ „ 1^ 1 " J 3 5 3 I » 1,063 lbs. 504 „ **2 3 5 H „ n 5, The total value of these constituents is about 8s. 6d. per head per year. The utilisation of sewage by irrigation requires that a large expanse of light absorbent soil shall be available for the recep- tion of the sewage, its oxidation and its assimilation by plants. Although precipitation of sewage (by means of lime and other substances) is practised, the large quantity of precipitant neces- sary renders the resulting sludge valueless as manure. When excrement is collected by the "pail system," without dilution, it can be treated with sulphuric acid, dried and disintegrated for use as manure, the product being known as poudrette. Guano. — This is the excrement of sea birds in a more or less altered condition. A distinction is drawn between nitrogenous and phosphatic guanos ; the former are either of recent origin, or have not been subjected to weathering, which is the case in such dry climates as that of Peru ; the latter (found in Austral- asia) have been so washed by rain as to contain little or no nitrogen. The manurial composition of the two classes is shown below : — Nitrogenous. Phosphatic. Per cent. Per cent. N, 7-5 0-4 p 2 o 5 , 14-5 35-6 K 2 0, 3-4 0-2 116 ARTIFICIAL MANURE MANUFACTURE. Dry Peruvian guano contains its nitrogen in the form of uric acid and urates ; when these have undergone partial decom- position, the guano becomes damp and contains ammonium carbonate, to fix which a " dissolved " guano is made by treat- ment with sulphuric acid, the ammonia being converted into ammonium sulphate and the calcium phosphate rendered soluble. An " equalised " guano is a Peruvian guano in which the per- centage of phosphates has been brought up by suitable admix- ture. The pressed cake made in crushing rape seed for oil (rape- cake), being of little value for cattle food, is sometimes used for a general manure. Other similar cakes are also employed. The nitrogen varies from 4 to 7 per cent.; P 2 0 5 , 1*5 to 3*0 per cent.; K 2 0, 1 to 2 per cent. ORIGIN AND DISTRIBUTION OF PETROLEUM. 117 CHAPTER V. PETROLEUM. Petroleum, or mineral or rock oil, or " naphtha," is essentially a mixture of hydrocarbons of the paraffin and olefine series, the one or the other predominating according to the source of the oil. The range of homologues* is exceedingly wide, comprising even gases such as CH 4 and ethylene, C 2 H 4 , and solid hydro- carbons such as those constituting paraffin wax — for example, triacontane, C 30 H 6O , and melen, C 30 H 60 . (A.) ORIGIN AND DISTRIBUTION.— Petroleum occurs in strata which consist largely of loose-textured conglomerates and sandstones (oil sands), its mode of distribution being similar to that of water in porous strata. In places it exudes at the sur- face of the earth, forming natural oil springs, but it is obtained in quantity by boring wells which tap the strata. Frequently, the oil is under such pressure from the gas associated with it that, when the superincumbent strata have been pierced, the oil gushes out in a fountain with great violence. Fountains of this character have occurred naturally for all historical time. The nature of the origin of petroleum is unknown. Various theories have been advanced. The most noteworthy of these are : — (1) That it is derived from the action of water on strongly heated iron carbide contained in the interior of the earth, such water having penetrated through crevices formed during volcanic erup- tions. The chief support for this view is obtained from the fact that petroleum generally occurs at the foot of mountain chains. This theory was propounded by Mendeleeff after a personal study of the Caucasian oil-bearing district. (2) That it is a product of the decomposition of animal remains at a high temperature and pressure. Engler is responsible for this view, which is supported by direct experiment on the distillation of animal fats under pressure. The small quantity of nitrogen found in petroleum militates against the credibility of this explanation, but it is possible that the nitrogen may have been removed by a natural distillation of the oil (the nitrogen remaining with the residue) from its original source to the position in which it is found. * It may be noted that, in chemical classification, those compounds which increase in molecular weight by the addition of CH 2 form an homologous series. This increase in molecular weight is accompanied by an approxi- mately constant alteration in physical properties— e.g., melting point and boiling point ; both these rise as the series ascends. 118 PETROLEUM. (3) That it has been formed by the decomposition of the remains of marine animals in contact with saline deposits, and the subse- quent resolution of the adipocere (the more permanent fatty constituents) into hydrocarbons and free C0 2 . The fact that salt invariably accompanies petroleum lends credence to this hypothesis, which is due to Zaloziecki. Petroleum is very widely distributed, but the bulk of that used comes from Pennsylvania or Baku. Other sources of minor importance are the deposits in Galicia, Canada, and British India. (B.) THE WINNING OF PETROLEUM. — The copious outbursts of petroleum that characterised the earlier stages of the industry (which in its present size and manner of working is comparatively recent, dating from about 1860) are now relatively rare, and the oil is won by sinking bore - holes (about 6 inches in diameter), which are often of great depth — e.g., as much as 2,400 feet and upwards. The method of sinking consists essentially in drilling a bore-hole to a depth of 200 to 300 feet by the use of a "drive-pipe," which is a steel tube with a cutting edge driven vertically downwards by a "maul." When the top part of the well is thus made and lined, the drilling proper begins. This consists in pounding the rock with a bit fixed at the end of a string of rods slung to a cable attached to a derrick — in order to allow of the string of tools being drawn up and suspended on occasion — and actuated by a beam-engine by which a reciprocating vertical motion is given. When a suffi- cient amount of the rock has been thus disintegrated, the tools are hung up by the derrick, and the detritus, which is suspended in the water that has trickled in, is removed by running down an iron tube fitted with a plunger and a valve, the apparatus being termed a sand pump. The well is lined with iron tubing as far as possible, the main object being to keep out the water that would otherwise find its way in. In the case of wells that do not flow spontaneously, an oil pump (which is simply a force pump driven from above) is let down and the oil thus brought to the surface. The oil is frequently accompanied by natural gas at a pressure of 400 to 500 lbs. per square inch, the gas consists chiefly of methane and hydrogen. The following may be taken as the average composition of the gas from the Pittsburg district : — Methane, 67 "0 per cent. Hydrogen, 22*0 Ethane, 5*0 ,, Nitrogen, 3*0 ,, Ethylene, 1-0 Oxygen, ..... 08 Carbon monoxide, . . . 0*6 ,, Carbon dioxide, . . . . 0'6 100-0 REFINING PETROLEUM. 119 Some wells yield oil containing a little gas in solution, others oil accompanied by much gas, and a third class gas exclusively. The gas is largely used as a fuel and for lighting in the districts where it is obtained, and, by imperfect combustion, for the pro- duction of a black pigment, "diamond black," or " carbon black" (q.v.). (C.) TRANSMISSION. — On account of the wells of any one oil-bearing district being scattered, it is found economical to collect the oil to central storage tanks and thence to the refineries on the sea coast by means of long pipe-lines, a pressure of about 1,200 lbs. per square inch being used in this transmis- sion. The trunk lines of pipes are 6 inches in diameter, and deliver the oil through branches to the refineries on their course. The pipes are kept clean by an iron scraper forced along by the flow of the oil. (D.) REFINING. — The refining consists essentially in frac- tional distillation and treatment of the distillates with sulphuric acid and caustic soda to remove impurities. The method adopted depends to some extent on the percentage of the more volatile portions, and whether it be desired to produce the maximum yield of illuminants. The difference between the yield of the various fractions of Russian and American petroleum is shown by the following figures : — Russian. American. Petroleum spirit, . Illuminating oil, . Lubricating oils, Residue and loss, . 4 39 32 25 25 60 } » 100 100 In America the distillation is not continuous, and is carried out in a crude oil still and a tar still, the oil being distilled in the first until the petroleum spirit and burning oils have come over, when the residue is transferred to the tar still, the distil- late from which furnishes paraffin wax and lubricating oil. The crude oil stills are either horizontal steel cylinders 30 feet by 12 feet 6 inches in diameter, or of the "cheese box" pattern 9 feet in height and 30 feet in diameter, with a dome-shaped top. Both stills are fired direct, and steam is blown in to aid distil- lation. When the maximum quantity of illuminants is required, the upper part of the still is exposed to the air, in order that the heavier portions of the oil may condense and drop back into the hotter part of the still and thus be "cracked" — i.e., decomposed into lighter hydrocarbons. When, on the other hand, lubricating 120 PETROLEUM. oils are required, this cracking is avoided, and the lighter por- tions are distilled over first to obtain a residue of " reduced oil " used for lubrication. In this case a vacuum is maintained in the still, and the use of superheated steam is substituted for direct firing. The tar still is a cylindrical vessel about 20 feet in length and 8 feet in diameter, and is heated finally to redness to get the full yield of oil. With both the crude oil and tar stills the condensers are essentially worms immersed in tanks through which cold water is circulated in the case of the former, and hot water in that of the latter, the hot water being necessary to prevent stoppages from the setting of the paraffin wax. In the distillation from the crude oil still, two main distillates are pro- duced — (1) the "benzine* distillate," and (2) the "illuminating oil." The former is redistilled by steam heat, and the following fractions may be prepared from it : — (1) Cymogene, which is essentially the gas butane, C 4 H 10 . This fraction is either burnt under the stills, or condensed by cold and pressure to a liquid boiling at 0° C. = 32° F., and having a specific gravity of 0*59. It is used in ice-making machines. (2) Rhigolene. — This is also gaseous when first distilled, and consists mainly of pentane and iso-pentane, C 5 H 12 . It is con- densed by cold to a liquid which boils at 18° C. = 64° F., and has the specific gravity 0'625. It is used as an anaesthetic, for driving gas engines, and for the pentane standard lamp (see Valuation of coal gas, Yol. I., p. 68). (3) Petroleum ether or gasolene containing hexane and iso-hexane, 0 G H 14 , and boiling about 60° C. = 140° F. ; its specific gravity is about 0*66. This is employed as a solvent for caoutchouc and oils, and is used for carburetting gas and preparing "air gas" — i.e., air laden with a combustible vapour. (4) Naphtha or ligroin, consisting of the next few homologues of the paraffin series, boiling point 80° to 110° C. = 176° to 230° F., specific gravity about 0*700, used for burning and as a solvent for oils and resins. (5) Benzine a slightly heavier fraction, boiling up to 150° CL = 302° F., specific gravity 0*740 and used as a turpentine sub- stitute. With respect to the fractional separation of these products, the same remarks that were made with regard to the fractionation of the distillate from coal tar (see Vol. II., p. 77) apply. The last and largest fraction, amounting to 40 per cent, of the whole, is sometimes deodorised by treatment with 0*5 per cent, of strong sulphuric acid in a vessel provided with a paddle agitator. The illuminating oil distillate, coming over between 150° and 300° C. = 302° and 572° F., is submitted to treatment with * This trade name must not be confounded with " benzene," which is the systematic name of the hydrocarbon, C C H 6 , obtained from coal tar. PARAFFIN OIL. 121 sulphuric acid (about 2 per cent.), with which it is agitated by a stream of air, for as long as the temperature rises. After settling, the acid liquor is drawn off, and a water spray is made to percolate through the oil until the issuing water is no longer acid. The oil is then agitated with 1 per cent, of caustic soda solution, specific gravity 1*09, and, preferably, finally washed with water. The use of the sulphuric acid is to remove the bulk of the defines as sulphonic acids, while the caustic soda is employed to remove such of these acids as are dissolved in the oil. The refined oil is known as kerosene, and is valued by its colour and flashing point. The former varies from pale yellow " standard white," to colourless, " water white," and the latter from 75° to 120° F. = 24° to 49° C. In this country the flashing point is determined by the "close test" made in the Abel apparatus. By "close test" is meant the method of ascertaining the temperature at which the oil evolves sufficient vapour to yield an explosive mixture with air in a closed vessel of standard dimensions. The Abel apparatus consists of a water bath, in which is an " oil cup " (containing a fixed quantity of the oil to be tested), and provided with a cover having a slide in the lid so arranged that it can be opened at intervals and a small flame introduced into the vessel. The oil in the vessel is heated by the water bath and its temperature is ascertained by a thermometer. The legal minimum for the flashing point of kerosene is 73° F. = 23° C, corresponding with 100° F. = 38° C. by the obsolete "open test," which was conducted in an uncovered vessel. Scotch burning oils of good class rarely flash below 100° F. (close test), a much preferable limit. The working up of the residue of the crude oil distillation in the tar still, produces a first runnings (20 to 25 per cent, of the contents of the still), which is turned back to the crude oil tank, or is treated and purified as a heavier grade of burning oil. The remaining distillate constitutes the paraffin oil; this is agitated with vitriol (5 per cent.) in agitators kept hot by steam jackets, then with water and caustic soda, and chilled by a freezing machine, when it becomes semi-solid from the separation of paraffin wax, and is pressed between sacking, the oil which drains away being used for lubrication. The wax is again pressed at a higher temperature to refine it (see Shale oil, Vol. II., p. 102).. The bulk of lubricating oils is, however, obtained from "reduced oil" (y.s.). " Yaselene" is a product from such oils prepared by the separation of paraffin wax and filtration through animal charcoal ; the first runnings from the filter are colourless and semi-solid when cold. It melts at 40° to 50° C. = 104° to 122° F., according to its grade. Spurious vaselene is made in Germany by dissolving paraffin wax in heavy hydrocarbon oil. Lubricating oils from petroleum are characterised by their fluorescence or "bloom." They are generally deodorised and 122 PETROLEUM. decolorised by filtration through animal charcoal, and are often " de-bloomed " by the addition of various substances — e.g., tur- meric, nitronaphthalene, and picric acid. This treatment is only adopted when it is designed to substitute mineral for fatty lubri- cants without risking detection at sight. After the lubricating oils have distilled over, a semi-solid distillate is collected, tech- nically known as " yellow wax ; " it contains anthracene and similar hydrocarbons ; when added to the lubricating oil it in- creases its density and raises the apparent yield of paraffin wax. The coke left in the still is about 12 per cent, of the charge. The refining of petroleum in Russia, at Baku, is conducted in horizontal cylindrical stills, and the process is often continuous, in which case the stills are connected by pipes in groups of four- teen or more, and are heated to the temperature at which the product proper to each still comes over. By this plan a constant flow of petroleum (which is previously heated in a separate vessel by contact with the residues from the stills, produced by a pre- vious operation) can be maintained, and the whole of the portion of the oil fit for burning is obtained from one or other of the stills, the last and most highly heated being no hotter (300° C. = 572°F.) than is consonant with the production of burning oil. The refining of the burning oil resembles the method used in America (v.s.). Heavier grades of burning oil than those made from American petroleum are prepared at Baku — e.g., solar oil and astralene, specific gravity 0*850 to 0-880; flashing point, astralene 50° C. = 122° F., solar oil 80° C. = 176° F. — but their use is mainly confined to Russia, where they are given fiscal advantages. The residual oil from these stills (astatki) (specific gravity, 0*900 to 0*910) is mostly used as fuel for the stills themselves, for steam-raising on the works, for locomotives and marine engines on the local railways, rivers and seas, and for metallurgical operations. The principle of the method of burning consists in spraying the oil, by means of a jet of steam, into the furnace, the parts immediately in contact with the flame being protected with firebrick to preserve them from local overheating. Petroleum residues have about one and a-half times the heating power of an equal weight of coal, but the cost of carriage pre- vents it in competing with coal in this country except for special purposes (see Yol. L, p. 57). A considerable quantity of the residue after the separation of the kerosene is, however, further distilled for lubricating oils, in smaller stills — sometimes worked by the continuous method already described, with the aid of superheated steam — until the distillate has the specific gravity of about 0*920. The distillate is then fractionated, and the first and second fractions (specific gravity 0*865 and 0*875), which are too light for lubricants, are sold for gas making, &c, and the remaining oil is collected in three fractions, forming three grades of lubricating oil, known respec- OZOKERITE. 123 tively as spindle oil (specific gravity 0885 to 0*895), machinery oil (specific gravity 0-895 to 0-910), and cylinder oil (specific gravity over 0-910). Other, intermediate grades are prepared, which differ according to the design of the maker. These oils are purified by acid and alkali in a manner similar to that used for kerosene. A kind of vaselene is made from the residue in the still by returning one-third of its weight of the first fraction (specific gravity 0*865), and continuing to distil with superheated steam. Russian petroleum, as opposed to American, is generally very poor in paraffin wax (0-25 per cent.), and this substance is not worked up. The absence of paraffin wax makes Russian lubri- cating oils better than American of the same grade, as they have less tendency to solidify on cooling. By destructive "distillation, astatki yields 30 to 40 per cent, of tar, containing 15 to 17 per cent, of 50 per cent, benzol. On destructively distilling the residual tar after the benzol is removed, 70 per cent, of a second tar is obtained, containing 7 to 10 per cent, of 50 per cent, benzol, 16 per cent, of naph- thalene, 2 to 3 per cent, of 30 per cent, anthracene, and 24 per cent, of pitch. There is also a good deal of gas of high illumin- ating power (five times that of coal gas). In instituting a chemical as distinct from a technical com- parison of petroleum from Russian and American sources, a large difference is at once visible. Thus, American crude oil consists almost wholly of paraffins of the general formula C n H. 2n + 2 , whereas Russian oil is composed of olefines (0 M H 2n ) and naphthenes (C n H 2 „ _ 6 H 6 ). The paraffins are more stable than the unsaturated hydrocarbons characteristic of Russian petro- leum, and are less liable to be attacked in the process of refining. The olefines readily form addition products, and are easily sulphonated, but the naphthenes, being addition products of ring hydrocarbons, containing as many hydrogen atoms as can be combined with the nucleal ring, are unable to form addition products provided the ring structure remain undisturbed. Under suitable conditions, however, the naphthenes of Russian petroleum can be oxidised — e.g., by a current of air in the pre- sence of caustic soda — and then yield acids which unite with the alkali essential for their production. It has been proposed to take advantage of this formation of soap-like salts, in order to convert Russian petroleum into a semi-solid fuel without the addition of soap from an external source (see Vol. I., p. 58). Ozokerite. — Ozokerite is a mixture of solid hydrocarbons, the composition of which corresponds with the formula C n H 2n ; it is regarded as an oxidation product of the hydrocarbons of crude petroleum, from which some hydrogen has been eliminated as water. It varies in consistency from a soft buttery mass to a 124 PETROLEUM. hard rock-like material generally black in colour. The largest deposits are found in Galicia. Its specific gravity varies from 0-85 to 0-95, and its melting point from 58° to 100° C. = 136° to 212° F. It occurs in veins 40 to 80 metres deep, which generally run through clay containing petroleum. The mining operations consist in sinking a shaft from which galleries are run along the veins. Gas occurs in the workings, and safety-lamps have to be used. The mineral is brought to the surface both in the form of lump and as earth containing ozokerite. The larger lumps can be melted for the refinery, while the earth is extracted by elutriation and the residues are boiled with water ; recently it has been proposed to extract the last traces with light petroleum. The process of refining consists in treatment of the crude wax with fuming sulphuric acid, which converts some of the hydro- carbons into sulpho-compounds, and afterwards with charcoal to decolorise it. The material is then known as ceresin, and amounts to 60 to 70 per cent, of the crude ozokerite. It has a melting point of 61° to 78° C. = 142° to 172° F., and is largely used for the manufacture of candles (see Vol. II., Chap. XL) and the adulteration of beeswax. There is also made an insulating material (okonite) which consists of a mixture of ozokerite and indiarubber. Asphaltnm. — This is the most condensed form of petroleum. Deposits of it occur in many countries, but the most noteworthy is that at the pitch lake of Trinidad. Asphaltum is a black material, varying from a very viscous fluid to a hard resonant rock; at Trinidad two kinds are obtained, the better being known as " Lake Pitch," the other as " Land Pitch." The former is soft, bituminous, and impregnated with gas, chiefly H 2 S and C0 2 . The latter appears to be lake pitch altered by oxidation, and is harder and free from gas. The following table shows the composition of typical samples, free from water: — Lake per cent. Land per cent. Inorganic matter (ash), Organic matter, not bitumen, Bitumen, .... 36-56 10-57 52-87 37-74 1068 51-58 100-00 100-00 Both qualities, as dug, contain about 27 per cent, of water. Although so similar in composition (stated in the proximate form adopted above), these kinds differ considerably in qualities ; lake pitch, when refined, softens at 180° to 192° F. = 82° to 89° C, and flows at 189° to 210° F. = 87° to 99° C, while the corresponding numbers for refined land pitch are 190° to 237° F. ASPHALTUM. 125 = 88° to 114° C, and 210° to 255° F. = 99° to 124° C. respec- tively. The process of refining consists in heating the pitch in stills to drive off the water and to allow the mineral matter to deposit ; the refined product is known locally as "epure" or asphalt. The specific gravity of the refined lake asphalt is 1*38, that of land asphalt is 1*43. The bulk of the asphalt obtained is used for paving, for which purpose it is heated with heavy paraffin oil, and this product, " asphalt cement," mixed with sand and other mineral matter, and applied while hot. " Asphalt Rock " — e.g., Yal de Travers asphalt — is a substance similar to Trinidad pitch, but containing up to 90 per cent, of mineral matter which is either siliceous or calcareous ; when used for paving it is mixed with rich native asphaltum, such as Trinidad pitch, to increase the proportion of bituminous matter, the product being called "mastic." 126 LIME AND CEMENT. CHAPTER VI. LIME AND CEMENT. Lime is always prepared industrially by the dissociation of calcium carbonate. This raw material occurs naturally in the following forms : — (1) Marble. — A crystalline calcium carbonate nearly pure when white, sometimes containing mineral and carbonaceous (in black marble) colouring matter. The cost and closeness of texture of marble prevent its use as a raw material for making lime. (2) Limestone. — This is a dense form of calcium carbonate, seldom so nearly pure as marble, generally containing silica, silicate of alumina and magnesium carbonate. When this last- named constituent is present to the extent of 5 per cent., the limestone may be termed dolomitic, and when 23 per cent, is present may be ranked as dolomite ; typical dolomite corre- sponds with the formula CaC0 3 .MgC0 3 , the magnesium carbonate, therefore, amounting to 45-66 per cent. Dolomites are harder and better building materials than are limestones, being less easily attacked by an acid atmosphere (see Vol. L, p. 6) ; the mixture of lime and magnesia produced by burning dolomite is only used as a basic lining for furnaces (see Vol. L, p. 145). The variations in the composition of limestone may be judged by the following analyses : — Typical Pure Limestone. Magnesian Limestone. Hydraulic Limestone. CaO, .... 55'54 27-22 44-84 MgO, 022 1685 1-15 C0 2 , .... H 2 0, .... 43-68 37-62 33-70 0-06 1-79 2-86 so 3 , . _ . 0-02 0 16 Insol. siliceous matter, 13-57 1302 Combined silica, 2 03 A1 2 0 3 , . . . 1*39 1-04 Fe 2 0 3 , 1-56 100 99-52 100-00 99-80 PRINCIPLES OF LIME-BURNING. 127 (3) Chalk. — Chalk is a less massive form than limestone of calcium carbonate, and varies in purity in the same manner. Ordinary chalk as quarried contains as much as 25 per cent, of water intermixed with it. The following analyses show the composition of two typical chalks used for lime and cement making : — Grey Chalk White Chalk (yielding a somewhat (yielding a "fat " hydraulic lime). lime). Moisture, 17-39 19-03 Sand and clay, .... 4-85 0-93 Combined SiOo, .... 0-78 0 43 Fe 2 0 3 + A1 2 0 3 ", .... 0-53 0-48 CaC0 3 , 73-84 76-60 MgC0 3 , 0-66 0-88 Alkalies, organic matter, and loss, 1-95 1-65 100-00 100-00 In general, carbonate of lime approximately pure will yield "fat" quicklime on burning, while, when siliceous and clayey constituents are present, a " poor " lime which slakes slowly and is more or less hydraulic is produced. Principles of Lime-burning. — When calcium carbonate is heated under ordinary conditions, it begins to dissociate at about 400° C. = 752° F., but the dissociation does not proceed far unless the carbon dioxide be removed from the neighbourhood. Indeed, in a closed space, at a temperature of 1,020° C. = 1,868° F., cal- cium carbonate can be fused in the atmosphere of C0 0 generated by its partial decomposition; the resulting product has the aspect and physical properties of marble. The necessity for removing the carbon dioxide diminishes as the temperature rises ; thus at 812° C. = 1,494° F. it may be allowed to accumulate until its pressure is 760 mm. — i.e., one atmosphere. In practice the re- moval of the C0 2 is effected by the natural draught of the kiln, for in this manner the pressure due to C0 2 is reduced, since much of the total atmosphere consists of other gases. Although in a lime kiln the temperature may exceed 812° C. = 1,494° F., and dissociation would be completed without the draught, yet the process of burning is much accelerated by removal of C0 2 in this way; the removal is also imperative, because CaO and C0 2 would otherwise reunite (in the presence of water vapour) as the tem- perature fell. It is obvious from these facts that the dilution of the atmosphere of the kiln by an inert gas like steam will favour the decomposition of the calcium carbonate. The heat of forma- tion of calcium carbonate from CaO and C0 2 is 42*5 Cal., whence it follows that 5-25 kilos, of fuel, having a heat of combustion 128 LIME AND CEMENT. equal to that of carbon, should suffice for burning 100 kilos, of CaC0 3 . In practice this quantity of fuel is much exceeded. Kilns for Lime-burning. — It will be seen from what has been said above that the conditions for successful lime-burning are a temperature not lower than 812° C. = 1,494° F. and a rapid draught of inert gases through the heated limestone. Many forms of lime kilns are in use, but they are reducible to two types — (a) that in which the calcium carbonate is in contact only with the products of combustion, being separated from the fuel itself, and (b) that in which the calcium carbonate and fuel are mixed. The former yields a better lime, inasmuch as it is not contaminated with ash, while the latter is more economical of fuel and can be more readily adapted for continuous running. (a) Kilns in which the Fuel is not in contact with the Calcium Carbonate. — One of the simplest forms is shown in Fig. 23. An ported above the fuel by other means — e.g., a rough grating of iron bars, &c. The product is known as " flare-lime." The pro- cess of burning lime without solid fuel is obviously one that should be well adapted for performance by the aid of the gas producer. The arrangement generally adopted consists of an annular kiln (Fig. 24), the space in the centre of which, A, serves for storing the limestone, so that it may be charged into the sur- rounding kiln at a fairly high temperature. The gas from a producer passes through flues in the walls of the kiln, and the air for its combustion is admitted by a channel at the bottom of the annular space, B, B, and meets with the producer gas at a point about one-fourth of the height of the kiln, C, C, where the true lime-burning begins, the quantity of lime below this point serving to heat the air thus admitted. (b) Kilns in which the Fuel is in contact with the Calcium Carbonate. — The simplest form of kiln of this type is cylindrical, or like an inverted cone in shape, with a side opening at the Fig. 23.— Lime kiln. egg-shaped firebrick kiln is filled with limestone sup- ported on an arch roughly built of blocks of the same material. The fuel is placed below the arch, and the products of combustion pass upwards through the lime- stone, which is thus heated to the required temperature and converted into quick- lime. Such a kiln only admits of discontinuous burning, and has to be charged for the next batch. The limestone may be sup- LIME. 129 bottom, fed from the top with mixed limestone and fuel, and emptied below through the side opening. The process can be carried on continuously, the charging at the top and unloading beneath proceeding regularly. The consumption of fuel is about 25 per cent, of the limestone burnt, but the product is necessarily mixed with the siliceous ash of the fuel, its value being thereby Fig. 24. — Lime kiln heated by producer gas. B, B, Annular kiln ; C, C, inlets for secondary air. impaired. Other forms of kiln, in which the fuel and calcium carbonate are in contact, are the Hoffmann ring kiln and the Dietzsch stage kiln (Etageofen). Lime. — The quality of the lime produced depends, as already stated, upon (1) the quality of the limestone, and (2) the nature of the ash of the fuel with which it has been burnt, assuming the systems mentioned in the last paragraph to have been used. Commercial lime of good quality contains 85 to 90 130 LIME AND CEMENT. per cent, of free CaO, the remainder being calcium carbonate left unburnt or re-formed by exposure to air, calcium hydroxide (from absorption of moisture after burning), and calcium silicates and aluminates produced by the action of the lime on the siliceous constituents of the limestone and fuel ash. Magnesia is also commonly present, and when occurring in as high a pro- portion as 25 to 30 per cent, it renders the lime useless for ordinary purposes ; the slowness of the hydration of the magnesia causes such lime to slake feebly and imperfectly. Technical terms are used to distinguish the qualities of commercial lime ; thus "fat" lime is lime containing a minimum of foreign matter, and slaking rapidly and violently to a smooth pasty mass of " slaked " lime. Good nit lime slakes with so large and rapid an evolution of heat that the temperature of the mass may rise as high as 150° C. = 302° F. " Poor," or " over-burnt," or " dead- burnt " lime is that which slakes slowly and with little evolution of heat, and yields a slaked lime less smooth and plastic than that formed by fat lime. The more siliceous and clayey matter a limestone contains, the more liable it is to be over-burnt, and to yield a poor lime. As the reaction between the lime and the siliceous matter (producing calcium silicates and aluminates, which become hydrated slowly and with little evolution of heat) only takes place at a comparatively high temperature, the pro- duction of poor lime from limestones containing these constituents may be avoided by cautious burning. Slaked lime dissolves in water, the solution containing 1 part of CaO in 780 parts of water at 15° C. = 60° F. Its solubility diminishes as the temperature rises, being rather less than half the above value at the boiling point. When lime is exposed to the air it becomes slaked by absorption of moisture, but there is j)ari passu an absorption of C0 2 . Such air-slaked lime approxi- mates to the composition CaC0 3 .Ca(OH) 2 . Mortar. — Common mortar (as distinct from cement mortar) consists of 1 part of slaked lime and 3 of sharp sand (the pro- portions being generally by measure), and enough water to make a paste. One measure of fat lime will yield from 2 to 3 measures of slaked lime, while 1 measure of hydraulic lime yields 1*3 to 1*7 of the slaked product. The principles upon which the setting of mortar depends will be understood from what follows. When freshly slaked lime is allowed to dry it sets to a hard mass, which, however, is considerably smaller in volume than the wet lime, and, therefore, forms shrinkage cracks. Admixture with sand prevents this. This first stage or "setting" depends on the general property of very finely-divided amorphous substances, such as kaolin, of drying to a hard caked mass. This change takes place with lime, and then a further stage ("hardening") occurs, due to the absorption of C0 0 from the air, the mortar becoming coated with the calcium carbonate, the insolubility PLASTER OF PARIS. 131 of which makes the mortar permanent under ordinary weather conditions. In thick walls access of air is so slow that un- carbonated lime remains in the interior for many years. The general effect of low temperatures upon mortar and cement during their application is to retard or prevent their setting. This fact is the canse of the abandonment of building operations during frost. Urgent work with cement in cold climates is conducted by the aid of steam heating at the point where the freshly mixed cement has been placed in position. Besides its use as mortar, lime is employed in all chemical industries as the cheapest form of alkaline substance. Plaster of Paris. — This material may be taken as a simple example of cements which set by hydration. It is manufactured by heating gvpsum, CaS0 4 .2H. 2 0, to a temperature of 120° to 130° C. = 248° to 266° F. This must be done out of contact with fuel, as the local heat of the burning particles that would be mixed with the gypsum (1) causes complete dehydration to 0aSO 4 , which is not plaster of Paris (v.i.), and (2) allows of the reduction of CaS0 4 to CaS, where the gypsum is in direct con- tact with carbonaceous matter. The gypsum is piled over arched fire-places, either in a rectangular chamber or in an egg-shaped kiln. Good plaster corresponds with the formula 2CaS0 4 .H 2 0, complete dehydration only occurring at 194° C. = 381° F., when CaS0 4 , which is but slowly acted on by water, is obtained. The mechanism of the setting of plaster of Paris may be under- stood from the following facts (Le Chatelier) : — When plaster of Paris (2CaS0 4 .H 2 0) is shaken with water, some of it is immediately dissolved. This portion then com- bines with water, becoming CaS0 4 .2H 9 0, which, however, is less soluble than 2CaS0 4 .H 2 0, so that crystals of the former hydrate are deposited, and more 2CaS0 4 .H 2 0 is dissolved by the same water. The process repeats itself until the whole quantity of calcium sulphate has crystallised in the form of CaS0 4 .2H 2 0. Obviously, when the water is only sufficient to make a cream or paste with the plaster, this cycle of reactions will convert the paste into one composed of crystals of CaS0 4 .2H 2 0, which, being needle-shaped and interlaced, constitute a coherent mass. Theoretically, about 13 per cent, of water, reckoned on the weight of the plaster, is necessary for its setting, but in practice at least 35 per cent, of water is used, as otherwise the setting is unmanageably rapid. Anhydrous calcium sulphate will set when mixed with water, but more slowly than plaster of Paris, becoming much harder than the latter. When gypsum is mixed Avith a small proportion of alum, and completely dehydrated, it sets more slowly than plaster of Paris, but less slowly than pure CaS0 4 . Other salts — e.g., borax — have been used for the same purpose. The mode of action in these bodies, which are present in the finished substance in inconsiderable quantity, has not 132 LIME AND CEMENT. been satisfactorily elucidated. A mixture of lime with a small proportion of calcium sulphate constitutes Scott's cement. Stucco is plaster of Paris set with a solution of size; it is capable of receiving a polish. Hydraulic Cements. — Hydraulic cements differ from com- mon lime mortars in that they are not dependent upon desiccation for their setting, nor on carbonation for their hardening. Their setting depends upon hydration, analogous to that characteristic of plaster of Paris (v.s.). They are distinguished from plaster of Paris by their insolubility in water, which is sufficient in the case of "hydraulic " cements — e.g., Portland cement — to allow of their use for structures immersed in water, such as docks and breakwaters. Hydraulic Lime. — This material is manufactured by burning limestone containing siliceous and clayey matter. True hydraulic lime contains but little alumina, the silica being so finely divided and evenly distributed as to combine with the lime on burning with the aid of but little fluxing material (A1 2 0 3 and Fe 2 0 3 ) — (see Portland cement, Vol. II., p. 139). Thus, lime made by burning, the famous Theil limestone (found at Ardreche in France) has the following composition : — CaO, MgO, Si0 2 (combined), .... Sand, ...... ALjOg, Pe 2 0 3 , S0 3 CO., and H 9 0, .... 740 per cent. 0-7 217 0- 3 1- 8 0-6 0-3 0 6 ioo-o Limestone, yielding hydraulic limes, which are in common use in this country, are less typical than the example quoted above, as they contain clay which gives rise to the presence of an appreci- able quantity of alumina in the lime produced. Thus, blue lias limestone has the following composition, an analysis being also given of a lime produced from a limestone of this class : — Limestone CaC0 3 , MgC0 3 , A1 2 0 3 , Si0 2 , Fe 2 0 3 , Alkalies Water and loss, Per cent. 71-55 1- 35 3'52 20-10 2- 20 0-78 0-50 100-00 Lime Insoluble residue, Combined Si0 2 , A1 2 0 3 , Fe 2 0 3 , CaO, MgO, S0 3 , C0 2 , H 2 0, Alkalies and loss, Per cent. 2 39 14-17 6-79 2 34 63-43 1-54 1- 63 3 64 2- 69 1-33 100-00 KOMAN CEMENT. 133 The reactions which take place on burning a limestone of this character consist in the attack of the siliceous and clayey matter by the lime, resulting in the formation of certain silicates and aluminates of lime (see Portland cement, Vol. II., p. 139) ; these remain mixed with some free lime for the saturation of which sufficient acid constituents (Si0 2 and A1 2 0 3 ) are not present. In actual practice the free lime takes no essential part in the setting, and may be conveniently slaked by the cautious addition of water, insufficient to hydrate the cementitious silicates and aluminates, before the hydraulic lime is put on the market. This is the custom in France where large quantities are used, but in this country the lime is generally sold unslaked, and water sufficient for the slaking and setting added at the time of use. This is undesirable, as perfect slaking of all free lime should be secured before the material is used as a cement, lest slaking after partial setting should occur and give rise to disruptive strains. Good hydraulic lime serves much the same purposes as Portland cement {q.v.), and though not possessing the strength of the latter, is a useful and cheap material of construction. It has the advantage, moreover, of setting slowly, and remaining plastic for a sufficient time to allow the slight settlement, inevitable in much new work, to occur and terminate before the joints of the structure become rigid. Roman Cement. — This cement is made by burning marl or any mixture of calcium carbonate and clay containing about 25 per cent, of the latter. Septaria Nodules, consisting of chalk and clay in the above proportions, are dredged on the Kent and Essex coasts, and burnt to Roman cement. The temperature of burning is below the "clinkering" point (see Portland cement, Vol. II., pp. 135, 138), which is characteristic of complete union of the lime with the acid constituents. Roman cement is reddish in colour, and has a specific gravity of 2*5 to 3-0. On mixture with water it sets rapidly, and can be used as a true hydraulic cement — i.e., to withstand the action of water. In its behaviour as a cement it is similar to, but weaker than, Portland cement. The following is an analysis of Roman cement : — Si0 2 , . 19-26 per cent. Insoluble residue, . . . . . 5*11 A1 2 0 3 , 13-24 Fe 2 0 3 , 7-68 CaO, 45-36 MgO, 2-63 S0 3 , 1-97 C0 2 , 3 06 H 2 U, 0-95 Alkalies and loss, 0*74 100-00 131 LIME AND CEMENT. Portland Cement. — Portland cement is the most important of hydraulic cements, and its nature and behaviour are in many respects typical of all cements 'which depend for their action on the changes which cementitious silicates and aluminates of lime undergo on admixture with water. It may be denned as a material produced by heating, to a clinkering temperature, an intimate mixture of calcareous, siliceous, and aluminous con- stituents, and finely grinding the resulting clinkered mass. Various raw materials may be used ; the calcareous material may be nearly pure calcium carbonate, such as chalk or lime- stone, or it may contain siliceous and clayey matter constitut- ing a marl ; the siliceous and aluminous material may be a "poor" (i.e., siliceous) clay, such as a river mud, or a marl rich in clay, or a gault clay — i.e., one containing calcium car- bonate. The proportions of these constituents must be so ad- justed that whatever the raw materials may be their mixture shall contain about 75 per cent. CaCO.,, the remainder being clay richer in silica than is pure kaolin. The manufacture is carried out in the following stages : — (1) Mixing the raw Materials. — Two systems of mixing are in nse. In the first, which is called the wet process, chalk and clay in the proper proportions are mixed with much water in a wash- mill, consisting of a circular basin, in which a vertical spindle carrying radial arms provided with rakes, rotates and beats up the raw materials to a thin "slurry/' The slurry flows through a grating to large reservoirs termed "backs," where it settles. After subsidence, which occupies some w T eeks, the water is drawn off, and the slurry, still containing about 50 per cent, of water, is removed for drying and burning (y.i.). By the second or semi-dry process the raw materials are mixed with sufficient water to form a paste (capable of flowing and of being pumped like a liquid), by means of a wash-mill similar to that used in the wet process. As no separation of coarse particles by elutriation and subsidence (such as is characteristic of the older, wet process) occurs in the semi-dry process, the slurry from the wash-mill is ground wet between millstones until no visible particles of chalk remain in it. Chalk is a more suitable raw material than limestone, as it can be washed to a slurry, whereas limestone must be first ground or burnt to lime before it can be mixed with the clay. (2) Drying the Slurry.— The slurry produced by either of the above processes is dried by the waste heat of the kilns (v.i.), or by that of the coke ovens used in some works for coking the coal previous to burning the cement. It is pumped on to "floors" which are made of iron plates, between which the w T aste gases circulate, and dries into irregular cakes ready to be fed into the kilns. (3) Burning to Clinker.— The dried, well-mixed raw materials BURNING CEMENT CLINKER. 135 must be raised to a clinkering temperature, which is attained at almost a white heat. The simplest form of cement kiln is the ordinary bottle kiln, which is a bottle-shaped brick structure lined with firebrick, at the bottom of which a pile of brushwood and coke is placed to serve for kindling the charge, consisting of alternate layers of dried slurry and coke. The burn- ing is discontinuous, and the consumption of fuel is about 40 per cent, of the weight of the clinker produced. The process is uneconomi- cal, more modern kilns con- suming a smaller propor- tion of fuel. The type of furnace kuown as a "stage kiln" (Etageofen) is much used abroad, though not in this country to any extent. As shown in Fig. 25, it consists of two vertical shafts placed back to back, and constituting separate kilns. The upper part, A, is not in the same vertical plane as the lower, B, but the two are connected by a horizontal chamber, C. The charge is introduced through the door, D, in the upper part of the shaft, where it is heated by the products of combustion from the lower part of the kiln. It is raked through the door, E, along the horizontal chamber, C, and falls into the lower part of the shaft, B, where the combustion attains the clinkering temperature, and the clinker being plastic tends to stick to the walls of the kiln. It is dislodged by an iron tool through the working doors, F, and falls into the chamber, G, where it is cooled by air entering at the grate, IT. The consumption of fuel in a Dietzsch kiln is from 10 to 20 per cent, of the clinker produced. Its chief drawback arises from the tendency of the clinker to ball together and stick to the walls of the kiln in its passage from •entrance to exit. What is probably the most economical form of kiln for burning Fig. 25.— Stage kiln. A, Upper part ; B, lower part ; C, con- necting chamber ; D, door for charg- ing ; E, F, working doors ; H, grate. 136 LIME AND CEMENT. cement is the Hoffmann ring kiln (a plan of which is shown in Fig. 26), but it needs the shaping of the raw material into bricks or blocks, for a reason that will be stated later. For this pur- pose the bulk of the slurry is dried completely, and then mixed with the rest, so that the product may be kneadable ; it is then shaped in a brick-making machine, and, if necessary, partly dried by a supplementary source of heat, the remainder of the drying being effected in the kiln. The Hoffmann kiln, as shown in the figure, consists of fourteen firebrick chambers, A, through the roof of which shoots, B, are arranged so as to distribute the fuel between the columns of blocks of cement to be burnt. Each Fig. 26. — Hoffmann riog kiln. A, Chambers ; B, shoots ; C, flue leading to chamber ; D, flue leading to shaft ; E, main shaft. chamber is provided with a flue, C, leading into the next cham- ber, and also a flue, D, leading to the central main shaft, E. The working of the kiln is as follows : — Each chamber contains its complement of bricks. Taking the case where the bricks in chambers 1 to 5 have been burnt and those in 7 to 12 are being burnt, those in 13 are waiting to be burnt and those in 14 are being unloaded ; No. 6, which is already hot enough to start combustion, is charged with fuel through the shoots, which are then closed. Ail flues to the central chimney except that from 12 are also closed, and the draught from No. 12 draws in air through the whole series from an opening in chamber 1 ; the air traverses these chambers full of hot clinker, becoming warmed COMPOSITION AND PROPERTIES OP PORTLAND CEMENT. 137 in its passage, passing from chamber to chamber by the flues, C. The products of combustion from 6 pass through the chambers. 7 to 12, heating their contents and then escaping nearly cool by the central shaft. By this means the charges in these chambers are systematically raised from the ordinary temperature to one just short of clinkering. The diversion of the gases from 12 to the central flue is effected by a shield in the flue between 12 and 13. This shield is often of paper, so that when the temperature rises sufficiently, it burns through and automatically includes No. 13 in the series ; the damper in the flue leading from 12 to the central shaft is then closed, and that in 13 opened. The contents of 6 is now thoroughly burnt, and 7 is charged with fuel, the whole series of operations being shifted on by one chamber, No. 1 (the most thoroughly cooled) being unloaded and the cold air allowed to enter through 2. No. 14, at the extreme end of the half of the set of chambers in the act of burning, is meanwhile filled with fresh bricks, and the cycle of operations indefinitely repeated. The continuous drying and burning of cement have also been effected in cylinders capable of rotation about an axis set slightly inclined to the horizontal and fed by producer gas, but the system, which presents many advantages in principle, has not yet come into extended use. Cement clinker being a highly basic material (v.i.) should not be burnt in an acid-lined kiln, although this is commonly done. An attempt to form a basic lining is often made by plastering the inside of the kiln with slurry. Recently, kilns have been lined with magnesia bricks, such as are used in steel furnaces, and a " neutral" lining of bauxite has also been employed. (4) Grinding the Clinker to Cement. — Well-burnt clinker is in the form of dark brown or greenish-black lumps, so hard as to need much power for comminution. As cement is usually so finely ground as to leave little or no residue on a sieve having 2,500 meshes per square inch, the choice of a grinding plant is of much importance. The clinker is first reduced in size by a stonebreaker, after which the grinding proper takes place. Usually, in this country, French burr stones set horizontally are employed, with or without sieves to size the product and to prevent coarse particles finding their way into the finished cement. Edge-runners are also used, and, abroad, ball-mills are extensively adopted (see Basic slag, Vol. II., p. 110). It may be said that as finer grinding is demanded by the consumers of cement, more economical systems than that of grinding by ordinary mill-stones will come into general use. The ground cement is generally stored, and turned over to aerate and slake any small quantity of unsaturated lime which it may contain, before it is put to use. (5) Composition and Properties of Portland Cement. — The fol- 138 LIME AND CEMENT. lowing table of analyses gives the composition of typical samples of dried clay, slurry and cement (for chalk analyses see p. 127): — Clay. Slurry. Percent. 75-32 0-40 251 1*31 0-41 12-68 323 4-14 Cement. Sand, . . . Combined SiO.,, AL,Oo, . . . FeA, . . . CaO, .... MgO, . . . . so 3 , . -. . . Combined %a- \ ter and loss, J Per cent. 28-42 30 32 15-49 7;74 2-04 1-96 1-96 12-07 CaCO,, . . . Fe.,0,; . . . ALO„ . . . CaO (not as \ CaCO,), . \ MgO,. . . . Sand and clay, Soluble SiQg, . Combined ft,0 ) and loss, . \ SiO, Insoluble residue A1,0„ . . . Fe:,0'.., . . . CaO, .... ! MgO,. . . . ! so, H,0 + CO,, . . Alkalies and loss Percent. 20-68 0- 82 9-50 4 06 61-96 1- 07 1-04 0 46 0-41 100-00 100-00 100-00 The fact that cement is generally burnt with coke containing 10 per cent, and upwards of siliceous ash, makes it necessary to use enough chalk to provide lime for the acid constituents of the ash ; whence it follows that a slurry containing a suitable per- centage of calcium carbonate for burning with solid fuel, would tend to yield a cement with an excess of lime if burnt with gaseous fuel. Variations in the content of ash and the quantity of fuel consumed, therefore involve variations in the composition of the slurry. Calculation of the composition of a cement from the known composition of the slurry from which it is made is, consequently, not exact unless the ash of the fuel be taken into account. The following is an outline of the chief reactions which occur in burning cement : — At a temperature of about 600° C. - 1,112° F. the clay is dehydrated, and at 800° to 900° C. = 1,472° to 1,652° F. the calcium carbonate is converted into caustic lime. A reaction then begins between the clay and the lime. Where the particles of lime and clay are in contact, fusible double silicates are produced, and serve as a flux to cause the union of the lime with the silica to form tricalcium silicate, which is the chief cementitious compound present in cement and is infusible per se, and calcium aluminates, which are fusible. The clinker of Portland cement is sufficiently basic to cause the ferric oxide of the clay to function, like the alumina, as an acid, and to form calcium ferrites. Completeness of reaction is never attained in practice, chiefly because it is impracticable to fuse the clinker, which is at most pasty, so that perfect commingling and con- sequent union of the acid and basic constituents are not at- tained. Local excess of acid constituents and local excess of basic constituents may occur in clinker, the mean composition of which is correct. It follows that clinker as drawn from the kiln COMPOSITION AND PROPERTIES OP PORTLAND CEMENT. 139 is a somewhat heterogeneous product. Three main materials can be distinguished therein. (1) Hard coherent dark clinker, con- taining tricalcium silicate (3CaO. Si0 2 ) as its essential constituent. {2) "Fallen" clinker or dust, resulting from the spontaneous disintegration of clinker containing deficiency of lime, and due to the presence of dicalcium silicate (2CaO.Si0. 2 ) as the pre- dominant constituent. (3) Underburnt clinker, yellow and pink in colour, in which complete reaction between the lime and clay has not occurred, and which contains free lime. To secure the best cement, only sound clinker should be ground, but it is usual to send all except greatly underburnt material to the crushers. It is probable that the fallen cement poor in lime and the under- burnt portion containing free lime may, nevertheless, serve as cement by mutual action on mixing with water, the said action being analogous to that taking place between puzzuolana and lime (p. 140). The important constituents of good cement are tricalcium sili- cate (3CaO.Si0 2 ), tricalcium aluminate (3CaO. A1 2 0 3 ), and trical- cium alumino-ferrite(3CaO. Al 2 0 3 .Fe 2 0 3 ). Besides these there are found as subsidiary constituents dicalcium silicate (2CaO.Si0 2 ), and monocalcium silicate (CaO . Si0 2 ) ; the former is remarkable for its change of state on cooling, for its crystals being twinned and contracting unequally at opposing faces, separate and thus cause any mass composed of it to fall to powder. It is the presence of this substance which induces the falling of cement. Sound cement contains no free lime (see Vol. L, p. 11). The setting of Portland cement is in nature similar to that of other hydraulic cements (save slag cement and puzzuolana cement) and is essentially a phenomenon of hydration. The successive changes that occur on mixing Portland cement with water to form a paste are as follows : — (1) Loose compounds of lime — e.g., calcium ferrites — slake and are decomposed ; (2) tri- calcium aluminate reacts with water and calcium hydroxide (this latter having been produced by the decomposition of tricalcium silicate (v.i.) and calcium ferrites) according to the equation — 3CaO.Al 2 0 3 + Ca(OH)., + I1H 2 0 = 4CaO . A1 2 0 3 • 12H 2 0— This causes the initial setting of the cement; (3) tricalcium silicate reacts with water thus : — 2(3CaO . Si0 2 ) + 9H 2 0 = 2(CaO . Si0 2 ) . 5H 2 0 + 4Ca(OH) 2 . The hardening of cement and the attainment of its character- istically great strength are due to this reaction. The products of hydration of the tricalcium aluminate and tricalcium silicate pass into solution, and subsequently crystallise from their super- saturated solutions thus formed, in a manner similar to that of plaster of Paris (p. 131). This explanation is confirmed by the ob- servation that the temperature of the cement after gauging with 140 LIME AND CEMENT. water does not immediately rise, but begins to do so after a few moments ; the period of delay probably corresponds with that of dissolution, and the rise of temperature indicates the beginning of crystallisation. Commercial Portland cement of good quality should contain the maximum possible proportion of tricalcium silicate and tricalcium aluminate, but should have no excess of basic constituents. Its composition should, therefore, fall within the limits expressed by the equation — CaO + MgO ^ Si0 2 + A 1,0, — In this equation the quantities are expressed in equivalents, not in percentages. Its meaning is that the total basic constituents of any cement expressed in equivalents must be equal to or less than three times the total acid constituents also expressed in equivalents, so that after the formation of tricalcium silicate and tricalcium aluminate there may remain no base unsaturated. All methods of stating the ratio of acids to bases in terms other than equivalents are necessarily meaningless. Puzzuolanic Cements. — Certain silicates decomposable by acids and partly soluble in alkalies, are sufficiently active to combine with slaked "fat" lime to form calcium silicates in- soluble in water. In consequence of this property, mixtures of these silicates and lime have long been used as hydraulic cement. Such are : — (1) Puzzuolana. — Puzzuolana is a volcanic tufa found largely in the neighbourhood of Naples and Rome. The following are analyses of each kind : — Neapolitan. Roman. Soluble silica, ...... Insoluble siliceous residue, A1A + Fe 2 0 3 , CaO, MgO, so 3 , H,,0 + C0 2 , Alkalies and loss, ..... Per cent. 27-80 35-38 19-80 5- 68 0 35 Trace 4-27 6- 72 Per cent. 32-64 25-94 22-74 4-06 1-37 Trace 8-92 4-33 100-00 100 00 (2) Trass is also a volcanic tufa, and is found in the Rhine district. Its composition is similar to that of puzzuolana. (3) Santorin earth, from the Greek island of Santorin, is a substance of like character. (4) Blast furnace slag is prepared by granulating a slag rich in lime — e.g., containing 50 per cent. CaO, 30 per cent. Si0 2 , 20 WATER GLASS. 141 per cent. A1 0 0 3 . The granulation is essential, as if the slag be allowed to cool slowly and assume a crystalline state its chemical energy is decreased, and it combines but feebly with lime. The granulation is effected by allowing the molten slag to flow from the blast furnace into a trough of running water. Cements are made from these materials by mixing them (preferably finely ground) with lime, in proportions varying from 1 : 1 of lime to 4 : 1 of lime. Slag cement is made on a considerable scale by mixing very intimately, in a ball-mill, finely- ground granulated blast furnace slag with about one-third its weight of slaked lime. It attains nearly as high a strength as Portland cement, but is usually slow in setting, taking 6 to 12 hours, this property being characteristic of cements of the puzzuolana class. Artificial Stone. — The cheapness and great strength of Port- land cement have led to its use in the manufacture of various kinds of artificial stone. Concrete (see Yol. I., p. 9) is a rough form of artificial stone, and the preparation of both materials is conducted on the same general lines — viz., the cementing together of an "aggregate" composed of fragments of natural stone by means of Portland or other suitable cement. The natural stone (e.g., granite in the form of chippings) is mixed with cement mortar (i.e., cement and sand), made into a plastic paste with water, and moulded into any desired shape. Such artificial stone is sometimes treated with a strong solution of silicate of soda {water glass) — (for the manufacture of water glass, v.i.). The effect of the sodium silicate is to react with the lime set free by the hydration of the cement (p. 139) to form calcium silicate, the caustic soda liberated being afterwards washed out. The strength of the stone is thus increased, and its porosity dimin- ished. Where Portland cement is not a constituent of the stone, the materials may be mixed with water glass, and saturated with calcium chloride solution, calcium silicate and sodium chloride (the latter removable by washing) being formed. Water Glass. — Water glass (soluble glass) is an alkali silicate, soluble in water. It is made by fusing silica, in almost any convenient form, with sodium or potassium carbonate. The addition of a little carbonaceous matter (e.g., small coal) aids the reaction, possibly owing to a tendency towards the forma- tion of Na 0 0 (or K 2 0) by the oxidation of sodium (or K), liberated by the carbon. When sulphate is substituted for carbonate, the presence of carbon reduces the sulphate to sulphide, which acts freely on the silica. Finely-divided silica may also be heated with a solution of caustic alkali under pressure, for the same manufacture. The reaction is aided by transforming insoluble forms of silica, such as flints, into the more soluble variety by heating them to redness, and quenching in water. Commercial soluble glass varies between 142 LIME AND CEMENT. the limits Na 2 0.4Si0 0 and Na 2 0. 2Si0 2 , the commonest grade being about .Na 2 0 . 3Si0 2 , and is made by fusing 2 parts of quartz sand with 1 part of sodium carbonate and 0*1 part of small coal. The solubility varies inversely as the proportion of silica, a glass rich in silica being very sparingly soluble. Con- sequently, a large proportion of soluble glass is sold in solution, as the solid is often slow to dissolve. Soluble glass is decom- posed by the feeblest acids, even C0 2 , gelatinous silica being separated. Besides being used for making artificial stone, soluble glass is employed for rendering wood fire-proof, as a detergent, and for protecting natural stone of a quality that does not weather well. CLAY INDUSTRIES. 143 CHAPTER VII. CLAY INDUSTRIES AND GLASS. CLAY INDUSTRIES. — Clay. — Typical pure clay is kaolin r 2Si0 2 . A1 2 0 3 . 2H 2 0, corresponding with the composition Si0 2 47*1 per cent., A1 2 0 3 39*2 per cent., H 2 0 13 7 percent. Such typical clay results from the weathering of granite, a rock which contains a felspar (orthoclase,K. 2 0. Al 2 0 3 .GSi0 2 ,or albite, Na 2 0. Al 2 0 3 .6Si0 2 ), a mica, generally potash mica, K 2 0. 3A1 2 0 3 . 4Si0 0 , and quartz. By the weathering process the alkalies are leached out, and the silicate of alumina is hydrated and washed away from the less finely-divided quartz. White granites which contain soft earthy felspar (see Vol. L, p. 3) are more easily weathered than those containing orthoclase, and yield an approximately pure kaolin. It will be seen that the purity of the clay resulting from this weathering process depends upon the composition of the parent rock, the perfection of the elutriation and the nature of other alluvial deposits with which the clay has become mixed. The following analyses show the composition of typical pottery clays containing much or little nearly pure kaolin : — • Pure Kaolin (Zettlitz). Kaolin with Quartz. Kaolin with Felspar. Kaolin clay substance,* Felspar, Quartz, Per cent. 90 Mi 11 2 3 Per cent. 63-8 0-7 855 Per cent. 55-9 38-2 5-9 * Containing — Pure Kaolin Kaolin with Kaolin with (Zettlitz). Quartz. . Felspar. Per cent. Per cent. Per cent. Silica, 45-15 45-3 47-1 Alumina, . 38 -1 37-1 360 Ferric oxide, 0 9 13 0-6 Lime, Magnesia, . 0 : 7 o-s I 3-3 Alkalies, . 1-8 2 0 ) Water, 13 3 121 12-9 144 CLAY INDUSTRIES AND GLASS. Clays of all classes are fitted for their use in making pottery by two main properties : — (1) The ease with which they may be moulded and shaped when wet, and (2) their change of state to a hard unalterable condition when fired. The former of these two properties appears to depend on the mechanical condition of the clay rather than on its chemical composition. Pure kaolin is less plastic than are clays containing certain impurities — e.g., free hydrated silica and ferric oxide. A comparison of the analyses of the clay substance of kaolin clays with those of the clay substance of eminently plastic clays, shows in the true clay substance (as distinct from quartz and felspar) of the latter class of clays, a slightly higher percentage of silica, ferric oxide and alkalies and a lower percentage of alumina and water. The change which clays undergo on heating is one of dehydration and agglomeration accompanied by much shrinkage. Pure kaolin is extremely refractory, being infusible at the tempera- ture of the porcelain furnace. The general effect of impurities, especially of bases, is to lower the fusing point of kaolin. The effect is, however, not confined to bases ; silica will also lower the melting point of kaolin by the formation of double silicates with such unsaturated bases as may be present in the kaolin as impurities. Further addition of silica (which is itself infusible at the temperature of industrial furnaces) will again raise the melting point. Equivalent quantities of bases lower the melting point in the following order : — K 2 0, Fe 2 0 3 , CaO, MgO, the last- named having the greatest effect, for equal weights. The clays fall into the following classes, according to their chief industrial use : — (1) Porcelain clay or Cornish clay, approximately pure kaolin, poor in plasticity, refractory, burning to a white or light cream colour. (2) Plastic clay, more impure than the foregoing, more plastic and less refractory ; it burns to a yellow-red colour, and is used for ordinary earthenware, and its commonest variety serves for brick making. Mixed with calcium carbonate it constitutes clay marls. (3) Fireclays. — These are clays found chiefly in the coal measures which, so far as the true clay substance is concerned, approach porcelain clay in composition (though often containing more iron), but contain more silica as quartz. They are highly refractory, dark in colour, and are used for furnace linings and crucibles. The varieties, rich in quartz, form a link between normal fireclay and such highly siliceous substances as Dinas " fireclay " (with 97 to 98 per cent. Si0 2 ) and- ganister, which are used for making specially refractory bricks. Bricks. — Common bricks are made of the commoner kinds of clay, containing sufficient sand to prevent undue shrinkage on burning. The clay is weathered, and large stones and lumps of limestone, pyrites, &c, which would tend to disintegrate the TILES. 145 bricks after burning by slaking and oxidation, are removed, and the clay pugged to a smooth paste, moulded into a rectangular rod and cut into bricks. The raw bricks are burnt in heaps or clamps with small fuel, such as breeze, or occasionally in closed kilns — e.<7.,the Hoffmann kiln (p. 136). The chief change produced by firing in the case of common bricks, consists in the dehydra- tion of the clay and a sintering of the more fusible constituents. The colour of the finished brick depends on the percentage of iron present, the proportion of lime in the brick earth, and the intensity of the firing. At moderate temperatures a yellow or red brick is produced, while if lime be present (gault bricks) the tint is light yellow or cream colour, and, if the temperature of firing be high, a grey, blue or black colour results from the formation of magnetic oxide of iron. Blue bricks are made from a clay rich in iron, and containing more or less marl, and are fired at a high temperature. Usually a salt glaze (p. 149) is given to such bricks, which are also fairly sintered throughout, and are, therefore, tolerably impervious. Glazed bricks are made more carefully and of better materials than ordinary bricks, and after firing are glazed in the same manner as stoneware (p. 149), usually with lead glazes rendered opaque with stannic oxide. Firebricks are made from fireclays mixed, if necessary, with sand, and frequently with already burnt fireclay. Such an addition prevents the brick from cracking on exposure to sudden changes of temperature. The following analyses exhibit the differences between common brick earth and a good fireclay : — Brick clay. Per cent. Fireclay. Per cent. Quartz, . 16-42 Quartz, . 84-59 Felspar, 3-27 Combined silica, . 511 Calcium carbonate, 4-45 Alumina, 5-40 ,, sulphate,. 0-95 Ferric oxide, 0'21 True clay substance, 74-91 Lime, . 0-20 Consisting of : — Per cent. Magnesia, 0 09 Silica, 46-96 Potash, . 061 Alumina, 36-42 Water, . 3-74 Ferric oxide, . 2 '80 Magnesia, 0-87 Alkalies, 0-91 Water, . 1204 The former contains numerous fluxing constituents — e.g., lime, ferric oxide and felspar — while the latter is nearly free from such substances, and is accordingly refractory. Tiles are made from clay suitable for bricks, but of rather better grade. They are burnt in kilns in the same manner as the better class of bricks. A mode of preparation which presents a certain economy consists in sifting the dried clay, slightly damping it by sprinkling, pressing the feebly coherent powder in a powerful press, and burning the raw tile thus produced. In producing tiles with coloured patterns (encaustic tiles) a layer 10 146 CLAY INDUSTRIES AND GLASS. of the best clay is put on to a body of coarse clay, which is still farther backed by a common clay. The face of the tile is pressed on to a plaster of Paris mould of the required pattern, and the indentations thus formed are filled with a slip consisting of clay mixed with the required colour, the tile thus ornamented being burned in saggers (p. 147) and glazed. Tiles are frequently glazed, the general methods being similar to those used for earthenware (p. 149). Pure kaolin would be useless for making pottery, as its in- fusibility and large contraction on heating prevent its consoli- dating to a sound clinkered mass. The first drawback is met by the addition of some flux — e.g., felspar — and the second by the admixture of an inert infusible aggregate, such as sand. The three main classes into which pottery can be divided are (1) porcelain; (2) stoneware; (3) earthenware. In the first, the body of the ware is clinkered throughout, and no hard line of demarcation exists between the glaze and the body of the ware. When thin it is translucent, and being made from the purest materials it is white. In the second, less pure materials are used, and the ware is coloured and opaque, but the body and glaze are similarly inseparable, and the body itself is impervious. In the third class, the body of the ware is pervious and presents no sign of sintering, and the glaze is adherent only, and not truly incorporated with the body of the ware. Porcelain. — Hard Porcelain. — This is made from a mixture of kaolin, felspar and quartz, which must be ground, sifted and levigated. A mixture used for Berlin porcelain consists of 55 parts of true kaolin, 22*5 of quartz and 22 -5 of felspar. The quartz is not added as such, being present in the kaolin used. The kaolin is made into a thin paste with water, the quartz (if needed) and felspar are ignited and quenched in water to disin- tegrate them, and also made into thin pastes, all three materials being mixed by pumping from one vessel to another, and then separated from the surplus water by filter presses, the resulting mass being in a kneadable condition. The plasticity of the paste is often improved by weathering ; the cause of this improvement is imperfectly understood. The vessel to be made is fashioned either on a potter's wheel or by moulding — i.e., by pressing the paste either in its moist form or after drying, powdering and slightly damping (so as to stick together), into suitable moulds,, or by casting the liquid paste in a plaster of Paris mould, which absorbs the water, leaving a coating of raw paste. In this last case repetition of the process can be carried on until the desired thickness is attained. The ware, however prepared, is allowed to dry very slowly, and is given a first baking ("biscuit firing") at a moderate temperature (700° to 800° C. = 1,292° to 1,472° F.), whereby the kaolin is dehydrated and the goods become strong enough to bear handling. The ware is protected from dust and PORCELAIN. 147 direct contact with the flame in the kiln by bsing enclosed in "saggers," which are boxes made of refractory clay and built up in columns in the kiln. During the first burning the ware shrinks about 3 per cent, of its linear dimensions. When ordi- nary glazed, as opposed to biscuit, porcelain is to be produced, the ware after the first burning is dipped in a slip of similar composition to the body of the ware, but more fusible. Thus Berlin porcelain is glazed with a mixture of kaolin, felspar, quartz, gypsum or marble, and broken porcelain. A typical glaze of this class has the composition 10 SiCX,, 1 A1 2 0.,, 0-7 CaO, 0-2 MgO, 0*1 K 0 0 (stated in equivalents). The materials for the glaze are reduced to an impalpable powder and made into a thin slip with water; the goods are dipped in this slip and retain a coating of the raw glaze, after which treatment they are dried and burnt a second time at a temperature of about 1,700° C. = 3,092° F., just short of the fusing point of platinum. During, the burning, the body of the ware clinkers and the glaze fuses, so that the resulting porcelain is impervious throughout, and is not dependent upon the glaze for its impenetrability. A further contractio?i of 7 to 9 per cent, on the original linear size of the goods takes place during this firing. During burning, the ware is placed in "saggers" as before, care being taken that no glazed portion of the porcelain is in contact with the sagger, lest it stick. Similarly, to avoid strain, the clay of which the saggers are made must shrink in firing to the same extent as the goods burnt. A kiln frequently used consists of two cylindrical cham- bers, one above the other, at the bottom of each of which are several firing grates. Openings from these grates into the kiln permit of the passage of the flame to the goods stacked therein. Flues from the top of the lower chamber pass into the upper, and thence through the dome-shaped top of the kiln, which constitutes a third chamber kept at a lower temperature, this division being used for the first firing. The burning usually takes about twenty-four hours, and the goods are allowed to cool for three or four days before opening the kiln. The progress of burning is watched through spyholes, and the temperature judged by the behaviour of Seger's cones, which are small pyramids made of different porcelain mixtures of known softening point, forming a series covering the whole range of; temperature in use in porcelain burning. The ultimate com- position and approximate fusing point of a few of these cones (the full series comprising thirty-six numbers) are given below: — Fusing Point. 1 10 20 0-G Al 2 O 3 +0*4 Fe 2 (X> 1 A1,0 3 1 AL.O., 8 SiO., 10 SiOg 10 SiOo 1*4 CaO 0- 7 CaO 1- 18 CaO 0-G K 2 0 0-3 K^O 0-08 K»0 1,150°C. = 2,102° F. 1,410° C. = 2,570° F. 1,700° C. = 3,092° F. 148 CLAY INDUSTRIES AND GLASS. Above this temperature, A1 2 0 3 and Si0 2 alone enter into the composition of the cones, the ratio being 1 A1 2 0 3 : 2Si0. 2 (corre- sponding with pure kaolin) for the highest temperature. A similar series for the control of the firing of soft glazes, which contains B 2 0 3 to lower the melting point, is also in use. In Berlin porcelain, as in other kinds still to be described, the com- position of the glaze should approximate as nearly to that of the body of the ware as is consistent with the greater fusibility of the former. The contraction of the cdaze during firing and its coefficient of expansion when finished, should be as nearly as possible identical with the same properties of the ware itself. It must "wet" the body of the ware and soak into it to some extent, so that no hard and fast line exists between them, and they are mechanically one. Colouring Porcelain. — Only metallic oxides which yield coloured silicates are available for decorating porcelain. Coloured glazes may be regarded as the ordinary colourless glazes with one or more of the oxides of heavy metals replacing lime or alumina. If the oxide be of the type RO, it is substituted for an equivalent of lime, while if it be of the type R 2 0 3 , it replaces alumina. For the colourations imparted by individual oxides, see Glass, Vol II., p. 158. The colouring of porcelain is done in one of two ways. In the first, the coloured glaze is applied to the biscuit ware before glazing with the ordinary colourless glaze, and the colour is thus protected in the finished ware. In the second method, a colourless glaze is first applied, and then fusible coloured glazes or enamels are painted on the surface of this, the whole being fired in a muffle at a temperature below the fusing point of the colourless glaze. In this case the colour is on the surface, and is unprotected. Soft Porcelain. — All varieties of soft porcelain may be regarded as intermediate in composition and properties between hard porcelain and glass. Thus, the soft porcelain formerly made at Sevres was prepared by mixing 80 parts of white sand, 22 of nitre, 7 of salt, 4 each of alum, gypsum and soda, and "fritting" the mass together until incipient fusion (sintering) took place. The frit was powdered, and 75 parts mixed with 17 of chalk and 8 of a calcareous marl, the whole being washed to a slip, moulded and burnt in the usual way. Unlike hard porcelain, soft porcelain receives its heavier firing the first time it enters the kiln. The subsequent firing to fix the glaze, which is a lead- alkali glass (see Flint glass, Vol. II., p. 158), is carried out at a lower temperature on account of the fusibility of the glaze. English soft porcelain is distinguished by the presence of calcium phosphate ; a typical mixture consists of kaolin 27 per cent., China stone (a Cornish clay rich in felspar) 27 per cent., bone ash 46 per cent. The glaze is a lead glass or a glaze containing B 2 0 3 , and the firing is conducted as for French soft porcelain. EARTHENWARE. 149 When a clay containing traces of iron is used, the yellow colour produced is corrected by the addition of a small proportion of oxide of cobalt to the paste. Soft porcelain is well adapted for ornamental purposes, but it is less resistant than hard porcelain, especially to rapid fluctuations of temperature, and the glaze is softer, and more liable to crack or " craze," as the formation of a network of hair cracks is termed. Biscuit porcelain is the name given to unglazed hard porcelain. Parian is that used for unglazed soft porcelain, both materials being used for statuettes. Stoneware. — Stoneware, like porcelain, is clinkered so as to be impervious, but its constituents have not been so near fusion as to yield a translucent ware. It consists of the same material as porcelain, but there is no typical soft variety — e.g., one containing bone ash. A comparatively large proportion of felspar is used, and flint is a characteristic constituent, frequently amounting to half the weight of the mass. The flints are pre- pared by calcining and quenching in water (the silica undergoing molecular change), by which treatment they become easier to grind. Wedgwood ware consists of a clay, but slightly refractory, together with kaolin, flint, and China stone (v.s.). Stoneware is fired at a somewhat lower temperature than porcelain, and generally without the use of saggers. Owing to the impervious- ness of the body of the ware, glazing is unnecessary, but for goods to resist corrosive liquids (e.g., acid jars, bouibonnes, cooling worms, &c.) a "salt glaze" may be employed. The process of salt glazing consists in throwing wet salt on to the fire at the end of the biscuit firing, whereby the salt is decom- posed, and hydrochloric acid and soda result, the latter attacking the surface of the ware and forming soda glass thereon. It is obvious that such glazing is only applicable to ware which is rich in silica, this serving as an acid to unite with the soda. In addition to its ordinary uses, stoneware is employed for making hard refractory paving tiles, the fact that it is clinkered throughout adding greatly to its durability. Earthenware. — This material is characterised by the fact that the body of the ware has at no time approached fusion. A typical paste for white earthenware consists of " ball-clay " (a highly plastic clay) 25 per cent., china-clay 32 per cent., flint 35 per cent., Cornish stone 8 per cent. In preparing the raw materials for such earthenware, magnetic iron oxide is removed by running the slip through a box containing magnets. The commoner varieties of earthenware are brown in colour, the iron of the clay not having been removed. Glazes for earthen- ware consist of mixtures of clay, sand, soda, borax and red lead. The chief firing takes place in the biscuit state, the second being at a lower temperature on account of the fusibility of the glaze. The glaze does not penetrate the body of the ware, and is 150 CLAY INDUSTRIES AND GLASS. easily detachable therefrom — a distinction from stoneware and porcelain. The common English kiln, for firing earthenware and stone- ware consists of a dome-shaped hood containing a circular oven with a bee-hive top. The flames from the fires, which are situated round the base of the oven, enter partly through flues running np the sides of the oven and partly underneath it ; the wares are imbedded in sand or ground flint in saggers with which the oven is filled save for spaces to allow the circulation of the flame. Holes in the crown of the oven admit of the escape of the flue gases into the hood which creates the necessary draught and protects the furnace from weather. In modern practice regenera- tive gas-firing is much used, and the Hoffmann kiln (p. 136) is also employed to a considerable extent. GLASS. — Glass is defined as a mixture of silicates, one of which is always the silicate of an alkali. It is amorphous, very difficultly attacked by water and acids, and usually transparent. No single silicate fulfils these conditions. The silicates of the heavy metals are usually coloured, and are, therefore, only used as constituents of coloured glasses. Most ordinary colourless glasses fall into two classes — viz., alkali-lime silicates and alkali- lead silicates — for these silicates, unlike most others, have but little tendency to crystallise on solidification. The mixture of silicates for glass making must be so chosen that it shall melt at a yellow heat * and be plastic at a temperature considerably below this. These conditions are fulfilled by mixtures rich in alkali silicates, but these are too easily attacked by water to be available as glass. Double silicates, free from alkali, are suffi- ciently resistant to water and acids, but need a higher working- temperature than is convenient for glass making. Most glasses correspond with the formula 3Si0 2 .RO, where RO stands for both alkali and lime (or lead oxide). The alkali and lime (or lead oxide) vary in proportion from 1:1 to 5:7 (in equivalents), corresponding with the formulae lsTa 2 0. CaO. 6Si0 2 and 5Na 2 0. 7 CaO. 36Si0 2 ; in these formulas K 9 6 may replace Na 2 0, and PbO may replace CaO. There are many varieties of glass — the chief of which will be described below — but the main raw materials, which fused together form glass, are comparatively few, and are included in the following list : — Raw Materials. — (1) Silica. — This is now almost always quartz sand. For the best kinds of glass it must be as free as possible from ferric oxide, to remove which treatment with hydrochloric acid is sometimes practised. For commoner glass 0*5 per cent. Fe 2 0 ; , is permissible. In England, Lancashire and Bedfordshire sand is esteemed for glass making, and on * For the temperatures corresponding with this and similar industrial terms, see Vol. I. , p. 83. RAW MATERIALS FOR GLASS. 151 the Continent deposits of great purity occur at Aix and Fon- tainbleau. Belgian sand is also much imported into this country. Quartz and flint are also forms of silica sometimes used. Whichever be adopted it is advantageous to heat to redness and quench in water to increase the ease with which the silica is attacked in the melting pot. (2) Alkali. — Sodium carbonate free from iron, made by either the Leblanc or the ammonia process, is the chief form of alkali employed in glass making. The reaction between sodium car- bonate and sand when fused together is represented by the following equation : — - Na 2 C0 3 + 3Si0. 2 = Na 2 0.3Si0 2 + C0 2 . Sodium carbonate has, however, been considerably displaced by sodium sulphate, which, when needed especially free from iron, is crystallised in lead pans for the glass industry. The same salt obtained as a bye-product from the Stassfurt deposits, is also used. Sodium sulphate is decomposed by silica at a high temperature, thus — Na 2 S0 4 + 3Si0 2 = Na 2 0.3Si0 2 + S0 3 . The reaction is facilitated by the addition of carbon, which reduces S0 3 to S0 2 , C0 2 being simultaneously formed. It will be seen that 71 parts of sodium sulphate are needed to replace .53 parts of sodium carbonate. This and the higher temperature necessary, tend to reduce the advantage gained by substituting the cheaper sodium sulphate for sodium carbonate. The use of carbon must be restricted lest Na 2 S be formed, which dissolves in the glass yielding a yellow or brown colour. A still cheaper source of soda for glass making would be salt, were it not that •the volatility of NaCl and the fact that steam is necessary for its decomposition by Si0 9 , have hitherto prevented its adoption on a manufacturing scale. Ordinary potash glass is made from crude carbonate of potash or wood-ashes, while refined potassium carbonate is used for the best grades. Potassium sulphate cannot well be substituted for the carbonate, as its decom- position in the manner practised for sodium sulphate takes place with difficulty. (3) Lime. — Pure marble is used for the best glass, and lime- stone or chalk for the common kinds. Marls (containing clay as well as CaC0 3 ) are sometimes used, a portion of their alumina entering into the composition of the glass. Many siliceous minerals, especially such as contain alkali — e.g., felspar — may be used for common bottle glass. (4) Lead oxide is most frequently used in the form of minium (red lead, Pb 3 0 4 ), more rarely as litharge (PbO) ; the excess of oxygen in the former is an advantage tending to prevent reduc- tion of the metal ; the latter is not only destitute of this excess, but frequently contains some metallic lead. 152 CLAY INDUSTRIES AND GLASS. (5) Cullet. — This is the technical term for broken glass, which material acts as a flux, aiding the reaction between the con- stituents of the new glass, and thereby hindering loss of alkali by volatilisation. For fine glasses care must be taken that the cullet approximate to the composition of the glass to be made. (6) Correctives of Colour. — These are of two classes, those which tint the glass with a shade complementary to that due to the impurities in the raw materials, and those which act as oxidising agents. Manganese dioxide, the best known of these additions has long been used under the name glass maker's soap, on account of its property of clearing away the green colour due to ferrous silicate in the glass. This it effects by oxidising the ferrous silicate to the slightly yellow ferric salt, and by yielding a violet manganic silicate complementary in colour to green ferrous silicate ; thus it possesses a double function. Manganese dioxide for glass makers' use must obviously be free from iron. Titanic acid also effects chromatic neutralisation. Nickel oxide and cobalt oxide are other reagents of the same class. Zinc oxide removes the tint due to sodium sulphide by double decomposi- tion with that body. Agents of the second or oxidising class are arsenious oxide (white arsenic) — which oxidises ferrous oxide, being itself reduced to metallic arsenic which volatilises — nitre and manganese dioxide, as indicated above. The raw materials of whatever class are thoroughly ground, sifted, and mixed in proportions consonant with the character of the glass to be made. These proportions must be modified so as to allow for the loss of alkali which occurs by volatilisation, and the amount which is likely to be removed as glass-gall (i.e., excess of sodium salts, chiefly sulphate, floating on the surface of the fused glass) ; the total deficit ranges from 10 to 20 per cent. Fusion of the Raw Materials to Glass. — The older and still common method of fusing glass consists in heating it in pots of refractory clay set in a furnace fired by external grates — so that only flame and gaseous products of combustion may come in contact with the pots — or with gaseous fuel used in a regener- ative furnace. According to more recent practice, the glass is melted in one large vessel or tank (instead of in several pots), the tank being set in a regenerative furnace very similar in construc- tion to a steel furnace. With regard to the details of melting the following may be said : — A glass-pot is circular, resembling a large flower pot, but, of course, without the whole at the bottom. It is from 3 to 5 feet in diameter, and of similar height. It is built up from fireclay, the best for the purpose being from Stourbridge, mixed with about one-fifth of its weight of old pots ground to powder. The ground pot is for the purpose of preventing shrinkage cracks when the new pot is fired, and its proportion varies with the quality of the plastic clay ; thus Stourbridge clay with some 40 per cent. GLASS FURNACES. 153 of sand, being but little plastic and not greatly liable to slirinkage y needs a smaller proportion of ground pot than a plastic clay richer in clay substances, and correspondingly poorer in sand. The pots require very slow drying (in rooms warmed to about 25° C. = 77° F. for three to twelve months), and very gradual baking (lasting from 3 to 7 days). Tn order both to protect the pot, and to avoid contaminating the charge with matter from the pot, a glaze is applied by melting a charge of cullet (broken glass) in the pot, a crust of glass being thus caused to adhere to the walls. The life of a glass-pot (during which it must not bo Fig. 27. — Glass Furnace (old type). A, Furnace chamber ; B, flues ; C, hood ; D, pots ; E, firegrate flue. F, short allowed to cool) varies from a few weeks to nearly a year, according to. the quality of its material and its conditions of use. A furnace of the older type without gaseous firing is shown in Fig. 27. The furnace itself, A, is a circular brickwork chamber with side openings which carry the flame and products of combustion through the flues, B, into the hood, C. The pots, D, are placed round the chamber, A, opposite openings in be- tween the flue openings. The firegrate, E, is situated below the furnace chamber, and the flames and hot gases are carried up the short flue, F, so that they may strike upon and be reflected from the domed roof of the chamber. The reason for covering 154 CLAY INDUSTRIES AND GLASS. in the space where the pots are heated is to prevent the soot and flue dust from falling back into the pots. In more modern practice the grate is charged from below, so that the products of each feeding of fuel may pass through the mass of heated fuel above it, and smoke be thus minimised. The furnace is fed with small coal, the depth of fuel is considerable, and there are air inlets both above and below the fuel, so that the grate becomes in effect a producer, and the firing is comparable with that of a furnace fed with producer gas. (Many pot furnaces are now fired by producer gas and worked in connection with regenerators.) Fig. 28. — Siemens tank furnace. A, Tank ; B, B, air channels ; Cc, C c, regenerators ; D, D, gas channels ; d, d, air channels to the regenerators ; E e, E e, hot gas chaunels. Mechanical stoking is advantageous in that it avoids admission of a large volume of cold air, such as takes place every time a hand-fired furnace is stoked ; the regularity of heating thus ob- tained is favourable to the life of the glass-pots, and to the quality of the glass. In order to avoid the expense involved in the use of numerous glass-pots, difficult to build and of short life, and also to facilitate continuous working, the Siemens tank furnace is now largely adopted. It is shown in Fig. 28. In the figure, A is the fireclay tank kept cool as to its walls by the circulation of air through the channels, B, B, B, B. The FUSION OF THE RAW MATERIALS TO GLASS. 155 regenerators, C c and C c, are worked in pairs as usual (see Vol. I., p. 67), the producer gas being supplied to them through the channels, D, D, and the air through the channels, d, d. The entrance of the heated gases to the furnace takes place through the channels E e, E e. The charge is introduced through the working door at one end of the furnace, and the finished glass is with- drawn at the other end, where the working platform is situated. To avoid the necessity of skimming the whole of the surface of the fused charge, a fireclay ring floats on the glass at the door where the molten " metal ; ' is withdrawn ; the function of this ring is to preserve a clean surface of glass within it, the glass-gall being prevented from entering, while the glass itself flows gradually up into the area enclosed by the ring as the upper layer is ladled out. The same purpose of freeing the glass from floating impurities and rendering it homogeneous, is served by transverse divisions of the glass tank provided with openings at their lower edges, so that the glass first fused at the far end of the furnace, where it is hottest, is forced to pass below one or more septa, and thus is skimmed and mixed, arriving at the cooler end uniform in texture and free from glass-gall. The tank can also be divided longitudinally, and several kinds of glass worked simultaneously in the same furnace. In the case of the older pot furnace, when the pots are in work they are quickly charged with alternate layers of cullet and the mixtures of raw materials ("the batch"). The quantity of the charge is restricted, so as to prevent the semi-fused mass, vesiculated with S0 2 or C0 2 , from frothing over. As the mixture melts, a further portion of the charge is added. When fusion is complete, decolorising and oxidising agents are added (p. 152); a scum of glass-gall collects on the surface, and is skimmed from time to time. After this " refining," the melt is sampled, when it should be found of good colour, free from lumps of unattached silica, bubbles and striae. In some twenty-four hours the glass is ready to be worked, and is ladled out. Recently, an attempt has been made to improve glass after the fusion of its raw materials, by passing a stream of oxygen into it while in the furnace, with the double object of mechanical agitation and oxidation of residual impurities ; a difficulty in effecting this has arisen from the ease with which leading tubes of most practicable materials are attacked by the fused glass ; platinum cannot be used, as it lacks rigidity at the temperature of the glass furnace. All the earlier methods of working glass depend on the use of the glassblower's pipe. Thus, in making hollow ware (blown bottles and flasks), a mass of " metal" (glass in a plastic state) is picked up on the end of an iron tube and blown into an elongated bulb, the shape of which may be modified by manipulation, or by the aid of a mould. For crown glass, a bulb is blown, opened 156 CLAY INDUSTRIES AND GLASS. into a goblet shape, and extended to a sheet by rapid rotation. For sheet glass, a bulb is blown, rolled to a cylindrical form, cut longitudinally, and extended to a flat sheet on a clay plate. By more modern processes, in which the glass can be worked in large masses at a high temperature, common articles — e.g., rougli tumblers and salt cellars — can be pressed, the operation con- sisting in dropping plastic glass into metal moulds, and applying mechanical pressure. Facility in handling large quantities of fully-molten glass has allowed of the manufacture of plate glass by casting the fused glass on to a table, constructed of thick cast-iron plates arranged to form a horizontal bed, and passing a roller over it. A table thus constructed in segments is pre- ferable to one made of a single plate, because such local arching as may arise from irregular expansion is distributed, and is at no point so great as would be the case with a single large plate ; consequently, less waste is encountered in grinding the plate glass to a plane surface. Plate glass is ground flat and polished by fixing the plate on a bed of plaster of Paris and grinding it by means of cast-iron plates carried on arms which revolve on a central axis. The first grinding is effected by sand and water, and the final surface obtained by emery, rouge, &c. Annealing and "Hardening" Glass. — All glass, if allowed to cool from the plastic state by direct exposure to the ordinary temperature, is liable to develop internal strains due to irregular solidification and consequent contraction. The strains may be so severe as to lead to spontaneous fracture. In consequence of this peculiarity, glass articles, from bottles to plate glass, are annealed in special ovens, either by passage on travelling bands through a long flue of gradually diminishing temperature, or by exposure while stationary to a temperature, short of fusion, which is lowered by degrees. When the cooling of a glass article is rapid, but uniform over the surface, the article is "toughened" and possesses greater mechanical strength than does annealed glass. Such toughened glass is prepared by plunging the red-hot goods into an oil bath, the temperature of which varies from 70° to 350° C. = 158 to 662° F. Although resisting shocks sufficient to break common glass, material pre- pared in this manner is in a condition of internal strain ; when fracture actually occurs at one spot it determines the disintegra- tion of the whole mass with almost explosive violence. An application of the same principle of rapid uniform cooling is found in Siemens toughened glass for street pavement lights, and similar purposes, which is made by casting glass into moulds of the same conductivity and heat capacity as the glass itself, reheating to the softening point of the glass, and allowing the glass and the mould to cool rapidly together. Devitrification of G-lass. — The object of ordinary glass annealing is to obtain the material free from internal strains, LEAD GLASS. 157 but the heating needed to allow of the self-adjustment of such pre-existing strains must not be so prolonged as to permit that complete re-arrangement of the molecules of the material — viz., their orientation into the form of crystals — which indicates a state of equilibrium naturally acquired. The production of such crystals causes the glass to become opaque and porcelain-like, whence the name of Reaumur's porcelain for devitrified glass — the substance having been prepared as a substitute for true porcelain. The change is purely physical, no chemical alteration (such as loss of alkali) being observed ; the glass can be restored to its vitreous condition by refusion. The influence of rate of cooling on natural mixtures of silicates comparable with glass, is similar to that on glass'itself. Thus, the slowly-cooled rocks, like granite, contain large crystalline individuals ; more recent eruptive rocks, such as lava, are micro- crystalline, while silicates of the obsidian order, which have been very quickly cooled, closely resemble glass in structure. Granu- lated blast-furnace slag (Vol. I., p. 133) is another instance. Typical Composition of Alkali-Lime Glass. — As already stated, both soda glass and potash glass (and glasses containing both alkalies) are made. There does not appear to be any great difference in the properties — e.g., fusibility — of potash and soda glass,* though glasses containing mixtures of the two alkalies in equivalent proportions are more fusible than those with either alone. The following are examples of ordinar}' - glasses of the soda- lime class : — Soda Glass, Rich in Silica. Combustion Tube, Bohemian Glass. Soda Glass, Poor in Silica. Per cent. Per cent. Per cent. SiO* . 77 0 73-1 68'6 Na.,0, . 15 5 31 17 7 K 2 0, . . 11-5 CaO, . 7-4 104 9 : 7 MgO, . . 0-3 A1 2 0 3 + Fe.,0.,, 0-4 40 MnO, . " . 0-5 Lead Glass. — This is a potash-lead glass, nearly free from foreign constituents, and approximates to a formula ranging from K 2 O.Pb0.5Si0 2 to 5K 2 0.7Pb0.36Si0 2 . Its freedom from iron causes it to be colourless, it exhibiting no green tint such as is characteristic of soda-lime glass. It has a considerable lustre, due to its high refractive index, which increases with the con- * The refractory character of the "potash" glass, used for combustion tubing in the laboratory, appears to be due rather to its high content of silica than to the nature of the alkali. 158 CLAY INDUSTRIES AND GLASS. tent of lead. Its comparative softness fits it for the manufacture of ornamental cut glass, which is fashioned by pressure against a wheel fed with emery, putty powder, &c. It melts at a lower temperature than soda-lime glass and is less easily de vitrified. A typical mixture for producing lead glass is 300 parts of sand, 100 of potassium carbonate, 150 of red lead, and 50 of litharge. The ease with which the lead may be reduced (communicating a black stain to the glass) necessitates, the use of a covered pot (Fig. 29). Lead glass is often termed flint glass, the name being especially applied to such as is prepared for optical purposes. The grades of lead glass richer in lead contain from 40 to 50 1 per cent, of lead oxide and are termed strass. Strass is used for the manufacture of imitation precious Fig. 29.— Pot for lead glass, stones on account of its high refrac- tive index. The softness of glass rich in lead affords an easy means of distinguishing false gems made of this material. Coloured and Opal Glass. — Coloured glass is produced by the addition of the oxides of heavy metals to ordinary glass mixtures, each metal communicating a colour depending on its nature and condition of oxidation. The decoration and colouring of porcelain are effected by the use of silicate mixtures similar to coloured glasses. Some of the more important coloured glasses are described below. Red glass. — Ruby-red glass is produced by adding about 1 per cent, of cupric oxide and 1 per cent, forge-scale (magnetic oxide of iron) to the glass (preferably a lead glass) to be coloured. The magnetic oxide — which may be replaced by iron filings, tin- foil, &c. — acts as a reducing agent and causes the formation of cuprous oxide, or, in the event of a more powerful reducing agent having been used, of metallic copper. The red oxide or metal is soluble in the glass at the melting point of the latter, so that on withdrawal from the furnace the glass is colourless or slightly tinted with cupric silicates (v.i.). Separation of the dissolved copper does not take place when the glass is rapidly cooled, but when the period of cooling is prolonged by placing the glass in a furnace kept at the point of incipient fusion, separation of an opaque layer of deep red colour takes place. Aventurin is a glass of this description containing 3 per cent, and upwards of copper. On account of the opacity of ruby-red glass made in this manner, it is chiefly used for "flashing" colourless glass — that is, applying a layer of the coloured to the colourless material. As a rule, the coloured glass is first taken COLOURED GLASSES. 159 on to the blower's pipe and is then dipped into the colourless mixture ; the glasses must obviously be of similar composition, so that they may weld well and their dilatation by heat be identical. Ruby glass is also made with gold as a colouring constituent, the phenomena of dissolution and slow separation of the metal being similar to those observed in the case of copper. The gold is applied by wetting the sand (in the glass raw materials) with a solution of gold chloride, drying and mixing with the rest of the ingredients. The quantity of gold requisite to produce the colour is very small, about 1 part in 10,000 sufficing. Other metals that are capable of dissolving in and separating from glass, are silver and lead, silver giving a yellow colour (v.i.), and lead a grey stain on cooling. A bluer shade of red than either of the foregoing is obtained by means of manganese, about 2 per cent, of Mn0 2 and 4 per cent, of nitre being added, the latter reagent preventing reduction of the manganese. Yellow glass is manufactured by the use of ferric oxide, lead antimonite (yielding a turbid glass), metallic silver and alkali sulphides, the latter being made in situ by adding sulphur to the charge, if it contain alkali carbonate or charcoal, if it be prepared with alkali sulphate. Uranium glass, made by adding 2 to 3 per cent, of an alkali uranate, has a green-yellow colour and is fluorescent. Selenium glass, now made by adding a selenite or selenate and a reducing agent to glass, has an orange or reddish colour. An orange colour can also be produced by the use of a mixture of ferric oxide and manganese dioxide, the yellow-brown caused by the ferric oxide and the red of the manganese being its components. Green glass, of somewhat dull and impure tint, is yielded by ferrous oxide ; yellow-green shades are obtained when ferric oxide is also present. Better greens are obtained from a mixture of cupric oxide and ferric oxide. Chromium oxide, Cr 2 0 3 , also gives a green with a yellow tone, and when used in considerable proportion renders the glass opaque ; the product being known as chrome aventurin. A mixture of CuO and Cr 2 0 3 gives an emerald green used for artificial gems. Blue Glass. — The chief colouring matter for blue glass is cobalt, about 0-1 per cent, of cobalt oxide sufficing. Cobalt glass is prepared in large quantities as a pigment (smalt) (see Yol. II., Chap. XV.). Pale blue glasses may be made with a small pro- portion of cupric oxide and by the partial oxidation of iron green glass. Violet glass is made by employing manganese dioxide in con- siderable quantity, the colour being apparently due to manganic silicate, manganous silicate being colourless. Black glass is actually glass containing any strongly colouring 160 CLAY INDUSTRIES AND GLASS. oxide, such as that of iron, cobalt or manganese, and so dark- coloured as to appear black. Nickel in the reduced state in glass renders it grey. Opal Glass. — The general method of preparing opal glass — by which term is meant glass of semi-transparent milky appearance — consists in adding to the glass mixture one of several materials, themselves white and opaque, which do not completely dissolve in the glass mixture. The oldest form of milk or enamel glass is that (usually made with lead glass) containing stannic oxide. More recently cryolite, fluor spar and calcium phosphate have been used. Translucent, as distinct from transparent, glass can also be made by rendering the surface of ordinary glass matt, either by grinding — e.g., with the sand blast — or by etching with gaseous hydrofluoric acid, or by dipping in the same acid containing an alkali fluoride. Dilute hydrofluoric acid alone etches glass, but leaves it transparent. The effect of fluoride in giving a matt surface is due to the formation of an alkali silicofluoride which is deposited in fine crystals on the glass. Coloured designs are produced by etching or grinding flashed glass. Painting on glass is executed by applying the metallic oxide capable of yielding the required colour, mixed with strass, to the surface to be decorated, and firing in a muffle at a temperature sufficient to fuse the easily-melted strass and not the body of the article. Colouring porcelain is a similar process, the colours being mixed with fusible glazes and applied above or below the glaze proper (see Porcelain, Vol. II., p. 148). Besides the compounds used to produce coloured glasses, pigments for porcelain include iridium oxide, platinum and uranium oxide for blacks, stannic chromate for pink, barium ehromate and lead chromate for opaque yellows. Gilding is practised by applying precipitated gold, burning on and burnishing. Special kinds of Glass. — Borate glasses containing B 2 0 3 , partly replacing Si0 2 , are made for optical purposes. B 2 ^5 ^ s a similar substitute for Si0 2 ; BaO and ZnO may replace CaO, and T1 2 0 may be used instead of alkali. The chief merit of glasses of this description consists in the high refractive indices which they possess. Glasses designed to avoid the alteration of the zero point of thermometers made from them are characterised by containing ZnO and B 2 O r> . Thus the following is a typical glass of this kind — Si0 2 , 52 per cent.; K 2 0, 9 per cent.; ZnO, 30 per cent. ; B 2 0 8 , 9 per cent. Properties of Glass. — The specific gravity varies from 24 to 2-6 for alkali-lime glass and 3 to 3*8 for lead glass. Thallium glass is the heaviest known, having a specific gravity of 5*6. The index of refraction of glass decreases as its content of silica PROPERTIES OF GLASS. 161 increases, and in general increases with increasing content of the lead oxide or other oxide capable of replacing lead oxide. Although all ordinary glasses appear to be unaffected by water, acids (except HF) and alkalies, when regarded from the stand- point of daily domestic use, yet they are slightly but distinctly attacked by most solutions, and display considerable instability and solubility in the laboratory. In general, glasses with a high content of silica are less easily attacked than those con- taining a considerable proportion of alkali — this being in accord- ance with the fact that acid silicates are commonly more refractory than those of more basic character. In laboratory practice it has been found that glass vessels are rendered more resistant to the attack of reagents by exposure to steam for a short time. 11 162 SUGAR AND STARCH. CHAPTER VIII. SUGAR AND STARCH. SUGAR. — The term sugar is used in two senses. In every-clay life it means, when employed without epithet, sucrose or u cane sugar"; by the chemist it is used generically for a certain class of carbohydrates. Adopting for the moment the more extended significance, the following sugars may be cited as of technical importance : — (A.) Sucroses of the general formula C 12 H.-, 2 O n . (1) Sucrose or cane sugar. (2) Lactose or milk sugar. (3) Maltose. (B.) Glucoses of the general formula C G H 12 0 6 . (1) Dextrose or grape sugar. (2) Lcevulose or fruit sugar.* These two groups are re]ated, in that the members of the first, on hydrolysis, become converted into those of the second, thus — CjoH^Oi! + H 2 0 = CqH v X)q + CcH 12 06. Of these two members of the second group, one is always dex- trose, while the other varies with the sucrose from which it has been obtained — e.g., cane sugar on hydrolysis yields dextrose and laevulose, lactose gives dextrose and galactose, and maltose forms dextrose. (A.) SUCROSES. — 1. Sucrose or Cane Sugar, C 12 H 22 0 1V — This substance — " sugar " in ordinary phraseology — is techni- cally the most important member of the sugar group. Although many other carbohydrates are sweet, the intensity of their flavour falls short of that of sucrose. f This fact has naturally led to the cultivation of plants producing sucrose rather than other sugars, in all cases where the product is required as a sweet food. The name "cane sugar" has become usual on account of the fact that, until about a hundred years ago, sugar was prepared almost exclusively from the sugar cane (Saccharum * The nomenclature of the sugars is in a state of flux, and consequently the older and more familiar names have been adopted here. In modern phraseology, according to one system, the sugars of the general formula CgH^Og are termed saccharides, whilst those of the general formula I ,II 22 O n are disaccharides. T Lsevulose is a possible exception. CONCENTRATION OF SUGAR CANE JUICE. 163 officinarum). At the present time the term has lost its appro- priateness, as more than half the world's production of sugar is now obtained from the beet {Beta vulgaris). The sugar from these sources, when perfectly refined, is identical in all respects^ though characteristic impurities differentiate the raw sugars and the lower grades of refined products (v.i.). Cane Sugar. — The sugar cane is grown in tropical and sub- tropical countries, the chief sources of supply being the West Indies, Brazil, Mauritius, Java, the Philippines, Sandwich Islands and Queensland. The cane grows to a height of 8 to 20 feet, the stems being 1^ to inches in diameter. When ripe it contains about 90 per cent, of its weight of juice, the juice itself containing 12 to 20 per cent, of sugar. The following analysis will serve as an example of a j uice of good quality : — Crystallisable sugar, 19*64 per cent. Uncrystallisable sugar, . . . . 0*30 ,, Ash, 0-25 Water, 79*44 „ Organic matter other than sugar, . . . 0'37 100*00 „ After cutting, the canes are worked up for sugar as quickly as possible, for delay means loss of sugar by decomposition. In the older methods of working, which are still largely used, the- cane is crushed between rollers, and the juice collected ; the residue, termed bagasse, is used as fuel; waste is thus occasioned, as this residue generally retains a notable amount (4 to 5 per cent.) of sugar. The juice, after filtration, is treated with lime (0*15 per cent.) to neutralise any acidity which may have de- veloped,* and is also usually treated with S0 2 , these additions serving to hinder fermentation and consequent loss of sugar. It is then heated to 170° to 180° F. = 77° to 82° 0., whereby coagulation of the impurities takes place, part appearing as. scum, which is skimmed off, and part depositing in the heating vessel. Concentration. — The clarified juice is then run into evaporating pans set in series over the fine of a furnace. Evaporation is con- ducted systematically, the weak juice entering the pan furthest from the fire, and being ladled from pan to pan until it reaches that nearest the fire, by which time it has arrived at its point of crystallisation. The size of the pans is graduated (the smallest being at the fire end of the flue), so that their content is appro- priate to the volume of liquid to be evaporated. The sugar having been brought to this point of concentration is separated from the portion of the juice which still remains liquid, either by drainage in perforated casks, or by means of a centrifugal machine or hydro-extractor, such as is shown in Fig. 30. * Any excess of lime combines with the sugar to form a " saccharate.'* 164 SUGAR AND STARCH. The former method of separation takes weeks to accomplish. The juice thus separated is either evaporated again and a second crop of crystallised sugar obtained, or it is fermented for the preparation of rum. A good deal of juice of this character con- taining sugar, which is uncrystallisable from the simultaneous presence of various impurities, is used for food under the name of treacle or molasses. The nature of this product may be gathered from the following analysis : — 25*87 per cent. 41-91 Invert sugar, * 25-50 Ash, 3-75 Organic matter (other than sugar), 297 „ 100-00 It is evident that several improvements in the economy of the process described above are possible. The following have been Fig. 30. — Hydro-extractor. adopted: — (1) The cost of evaporation has been diminished by the use of vacuum pans (see p. 171), and by adopting evapo- rators of the Wetzel type, in which a revolving frame-work of steam-pipes dips into a trough of the juice to be evaporated and becomes covered with a film of liquid, which is evapo- rated to dryness as the frame -work performs that part of its revolution which takes place in air (see Concentration of glycerin, Vol. II., Chap. XL). (2) Centrifugal separators are used instead of the method of draining in perforated casks described above, and thus a considerable saving of time is effected. (3) A more radical alteration consists in substituting a process of diffusion for that of crushing, for winning the juice * The name given to the mixture of dextrose and loevulose obtained by "inverting" sucrose (p. 188). EXTRACTION OF BEET SUGAR. 165 from the cane. This process is similar to that in general use for the extraction of beet sugar (q.v.), and gives an output which is stated to be about 15 per cent, higher (reckoned on the total sugar in the cane) than that obtained by the older method of crushing between rolls. The stouter cell walls of the cane pre- vent this process being as effective as it is for beet. The quality of raw cane sugar varies largely on account of the different methods of extraction, clarification and evaporation adopted, but a typical sample will contain about 89 per cent, of sucrose, 4 per cent, of glucose, 4 per cent, of moisture, 1*5 per cent, of ash, the balance being various organic impurities. The method of refining is described below, after the extraction of sugar from sources other than the sugar-cane has been dealt with. Beet Sugar. — The plant used is a variety of the common beet, improved by careful cultivation. The cells in the parenchyma of the beet are narrow close tubes, having the usual layer of proto- plasm adhering to the cell-wall, and containing the cell-sap which is present in such abundance that it constitutes about 96 per cent, of the weight of the root. The sap contains 20 per cent, of solid matter in solution, the chief constituent of this being sucrose, together with a little raffinose, C 18 H 39 0 16 ,5H 2 0. Minor substances present are albuminous and colouring matters, asparagine, betaine, CH 2 [N(CH 3 ) 2 ]C0 2 CH 3 — which collects in the residues from the sugar and is used as a source of trimethylamine — glutamine, pectinous substances, coniferine — which yields vanillin during the treatment of the beet juice — and various organic acids (tartaric, malic, &c), as well as the usual mineral constituents of plants. Extraction. — In manufacturing sugar from beet, the roots are freed from dirt, rasped, and the resulting pulp placed in woollen bags, and the juice squeezed out by an hydraulic press, the yield being about 77 per cent, of juice as compared with 96 per cent., the amount contained in the roots. On account of the cost of cartage, the beets grown in outlying fields are frequently crushed between rollers on the spot, and the juice, after treatment with about 1 per cent, of lime, is conveyed by pipe-lines to the central factory where it is worked up. This method of extraction is in use in France, but' in Germany has been almost entirely displaced by the diffusion process. In this process the beet is shredded into small thin strips so as to expose an ample surface to the water with which it is subsequently extracted ; these strips or COSettes (which are about j- inch in breadth and ~j inch in thickness) are brought into contact with water, and the sugar in the beet- sap diffuses out through the cell wails while colloid substances remain in the cells. Thus, at a single operation, a juice is ob- tained which is less impure than that procured by any process of expression in which the cell walls are crushed and broken. 166 SUGAR AND STARCH. It might be thought that the diffusion process would yield a bulky diffusate, the evaporation of which for the recovery of the sugar would be a costly operation ; but this is not the case, as the diffusion is carried on systematically, and thus the quantity of water needed is reduced to a reasonable limit. Several forms of apparatus for systematic extraction are used in the diffusion process, typical examples of which will be described. A common form of diffuser consists of a "battery" of cells connected to- gether so that water can be caused to travel from one to the other through the series. The sliced beet is filled into the cells and the water circulated, traversing in its passage between each pair of cells a tubular heater, in which it is warmed to a tempera- ture ranging from 20° to 90° C. = 68° to 194° F. It is usual to graduate the temperature in the heaters between the cells, it being gradually raised from the lower to the upper limit quoted a,bove in passing through the series of cells. A high temperature favours the rapidity of diffusion, but impairs the quality of the juice to some extent. When the apparatus is in regular opera- tion the fresh water comes into contact with nearly exhausted beet, while the nearly saturated water is used to extract fresh beet with its full complement of sugar. Of the whole series of •cells — commonly 10 to 12 in number — one, containing the ex- tracted beet, is being emptied, while another is being filled with fresh beet, and the remainder present a regular gradation of extraction. The quantity of water above that contained in the sap of the beet itself is thus kept comparatively small, and nevertheless repeated treatment with wash water of decreasing content of soluble matter is secured. The cells are generally arranged in a circle for convenience of working, and a radial spout delivers the sliced beet from a central hopper into any desired cell. A second form of diffuser may be mentioned as it is an obvious •extension of the idea underlying the apparatus described above. It consists of two concentric cylinders with a screw-shaped guide in the annular space between them. The inner cylinder rotates and forces the sliced beet along the screw in the annular space, ■causing it to meet a current of water into which the juice diffuses. The fresh water meets the exhausted beet, and the water rich in sugar (and thus largely deprived of its extractive power) makes its exit from the end at which the fresh beet onters, both systematic extraction and continuous working being- secured. The temperature of the liquid can be regulated by the use of steam coils. Whichever process of diffusion is used, a good degree of ex- haustion is obtained, the spent beet containing little or no sugar, but sufficient nutriment to make it available as fodder. It is, of course, very wet, about 92 per cent, of its weight consisting of water, and is generally pressed and, preferably, dried before PURIFICATION OF BEET SUGAR JUICE. 1G7 it is utilised as food. Its nutritive value is indicated by the following analysis of the dry material : — Water, . . . . . . . 5*34 per cent. Albumin, 7 34 ,, Proteids (as distinct from albumin), . . 1*04 ,, Fat, 0-90 Starch, 56*62 Non -nitrogenous extractive matter, . . 2 '65 ,, Crude fibre, 20 67 True ash, ....... 5'10 ,, Sand, 0-34 100-00 The crude juice is fairly free from suspended matter, but is nevertheless strained through sieves before defecation. As in the case of juice from the sugar cane, it is necessary to purify beet juice before concentration by treatment with lime, which neutra- lises any acid substances which might invert (p. 188) the sucrose in the juice. In modern practice, enough lime — viz., about 3 per cent, of the weight of the beets from which the juice has been obtained — to convert the whole of the sucrose into calcium mono- saccharate (C 1 . > Hr, 2 0 11 CaO,H 2 0) is added, and the saccharate is decomposed immediately it is formed by treatment with C0 2 , which is blown into the vessel in which the defecation with lime is effected. It appears that the comparatively bulky precipitate of calcium carbonate which is thus formed carries down with it much of the colouring matter and various impurities, yielding a better juice than that obtained by employing a smaller quantity of lime, such as would suffice for neutralising the organic acids naturally present in the juice. The process is carried out in a covered tank heated by close steam (to avoid dilution of the juice) and provided with a perforated delivery tube through which C0 2 can be blown in. The order of operations consists in the admission of the juice to be defecated, the addition of lime either as milk of lime or unslaked in small lumps, and heating and carbonating the resulting mixture. Excess of C0 9 must be avoided, as carbonic acid is capable of causing a certain amount of inversion (p. 188). The gas is, therefore, admitted until the alkalinity of the juice corresponds with the presence of about 0 - l per cent, of lime. To complete the defecation, the juice after filtra- tion from the sludge (which consists chiefly of calcium carbonate) is re-treated with a smaller quantity — e.g., 0-5 per cent. — of lime, and the carbonation repeated ; a liquid approximately neutral is thus obtained. The neutralisation of the lime by C0. 2 is neces- sary, inasmuch as it would otherwise, on boiling, react with the albuminous substances contained in the crude juice, and yield soluble decomposition products instead of forming a precipitate and freeing the juice from impurities of the albuminous class. CONCENTRATION OF BEET SUGAR JUICE. 169 The C0. 2 is usually obtained in the form of lime-kiln gases, pro- duced either in ordinary kilns or in those of the Dietzsch type (see Lime and Cement, Yol. II., p. 135). The kilns are provided with collecting flues, through which the gas is drawn off; it is then scrubbed and freed from S0 2 * and dust. Where the residues- from the refining process (molasses) (y.i.) are fermented for spirit manufacture, another source of C0 2 is available (see Brewing and Distilling, Yol. II., p. 199), but no application of this fact appears to have been made on a manufacturing scale. Seeing that lime is needed in any case, C0 2 as a bye-product is inevitable. The final removal of the sludge formed during the lime purification is effected in filter presses of such construction (Fig. 31) that the sludge can be washed and adhering sugar recovered. By this means the content of sugar is reduced to 2 to 3 per cent, of the weight of the dried sludge, which amounts to about 10 per cent, of the beets treated. The sludge is composed of about 75 per cent, of calcium carbonate, the balance consisting of the calcium salts of the organic acids of the juice, small quantities of magnesia and alkalies, and a. certain amount of insoluble organic matter. As it contains on an average 1 to 2 per cent, of P 2 0 5 , 0-3 to 0*5 per cent. N, and 0*2 to 0*3 per cent. K, it finds a use as a manure. When purifi- cation in this manner is carefully conducted, the juice is not necessarily decolorised by animal charcoal, but in general the use of this material is found requisite. The method of treatment is similar to that practised in the purification of the refined juice after concentration (v.i.). An alternative plan at this stage con- sists in treatment with sulphur dioxide and filtration through sand, which eliminates residual lime as calcium sulphite, and also decolorises the liquid. The S0 2 is usually applied by blowing the products of combustion from a small kiln burning sulphur into the juice, care being taken that the point of neutrality is not overstepped. The antiseptic properties of the small quantity of sulphite remaining in solution are useful in preventing ferment- ation of the purified juice. Phosphoric acid has been suggested as a precipitant for residual lime, on the ground that it causes a better removal of the organic matter (other than sugar) than can be effected by C0 2 . The sludge containing calcium phosphate has a manurial valuecorrespondingwiththatof the phosphoric acid used. Concentration. — The juice purified by the methods given above, is somewhat dilute from the addition to it of the washings of the sludge separated by the filter press, and has a specific gravity of about 6° Beaume — i.e., l*043f — corresponding with a * This gas is removed, not on account of its being objectionable as far as the sugar is concerned, but because it attacks the fittings of the pumps used to draw it from the kilns. t The strength of sugar solution is sometimes stated in " degrees Brix," which are designed to represent the percentage of sugar directly ; thus,, juice of 10° Brix contains 10 per cent, of sugar. 170 SUGAR AND STARCH. content of about 11 per cent, of sugar. It is concentrated in " multiple effect " evaporators, the principle of which consists in the use of the steam from one pan, boiling under a pressure somewhat less than that of the atmosphere, to heat the liquid in the next pan, boiling under a still smaller pressure. A series of three such vessels (triple effect), the contents of which boil under •continually diminished pressure, is usually found the most efficient arrangement, doubtful economy being obtained on extending the system to four or more pans. An apparatus of recent design, which has found considerable application in sugar •concentration, is the Yaryan evaporator, the essential parts of which are shown in Fig. 32. The juice to be concentrated flows from the pipe, A, through a series' of horizontal tubes, B, set in Fig. 32.— Multiple effect evaporator. A, Inlet pipe ; B, tubes ; C, cylinder ; D, drum ; H, chamber ; F, pipe for exhaust steam ; G, box for catching spray. a cylinder, C, serving as a steam jacket. During its passage through these tubes, its temperature is raised by the heat transmitted from the steam through the walls of the tubes, and it boils under the diminished pressure, which is maintained by an ordinary exhaust pump. The steam and liquid emerge into a, short, wide drum, D, at one end of the heating cylinder, and the steam is drawn off by the pump through the pipe, F, while the liquid collects in the chamber, H. Any liquid carried over as spray by the steam on account of the tumultuous boiling of the juice, is caught in the box, G, in which the steam is com- pelled to take a circuitous course, and to pass through narrow tubes and passages, and thus to deposit any suspended matter which it may contain. The liquid separated in this manner is returned to H. The exhaust steam from G serves to heat the CONCENTRATION IN A VACUUM. 171 liquid in the tubes of the next evaporator, the exhaust steam from which in turn heats the third member of the series. The diminution of pressure is progressive, as mentioned above ; the pressure in the last evaporator being as low as can be obtained in practice. The advantage of this arrangement is that the juice is never heated to its boiling point under atmospheric pressure, and thus loss of sugar by inversion (p. 188) is largely decreased. The economy of heating also obtained is considerable, a matter Fig. 33 — Vacuum pan. A, Vacuum pah ; B, double bottom ; C, steam coil; D, head; E, valve. of moment, seeing that the quantity of water to be removed is very large. A short boiling at atmospheric pressure of the concentrated juice before the crystallisation of the sugar there- from, is found necessary in order to complete the clarification, the low temperature of the triple effect apparatus not sufficing to coagulate the whole of the impurities removable at this stage. The juice is brought by this process to a concentration of 2(T to 30° Beaurne (specific gravity 1*16 to l - 263), and contains 35 to 55 per cent, of sugar. Any residual lime is removed 172 SUGAR AND STARCH. by addition of sulphurous acid or phosphoric acid, and the juice is filtered either in a filter press or through animal charcoal. Concentration is then continued in a vacuum pan. The older form of this apparatus consists of a globular copper vessel, A (Fig. 33), with a double bottom, B, and a steam coil, C, for heating its contents. The upper part of the vessel is fitted with a head like a still, D, connected with an exhaust pump, by which means a vacuum is produced and maintained in the pan. The juice, when sufficiently concen- trated, is drawn off through the valve, E. Cylindrical iron vacuum pans are also used in modern practice. In working the vacuum pan, the concentrated juice (previously warmed) is run in, and steam at 50 to 60 lbs. pressure is admitted to the double bottom and coil. The exhaust pump reduces the boiling point of the concentrated juice to C0° to 80° C. - 140° to 176° F., and evaporation proceeds until the contents of the pan has reached a concentration such that it contains 70 to 90 per cent, of sugar. The product is termed massecuite. A juice with but little impurity yields a mass of sugar crystals (mixed with syrup) at this stage, the crystals being fine if the concentration has been rapidly executed, and coarse if the contrary condition has obtained. An impure juice gives a syrup from which crystals are deposited only after standing for some time. The satis- factory conduct of the concentration requires much personal skill and experience. It has lately been pointed out that the use of moderately high pressure steam (50 lbs.) is not advantageous, as local overheating of the massecuite may occur. Steam of low pressure (of course in correspondingly larger amount, involving the use of larger heating surfaces) is distinctly preferable. The massecuite is separated in a centrifugal machine, the crop of crystals being termed first jet sugar. Two succeeding crops of inferior quality (second and third jet) can be obtained by boiling down the mother liquor, the final residue of which constitutes beet molasses; methods of utilising this material are described below. About 70 per cent, of the sugar in the beet is obtained crystallised as raw sugar of one or other of these grades. Utilisation of Uncrystallised Sugar. — The difference between the quantity of sugar contained in the beet and that obtained as raw sugar, in a saleable condition, by the processes described above, amounts to about 30 per cent, of the whole. Of this about one-half (15 per cent.) is lost in the course of manufacture, and the remaining 15 per cent, is left in the molasses separated from the sugar crystals by treatment of the boiled-down purified juice in a centrifugal machine. The crystallisation of this residual sugar is rendered impracticable by the presence of organic substances, other than sugar and of mineral matter. The raffinose (p. 165) present in THE OSMOSE PROCESS. 173 the beet also becomes concentrated in the molasses. At one time this residue was chiefly utilised for the manufacture of spirit, it being unfit for food on account of its nauseous flavour. As already stated, cane-sugar molasses is edible. According to modern practice, beet molasses is usually worked up for crystal- lisable sugar, by one or other of the processes about to be de- scribed. Choice between utilisation for sugar or spirit making depends largely on the fiscal regulations of the country in which the manufactory is situated, this part of the manufacture being — as indeed is the whole industry — hedged about by privileges and restrictions purely arbitrary in character. The method of preparing spirit from molasses differs in no essential respect from the processes of fermentation and distillation applied to other saccharine materials (see Brewing and Distilling, Vol. II., p. 189), and needs no further comment. The recovery of crystal- lisable sugar, however, is effected by methods of comparative complexity. An average sample of beet molasses has the following composition : — Per cent. Sugar, 50-0 Organic matter (other than sugar), . . . 20*0*' Potash, ........ 5 '5 Mineral matter (other than potash), . . . 4*5 Water, 20 '0 100-0 (1) The Osmose Process. — This depends upon the fact that when molasses is separated from water by an osmotic membrane — e.g., parchment paper — the salts in the molasses diffuse more quickly than the sugar into the water ; a portion of the sugar left in solution can be recovered on evaporation. Some dilution from the incoming water takes place under these conditions, but the process has the advantage of simplicity and of requiring no addi- tion, other than water, to the molasses to be treated. The organic matter (other than sugar) present in the molasses diffuses even more slowly than the sugar, and remains in the liquor sent for concentration ; its presence hinders the separation of the whole of the sugar, and necessitates the return of the molasses produced by concentration and subsequent centrifugal separation, to the osmose apparatus. Three osmotic treatments of the same portion of molasses are as many as can be profitably performed, about half the total sugar in the molasses being thus recovered. The process is carried out in an apparatus somewhat resembling a filter press in structure, consisting of a series of compartments separated by septa of parchment paper (see Paper and Pasteboard, Vol. II., Chapter XIV.). The molasses is fed into alternate compartments, and the water into the intermediate divisions. * Containing 1*9 per cent, of nitrogen. 174 SUGAR AND STARCH. The weak saline solution obtained by the passage of the water through the second series of compartments is usually too dilute for use save as liquid manure. In France and Belgium, where beets yielding much nitrate are grown, the water from the osmose process is sometimes worked up for potassium nitrate. The residual molasses, though poorer in mineral salts, is richer in colloidal organic matter than is the original molasses, and generally goes finally to the distillery. (2) Processes depending on the Formation of Compounds of Sugar with the Alkaline Earths. — The property possessed by sucrose of forming loose compounds — saccharates or sucrates — with lime, strontia, and baryta is turned to account in various processes for the recovery of crystallisable sugar from beet molasses. The following are typical methods of this class : — (a) The Elution Process. — The molasses is mixed by means of an edge-runner with about 25 per cent, of its weight of quicklime, but little reaction taking place as long as the mixture is kept cool ; on this account the pan of the edge runner is artificially cooled. When incorporation is complete, the mass is transferred to small iron chambers, in which its temperature rises spon- taneously to 100° C. = 212° F. or higher, and combination of the sugar with the lime to form tricalcium saccharate (3CaO, C 12 H 02 O n , 3H 2 0) takes place, accompanied by expulsion of the surplus water and the formation of a hard porous mass. This product is broken up and extracted systematically with weak alcohol (35 per cent.), impurities being dissolved and the calcium saccharate left fairly free from foreign matter. The extraction is carried out in an apparatus resembling a battery of diffusion cells (p. 166). The alcoholic extract is distilled and the alcohol re- covered, the aqueous residue being used as a manure. The alcohol left clinging to the calcium saccharate is removed by steaming and is also recovered. During the steaming the tricalcium sac- charate is partly decomposed, yielding monocalcium saccharate, C 12 H 22 O n CaO,H 2 0,and lime. The complete separation of the lime can be effected by treatment with C0 2 , but the monocalcium sac- charate is often substituted for lime, in the early stages of the win- ning of raw sugar, for neutralising the acidity of the diffusion juice (p. 167); the acid thus neutralised of course liberates an equivalent quantity of sugar which is worked up with the bulk. Various modifications of the elution process have been devised, differing chiefly in the manner in which the calcium saccharate is produced, but their underlying principle is identical with that enunciated above. Staffen's process is distinguished from its congeners by the fact that the use of alcohol is dispensed with. The molasses is diluted with water until its content of sugar is about 7 per cent., and to it quicklime is added in small portions, the total quantity being about equal to the weight of sugar present. The liquor is well stirred during admixture to prevent the temperature STRONTI A. PROCESSES. 175 rising above 15° C. = 59° F. At first the lime goes into solution, but eventually it separates again as tricalcium saccharate accom- panied by excess of lime. The mass thus obtained is filter-pressed, and the saccharate used instead of lime in purifying the crude juice (p. 167). The expressed liquid is utilised as manure and the washings are used for diluting the next batch of molasses. (b) Strontia Processes. — Several processes have been devised, notably by Scheibler, in which strontia is substituted for lime in recovering sugar from beet molasses. The earlier of the pro- cesses due to this chemist consists in treating the molasses with strontium hydroxide in sufficient proportion to form distrontium saccharate, 2SrO . C 10 H 22 O i:i , and to leave an excess of strontium hydroxide, in a solution of which the saccharate is almost in- soluble. The precipitate is thrown on a filtering cloth stretched over a horizontal semi-cylindrical vessel. The air beneath the filtering cloth (which is, of course, supported by a perforated plate) is exhausted, and the de-sugared liquid pulled through. The distrontium saccharate is washed with a hot solution of strontium hydroxide, turned out into iron boxes by inverting the filter, and treated with water at a temperature below 15° 0. = 59° F. ; cold-air chambers are requisite in warm weather for this part of the process. The saccharate is decomposed, giving crystals of strontium hydroxide and a solution of sugar, which is freed from residual strontia by treatment with C0 2 , and concen- trated in a vacuum pan in the usual way. That part, of the strontium hydroxide which crystallises is immediately avail- able for further use, while that precipitated as carbonate is causticised by burning in a special kiln (y.i.). A more recent modification by Scheibler depends on the formation of mono- strontium saccharate, SrO.C 12 H 22 O n , when a solution containing about 25 per cent, of sugar is treated with strontium hydroxide at about 70° C. = 158° F. A slight excess of strontium hydroxide is used, and the temperature is maintained above that at which the formation of distrontium saccharate takes place. The in- stability of mono-strontium saccharate is such that the addition of a crystal of strontium hydroxide determines the precipitation of the same hydroxide, and that of a crystal of monostrontium saccharate causes the same salt to be thrown down. To the liquid is, therefore, first added a crystal of monostrontium saccharate, and the precipitate filtered off ; the filtrate is boiled with strontium hydroxide, yielding distrontium saccharate as a precipitate, which is used instead of strontium hydroxide for treating a further portion of molasses, another crop of mono- strontium saccharate being thus obtained. The total yield of monostrontium saccharate is decomposed by dissolution in water, thorough cooling, and the addition of a crystal of strontium hydroxide. The recovered strontium hydroxide can be used again in the process ; the sugar is freed from remaining strontia 17G SUGAR AND STARCH. by means of C0 2 . The filtrate from the distrontium saccharate obtained above yields on crystallisation crude strontium hy- droxide ; residual strontia is recovered as carbonate, and the final nitrate contains the impurities of the molasses; it is worked up for potash or used as manure. The strontium hydroxide used in this process is generally prepared in the sugar factory by burning native strontium car- bonate (strontianite) to caustic strontia, much in the same way as limestone or chalk is burnt to caustic lime.* A gas furnace is preferable for this purpose, as the comparatively costly strontia is thus not contaminated with the siliceous ash of solid fuel, and for a like reason the furnace should be basic-lined (see Vol. I., p. 8). Strontia being a more powerful base than is lime, has a stronger tendency to act upon acid materials {e.g., siliceous bricks) and also requires a higher temperature for the decom- position of its carbonate. The strontium carbonate obtained as a bye-product in the process for winning crystallisable sugar from molasses, is taken from the filter press, moulded into bricks, and burnt in the same manner as the native carbonate. The caustic strontia is hydrated and dissolved in water, the hot solu- tion, containing about 13 per cent, of SrO, being run off and allowed to crystallise, nearly the whole of the strontia being deposited in the hydrated state as Sr(OH) 2 . 8H. 2 0. The saccharates formed by the use of baryta instead of strontia have also been used for the separation of sugar from molasses, but the processes thus devised are essentially similar in prin- ciple to those depending on the formation of the corresponding strontia compounds. (3) Processes depending on the Direct Removal of Potash. — Several processes of this type have been devised, but only one has been practised on any considerable scale. The alum process of Duncan and JSTewlands consists in heating the molasses with a strong solution of aluminium sulphate, in such quantity as suffices to form alum with the potash salts present. The alum is separated, the liquid treated with lime, heated to 160° F. = 71° C, and filtered, the nitrate containing sugar in a crystal- lisable condition. The value of the alum obtained as a bye- product is said to cover the cost of the aluminium sulphate used. Another method of utilising beet molasses consists in ferment- ing and distilling (as mentioned above), and working up the residues after charring (Schlempekohle) for potash (see Minor Chemical Industries, Vol. II., Chap. XVIII. ). Minor Sources of Sugar. — Although by far the major part of the sugar consumed by civilised nations is obtained from the * Gcdestine (native strontium sulphate) is also used as a source of strontia. REFINING RAW SUGAR. 177 sugar cane or the beet, yet there exist several minor sources of supply that have a certain local importance. The trade in these classes of sugar is so inconsiderable that the preparation is con- ducted in a crude and simple manner, involving the application of no chemical principle other than those already included in the description of the chief sources of sugar. Maple Sugar. — This is obtained from the juice which flows from incisions in the sugar maple (Acer saccharinum). The juice is merely boiled down until it solidifies, forming a crude sugar, consumed in rural districts in the United States and in Canada. Palm sugar is won in a similar manner from the juice of the data palm (Phoenix sylvestris) and trees of like species. Sorghum Sugar. — Extensive experiments have been made in the United States on the cultivation of Sorghum saccharatum, which is a graminaceous plant, the juice of which contains sugar (5 to 10 per cent.). Hitherto the results have been of little industrial value on account of the fluctuation of the content of sugar, and the presence of non-saccharine constituents in the juice which hinder the crystallisation of the sugar. Refining Raw Sugar. — A good deal of raw cane sugar — i.e., sugar obtained by simple separation by draining, or by means of a centrifugal machine, from the product of the concentration of the purified juice — is consumed as "moist sugar" (Demerara), though much that is sold under this title is merely one of the lower-grade products of the refining process. Raw beet sugar is not fit for food on account of the objectionable flavour possessed by its impurities. The process of refining is essentially the same for sugar of all sources, although, of course, a raw sugar of fair purity is treated more easily than one containing much foreign matter. Sugar, when completely refined, as in the case of loaf sugar of good quality, is almost pure sucrose, and is of identical flavour and sweetening power whatever its origin. The super- stition that refined beet sugar is inferior in sweetness to cane sugar has arisen from the fact that formerly, when beet sugar was less completely refined than it is at present, its sweetness was diminished and its flavour impaired by the small quantity of alkali salts which it contained. Repeated tests have shown that it is impossible to distinguish the source of refined sugar by taste. Raw sugar varies considerably in composition, but a common content of sucrose is 90 to 95 per cent., the balance consisting of water, mineral constituents, organic matter other than sugar, and a little invert sugar. The system of refining generally practised is carried out in the following stages : — Dissolution. — The raw sugar is dissolved in water by the aid of open or close steam, a solution containing about 50 per cent, of sugar and having a temperature of about 70° C. = 158° F. being obtained. When very crude sugars are refined, defecation by 12 178 SUGAR AND STARCH. the addition of blood, and heating until coagulation of the al- buminous matter thus introduced occurs, is sometimes necessary. Filtration. — The solution, if of beet sugar, may sometimes be filtered in a filter press, but if of cane sugar, usually needs a different method of treatment. In this case it is filtered through bags of a cotton fabric ("twill"), arranged in an apparatus known as a Taylor filter. This consists of a cast-iron box covered with a perforated plate, from which depend long, narrow bags of hemp. Inside each bag is the filter bag proper, of twill, as stated above. The mouth of each twill bag is tied on to a nozzle set in one of the perforations of the plate covering the cast-iron chamber. This plate forms the bottom of a shallow tank resting on the chamber, and serving to distribute the sugar solution to the whole of the bags. By means of the large filtering surface exposed by the bags, filtration proceeds at a fair rate in spite of the slimy character of the suspended matter in the sugar solu- tion. The bags after use are either washed in situ, or turned inside out and washed in tanks. In the former case, the weak liquor is used at once for dissolving a fresh batch of sugar, while in the latter case the turbid liquor is defecated with lime, filtered in a press, and then used for the same purpose. Decolorisation. — This is effected by means of animal charcoal (g-v.). The charcoal is packed in large iron towers, provided with a perforated false bottom and a filtering cloth. The clear, warm sugar solution is run on to the charcoal at the top, and the air expelled at the bottom until the tower is full, when it is allowed to stand for some hours. The clear, decolorised liquid is then drawn off at the bottom of the tower, while fresh liquor is run on at the top, the operation being continued until the liquid ceases to be satisfactorily decolorised. When the yellow colour of the liquor shows that the decolorising power of the charcoal has been exhausted, the supply of fresh liquor is stopped, and a stream of water is substituted ; a good deal of liquor still remaining in the tower is thus expelled without being much diluted by the incoming water, but the remainder (" char water ") is comparatively poor in sugar, and has to be returned to the cycle of operations — e.g., used for dissolving the raw sugar. The function of the char (which usually contains about 10 per cent, of impure carbon — having a content of 10 per cent, of its weight of nitrogen — 80 per cent, of calcium phosphate, and about 10 per cent, of calcium carbonate) consists in the withdrawal from the sugar solution of many of its impurities, both organic and inorganic ; calcium saccharate, which may be present in the liquor, may be decomposed, and the sugar therein set free. The rationale of the action is not well understood. Wood charcoal, although richer in carbon, cannot be substituted for animal charcoal. The fine state of division of the carbon in the latter, spread as it is over nine times its weight of mineral EVAPORATION OF THE DECOLORISED SUGAR LIQUOR. 179 matter, is probably one cause of its efficacy, but its content of matter other than C, notably N, also appears to be concerned in its decolorising influence. The char after use is "revivified" by washing and reburning. The washing is generally effected by prolonged treatment of the char with boiling water, but some- times hydrochloric acid is used, in amount calculated to dissolve the lime salts taken up from the sugar solution, while leaving those naturally present in the original char unattached. The organic matter may be also eliminated by allowing fermentative decomposition to set in, and washing out the products of the changes thus produced. The washing, however performed, is followed by " reburning," the process consisting in heating the char, out of contact with air, to a temperature of about 1,200° F. = 649° 0. A pipe kiln is generally adopted for reburning, though revolving cylinders, externally fired, are sometimes used. In the case of the former, the char is fed into the upper ends of cast-iron pipes of elliptical section, set vertically in groups, and heated from below by a furnace. The wet char thus enters at the cooler end of the pipes, is there dried, and is more strongly heated as it descends, finally emerging at the lower and hotter end of the pipes into sheet-iron cooling pipes provided with valves, so that successive portions of the reburnt char can be dropped out and conveyed to the decolorising towers. After repeated reburnings, the char ceases to act efficiently, and is sold as manure. Evaporation of the Decolorised Liquor.— The liquor is boiled down in a vacuum pan similar to that used in concentrating* purified juice for the production of raw sugar. A typical pan of the older spheroidal type has been already shown diagram- matically in Fig. 33. The body of the pan has one or two glazed openings, so that the process of concentration can be watched, and a " proof-stick " or rod for taking samples without opening- the pan is also provided. The boiling down is carried on at a- temperature ranging from 120° to 'l90° F. = 49° to 88° C, according to the quality of the sugar to be produced. In general the larger the size of the crystals required, the higher the temperature adopted. The advantages of the use of a vacuum pan have been already mentioned under concentration of purified juice. The product from the vacuum pan termed massecuite is run into a receiver and transferred to a centrifugal machine in which the crystals are freed from adhering syrup. The syrup is worked up for a fresh batch of lower grade sugar, and the final liquid portion, which fails to yield crystallisable sugar, is sold as treacle. The crystals may be sold as such or moulded into cube sugar (v.i.). Moist sugar, which is white when separated from the massecuite, is often coloured yellow to imitate genuine moist sugar, such as Demerara. For this fraudulent purpose artificial 180 SUGAR AND STARCH. dyestuffs are freely used. Even in genuine Demerara, steps are taken to fix the natural colour by the addition of stannous chloride solution to the magma from the vacuum pan ; most of the tin is drained away with the molasses, but from | to J grain of tin per lb. of sugar may remain. Preparation for the Market. — The refined sugar may be sold as crystals, or in loaves or cubes. Sugar loaves are prepared by running the massecuite into conical moulds, the small end of which is somewhat rounded, departing from the shape of a true cone in order to facilitate the removal of the sugar from the mould. In the smaller end of the mould is a hole closed by a peg. After filling, the moulds are set, each with its small end downwards, and the liquor adhering to the crystals of the massecuite is allowed to drain away. A layer of sugar at the wider end of the mould is removed and made into a magma with a nearly saturated solution of refined sugar, and then poured back into the mould. The loose pulpy mass thus forms a, sort of filter bed which aids the even distribution of the solu- tion of sugar caused to percolate from the wide to the narrow end. As the liquor filters through and runs out at the lower end, a fresh portion is poured on to the upper end, the operation being repeated until all the originally adhering liquor of the massecuite is expelled. The sugar loaf is then allowed to drain, removed from the mould, and dried by hot air. Various other methods of making "lump" as distinct from "loaf" sugar are in use. Thus, cubes of sugar may be prepared by filling pure white crystals of sugar, moistened with a little pure solution of sugar, into cubical moulds set in the external surface of a rotating drum, and consolidating the mixture by regulated pressure. The soft moulded cubes are removed automatically and stoved. Sugar candy is prepared by simply allowing a solution of sugar to crystallise on threads strung in the vessel containing the solution. The white variety is pure sugar; the yellow or brown should be less pure cane sugar, retaining a portion of those constituents which give it the pleasant flavour character- istic of genuine Demerara ; refined sugar artificially coloured is, however, often substituted. Well- refined white sugar, from whatever source and of whatever form it may be, contains 99*8 to 99-9 per cent, of sucrose; the balance is chiefly water, only traces of ash and organic matter other than sucrose being pre- sent. The faint yellowish tint sometimes retained even by well- refined sugar is hidden by the addition of a small quantity of some blue colouring matter, usually ultramarine. Pure cane sugar has a dextro-rotatory power of a D = 66'5°. 2. Lactose or Milk Sugar, 0 l2 H 22 O n .H 2 O.— This may be regarded as a purely pharmaceutical preparation, the manufac- ture being, of course, insignificant compared with that of sucrose. STARCH SUGAR. 181 Milk contains about 5 per cent, of milk sugar, which can be extracted by the following method : — The bulk of the fat is removed by a separator for butter making, and the " separated " milk heated to from 75° to 85° C. = 167° to 185° F., and treated with 10 per cent, of milk of lime, whereby the residual fat and casein are precipitated. Saturation with CO., follows, as in the purification of beetroot juice (v.s.), and the purified liquid is con- centrated and the milk sugar crystallised. It may be purified by dissolution in water and precipitation by alcohol. Milk sugar is less soluble than cane sugar, requiring about 5 parts of cold water. It is dextro-rotatory, the normal rotation being a D = 52*5. A recently-prepared solution exhibits the phenomenon of bi-rotation, or of semi-rotation, according to the method of its formation ; on standing or heating, normal num- bers are obtained. 3. Maltose, C 12 H 22 O n .H 2 0, is prepared commercially in small amount. It is formed by the action of diastase on starch (see Brewing and Distilling, Vol. II., p. 197). If required ap- proximately pure, it is separated from the mass obtained by acting upon starch with malt, by extracting with alcohol of specific gravity 0*820, and allowing the solution to crystallise. It is slightly sweet, readily soluble in water, and its solution has a dextro-rotation of 140°. (B.) GLUCOSES. — 1. Dextrose {grape sugar), C 6 H 12 0 6 .H 2 0, occurs in the juice of ripe fruits, accompanied by its isomeride., lsevulose, and frequently by sucrose. The quantity varies from 10 to 15 per cent, in grapes to 1 to 4 per cent, in peaches and plums. Dextrose is very soluble in both cold and hot water, in this respect resembling cane sugar. It has about two-fifths the sweetening power of cane sugar. It has a rotatory power of a D = 52*5, and exhibits the phenomenon of bi-rotation. On heating to 170° C. = 338° F. it is converted into the anhydride glucosan, C 6 H 10 O 5 , the taste of which is scarcely sweet. At a higher temperature, 200° to 220° C. = 482° to 518° F., it yields caramel, much used as a colouring material for beer and other liquids. Caramel may also be prepared by heating cane sugar. Dextrose was at one time prepared from grapes, but now it is made by the hydrolysis of starch, the product being commercially called starch sugar. Starch Sugar. — The starch, which is usually that from potatoes or maize, is made into a cream with cold water, and run into boiling dilute sulphuric acid. Heating is continued until starch is no longer present, and the hydrolysis is considered complete. The main reaction ultimately obtained may be represented thus — (C 6 H 10 O s )„ + wH 2 0 = nC 6 H 12 0 6 , but it takes place in stages, and is far more complex than 182 SUGAR AND STARCH. appears from this equation.* Smoothness of conversion is favoured by using a dilute acid {e.g., 0-5 per cent.), but the pro- cess is then slower than with a more concentrated solution. A temperature above 100° 0. hastens the conversion, bub involves risk of caramelisation. Hydrochloric and oxalic acid may be used as inverting agents in place of sulphuric acid, but the last- named is generally employed on account of its cheapness and its •ease of removal subsequent to the conversion of the starch. After treatment with sulphuric acid, the liquor containing the dextrose is neutralised with chalk made into a cream with water, the calcium sulphate is separated by means of a filter press, and the nitrate decolorised by animal charcoal (p. 178), and concentrated in a vacuum pan. Care must be taken to eliminate any trace of alkali before concentration, as dextrose is readily attacked by alkaline substances. The starch sugar thus prepared contains about 70 per cent, of dextrose, 5 to 10 per cent, of dextrine, and 10 to 20 per cent, of water ; small quantities of maltose, ash, and indeterminate organic matter being also present. For most uses to which dextrose is put — e.g., as a source of alcohol in beer and other fermented liquors — it is not required pure. When pure dextrose is required, it has to be crystallised from methyl alcohol, as its separation from its mother liquor cannot be effected by means of a centrifugal machine in the manner adopted for sucrose, the crystallisation of which takes place more readily than does that of dextrose. Much crude dextrose is used in preparing sweetmeats and factitious honey. Lack of sweetness is compensated for by the addition of saccharine (q.v.). Dextrose is also used for making caramel, which is prepared by evaporating a slightly alkaline solution of starch sugar to dryness, and heating to 220° C. = 518° F., or to a higher tem- perature when a product soluble in strong alcohol is required, as in the colouring of spirits. Beer, vinegar and sauces are -commonly coloured by caramel obtained at the lower tempera- ture, as the need for solubility in alcohol does not then arise. 2. Leevulose (fruit sugar), C 6 H 12 O c , is the constant con- comitant of dextrose when sucrose is inverted (v.i.). It has a rotatory power of a D = - 98-8°, this being greater than that of dextrose, and in a contrary direction. Thus, it follows that invert sugar consisting of equal parts of dextrose and leevulose is lsevo-rotatory. Leevulose is somewhat sweeter than cane sugar. It has a small use medicinally for diabetic patients, and is pre- pared from invert sugar by taking advantage of the fact that the compound which it forms with lime, C 6 H 12 O 0 CaO.H 2 O, is sparingly soluble in water, whereas the corresponding deriva- tive of dextrose dissolves readily. It is also formed on the hy- drolysis of the starch-like carbohydrate inulin, (C 6 H 10 O 5 ) 6 . H 2 0. * Dextrin is an intermediate product, and a portion is usually present in the crude dextrose ultimately obtained. STARCH. 183 Invert sugar is prepared from sucrose by subjecting it to hydrolysis, the process being termed inversion, inasmuch as the dextro-rotation of the original sugar is changed into a lsevo- rotation which is approximately the algebraical sum of the rotations of dextrose and lsevulose. The hydrolysis of sucrose is readily effected by heating with a dilute acid. Even carbonic acid is capable of causing inversion. Invert sugar finds applica- tion in the preparation of sparkling wines, the after-fermentation taking place more easily with it than with sucrose (see Chamj^agne, Vol. II., p. 208). Honey consists essentially of invert sugar, though the nature of the saccharine material supplied to the bees influences the product. STARCH. Starch, (C 6 H 10 O 5 ) n , is a carbohydrate occurring abundantly in all plants. By far the greater part of the starch grown for consumption is used in the form in which it exists in cereals — i.e., associated with fat, nitrogenous matter and mineral con- stituents. A fraction, however, which is absolutely large though relatively insignificant, is extracted from starch-bearing plants in a state of approximate purity, and used for special purposes (v.i.). Starch being a constant product of vegetation, its profit- able extraction is naturally restricted to the treatment of a comparatively few plants exceptionally rich in starch, and yielding it with unusual ease. No rarity compels its winning from less facile sources. The composition of various typical starch-yielding materials is given in the following table : — Potato. Wheat. Maize. Rice. Per cent. Per cent. Per cent. Per cent. Starch, 20-7* 70-0 68-4 76-5 Woody fibre, 1-4 2-5 2-5 0-6 Nitrogenous matter, . 2-0 12 4 9-9 7-8 Fat, . . . . 0-2 1-7 4-6 0-9 Ash, . 10 1-8 1-5 10 Water, . . . 747 11-6 13-1 13-2 100-0 100-0 100-0 100-0 Although no chemical difference, greater than can be ascribed to the influence of accompanying impurities, exists between starch of different origins, yet the size and structure of starch granules from dissimilar plants are very various, each being characteristic of the source whence the starch has been derived. Thus the average diameter of the starch granule of the arrow- * When calculated on the substance containing 10 to 12 per cent, of water, the content is similar to that of the other materials quoted. 184 SUGAR AND STARCH. root is 0*140 mm., while that of the starch granule of rice is 0*022 mm. The differentiation of starches by size and shape of granule belongs to the province of analytical chemistry. Manufacture of Starch. — The winning of starch from starch- bearing plants is mainly a mechanical process, consisting in comminuting the raw material, washing out the starch by sus- pension in water, and purifying it by levigation. Certain chemical principles are, however, involved, neglect of which is greatly detrimental to economy of working. Potato starch serves as an example of a starch obtained by methods almost wholly mechanical. Potatoes are grown for starch making on the Continent, especially in Germany. They are liable to disease, which greatly diminishes the content of starch, and when stored tend to lose starch by vital oxidation, particularly if sprouting occur. When exposed to frost, a con- version of starch into sugar takes place, the well-known sweet flavour of a frost-bitten potato being due thereto. A rough works test of the content of starch is usually made by taking the specific gravity of 10 to 12 lbs. of potatoes, the specific gravity rising with the percentage of starch present, being about 1-08 with 14 per cent, of starch, and 1*14 with 27 per cent. The potatoes are well washed, and then pulped in a rasping machine, which consists of a rotating horizontal cylinder furnished with internal serrated blades, against which the potatoes are pressed. It is important that the cells containing the starch should be torn open, as otherwise the starch is not extracted in the subse- quent processes. Even with the best modern raspers a loss of 20 to 25 per cent, of the starch is usually incurred. (A portion of this retained starch may be recovered by a second rasping process, or by grinding the rasped product after the bulk of the starch has been removed.) The pulp is washed upon brass wire sieves, and the starch is carried off in suspension in the water, the larger fibrous debris of the cells of the potato being left on the sieves. The liquid contains in suspension, besides starch, any fine sand from the potatoes and the finer debris of the potato cells, and in solution, salts, albuminous and non-nitrogenous extractive matter. It is run into collecting vats, well stirred,, and run off, leaving the sand; thence it passes to settlers, in which it is allowed to remain for some hours. The layer firsV deposited is nearly pure starch, while upper and later layers contain such fibrous organic matter as has passed through the sieves during the washing of the pulp. The lower layer is white^ whilst the upper is greyish in tint and can be scraped off and re washed. Separation is better effected by centrifugal machines, which both drain the water off and segregate the starch and fibre in the manner of an ordinary centrifugal separator. The "green" starch, in the form of a slurry or paste, containing from 25 to 50 per cent, of water, according to the method of separation em- RICE STARCH. 185 ployed, is dried, first at a low temperature to prevent its gela- tinisation, and finally at 60° to 70° C. = 140° to 158° F. As put on the market in an air-dried state it contains 16 to 18 per cent, of water. A large proportion of commercial potato starch is not dried, but used at once in the "green" state for conversion into starch sugar by hydrolysis, in the manner described above (see Starch Sugar, Yol. II., p. 181). The residue left from the extraction of the starch still contains about 66 per cent, of its total dry weight of starch, together with small quantities of nitrogenous matter, and serves as a fodder of indifferent quality. The water from which the starch has been deposited in the washing process contains a trifling amount of mineral manurial constituents, such as potash and phosphoric acid, and some nitrogenous matter; it may, therefore, be utilised where irrigation is practicable. Diseased potatoes are sometimes worked up for their starch by being subjected to a preliminary process of fermentation, similar to that described below for the production of wheat starch (q.v.). Wheat Starch. — Starch may be prepared from wheat, either by opening up the grains of wheat by a spontaneous fermentative or putrefactive action, or by simple washing aided by treatment with caustic soda. According to the first method, the wheat is allowed to swell in water and is then crushed in bags, the starch being thus extruded and carried away by a stream of water. The water, containing starch in suspension, is run into tanks, where it remains for a fortnight or three weeks, during which time fermentation sets in at the expense of the gluten, which has accompanied the starch when it was first washed out of the grain. If the fermentation be controlled so that the putrefactive stage is not reached, the starch is but little affected, and can be separated and purified from gluten by systematic washing, in the manner already described for potato starch. The green starch is removed and dried in the usual manner. Fermentation for removing the gluten can be dispensed with by using as a solvent for the gluten caustic soda of specific gravity 1*013, in such quantity as to keep the liquid always slightly alkaline. That portion of the gluten which is not dis- solved by the caustic soda is removed by a fine-meshed sieve, while the portion in solution is washed away or precipitated as described under Rice starch. The yield of starch of good quality is higher than that obtained in the more primitive processes. The irregular sticks, roughly rectangular in section, which are generally preferred by the domestic consumer of starch, can be- prepared by tightly wrapping a moist cake of starch in paper and drying the confined mass. Contraction sets in with approximate regularity, yielding sticks of the form familiar in the laundry. Rice Starch. — The rice plant (Oryza sativa) may contain as 186 SUGAR AND STARCH. much as 80 per cent, of starch, and is thus a richer raw material than are potatoes or wheat, but on account of the refractory character of the gluten associated with the starch, the liberation of the starch granules needs to be effected by treatment with a dilute alkaline solution. Unless the solution be kept weak, gelatinisation of the starch may occur, and acids are inconvenient for opening up the grain, as their use makes that of metal machinery and fittings unsuitable. The raw material used for the manufacture of rice starch generally consists of the waste and broken grains obtained as a bye-product in dressing rice for consumption as a food. Typical material of this class contains about 12 per cent, of water, 76 per cent, of starch, 9 per cent, of albuminous matter, and small quantities of fat, crude fibre, ash, and carbohydrates other than starch itself. This material is placed in tanks provided with perforated false bottoms, and treated with caustic soda of about 1 per cent, strength. The liquor is run off after about eighteen hours, and the rice again treated with a fresh portion of caustic soda solution for a further period of twelve hours. It is then ground to the utmost possible fineness, the mass being ground while wet with the same dilute caustic soda solution. The milky liquid is then passed through sieves which retain a good deal of the swollen gluten, and after- wards run into tanks and allowed to settle, the starch being ultimately washed in a manner similar to that adopted with other raw materials (v.s.). The gluten contained in the washing waters can be precipitated by acidifying them, and used as a fodder. Maize Starch. — According to Archbold an average sample of maize contains 11 per cent, of water, 55 per cent, of starch, 16 per cent, of woody fibre, 8 per cent, of albuminous matter, small quantities of carbohydrates other than starch, and nearly 5 per cent, of fat, and an equal quantity of ash. The large proportion of non-starchy materials, notably fat and gluten, renders the process of extraction of the starch somewhat complex. The manufacture is chiefly conducted in the United States, the process in use being known as the "sweet" process, the phrase thus differentiating it from the fermentative process for wheat, which is " sour." The preliminary treatment of the grain in- cludes the removal of the germ, which is of considerable size, and disproportionately ricli in fat. The maize is steeped in soft water for about a week, until, indeed, incipient purification occurs, and the maize is sufficiently soft to grind. At this stage sulphuretted hydrogen is evolved from the maize, and in order to avoid this unpleasant product the steeping process is some- times expedited by working at as high a temperature as 140° F. = 60° C, and allowing a continuous flow of water to pass through the softening tanks. A large quantity of matter is thus dissolved, and is generally run away as waste. The softened grain is finely DEXTRIN. 187 ground, and the starch separated from the residual gluten and woody fibre by passage through sieves. The starch passing in suspension through these sieves is run into a vat, allowed to settle, and treated with caustic soda in dilute solution. Some of the gluten is by this means dissolved, while another portion is precipitated, the starch being freed from both by the usual processes of subsidence and elutriation. Care has to be taken to keep the liquid in the settling vats cooled, lest fermentation set in. The starch is finally allowed to settle, and is dried in the manner already mentioned. Various starches are prepared for eating from special plants, such as the arrowroot (Maranta arundinacea), the root known as cassava or manioc, and the pith of various palms, the finished product of which is known as sago. Save for greater care in preparation, designed particularly to obtain a white product, the preparation of these edible starches differs in no essential respect from that of those which have been already dealt with. The slightly yellow tint of ordinary starch is generally hidden by the addition of a small quantity of a blue colouring matter, such as ultramarine. The uses of starch may be divided into two classes. The first class includes all those uses which depend upon its chemical status as a carbohydrate. The preparation of starch sugar, and the consumption of starch as a food are the chief examples of this class. The second main class of uses to which starch is put, depends upon the fact that starch pro- ducts are pre-eminently colloidal, their solutions having a high viscosity and considerable adhesiveness. These qualities are taken advantage of in the dressing of textile materials, and in thickening colouring matters for calico-printing. Starch itself is incapable of acting as a stiffening or glutinous ma- terial, because it is perfectly insoluble in water or any other solvent. When heated with water, however, the starch granules swell and yield a gelatinous mass known as starch paste. A small quantity of starch thus heated to the point at which the swelling of the granules occurs, is capable of forming a coherent jelly with a large quantity of water, the phenomenon being apparently identical with that observed in the case of gelatin. The chief educts of starch which are of commercial importance may be conveniently dealt with as follows : — Dextrin or Dextrine {British Gum). — The term dextrin is ap- plied somewhat loosely to the earlier products of the hydrolysis of starch. The sugar yielded by the action of diastase on starch is maltose (p. 181), and at one time dextrin was supposed to be a single substance, intermediate in composition and chemical locus between starch and maltose. It is now, however, generally con- ceded that dextrin and maltose are produced concomitantly from the hydrolysis of starch, and that at least two dextrins are to be distinguished ; they are characterised by their behaviour with 188 SUGAR AND STARCH. iodine, one giving no colouration, while the product of the other is red (see further, p. 197). Commercially, dextrins are not classified in this manner, but are differentiated by their respective methods of preparation. The first method of manu- facture consists in roasting dry starch at a temperature of 220° to 250° C. - 428° to 482° F., either over a direct fire, or, better, in an oil bath, or by superheated steam. Revolving roasters are often used. The process is continued until the starch has acquired a brownish colour and has become soluble in water. The second method is carried out by moisten- ing the starch with about 1 per cent, of hydrochloric or nitric acid, and slowly heating it in open dishes until a temperature of about 100° C. = 212° F. has been reached, and the acid has been evaporated. The sugar accompanying dextrin made by the use of an acid is dextrose. Dextrin made in this manner is lighter in colour than that obtained by direct roasting, and is thus better fitted for certain uses. On the other hand, any residual trace of acid is an objection for many uses. A special grade of dextrin of light colour, and having the translucent appearance of gum arabic, is also manufactured as a substitute for natural gum. The chief uses of dextrin are for purposes in which its vis- cosity and adhesiveness are of value — e.g., as a gum substitute (mentioned above), for stiffening textile materials, for giving a gloss to paper and cardboard, and producing a " head " on beer and aerated liquids. FERMENTATION. 189 CHAPTER IX. BREWING AND DISTILLING. I. FERMENTATION. — General Principles.— The term fer- mentation originally meant an appearance of boiling due to the escape of gas from a liquid, but it has acquired a wider sig- nificance, and includes the various chemical changes induced by the presence of some nitrogenous organic product or micro- organism, which is called a ferment. This class of chemical change is essentially characterised by the fact that a very large amount of material is affected by an inconsiderable quantity of the ferment. Ferments are of two kinds, unorganised and or- ganised. The former are definite chemical compounds, of the character of albuminoids, and are not living organisms ; they produce changes which are, as a rule, simpler in character than those caused by organised ferments, and are often of the nature of the change called hydrolysis, which is also brought about by such agents as dilute acids. Unorganised ferments are termed enzymes. An instance of the action of an enzyme is afforded by the con- version of cane sugar (which rotates the plane of polarisation to the right), by means of the enzyme invertase, into a mixture of dextrose and laevulose (which turns the plane of polarisation to the left), the process being accompanied by the assimilation of water (Hydrolysis, p. 183). In the case of the organised ferments, the decomposition is more profound, and up to the present appears to be the direct effect of the life of the organism, inasmuch as it has hitherto not been dissociated from the living cell. The change is, however, supposed by some to be due to the action of an enzyme which has been formed by the living cell. The best example of such decomposition is that afforded by yeast, which is more fully dis- cussed later. The ordinary organised ferments are generally classified into moulds or fungi, saccharomycetes or yeasts, and ■schizomycetes or bacteria. The effect of the first of these is illus- trated by the fermentation of alcohol into acetic acid in the brewing of vinegar, that of the second by the fermentation of sugar into alcohol, that of the third by the fermentation of milk sugar into lactic acid (q.v.). It must be understood that the very large variety of organised ferments renders it difficult to identify 190 BREWING AND DISTILLING. any one species with any particular fermentation, several being usually present in any fermentable liquid. Moreover, inasmuch as these microscopic organisms can be transmitted in the floating dust of the air, a fermenting liquid containing a single kind speedily becomes contaminated with others, unless the air having access to it be filtered. This doubtless serves to explain why special districts produce special fermentations. Certain organ- ised ferments flourish in air and are killed by its exclusion ; they are, in consequence, called aerobic, while others having the re- verse properties are termed anaerobic. This question belongs to the domain of biology rather than to that of chemistry. II. BEER. — Beer may be considered as a dilute solution of alcohol and albuminous matter, obtained by the action of yeast on saccharine material, flavoured by an innocuous bitter principle. (A.) RAW MATERIALS. — 1. Amylaceous and Sacchar- ine Matter. — Beer was originally made by malting barley and fermenting its aqueous extract. The substance in barley capable of yielding alcohol is starch, which, however, is not directly fermentable, but has to be converted into sugar ; this is effected by malting. When this fact was fully realised, it became cus- tomary to economise barley by substituting sugar from other sources. Moreover, inasmuch as more of the active principle (diastase) which converts the starch into sugar, is produced during malting than is necessary for the conversion of the starch in the barley itself, more amylaceous matter may be added in the form of unmalted barley, and thus part of the expense of malting saved. Consequently, brewing no longer consists merely in fermenting the aqueous extract of malt. Malt. — For satisfactory malting a well-developed barley is essential, as only such has a high content of starch, and will ger- minate well. Good barley has the following characteristics : — It is light-yellow in colour, the grains are dry, even in size and have thin husks, and it is free from bacteria and moulds. Malting is generally carried out as a separate trade from brewing, and consists of the following main processes : — (1) Steeping. — The barley is slowly run into a cistern of iron or cement filled with water, which must be clean and free from organic impurity ; the sound grains sink to the bottom, while the unsound grains (together with dirt and dust) can be skimmed off the surface and used as cattle food. The water is changed every twelve to twenty-four hours, the process lasting altogether forty to seventy hours. The object of the process is to supply sufficient water for the subsequent germination. Frequently the barley, when taken out of steep, is placed in a couch or heap to keep in the heat of germination, and thus aid the process. (2) Flooring.— The steeped grain is spread on the malting floor, which is preferably of concrete, to a depth of 3 to 12 inches, according to the temperature, which should not exceed 12* MALT. 191 C. = 54° F. On this account malting is difficult to practise in the summer. After the first twenty-four hours the grain is " ploughed," or turned over, twice a day for two or three days. When the acrospire or plumule of the grain has grown to a length of about three-quarters of the length of the grain itself, the rootlet is about twice the length of the grain, and the grain itself has attained a proper degree of " mealiness," this portion of the process is completed. During this operation, the grain is kept moist by periodical sprinklings with water. An improved method of malting is that known as pneumatic malting, inasmuch as better control over the supply of air and moisture to the germinating grain is afforded. On the Saladill system, which may be taken as typical, the steeped barley is run into rectangular iron germinating cases with perforated false bottoms, where it is allowed to heat as in a couch. When it is desirable to check the heating, air which has been forced over cylinders that are kept wet is driven under the false bottom. Oxygen is thus supplied to the grain, carbon dioxide (a product of the vital processes) is removed, and the temperature is regul- ated. Subsequently, the grain is stirred by means of agitators. When germination has reached the proper point, the grain is elevated to the malt kiln. (3) Drying. — The germinated barley is called green malt, and contains the maximum amount of diastase, so that if this alone were needed the grain would be ready for the brewer ; but a desiccation at a high temperature is essential, both for arresting the germination and for killing any mould or fungoid growths that may have appeared, and also for developing certain changes which impart flavour to the resulting beer. Dried malt can also be stored, and is more easily ground than green malt. The temperature of the drying kiln determines whether the malt shall be "pale," "medium," or " high-dried," each kind being used according to the class of beer to be produced. The malt is spread out to a depth of 8 to 10 inches on the floor, which consists of a series of perforated earthenware plates built in a kiln of square section, and heated by a, number of baskets of live coke suspended beneath. Each kiln may contain several floors, two being a usual number, and the malt is loaded first on to the top floor, where it is dried at 120° F. = 49° C. until some 90 per cent, of the moisture is gone, then dropped through on to the lower floor, where it is dried at 180° to 190° F. - 82° to 88° 0. This applies to pale malts. Medium and high-dried malts are finished at 200° to 230° F. = 93° to 110° 0. (4) Screening.— The rootlets of the dried malt are removed by being trodden by men, and subsequently passed over a " water-fall " malt screen, which also removes dust. The finished malt is stored in bins, due attention being paid to the exclusion of moisture. Malt which has absorbed water, or become " slack," yields an unsatis- factory beer, and is generally re-dried before use. W2 BREWING AND DISTILLING. The chemistry of the production of green malt resolves itself Into the chemistry of germination. The proximate constituents of barley are — (1) Water; (2) carbohydrates,* including starch as the main constituent (39 to 57 per cent.), dextrin, a-amylan (2 to 4 per cent.), gum (3 per cent.), cane sugar (1*5 per cent.), ex- tractives soluble in water, and cellulose the largest constituent of the woody fibre ; (3) fat; (4) albuminoids, including mucedin, fibrin, casein, and albumin, together with the ferment diastase ; (5) ash, consisting of the bases potash, soda, lime, magnesia, ferric oxide, and the acid-radicles of phosphoric, sulphuric, silicic acids and chlorine. The proportions of these constituents are shown by the following analysis, beside which is given one of pale malt : — Barley. Malt. Per cent. Per cent. Water, 14*05 5-83 Carbohydrates, .... 63-66t 65-38J Woodv fibre, ..... 7-09 11-57 Fat, 2 05 1-65 Albuminoids, ..... 10-58 13-09 Ash, . . 2-57 2-60 100-00 100-12 Barley for brewing should be rich in carbohydrates and poor in albuminoids, of which a fine malting barley should not contain more than 8 to 9 per cent. The germination of barley produces a change in the nature of the albuminoids and a consequent change in the carbohydrates. The diastase naturally present in barley differs from that produced from the albuminoids during germination in that it cannot liquefy starch paste, but it resembles the latter in respect of its power to convert starch which has been already liquefied or rendered soluble, into maltose and dextrin. The diastase of malt is thus of two kinds, that which existed in the barley, and that produced by germination, and it is the production of the latter which is the object of malting, for it is able to transform the starch directly into maltose and dextrin. The nature of the change that produces this substance is not well understood. The quantity produced is relatively small — about 2 per cent. — and is measured by the "diastatic power" of a watery extract of the malt. By this term is meant the amount of maltose pro- * These include carbohydrates of the pentose type — general formula C5H10O5, or some multiple of this. These bodies are not fermentable by yeast, and to a large extent remain in the "brewer's grains " (7. v.). + Mainly starch. X About one-third of this is fermentable sugar. MALT ADJUNCTS. 193 •duced by the action of the malt extract on starch, this being measured by the reducing effect of the resulting solution upon Fehling solution (an alkaline solution of cupric tartrate). Thus, the diastatic power of a malt extract is said to be equal to 100 when 0*1 c.c. of the extract of 25 grms. of malt in 500 c.c. of water converts sufficient starch paste into maltose to reduce 5 c.c. of Fehling solution (Lintner's standard). Diastase may be isolated from malt by extraction with 10 to 30 per cent, alcohol, precipitation of the clear filtrate after the elapse of eight hours with absolute alcohol, dissolution of the precipitate in water and re-precipitation with alcohol. When thus prepared it is a white amorphous substance, not perfectly definite in composition, but containing approximately — C, 44-33 per cent. H, 6-98 % 8-92 S, 1-07 O, 32-91 Ash, 4-79 100-00 Although diastase forms a small quantity of sugar from starch in the grain itself, yet its chief action takes place in aqueous solution during mashing (q.v.). The production of "mealiness" in malt, which has been attributed to the change of the starch, has been shown by Brown and Morris to be due to the dis- appearance of the cell-walls of the starch granules. During malting a small portion of the starch is completely burnt to H 2 0 and C0 2 , a rise of temperature resulting. The action of diastase is weakened by heating to G5° to 70° 0. = 149° to 158° F., or by separation from the grain by treatment involving precipitation with alcohol, as described above. Its solutions are partly coagulated at 75° C. = 167° F. (like those of albumin), and its activity diminished. Its power is not, however, wholly removed even by drying at 100° C. = 212° F. Antiseptics, such as many metallic salts and bodies like salicylic acid, also restrain its action, diastase being similar in this respect to organised ferments. Malt Adjuncts. — As has been already mentioned, the maximum effect is obtained from the diastase of malt by causing it to saccharify other starch than that of its parent barley. Such are the starches of maize, rice, and, for " white beer," wheat. It is more usual to add sugars to the wort (q.v.), in which they are fermented together with the maltose of the malt. The sugars generally employed are cane sugar, invert sugar — which is most largely used — and glucose. Refined cane sugar has to be inverted by the yeast before fermentation, and to a certain extent weakens 13 194 BREWING AND DISTILLING. the yeast, favouring the production of lactic acid, so that it is preferable to invert the sugar first. Concerning the production of these sugars see Chap. VIII. of this volume. 2. Hops and Bitter Principles. — Of these, the bitter prin- ciple of hops is the chief and only legitimate bitter used in beer. Hops are the female flower of the plant, Humulus lupulus ; the male flowers being useless, the plant bearing them is not culti- vated. The proximate constituents of hops are fibrous matter (woody fibre), nitrogenous substances, sugars, gums, lupulin or "hop meal," tannin, and mineral matter. The constituents that are of importance for brewing are the lupulin and tannin. The former is a yellow resinous dust that can be separated from the hop flowers by sifting, and consists of glands which contain the essential oils and bitter principles, such as resinous alkaloids. It is technically known as " hop flower" or " condition," and is undoubtedly the essentially useful portion. In quantity it ranges from 5-3 to 17 5 per cent., and in the best hops should approximate to the latter number. The essential oil amounts to 025 to 035 per cent., the quantity diminishing as the age of the hop increases. The aroma of the hop is apparently due to these oils. The chief bitter principle of the hop is the resinified product of lupulic acid. Lupulic acid is not in itself bitter, but the resins produced by its oxidation have a strong bitter taste. This and the other resins which are present in hops appear to have an antiseptic action which hinders secondary fermentations, and they are thus useful in preserving the beer. Concerning the alkaloids but little is known ; hope'ine, choline and traces of morphine are said to be present. The tannin in hops varies from 1*5 to 5 per cent. ; it is doubtless useful in the copper (q.v.) for precipitating albuminous matter. The hops, after picking, are dried in a kiln resembling a malt kiln, and frequently il sulphured " by burning 1 to 2 per cent, of sulphur in the kiln, to bleach them should they be of a bad colour. In judging such hops allowance must be made for the possible defects thus concealed, the colour of the hops being a considerable cri- terion of their value. Where hops are added to the beer in cask, the sulphur dioxide is liable to become reduced to sulphuretted hydrogen, producing "stench." The practice of sulphuring is easily detected by analysis. The sprinkling of flowers of sulphur on the hops during their growth to destroy parasites is less ob- jectionable. Hop substitutes are used for the sake of cheapness. Those commonly employed are gentian, camomile and quassia. Their use is illegitimate. 3. Water. — The water used both in the preparation of malt and in actual brewing should be free from contamination with organic matter and from the micro-organisms that occur in im- pure water. The next most important consideration in regard WATER FOR BREWING. 195 to the water is the quantity and nature of the mineral matter dissolved in it. "When this consists largely of gypsum (calcium, sulphate), the water is well adapted for the production of pale ale, and it is on this account that the Burton water is famous. Those- waters which contain too little gypsum for brewing pale ale are successfully applied for the production of mild ale. Waters con- taining no gypsum, but rich in alkali sulphates and carbonates, are adapted for producing black beers. The following analyses- illustrate these differences : — Grains per Gallon. Pale Ale. Mild Ale. Black Beer (Stout). CaS0 4 , .... 40 25 0 MgS0 4 , .... 8 5 0 CaC0 3 , .... 15 15 3 MgC0 3 , .... 1-5 K 2 S0 4 , .... 10 5 7 k;co 3 , .... 9-5 Na 2 C0 3 , .... 6 5 MgCl 2 , .... 5 3 NaCl, .... 30 20 15* Si0 2 , .... 05 The mild ale type of water is a fairly common one, so that- such beers are brewed in many districts. The London deep-well water is of the third type, and produces good black beers; but since the knowledge of the characteristics necessary in waters for definite beers has been acquired, the waters of the second and third type have been transformed into waters of the first- class by the addition of the requisite amount of gypsum. To change waters of the third type into those of the second, gypsum and kainit* are added. To produce water of the first class from a neutral water (one containing no sodium carbonate), it is only necessary to add calcium sulphate to the water (" burtonising "),, which can be conveniently effected by running the water through a wooden vat provided with a false bottom and packed with small lumps of gypsum, care being taken that the gypsum dissolved by the water shall fee regular in amount. It is frequently necessary to add more magnesium sulphate and calcium chloride. In treating a water of class three, the alkaline carbonates must be removed by the addition of calcium chloride, which forms calcium carbon- ate and sodium chloride. The subsequent treatment is the same as for class two. The influence of the salts dissolved in a water in the brewing process will be referred to on p. 199. * A mineral composed of potassium sulphate, magnesium sulphate, mag- nesium chloride and water, frequently mixed with sodium chloride. 196 BREWING AND DISTILLING. 4. Yeast. — This is more conveniently dealt with under the head of processes of beer manufacture (see also Fermentation, Vol. II., p. 189). (B.) PROCESSES. — 1. Mashing.— The first step in the preparation of a beer is the production of the liquor to be fer- mented, called the wort. For this purpose the malt is first ground between smooth steel rollers, the object being to crush but not to powder the grain, so that the meal may be readily sepa- rated from the husk. The ground malt or grist falls from the rollers into a grist case, traversing in its passage a magnetic separator, which removes particles of iron incidentally present. The grist then falls into a cylindrical vessel set horizontally, where it meets the water previously heated to 160° to 170° F. = 71° to 77° C, and is thoroughly mixed with the water by means of an agitator consisting of a horizontal shaft carrying spokes which just clear the walls of the cylinder. This apparatus is known as a Steel's masher. From this vessel the malt passes to the mash tun, which may be 18 feet in diameter by 8 feet deep, and may serve for the mashing of 100 quarters of malt ; it is an oaken vessel provided with a perforated false bottom and with a vertical shaft actuating arms carrying rakes which keep the contents of the tun in motion. The same shaft serves to carry the sparger, which consists of a set of perforated radial arms through which water is supplied for washing the malt (sparging). The mash tun is fitted with "underlets" for the admission of water below the false bottom. A number of draw-off pipes are also provided. When all the grist has entered the tun, the residue from the Steel's masher is washed into the tun, and the temperature of the mash ascertained. Should this be below 140° F. = 60° C, hot water is introduced through the underlet to bring it to between 140° to 150° F. = 60° to 66° C. The tun is covered, and the mash allowed to stand for about two hours. Should the starch of the malt be difficult to liquefy and saccharify, a second mashing is made by the admission of fresh water through the underlet. The wort is drawn off almost completely, and the exhaustion of the malt finished by sparging with hot water through the pipes referred to above. This process is continued until the specific gravity of the wort is l - 005. According to the practice of some continental breweries, a portion of the malt is boiled with water and returned to the mash tun, this process being twice repeated, instead of infusing the malt with hot water, as described above. In the process of mashing, the diastase of the malt converts the starch into maltose and dextrin. Inasmuch as ordinary starch is insoluble in water, it must first be rendered soluble before it can be hydrolysecl. This is effected by the particular form of diastase characteristic of malt, as distinct from that of barley. The soluble starch is then converted into malto- dextrin BOILING WORT FOR BEER. 197 and erythro- dextrin. An equation representing this change is — (1) 5(3C 12 H 20 O 10 ) + H 2 0 = j ^ H ^°" + 4(3C 19 H 20 O 10 ). Soluble starch. Malto-dextrin. Erythro-dextrin. The next action is the hydrolysis of malto-dextrin into maltose — <2> {£5ft + 2H 2 0 = 3C lAA , Malto-dextrin. Maltose. The erythro-dextrin undergoes a change by assimilation of water into malto-dextrin and achroo- dextrin — (3) 4(3C 12 H 20 O 10 ) + H 2 0= {^^o + 3 ( 3C ^ H 2oOio). Erythro-dextrin.* Malto-dextrin. t Achroo-dextrin.* The malto-dextrin is converted into maltose as in equation (2). The achroo-dextrin is further converted into malto-dextrin by the assimilation of water, and this in turn into maltose. The final products, under ordinary conditions of mashing, appear to be maltose and an achroo-dextrin, 3C 12 H. 70 O ]0 , less complex in grouping than that produced in the earlier stages. The precise reactions occurring during mashing are regulated by the tem- perature prevailing and the rapidity with which the temperature is raised. As soon as the temperature rises to 140° F. = 60° C, the action of the diastase begins to be checked, and this restric- tion means that much of the malto-dextrin suffers no further alteration. Such as remains is not directly fermented by the yeast in the fermenting vat (q.v.), but suffers fermentation in the cask, producing beneficial effects on the beer. The propor- tion of starch converted into maltose is about four-fifths of the whole, the rest being present as dextrin. 2. Boiling. — The wort, cleared by running through the spent malt (brewer's grains), flows from the mash tun either directly into the copper, or into an intermediate vessel (" underback "), in which, however, it must not remain long enough for its tem- perature to fall appreciably. While the copper is being filled the fires are lighted, so that the temperature may be kept up, and the hops are added in proportion, varying from 10 to 20 lbs. per quarter of malt in the wort, according to the character of beer to be produced, and if any other saccharine matter than malt is to be added it is also introduced at this stage. The hops are added pari passu with the malt, a final dose being used just before the completion of the boiling, so that the whole of the aroma is not lost by evaporation. The boiling generally lasts * Erythro-dextrin and achroo-dextrin are so called because they give red and colourless products respectively when treated with iodine. t This composition must be taken only as representative of the class of bodies known as malto-dextrins, as their exact composition varies with the conditions of formation. 198 BREWING AND DISTILLING. from two to three hours, and during the process all diastatic action is stopped, and a. large proportion of soluble albuminoids becomes coagulated and precipitated. The proportion of maltose and dextrin in the wort is determined by ascertaining the specific rotatory power by the polarimeter* at various stages of the boiling. The wort is generally boiled on an open fire, but sometimes by closed steam, which must be of high pressure to give a sufficient temperature to boil thoroughly, and to sterilise the wort in order that the beer may be sound. 3. Cooling. — The wort from the coppers is run into " hop- backs,'' in which it is drained from the exhausted hops, these l)eing afterwards sparged to remove the adhering wort. It is then cooled by exposure to a good draught in shallow tanks (coolers), and then passed over vertical refrigerators, consisting- of copper pipes through which water is circulated. In ordinary English practice the temperature has to be reduced to 5S° to 60° P. = 14° to 16° C. in the course of six hours for the whole of one brewing. Cold spring or well w r ater suffices for this. In Germany, where bottom fermentation (q.v.) is in vogue, the tem- perature is lowered to 5° C. = 41° F., and for this purpose the lower parts of the refrigerators are supplied with water, the temperature of which has been reduced to near 0° C. — 32° F. "by means of freezing machines. During cooling not only is the temperature lowered to the point suitable for fermenta- tion, but the wort is also aerated, and a certain amount of albuminous matter (known as " cooler grounds ") deposited. While the hot wort is cooling in the coolers — as distinct from the refrigerators — the oxygen which is taken up chemically changes some of the resins from the hops, causing them to coagulate into particles which sink readily and thus carry down suspended matter, clarifying the wort. On the refrigerators the air is dissolved and serves for the respiration of the yeast in the subsequent fermentation. The infection of the wort with bacteria and wild types of yeast, derived from the floating matter in the air, during cooling, is to be avoided as much as possible, and it has been proposed to supply sterilised air to the refrigerating rooms. The average composition of the air-dried solid matter in wort from medium dried malt, may be taken as represented by the following figures : — Per cent. Maltose, 57'01 Dextrin, 14 '92 Lactic acid, ....... 0*56 Soluble albuminoids, . . . ' . . . 2*09 Colouring matter, ash, <&c, . . . . 1"49 Total dry solids, . . . . 76*07 * For the coustruction and use of the instrument, see Allen's Commercial Organic Analysis, vol. i., pp. 16, 194. FERMENTATION OF WORT FOR BEER. 199 The influence of the water used for mashing and boiling (q.v.) is very considerable. The calcium and magnesium carbonates in the water are, to a certain extent, thrown out of solution during the preliminary heating, and, remaining in suspension, effect the neutralisation of sundry organic acids (such as lactic) which are present in the malt. The presence of calcium sulphate is beneficial in causing the precipitate of albuminous matter which is produced during boiling, to take a flocculent instead of a, pulverulent form, and thereby to be more easily separable. The objection to alkali carbonates in a water for mild or pale ale is that injurious nitrogenous matters are liable to be dissolved by their aid. Much colouring matter is extracted from the malt by alkaline waters, and this is the reason of their use for black beer. Certain excessively bitter resins from the hops are also ex- tracted by alkaline waters. Sodium chloride is a very beneficial constituent of a brewing water, exercising an antiseptic action during fermentation, and influencing the flavour of the finished product. 4. Fermentation of the Wort. — The cooled wort is run into fermenting tuns,* which are large wooden vats provided with coils of pipes (attemperators) through which either warmed or cooled water may be circulated to regulate the temperature of the wort. When a portion of the wort has been run in, the yeast is added, in the proportion of 1 to 4 lbs. per barrel of wort, the quantity depending upon the quality of beer to be brewed, strong beer needing most yeast. This process is known as " pitching " the wort. The rest of the wort is then run in, and the temperature (which is to begin with 60° F. = 16° 0.) allowed to rise by the action of the yeast to about 70° F. = 21° C, which it should attain at the rate of about 1° F. in 6 hours. This rate must be maintained by the use of the attemperators. The surface of the wort during fermentation becomes covered with a froth consisting of yeast, in " top fermentation " according to English practice, blown up with carbon dioxide. The appearance and motion of the froth serve the brewer as an index of the progress of the fermentation. As the conversion of the maltose into alcohol and carbon dioxide proceeds, the specific gravity of the liquor falls, and the wort is said to " attenuate." When the above-mentioned temperature (70° F.) has been reached, the attenuation will generally be about one-half — i.e., a wort of specific gravity 1*050 will have become attenuated to 1*025. The closest attention on the part of the brewer is required during the process of fermentation, temperature and specific gravity having to be carefully noted. Fermentation is generally * Owing to excise regulations in this country, the wort is first received in a collecting vessel until the volume and specific gravity have been ascertained by an excise officer. 200 BREWING AND DISTILLING. complete in two or three days. In making lager beer according to German practice, " bottom fermentation " is employed, the* name implying that the yeast grows at the bottom of the fermenting tun. For the proper execution of this process, a temperature of 5° to 6° 0. = 41° to 43° F. should not be exceeded, on which account the fermentation is either conducted in cellars or in rooms artificially cooled, whereby the manu- facture can be continued throughout the year. The general principles of fermentation have been already explained (p. 189). The conversion of sugar into alcohol is effected 1 by organised ferments, of which the Saccharomycetes are the most important. The best known of these are those composing the usually complex mixture called yeast, and the ginger-beer plants which has recently been shown by Marshall Ward to be a symbiotic association of a yeast and a bacterium. The alcoholic fermentation induced by this plant appears to be the work of the yeast, but this is aided by the bacterium, the former being enabled to carry the fermentation further by reason of the removal of inhibiting products by the bacterium. The aid thus afforded is what is implied by the term symbiosis, for all yeasts are ultimately killed by their own products. Yeasts are single- celled vegetable organisms, which multiply either by budding (gemmation) or fission (formation of ascospores ; endogenous division). Of these two methods of reproduction that by gemma- tion appears to be normal ; if nourishment be scanty, ascospores are formed. Like other plants, yeast must be provided with the mineral matter constituting its ash. This is found in sufficient quantity in ordinary wort, in which is a proportion of the mineral constituents of the barley whence it is derived. The wort also contains much sugar and some nitrogenous matter, and is a suitable medium for the rapid growth of the yeast. The com- position of yeast (bottom yeast) is shown by the following analysis : — Per cent. Cellulose and mucilage, ...... 37 Albuminoids, 36 , , soluble in alcohol, .... 9 Peptones, 2 Fat, 5 Extractive matters (leucin, glycerol), ... 4 Ash, 7 100 These results refer to the dried material. Fresh yeast contains from 40 to 80 per cent, of water. The composition of the ash differs slightly, according as the yeast is. for top or bottom fermentation. CHEMISTRY OP FERMENTATION. 201 Top. Bottom. K 2 0, 38-8 28-3 CaO, 10 4 3 MgO, 6 0 8-1 P 2 0 5 , 53-9 59-4 Si0 2 , Trace 0 The rationale of the conversion of sugar into alcohol by yeast is still uncertain. The explanation most commonly accepted rests on the assumption that sugar is broken down into alcohol and C0 2 in the yeast cell ; the other having most claims to con- sideration consists in the view that the decomposition of the sugar is effected by molecular vibration, set up by the protoplasm (or living nitrogenous contents) of the yeast, and extending a short distance beyond the yeast cell. In any case the main reaction is represented thus : — (1) C 12 H 22 O n + H 2 0 = C 6 H 12 O c + C 6 H 12 0 6 . Maltose. Dextrose. Lsevulose. Invert sugar. (2) C 6 H 12 0 6 - 2C,H e O + 2C0 2 . Whatever sugar is used by the yeast it is first converted into dextrose and another sugar of the same series. Thus, cane sugar,, of which maltose is an isomeride, becomes converted into dextrose and lrevulose, and milk sugar into dextrose and galactose. Both these products are fermented, but the dextrose undergoes the change more rapidly. The reaction represented in equation (1) is called " inversion," and is effected by a soluble unorganised ferment secreted by the yeast, called invertase ; the quantity of sugar which the yeast will ferment is independent of the original nature of the sugar — that is to say, the organism is not im- poverished in fermentative capacity by having to effect the inversion of the sugar. The fermentation is invariably accom- panied by the formation of secondary products, chief among- which are glycerin and succinic acid. 100 parts of cane sugar- yield 105*36 of invert sugar, and are fermented to the following products : — Per cent. Alcohol, 51*11 C0 2 , 49 42 Succinic acid, ...... 0*67 Glycerin, ....... 3*16 Cellulose, fat, &c. , 1 00 105-36 202 BREWING AND DISTILLING. The simplest equation representing the production of the bye- products is — 4C 6 H 12 0 6 + 3H,0 = C 4 H G 0 4 + GC 3 H 8 0 3 + 2C0 2 + 0. Succinic acid. Glycerin. The oxygen serves for the respiration of the yeast. It appears that the purer the yeast the lower the proportion of bye-products formed, but they are never absent. The formation of alcohols higher in the series than ethyl alcohol — collectively known as fusel oil — occurs to some extent in the fermentation of wort, but it is doubtful whether they are the products of the action of pure yeast (Saccharomyces cerevisiee) or of adventitious varieties. For the most rapid propagation of yeast certain conditions must prevail — e.g., the percentage of sugar in the nutrient liquid should lie between 2 and 4, and the temperature must range between 25° .and 30° C. = 77° to 86° F. ; should the percentage of sugar exceed 35, or the temperature rise above 35° 0. = 95° or fall below 0° C. = 32° F., the growth of the yeast will be arrested ; the carbon dioxide evolved also serves to some extent as a retarding agent. When the percentage of alcohol in the fermented liquor exceeds 20, the growth of the yeast is also inhibited. In perfectly pure sugar (free from nitrogenous matter and ash), the yeast will only grow by feeding on the nutrient matter it already contains. Saccharomyces cerevisiee exists in two forms, that characteristic of top fermentation, already described, and that producing a bottom fermentation, used for lager beer, which is now brewed to some extent in this country as well as in Germany. Bottom yeast consists of round or oval cells, 8 to 9 [l * in diameter, which are slightly smaller and less aggregated and branched than top yeast. Its mode of reproduction is, however, similar. It is active at 4° to 10° C. = 39° to 50° F., and during the fermentation it collects at the bottom of the tun. Before modern brewing methods, resting on a knowledge of chemical and biological principles, were generally adopted, brewers' yeast was a mixture of various saccharomycetes with moulds and bacteria, and the course of the fermentation, and therefore the quality of the product, were largely a matter of chance. Nowadays, the need for fairly pure yeast is recognised, and microscopical examination is used to judge of its quality. The cells should be of uniform size, plump, transparent, and with- out a granulated appearance. Dead cells and rod-like organisms {Bacteria) should be absent. The yeast is never entirely free from the latter, but certain standards are laid down.f In bulk, the yeast should have a rich cream colour and a clean sweet * P — ttVt mm - tFor detailed account see A Text-book of the Science of Brewing, by Moritz and Morris. CLEANSING OF BEER. 203 smell. A more systematic method consists in preparing pure cultivations of yeast. The principle upon which this depends is the approximate isolation of the organism to be cultivated from accompanying growths, in a flask of nutrient liquid which has been previously sterilised by boiling. When a microscopical examination of the yeast in each cultivation made, shows that the characteristics of Saccharomyces cerevisice predominate in any one of them, the growth of that cultivation is further encouraged in order to obtain a pure yeast for brewing. On a large scale pure yeast is sown in sterilised wort, the process being carried out in sterilised copper vessels, access of air to which can only take place through filters of cotton wool to exclude germs, and the growth of pure yeast thus obtained is used to ferment the beer in the tuns. This plan is not practised in this country, owing to Excise difficulties, but it is employed abroad, notably in Germany. 5. Cleansing of the Beer. — When the wort has reached the proper attenuation, the beer has to be freed from yeast. This is done by several methods, of which the chief are — (1) the "union ; ' method, (2) the " skimming" system, and (3) the " stone square " system. (1) The union method is an improvement on the old London cask method, which is used for beers that are to be consumed shortly after brewing. It consists in running the beer with the yeast into casks or "unions " holding 4 barrels apiece, and fitted with attemperators and a swan-neck pipe, opening over a trough common to a set of casks. The beer is run into the " feeding- back " and thence into the casks, where the fermentation con- tinues, and the yeast rises, separates, and flows over through the pipe into the trough. The beer accompanying it is separated and returned to the feeding-back. After the fermentation is completed and the yeast ceases to flow over, the pipes are removed from the casks, and these are bunged up and allowed to settle. Among the advantages of this system are the exclusion of air during cleansing, the thorough separation of yeast due to the moderate size and shallowness of the vessels, and the fact that where it is practised the use of attemperators in the fermenting tuns is not essential, the beer being run into the unions as soon as it has reached a temperature of 70° F. = 21° C. (2) The skimming system consists in running the beer with the yeast into a " skimming-back." which is a large wooden tank provided with attemperators and fitted with large funnels of tinned copper (" parachutes "), the mouths of which are on a level with the surface of the liquid. The yeast is skimmed from the surface by a board into these funnels, and is thus removed. {3) The stone-square system consists in having two stone or slate vessels, one above the other, communicating by means of a manhole, which is provided with a collar about G inches high. 204 BREWING AND DISTILLING. There is also a valve between the two vessels. The fermenting wort is run into the lower vessel, and is pumped at intervals into the upper oue until the right attenuation is reached ; at the last return the yeast will collect in the upper vessel, being prevented from reaching the lower one by the collar round the manhole. The yeast collected by any of these methods is washed, and the surplus above that required for the next "pitching" is pressed and sold, largely to distillers (see Spirit, Vol. IT., p. 211). The yeast for pitching is used again as soon as possible, and in the interval should be kept cool and dry. 6. Racking and Finishing Processes. — The cleansed beer is occasionally run directly into cask, but the better plan is to employ a " settling " or " racking back." In this vessel the remaining suspended matter is deposited, and the beer may be here treated with a " priming " of sugar — which affords material for subsequent fermentation in the cask, and acts as a sweetening agent — be coloured with caramel (burnt sugar), and be preserved with antiseptics such as bisulphites, salicylic acid, sodium fluor- ide, &c. After the beer has been in the racking back for several hours, it is drawn off into trade casks, if for immediate con- sum ption, or into storage casks or vats. In the former case it is clarified by the addition of " finings " — i.e., isinglass dissolved in dilute sulphurous acid."^ The isinglass forms a precipitate with the tannin of the beer, and in settling carries down suspended matter. The clarification of beer is sometimes aided by filtration through wood shavings ; for these it has lately been proposed to substitute shavings of aluminium. Beer in cask undergoes a secondary fermentation at the expense of residual malto-dextrin, and is thus aerated and kept in good condition. The finished beer is liable to various diseases, the chief of which are acetic fermentation induced by Bacterium aceti (see Vinegar, Vol. II., p. 219), which renders the beer sour, its action being favoured by access of air, and " ropy fermentation," probably due to the action of Bacillus viscosus. Such defects are largely produced by impure yeast and contamination of the beer by foreign micro-organisms ; these causes are avoided by perfect cleanliness and the use of pure cultivations of yeast. Careful attention to the quality of water employed and proper treatment of the wort are also requisite. Details of such matters must be looked for in monographs on the subject. The following analyses (p. 205), by Graham, illustrate the composition of typical samples of beer. During the secondary fermentation in cask, carbon dioxide is evolved, and imparts to the beer its characteristic effervescence ; at the same time it serves to exclude air from the cask. In order to maintain these conditions, beer is often kept under pressure from a reservoir of liquid carbon dioxide, which also * The practice of using sour beer as a solvent is to be condemned. WINE. 205 serves instead of a pump to raise it from the cellar for distribu- tion. Much carbon dioxide is now recovered from the fermenting tuns, liquefied by pressure, and used for this and other purposes. Burton Milrl Alp Burton Dublin Pilsener T.ifrpv T^ppt* Maltose, 2-13 1-62 3 45 0-69 Dextrin, 3 C4 2-60 3-07 2-65 Albuminoids, 0 26 0-16 0 26 0-20 Lactic and succinic acids, 0-18 017 0-17 0-09 Ash, colouring matter, ) and hop extract, . \ 0-53 0-87 1-76 0-59 Total solids, . 674 5-42 8-71 4-22 Acetic acid, . o-oi 001 0-01 0-02 Alcohol, 678 5 44 5-50 3-29 III. WINE. — Wine is an alcoholic liquor made by the fer- mentation of grape juice. The successful cultivation of grapes for wine production can only be effected in climates where the full proportion of sugar in the fruit can be obtained. Further, it appears that each country has a type of vine adapted for growth in it, and that vines do not flourish in a region other than that in which they originate. The grape is better adapted than any other fruit for the production of wine, because of the large content of sugar in the juice and the fact that a consider- able proportion of the acid separates as potassium bitartrate after fermentation. The grape contains 95 to 97 per cent, of juice, which is a solution of sugar, organic acids, albuminous matter, mineral matter and extractive matter. The following figures {Neuhauer) illustrate the proportion of these constituents in grapes of selected and of second quality : — Selected. Second. Per cent. Per cent. 18*59 16-35 0-53 0-60 Albuminoids, ..... 0-25 026 Mineral matter, ..... 0-29 0-27 Extractive matter, .... 4-71 4-21 Total solids, .... 24-37 21-69 Water, ..... 75 63 78-31 100 00 100-00 Specific gravity, .... 1-094 1-085 Ratio of acid to sugar, 1 : 35 1 : 27 206 BREWING AND DISTILLING. When the grapes are beginning to ripen, the proportion of free acid to sugar is large, decreasing as the ripening pro- ceeds. In unripe grapes, which are still sour, this ratio may be as high as 1 : 10, and malic acid is present, being eliminated as the grapes become ripe, while tartaric acid is not destroyed, but goes to form potassium bitartrate. The grapes must not be allowed to become over-ripe before being gathered, as they lose sugar by oxidation and are liable to be attacked by low growths, like moulds. Certain growths, however, though nourished at the expense of the sugar, are not altogether harmful, as their life-products impart an agreeable bouquet to the wine. Grapes are liable to various diseases in all periods of their growth, the most fatal of which are known as " oidium " and "phylloxera." These are combated by dressing the vines with various antiseptic compounds, such as sulphur and copper salts. The grapes are gathered, and if for red wine are picked from the stalks, because the stalks contain much tannin • this would be extracted during fermentation, which, for the sake of the red colour, takes place in contact with the skins, "marc." For white wines the juice is at once separated from the marc and stalks, thus avoiding sepa- rate picking. The juice is extracted in a press, or by passage through grooved rollers, care being taken not to bruise the seeds and stalks. A further quantity of juice is obtained by a second pressing. The percentage of juice ("must") is about 95 per cent, if the stalks have been removed, and 70 per cent, if they remain. The fermentation of the must is allowed to take place spontaneously, and is effected mainly by the yeast named Saccharomyces ellipsdideus. The reason why the spontaneous fermentation is carried out by this particular organism is that the ferment is widely distributed in wine-growing countries, and that it grows especially freely in must, monopolising the nutrient matter and starving out other organisms. The fermentation is carried out in barrels for white wines — the bung hole being left open — and in open vats for red wines. Top fermentation and bottom fermentation are practised, as for beer. The former is the commoner, and is performed at a temperature of 15° to 25° C. = 59° to 77° F., the latter, chiefly used for Rhine wines, requiring a temperature not exceeding 15° C. = 60° F. A fairly high temperature — e.g., 27° C. = 80° F. — favours the production of a wine in which the sugar is not completely converted, and which is, therefore, sweet and poor in alcohol, but with a good flavour. The main fermentation is complete in three to fourteen days, when the yeast falls to the bottom ; the wine is then racked into clean casks. The " young wine " thus obtained undergoes a further fermentation, and as the percentage of alcohol increases, albuminous substances and tartrates are deposited — the latter being less soluble in alcohol than in COMPOSITION OF WINES. 207 water — forming the crust known as " argol " (see Tartaric acid T Yol. II., Chap. XVIII.). When the marc is also allowed to ferment, the wine is highly coloured, owing to the extraction of the colouring matter of the skins by the alcohol. Such extractive matter helps to preserve the wine, on which account, and because of the presence of tannin, red wines usually keep better than white. Secondary fermentation in cask for wine on draught can be prevented by careful heating to a temperature of 55° to 60° C. = 131° to 140° F. in a separate apparatus, and storing in sterilised casks. Besides the alcohol produced by the fermenta- tion of grape sugar, bye-products such as glycerin and succinic acid occur, similar to those formed from maltose in the manufacture of beer, and in addition to these, certain ethereal salts (esters) which impart to the wine its characteristic bouquet. The per- centage of alcohol naturally present in wine is limited by the inhibiting effect which alcohol has upon the yeast. The usual quantity is from 6 to 12 per cent. Stronger wines are "fortified" by the addition of spirit. Besides these constituents, wine contains metallic salts of organic acids and extractive matter, including tannin and organic acids. Chemically, it is dis- tinguished from beer by the presence of tartaric acid (which is characteristic of wine, as acetic acid is of beer), of a large proportion of salts, metallic and ethereal, and of tannin. At the same time it is devoid of bitter principles. The following table (Fresenius and Borgmann) shows the composition of some typical wines : — Grams per 100 c.c. Hock. Claret. Moselle. Alcohol, 8-77 8 56 8-08 Extract, 2-32 2 44 211 Mineral matter, . 0-22 0-25 0-18 Acidity,* . 0-66 0-54 0-79 Glycerin, 0-92 0-86 0-73 80 3 , .... 0-05 o-oi 001 P 2 0 6 , .... 0-04 0-03 0-05 In pure natural wine the proportion of glycerin to alcohol is never less than 7*8 : 100. This serves as an index of the genuine character of the wine. The following are analyses (by Dupre) of " fortified ,; wines : — * Presumably stated in terms of tartaric acid. 208 BREWING AND DISTILLING. Grams per 100 c.c. 1 Port. Sherry. Madeira. Specific gravity, .... 0-9974 0-9979 0 9939 Alcohol, 17-53 17 20 17-75 Extract, ..... 5-39 5-35 4-35 Glucose, ..... 2-28 2-97 2-08 Mineral matter, .... 0-26 0-55 0-39 Acidity (tartaric acid), . 0-49 0 52 0-54 PA, 0 03 0'02 0-04 Alcohols higher in the series than ethyl alcohol are sometimes present in wine. The principal substance imparting the vinous bouquet is said to be cenanthic ether, but others are undoubtedly present, and each vintage appears to have its own characteristic ethers, said by some authorities to be due to the type of yeast used ; some such flavouring matters are developed during storage. The colouring matter in white wines appears to be an oxidation product of the extractive matter in the juice. In red wines the colour is derived from the husks and seeds of the grape, and is only red in the presence of acid, being changed to green by alkali. Brown sherry is coloured with caramel (see Sugar, Vol. II., p. 182). Another change which takes place during storage is the deposition of some of the potassium bitartrate, together with colouring matter in the form of " crust," such as is seen in port. The addition of plaster of Paris to must hastens the fer- mentation, and is said to render the wine more stable, and to improve its colour. The chemical effect is to precipitate the tartaric acid as calcium tartrate, potassium bisulphate being formed. This reacts with the potassium phosphate present, forming free phosphoric acid and neutral potassium sulphate. It thus happens that a " plastered " wine is relatively richer in potash and phosphoric acid than one which has not been so treated. The practice is generally condemned. Sparkling wines, such as champagne, are allowed to undergo a secondary fermentation in bottle. Thus, in the case of cham- pagne, the racked new wine is mixed with old wine, and if there be not sufficient sugar to continue fermentation cane sugar or invert sugar is added immediately before bottling. The bottles are stored horizontally, and before being marketed are inclined until the sediment falls into the neck, when the cork is dexterously released, so that the pressure, due to dissolved C0. 2 , may expel the sediment. IV. MINOR FERMENTED LIQUORS.— Besides beer and wine, other potable liquors containing alcohol are produced by the fermentation of saccharine matters, such as the juice of the BRANDY. 209 apple (for cider), and of the pear (for perry), and sugar itself (for ginger-beer). In making cider the apples are pulped, the juice is expressed and allowed to ferment spontaneously at a temperature of 4° C. =40° F. The liquor is racked, and a secondary fermen- tation takes place at as low a temperature as possible. Good cider should contain from 5 to 6 per cent, of alcohol and 2 to 3 per cent, of sugar. Ginger-beer brewed from sugar by the action of the ginger-beer plant or of yeast, contains alcohol up to about 2 per cent. V. SPIRIT. — The production of potable liquids containing alcohol dates from prehistoric times, but until chemical researches had been carried out by the alchemists and the process of distil- lation evolved, such liquids were not of greater strength than can be obtained directly by fermentation. When it was found that spirit of greater strength could be produced by distillation, the process became commercially valuable. Raw Materials. — The earliest raw material used for the manufacture of spirit was wine. On distilling any ordinary wine, alcohol and water pass over, the former predominating in the first fractions, which are, therefore, richer in alcohol than was the wine. The distillation of wine for the production of spirit is still practised for the manufacture of the best brandy (cognac). When the rationale of fermentation became known, the fermentation of alcohol from sugar, both that naturally pro- duced and that obtained from starch, was utilised for obtaining spirit. Thus, nowadays, wine, sugar, and starch are all used for the manufacture of spirit, the nature and flavour of the product depending mainly on the class of raw material adopted. Potable spirits may be divided into two classes — viz., those produced by the distillation of materials which impart to them a characteristic and agreeable flavour, and those formed from materials which are treated to yield a spirit destitute of flavour- ing matter, and needing, therefore, to be artificially flavoured in order that it may be marketable. The former class was that originally manufactured {e.g., brandy), the production of the latter class being a comparatively modern industry. Brandy is the product of the distillation of wine ; the best is known as cognac, from the place of that name, and is made from the brandy grape, a small white berry which yields a very acid juice, and is fermented for the express purpose of producing this spirit. Brandies from other districts are made from the wines from different grapes, each communicating a characteristic flavour to the spirit. The average yield is 10 to 15 per cent, of the wine employed. The following figures show the composition of a sample of cognac (specific gravity 0'93) : — 14 210 BREWING AND DISTILLING. Per cent, (by weight). Ethyl alcohol, 54'6b3 Normal propyl alcohol, ..... 0'029 Isobutyl alcohol, 0-007 Amyl alcohol, 0'204 Furfural, 0*002 Wine oil, 0*008 Acetic acid, ....... Trace. Butyric acid, Trace. Isobutyl glycol, 0'002 Glycerol, 0'005 Water, 45-080 100-000 The colour of brandy is acquired from the cask in which it is stored, save in the case of brown brandy, which is coloured by the addition of caramel. Whiskey. — The raw material used for the production of whiskey is barley, which may be entirely or partially malted ; malted barley is used for Scotch whiskey, while for Irish whiskey a mixture of malted and unmalted grain is employed. The malting process is similar to that used by the brewer (see Beer, Yol. II., p. 191), the drying being effected over peat fires, which impart the characteristic smoky flavour to the whiskey. The dried malt is crushed and washed with hot water, as in a brewery, but under such circumstances as shall ensure the production of a wort containing more maltose and less dextrin than that in- tended for beer. The temperature employed is at first 160° F. = 71° C, and is raised until, at the third mashing, it reaches 185° F. = 85° C. The wort, when separated from the grains, has a specific gravity of 1 -040. The spent grain, known as " draff," is similar in composition to brewers' grains, and is sold as cattle food; the composition of a sample is given by A. H. Allen {Journal of the Society of Chemical Industry, 1891, p. 305) as follows : — Per cent. Moisture, 10*32 Oil, 6-70 Albuminoids, 19 - 88 Carbohydrates, digestible fibre, &c, . . . 41-06 Woody fibre, 19*00 Ash, . 3-04 100-00 The wort is cooled to 70° to 80° F. = 21° to 27° C. by re- frigerators as quickly as possible, lest it become sour, and the ■ fermentation is started at as low a temperature as is practicable, it being found that fewer bye-products (fusel oil) are then obtained. The boiling of the wort for sterilisation is omitted by the distiller WHISKEY. 211 as the fermented liquor is only a stage in the process and is not stored. The surplus yeas^ of the brewer, in as pure a condition as possible, is used for the fermentation ; impure yeast contains the acetic acid and other ferments, leading to loss of alcohol and production of aldehyde, an objectionable impurity. The fermen- tation is pushed as far as possible in a tun cooled by attemperators (see Brewing, Vol. II., p. 199), and the yeast is left in the fer- mented liquor or "wash," fresh yeast being required for each fermentation. The alcohol in the wash amounts to 10 to 12 per cent., and corresponds with about 80 per cent, of the saccharine matter employed. The distillation of the wash is conducted in an ordinary still (pot still) of 6,000 to 12,000 gallons capacity, similar in shape to that used for distilling water in the laboratory, made of copper and fitted with an agitator to prevent the solid matter in the wash settling and charring on the bottom. The still is fired direct, and a small quantity of soap is sometimes introduced to prevent frothing. The distillate from this first still is poor in alcohol, and is known as " low wines ; " the residue in the still ("pot-ale") contains 3 per cent, of solid matter in solution, in- cluding about 1 per cent, of lactic acid, which has lately been recovered and used as a substitute for acetic acid and tartaric acid in wool dyeing. The first distillate is redistilled in a second still similar to that just described, save that a stirrer is not necessary. The second distillate is collected in three fractions — namely, " fore-shots," " clean spirit," and "feints"; "spent lees ; ' are left in the still and subsequently run to waste. The first and third fractions are impure, becoming milky on dilution with water, and are redistilled with the next batch of low wines. The middle fraction is "new whiskey," and has a strength of 13° to 50° over-proof (for an explanation of the term " proof," see below) ; it is brought to standard strength of 10° to 25° over- proof by the addition of water, and allowed to mature in cask. The nature of the products of the fermentation of whiskey wash are similar to those of. the fermentation of brewers' wort, but, as the process is carried farther, the formation of secondary products, particularly of alcohols higher in the series than ethyl alcohol, is greater. The impurities precipitated by water in the fore-shots, appear to consist largely of fatty acids (some of which may be derived from the soap used), but those precipitated from the feints consist chiefly of higher alcohols, which constitute the so-called fusel oil. The chief substance present in this body is inactive amyl alcohol, to which its evil odour may be attributed. With regard to the supposed injurious action of fusel oil on the system, Allen (loc. cit.) has shown that it may be freely imbibed without ill effect. The quantity present in whiskey is not greater than 0-1 per cent.; the ethyl alcohol present is usually 55 to 64 per cent., Irish whiskey being usually the stronger. 212 BREWING AND DISTILLING. Besides these higher alcohols, furfural is present in whiskey, and is characteristic thereof; it appears to be produced by the slight charring of the solid matter in the wash. The maturing of whiskey appears to be due in part to oxidation, but more largely to an absorption by the wood of the cask analogous to that exerted by wood charcoal, in the purification of silent spirit (q.v.). The use of a sherry cask for storing whiskey is two-fold, impurities being absorbed from, and flavouring matters imparted to, the spirit. Gin. — Whereas whiskey and genuine brandy are prepared in pot stills, in which but little fractionation takes place, gin — which is a liquor flavoured by the addition of flavouring materials to plain spirit in the process of rectification or redistillation — is manufactured in " patent " stills, such as are used for the produc- tion of pure alcohol. The raw material is a mixture of malted and unmalted grain, from which a mash is produced and fer- mented in the usual way (pp. 210, 211). The distillation is generally effected in a Coffey still, which is shown in Fig. 34. This apparatus consists of two columns, generally made of wood lined with copper. The first, A, is termed the analyser, while the second, B, is called the rectifier. The pipe C passes from the top of the analyser into the bottom of the rectifier. Internally the columns are divided by perforated copper plates (generally eleven in the analyser and fourteen in the rectifier), each of which is provided with two valves, having the appearance of the letter T in the figure. Each division of the column is con- nected to the next by a tube, D (a "dropping pipe"), which projects about 2 inches above the surface of the plate in which it is inserted, and terminates in a collar-shaped trap on the plate below it. The top of the rectifier is slightly modified, the fifth plate from the top being unperforated, but provided with a large opening, E, with a neck. The dropping pipe of this plate opens into a pan which is deeper than those under the dropping pipes of the other plates, and has a draw-off pipe, F. The upper divisions of the rectifier have the form of ordinary baffle plates. The whole of the upper portion of the column is the finished- spirit condenser. The wash (fermented mash) is stored in the vat, G, and flows into the well, H, from which it is forced by the pump, K, through the pipe, L, which passes through the rectifier ; L is made up of a series of parallel portions connected with the bends, M, placed outside the rectifying column. The lower end of this pipe passes upwards to the top of the analyser, where the wash is delivered into the trap on the topmost plate, whence it flows from plate to plate, encountering steam from the boiler, 1ST. The pressure of steam and alcohol vapour prevents the passage of the wash through the perforations of the plates, and compels it to fall from plate to plate through the dropping pipes. Sur- plus pressure is relieved by the valves in the plates. It will be 214 BREWING AND DISTILLING. understood that at the beginning of the process the apparatus has been completely filled with steam, so that the wash is heated nearly to boiling point before it enters the analyser. When the circulation has been started, the wash is continuously exposed in the analyser, in layers, to the action of the steam, which is at its lowest temperature at the top of the column, so that it is only from the top plate that the constituent of lowest boiling point (the alcohol) can pass away. It does so, together with the steam, through the pipe C, and is delivered at the bottom of the recti- fier, during its passage up which it becomes concentrated by the condensation of the steam in contact with the pipes conveying the wash. The condensed steam, together with the impurities of higher boiling point (fusel oil), falls from the pipes on to the plates in the rectifier, and, by being thus delayed on its down- ward course, is deprived of the bulk of its alcohol. Lest the condensed water should still retain much alcohol, it is returned to the well, H, through the pipe P, to be again circulated with the wash. The concentrated and purified spirit comes in contact with the pipes conveying the coldest wash in the upper part of the rectifier, its cooling by this means being promoted by the presence of the baffle plates. The greater portion of it is thus ■condensed, and is ultimately collected as finished spirit through the pipe F. The more volatile impurities {e.g., aldehyde) fail to be condensed in the rectifier, and pass away with such steam as remains uncondensed through the pipe R, and are either allowed to escape or are condensed and worked up again, according to the practice of the distiller. The spent wash flowing from the bottom of the analyser is used for heating the feed water of the boiler. It will be seen that the Coffey still works much more system- atically and economically than the ordinary pot still, inasmuch ■as the higher boiling constituents are continuously removed without redistillation in a second still, and the heat of conden- sation is utilised in warming the mash before distillation. On account of the perfect fractionation which is effected by the Coffey still, it is not adapted for the production of whiskey and similar spirits that depend for their flavour on the presence of character- istic impurities. The plain spirit from the Coffey still is re-distilled in a pot still, such matters as are to impart flavour to the gin being added to the contents of the still. The substances chiefly used are a,ngelica root, almond cake, calamus root, cardamoms, cassia, cinnamon, coriander, juniper, liquorice root, orris root and sweet fennel. These yield essential oils, which distil over with the spirit. The addition of salt to the contents of the still is found to favour the extraction of these flavouring matters. For the production of sweetened gin, syrup is added to the re-distilled spirit. It is sometimes customary to add a little sulphuric acid to the contents of the still, in which case fragrant ethers pass ALCOHOL. 215 over into the distillate. Such is the case with " Plymouth gin." " Hollands " differs from ordinary gin made in this country, in respect of the fact that it is made from rye and distilled from a pot still, its chief flavouring matter being juniper. The average strength of gin is about 17 to 22 per cent, under proof (37 to 40 per cent, of absolute alcohol by weight). It is often largely adulterated with water. " Absinthe " is a form of gin flavoured with wormwood, as well as with the ingredients above-mentioned. Rum. — Rum is imported from the West Indies — chiefly from Jamaica — where it is made for the most part from molasses (see Sugar, Yol. II., p. 164) or other refuse sugar. The fermentation is brought about by adding spent wash, to provide the necessary nutritive matter, to the sugar solution, containing 12 to 16 per cent, of sugar, and allowing spontaneous fermentation to ensue. The wash is then distilled in a form of pot still (the Pontifex still) until the bulk of the alcohol has come over, the " low wines" thus obtained being redistilled. Hum owes its flavour to the presence of ethyl formate and butyrate, and its colour to caramel, or to the extractive matter it takes up from the casks in which it is kept. Rum is usually 20° O.P. — i.e., it contains 60-8 per cent, by weight of absolute alcohol. Alcohol {Commercial Spirit). — Alcohol is prepared from many saccharine materials for industrial purposes, and for adulterating genuine potable spirits such as those described above. For the latter purpose, German spirit is largely used, made from potatoes, a somewhat cheaper source than the materials used in this country. Any starchy material will serve for the production of alcohol, and the real question is one of cost, which varies with the locality in which the manufacture is carried on. The saccharification of the starch is usually effected by the action of the diastase of malt, the quantity of malt requisite, according to German practice, being about 5 per cent, of the weight of potatoes used. It is reckoned that the work of saccharification is executed by half this quantity, the remainder serving as nutrient matter for the yeast in the subsequent fermentation. This extra nutrient matter is necessary on account of the small proportion of albu- minous matter in potatoes and similar starchy materials. It is for this reason that the cheaper process of saccharification by boiling with a small quantity of acid (see Starch sugar, p. 181) is not a completely effective substitute for the use of malt. The method of mashing has been already described under the head Whiskey, Yol. II., p. 210 ; the "pitching" temperature is as low as is practicable (23° to 25° C. = 73° to 77° F.). The distillation of the wash is carried out in stills of the Coffey type, which produce alcohol containing 86 to 95 per cent, of absolute alcohol, and about 0-4 per cent, of higher alcohols, and similar impurities, collectively termed fusel oil. The kind of spirit 216 BREWING AND DISTILLING. prepared from different raw materials is shown by the following figures : — Alcohol per cent, by weight. Fusel oil per 100 parts absolute alcohol. Potatoes, .... 89'04 0-328 j> • • • • j Turnips, .... 89-71 0 256 80-50 0-793 7810 0818 Maize, ..... 81-95 0-207 Molasses, .... 81'35 0-374 The raw spirit also contains some aldehyde, the presence of which is attributed to impurities in the yeast, which also cause the formation of higher alcohols. Aldehyde occurs more largely in spirit which has been fermented in warm weather than in that prepared under normal conditions of temperature. The value of this first distillate or " crude spirit " depends not only on its content of alcohol, but on the proportion of spirit free from im- purities which it yields on redistillation. As already stated under Whiskey, it is generally supposed that fusel oil is objectionable in spirit which is to be used for drinking, but it is doubtful whether it can be condemned as actually deleterious, though its flavour is certainly nauseous. The spent wash is used as cattle food. The crude spirit is purified by dilution with about an equal quantity of water — more water being needed the richer the spirit is in fusel oil — and filtration through wood charcoal, packed in columns varying in height from 7 to 30 feet, and about 3 feet in diameter. The wood charcoal, which is found to be more effective than animal charcoal, is used in pieces the size of peas or nuts, and acts partly by mechanical absorption, and partly chemically by inducing oxidation. As a consequence of this oxidation alde- hyde and even acetic acid are formed. When the charcoal ceases to act, it can be revivified by steaming out the alcohol and ignit- ing the charcoal with exclusion of air, but this latter treatment is not much practised, although the alcohol is always recovered. The alcohol steamed out of the charcoal might be expected to contain a considerable proportion of the fusel oil that has been removed, it is found, however, that but little fusel oil is recovered, most of it being oxidised during the process of filtration. The substitution of powerful oxidising agents — such as potas- sium permanganate, chromic acid, ozone and manganese dioxide — for charcoal has been proposed, but their use has not been attended with success, since they cause the production of much aldehyde and acetic acid, and, therefore, of ethyl acetate, from the ethyl alcohol. Of other methods which have been proposed may be mentioned that consisting in the extraction of the fusel oil by COMPOSITION OF FUSEL OIL. 217 treatment of the diluted crude spirit with petroleum ether, and that consisting in shaking the spirit with potassium carbonate, which forms a lower oily layer containing the higher alcohols and aldehydes ; these, however, have not come into use. The filtered spirit is then rectified in a column still. The following figures represent the output of a still of this kind, working on diluted and filtered crude potato spirit : — Per cent, by Volume. First runnings (95 per cent, strength), .... 4 Second quality spirit (96*2 per cent, strength), . . 3 First quality ,, (96*4 per cent, strength), . . 37 Second quality ,, (96 per cent, strength), . . 0*5 The first runnings are too impure for drinking purposes, but are used for burning, for the preparation of vinegar (v.i.), and for such technical processes as the manufacture of mercuric fulminate (see Explosives, Chap. XVII.). The second quality con- tains 0*02 per cent, of fusel oil per 100 parts of absolute alcohol, and gives a perceptible aldehyde reaction. The better qualities contain no fusel oil, and only a trace of aldehyde. They consti- tute " silent " spirit, so-called because it affords no indication of its origin. The greater portion of this alcohol is flavoured for consumption, as brandy and other spirits, and is used for the fortification of wine. A smaller quantity is employed for phar- maceutical purposes and the manufacture of essences and scents. When "absolute" alcohol is required — i.e., such as approaches in strength to 100 per cent, of alcohol — it is made by dehydrating the weaker spirit by means of quicklime, and redistillation. The character of fusel oil depends to some extent on the material mashed, and on the method of manufacture — e.g., the oil from grain or potatoes consists largely of the amyl alcohols — inactive amyl alcohol preponderating ; that from the marc of brandy contains much normal propyl alcohol ; that from beet contains iso-primary butyl alcohol as the predominating con- stituent. Fusel oil is but little used ; its chief applications are as a solvent in chemical industries, as a source of the ethereal salts ; thus it serves for the preparation of amyl acetate which is used for flavouring confectionery and as a solvent for celluloid (q.v.). A sample of fusel oil from potatoes had the following composition : — Per cent, by Volume. Iso-propyl alcohol, 15*0 Propyl „ 3-0 Normal butyl alcohol, 6 5 Iso- butyl ,, . . . . . 5*0 Inactive amyl ,, 27*5 Active ,, ,, ..... 60 Higher alcohols, 17 0 Ethyl alcohol, &c, 7 5 Water, 12 5 100-0 218 BREWING AND DISTILLING. Liqueurs. — These alcoholic liquids consist of "silent" spirit (q.v.) flavoured with various essences and containing much sugar. They are often artificially coloured. They contain from 40 to 50 per cent, of alcohol and from 25 to 50 per cent, of cane sugar. Alcoholometry. — Inasmuch as the taxation of alcohol is a con- venient source of revenue, much attention is paid to the strength of alcoholic liquors. The most usual method of ascertaining this value consists in taking the specific gravity of the alcoholic liquor or of the distillate from it, should it contain soluble non- volatile matter, which would affect the specific gravity. Pure alcohol has a specific gravity of 0-7938 at 15-5° C. = 60° F., and boils at 78*4° C. = 173-1° F. When mixed with water the volume of the mixture is less than the sum of those of the con- stituents, so that the specific gravity of mixtures are not calcul- able, and elaborate tables have been prepared empirically. The Excise system of stating alcoholic strength is in terms of degrees over or under "proof." Proof spirit was originally defined as of such strength that gunpowder moistened with it would just inflame when the alcohol was kindled. Now, it is defined to be a liquid of such a specific gravity at 51° F. that 13 volumes shall weigh the same as 12 volumes of water at the same temperature. Such alcohol has the specific gravity 0-91984 at 15-5° C. = 60° F., and contains 49*24 per cent, by weight of absolute alcohol ( = 57*06 per cent, by volume). On this basis the term " under proof" means that the spirit contains so much water more than proof spirit per 100 measures, as is expressed in degrees below proof. Thus 20 U.P. means a spirit containing, at 60° F., 80 measures of proof spirit and 20 of water, and similarly 20° O.P. signifies a spirit of such strength that 100 measures, at 60° F., will be proof spirit when diluted with water to 120 measures. Absolute alcohol on this system is 75J O.P. Methylated Spirit. — For the advantage of those who require alcohol for manufacturing purposes, a spirit is allowed to be sold free of duty, under certain restrictions, which is denatured by the addition of one part of wood naphtha to nine parts of rectified spirits of wine — i.e., the strongest alcohol that can be obtained by ordinary distillation without a fractionating column. Rectified spirit has a specific gravity, at 60° F., of 0-838, and contains 84 per cent, by weight of alcohol. Wood naphtha (see Destructive distillation, Vol. II., p. 94) was chosen as interfering least with the industrial use of alcohol while rendering the spirit unpotable, Recently, however, it has been alleged that such methylated spirit is consumed as a beverage to the injury of the revenue, such consumption being possibly due to the greater purity of modern wood naphtha. In consequence of this, the use of spirit denatured with wood naphtha has been further restricted, and the bulk of methylated spirit as now sold is pre- pared by adding not less than § per cent, by volume of mineral VINEGAR. 219 naphtha " of specific gravity not less than 0*800. " This mixture is objected to by manufacturers as it becomes turbid on dilution, owing to the separation of the hydrocarbons constituting mineral naphtha. A different system obtains in Germany, duty-free spirit being there usually denatured by the addition of 2 per •cent, of wood spirit rich in acetone and 0'5 per cent, of pyridine bases (see Tar distillation, Vol. II., p. 78). Industries for which such spirit cannot well be used are supplied with alcohol containing a constituent sufficiently nauseous to prevent the use of the spirit as a drink, but unobjectionable for the particular trade purpose. Thus spirit for varnish makers may be denatured by the addition of 0*5 per cent, of oil of turpentine. VI. VINEGAR. — When wine, beer, or other alcoholic liquor containing nitrogenous matter is left exposed to the air, it soon becomes sour from the conversion of the alcohol into acetic acid. This change can be effected by oxygen in the presence of porous substances — e.g., spongy platinum — the alcohol being oxidised according to the equation — CH3.CH3.OH + Oo = CHo.COOH + HOH. The oxidation of alcohol, however, in this manner is accompanied by the formation of aldehyde, CH 3 COH, the lowest oxidation- product of alcohol. Moreover, vinegar is not merely dilute acetic acid, but contains as essential constituents aromatic and extractive matters. In practice, the oxidation of a dilute alcoholic liquor is effected by the agency of micro-organisms, chief among which are Mycoderma aceti and Bacterium aceti, the liquor being spontaneously infected by contact with the air. During the growth of this organism oxygen is absorbed and acetic acid produced, the mycoderma forming a skin (mother of vinegar) on the surface of the vinegar. It seems that the oxida- tion takes place without the intermediate formation of aldehyde, this occurring only when the mycoderma is losing its activity. Succinic acid appears to be formed in small quantity. In the course of time the organisms will oxidise the acetic acid itself to H 2 0 and C0 2 . As in the case of other micro-organisms, it is essential that the nutrient liquid should contain mineral salts — viz., those of potash, magnesia, ammonia and phosphoric acid. The content of alcohol in the nutrient liquid should not much exceed 10 per cent., nor, for rapid growth, should it be less than 3 per cent. The most favourable temperature for the growth of the organism is about 30° C. = 81° F. There are two main processes for making vinegar. In the one, the old Orleans process, which is practised chiefly in France, the access of air to the alcoholic liquid takes place solely by diffusion, so that the acetification takes a considerable time, and the pro- cess is known as the "slow vinegar process." In the other, a large surface of the liquid is exposed to the air, which is caused 220 BREWING AND DISTILLING. to circulate over it, so that the process is completed in a far shorter time, on which account it is called the " quick vinegar process." Rapidity is only obtained at the cost of alcohol and vinegar, which are carried away by the circulating air, particu- larly if the temperature be allowed to rise unduly, as it may from the more rapid oxidation of the alcohol. The slow vinegar process is used for making vinegar from wine, which should preferably be " full-bodied " and one year old. Vinegar from white wine is most esteemed. The wine is clarified by contact with beech shavings, and is then diluted if it contains more than 10 per cent, of alcohol, and run into casks of 50 to 100 gallons capacity, with holes for the admission of air, and placed on their sides on trestles. These casks have been pre- viously one-third filled with strong boiling vinegar, in order to prevent them from flavouring the wine undergoing acetification. After eight days the wine is added in quantities of about 2 gal- lons, this quantity being again added at the end of every period of eight days until the cask is two-thirds full. Portions are drawn off to promote the circulation of air, and more wine is added as the process proceeds, the temperature being kept at about 25° C. = 77° F. by ventilation or artificial heating. The pro- gress of the fermentation is judged by the periodical withdrawal of a sample from the top, a white froth indicating its completion;, the process takes many weeks to carry out. It is usual to pass the vinegar through a rough filter, made of wood shavings or refuse from grape presses ; this retains the Mycoderma, and com- pletes the acetification of the alcohol. Upright tuns with false bottoms on which grape-press refuse is packed, are sometimes substituted for casks laid horizontally. In these the rate of manufacture is somewhat more rapid. The quick vinegar process is adapted for the acetification of any appropriate alcoholic liquid, so that it is used in this country where vinegar is largely made from the alcoholic wash from a. malt mash. Mashing and fermentation are conducted very much as in the process of brewing, save that the wort is well aerated in the fermenting vat, in order to induce more thorough fermenta- tion, and the process is completed at a lower temperature,, whereby the activity of foreign organisms is diminished. For the best production of vinegar the wash should be as bright as possible, and should, therefore, be allowed to settle and filtered before acetification. Quick vinegar vats are wooden vessels, about 15 to 20 feet in height, 11 feet in diameter at the bottom and 8 feet at the top. The temperature of the vessel is regulated by a tin worm at the- lower part, above which is a false bottom carrying a " filling " of beech wood shavings or twigs, which are previously steamed and soured with the vinegar. Above this, and below the lid of the vessel, is a revolving sparger of wood or ebonite, though other QUICK VINEGAR PROCESS. 221 methods of distributing the wort over the twigs are also in use. Perforations in the upper and lower part of the vessel serve for the circulation of air, which is slightly heated and regulated by- closing the air holes above mentioned. The wash is pumped through the sparger and trickles over the filling, meeting the up-draught of air and having its alcohol oxidised to acetic acid by the action of the mycoderina, which collects on the twigs and shavings in the form of a slime ; this growth necessitates the occasional cleansing of the apparatus. The oxidation of the alcohol is most satisfactory when the temperature due to the heat of the reaction rises to about 37° C. = 99° F. Too little air causes the production of the first product of oxidation of ethyl alcohol — aldehyde — which is very volatile and easily detected by its characteristic odour. Too much air is also to be avoided, as causing volatilisation of alcohol and acetic acid. In any case the loss of alcohol is considerable, averaging 12 per cent, of that contained in the wash. Complete acetifi cation at one operation can be effected with liquors containing not more than 4 per cent, of alcohol, stronger solutions needing repeated treatment, with the addition of fresh raw material if a strong vinegar be required. Although vinegar containing as much as 12 per cent, of acetic acid can be thus produced, the strongest usually manufactured is of about half this strength. The manufacture of vinegar by this process takes from eight to twelve days. The air from the vats is sometimes passed through water to absorb the vapours of alcohol, aldehyde and acetic acid which it contains. The manufacture of vinegar is usually conducted with little regard to those principles of fermentation by means of pure culti- vations which have been worked out for beer brewing, the necessity for the presence of definite organisms, and for the exclusion of foreign germs by filtration of the air, being com- monly ignored. Such diseases as the vinegar fly and vinegar eel are in consequence fairly common. Vinegar has special characteristics, according to the raw material from which it is brewed. Thus, there are found on the market cider vinegar, perry vinegar, ale vinegar, and sugar vinegar, as well as the commoner varieties, malt and wine Vinegar. Malt vinegar is brown and aromatic, owing this latter quality to the presence of ethereal salts, chiefly ethyl acetate, which is also sometimes added. The several qualities are designated by numbers, which express the number of grains of dry sodium carbonate which will neutralise 1 fluid ounce of the liquor. The specific gravity of malt vinegar varies from 1'021 to 1*025, and it contains from 3 to 6 per cent, of acetic acid, besides a little alcohol, and 5 to 6 per cent, of extractive matter. In order to preserve weak vinegar it is legally permissible to add 0-185 per cent, of sulphuric acid, but the practice is not adopted by manufacturers of repute. The expression "proof vinegar" 222 BREWING AND DISTILLING. means vinegar containing G per cent, of acetic acid. Wine vinegar is pale yellow if made from white wine, and reddish- brown when made from red wine. It is more alcoholic than malt vinegar, and, therefore, has a lower specific gravity, 1 '014 to 1-022; it contains from 6 to 12 per cent, of acetic acid. Potassium bi tartrate, usually present to the extent of 0*25 per cent., is a characteristic constituent. Malt vinegar is sometimes distilled, the product being known as white malt vinegar. Factitious vinegar is made from the acetic acid obtained by the destructive distillation of wood, diluted with water coloured with caramel and flavoured with ethyl acetate. The bulk of cheap vinegar sold in this country is of such nature. It does not contain the phosphates, tartrates, and nitrogenous matter characteristic of genuine vinegar. FATS, LIQUID AND SOLID. 22S CHAPTER X. OILS, RESINS AND VARNISHES. L FATS, LIQUID AND SOLID.— Ail greasy substances of animal and vegetable origin may be classified as oils, including^ in the term solid oils (fats) and liquid oils (oils in the limited sense of the word). These substances are characterised by their unctuousness, by their insolubility in water, solubility in such solvents as ether, benzene and carbon bisulphide, and by their leaving a greasy stain on paper, which does not disappear by evaporation. Chemically, they are ethereal salts of the fatty acids ; * the alcohol radicle of the salt is generally that of glycerin (glyceryl), but in certain waxes (liquid and solid) radicles of higher alcohols than glycerin occur. The misnomer glyceride is conventionally applied to fats of the former class. The number of fatty acids found in oils is large, but the chief occurring in oils of industrial importance may be given : — General Formula. Name. Formula. Melting Point. CJWiCOOH C n H 2 «-iCOOH C„H 2n _ 3 COOH C„H 2n _ 5 COOH C«H 2n _ 2 (OH)COOH Butyric acid Valeric acid Laurie acid Palmitic acid Stearic acid Arachidic acid Cerotic acid Oleic acid Dceglic acid Erucic acid Linoleic acid Linolenic acid Iso-linolenic acid Ricinoleic acid Iso-ricinoleic acid Rapic acid C 3 H 7 COOH C 4 H 9 COOh[ C n Ho 3 COOH C 15 H" 31 COOH C17H35COOH C9H39COOH C 2G H 53 COOH C 17 H 33 COOH C 18 H 35 COOH CiH^COOH C~ 17 H 31 COOH C 17 H 29 COOH C 17 H 20 COOH C 17 H 3 .,lOH)COOH C 17 H 3 ;(OH)COOH C 17 H 3 o(OH)COOH -3°C.= 27° F. 43-5°C. = 110° P. 62° C. = 144° F. 70° C. = 158°F. 75°C. = 167°F. S1-5°C. = 179°P. 14°C.= 57° P. 16°C.=: 61° F. 34°C.= 93° F. The majority of solid fats consist largely of glyceryl stearate and palmitate.f The radicle glyceryl (C 3 H 5 ) replaces 3 atoms * Acids belonging to the fatty as distinct from the aromatic series, not necessarily homologues of acetic acid. t The terms stearin, palmitin and olein are used as synonyms for glyceryl palmitate, stearate and oleate respectively. 224 <5JLS, RESINS AND VARNISHES. of hydrogen, so that the formulae for the above salts are (C ir H 35 COO) 3 C 3 H 5 and (Ci 5 H 31 COO) 3 C 3 H 5 . The predominant constituent in most liquid fats ( oils ) is glyceryl oleate, (C l7 H 33 COO) 3 C 3 H 5 , while " drying " oils (v.i.) contain glyceryl salts of the acids of the linoleic and linolenic series. The specific gravity of oils and fats which have these substances as their chief constituents is lower than that of water, varying from 0-913 to 0-937. The fats and oils have no boiling points, decomposition setting in when they are heated to 200° to 300° C. = 392° to 572° F. They cannot be distilled without decomposition, even under reduced pressure, in this respect contrasting with the fatty acids from which they are derived. Towards the higher limit of temperature given above, darkening generally occurs, carbon dioxide and much acrid vapour containing acrolein (C 2 H 3 COH) being evolved. On exposure to air and light, all oils and fats gradually suffer change. A distinction may be drawn between those which tend to "dry" — i.e., to become converted by oxida- tion into solid resinous substances * — and those which do not exhibit this property (" non-drying oils "). The latter instead of drying become rancid. This change appears to be independent of bacterial action, and of that of unorganised ferments, and to need the conjoint influence of air and light. It results in the pro- duction of free fatty acids, generally poorer in carbon and richer in oxygen than are those characteristic of the fat, but the degree of rancidity, as implied by the nauseous smell and taste of the fat, has no direct relation with the percentage of free fatty acid. Nitrogenous substances, which are constant constituents of un- refined fats and oils, both animal and vegetable, appear to increase the rate at which rancidity develops. The breaking down of the fat into fatty acids as the main product must be accompanied by the decomposition of the glyceryl radicle, or the liberation of the glycerin corresponding therewith, but the exact fate of this constituent of the fat is at present unknown. Like other ethereal salts, those of glyceryl are capable of con- version into the corresponding alcohol (glycerin), and an acid or salt of that acid. The term hydrolysis may be used to signify this change, however produced; true saponification (v.i.) is a particular case of hydrolysis. Thus, treatment with water at sl high temperature resolves glyceryl palmitate in the following manner : — (C 15 H 31 COO) 3 C 3 H 5 + 3H 2 0 = C 3 H 5 (OH) 3 + 3C 15 H 31 COOH. Glyceryl palmitate. Glycerin. Palmitic acid. This may also be effected by heating with sulphuric acid, the * Compare the drying of linseed oil described below. ANALYTICAL CONSTANTS OF FATS AND OILS. / 225 exact rationale of this change being scarcely understood, or by heating with a sufficiently powerful base, with which the liberated fatty acid will combine, the process being known as saponifi- cation, e.g. : — (C 17 H 33 COO) 3 C 3 H 5 + 3NaOH = C 3 H 5 (OH) 3 + 3Ci 7 H 33 COONa Glyceryl oleate. Glycerin. Sodium oleate (soap). The group of fatty bodies known as waxes (the term including both liquid and solid substances) is sharply distinguished from ordinary fats and oils in that its members do not contain glyceryl, but are ethereal salts of alcohol radicles which only replace one atom of hydrogen (instead of three). Thus, beeswax contains the radicle of myricyl alcohol (C 30 H G1 OH), being myricyl palmitate, C L -H 31 COO(C 30 H 61 ). The waxes are generally more stable in air than are glyceryl derivatives, showing no tendency to dry or to become rancid. On hydrolysis, they yield their characteristic alcohols and acids in a manner similar to that of ordinary fats, though usually with somewhat greater difficulty. Although several ethereal salts may be regarded as the pre- dominant constituents of specified fats and oils, yet each indi- vidual fat or oil invariably contains two or more ethereal salts, similar in properties and differing but little in ultimate compo- sition. The difficulty met with in attempting to separate the proximate constituents has given rise to the use of indirect methods of analysis and investigation, which although they do not in all cases determine accurately the nature and proportions of the constituents of any given oil, yet afford data sufficient for determining the identity of any given oil, and for giving an insight into its composition. Thus, the percentage of halogen (notably I and Br) which an oil will absorb under standard conditions, gives a measure of its content of ethereal salts of un- saturated fatty acids ; this value is termed the iodine or bromine number or absorption. Similarly, although it is impracticable to determine the molecular weight, or even the equivalent weight (because of the difficulty of complete proximate analysis), of the several constituents of an oil, with the view of ascertaining the nature of each ethereal salt present, yet a mean number for this value, characterising different classes of oils (v.i.), may be obtained from the percentage of base neutralised in the saponification of the oil. When this percentage is calculated in terms of an equivalent of the base, the mean equivalent weight of the oil is obtained. The mean equivalent weight of the oil is termed the saponification equivalent. Thus, oils consisting chiefly of ethereal salts with a high equi- valent weight have a high saponification equivalent, and those with a low equivalent weight a low saponification equivalent. Examples of each will be found below. 15 226 OILS, RESINS AND VARNISHES. PREPARATION AND PROPERTIES OF THE CHIEF COMMERCIAL FATS AND OILS. — A convenient classifi- cation of the chief commercial fats and oils is that employed by Allen, which is based on a joint consideration of the origin, properties and constitution of the oils and fats classified. (1) Olive Oil Group. — The members of this group are liquid vegetable oils containing glyceryl oleate as a principal constituent. They are non-drying oils, and are very liable to become rancid. Their specific gravity ranges from 0-914 to 0-920. Their halogen absorptions and saponification equivalents are moderate. Thus the iodine absorptions are from 80 to 100, and the saponification equivalents from 285 to 296. They show great tendency to solidify when exposed to nitrous acid, this solidification, charac- teristic of these oils, being known as the elaidin reaction, and probably consisting in a process of polymerisation which oleic acid and glyceryl oleate are capable of undergoing. The chief members of this group are olive, almond, and earth- nut oil. (2) Rape Oil Group. — These are liquid vegetable oils from the Crucifercti containing glyceryl salts of acids of the oleic series, the most characteristic being brassic or erucic acid, C 21 H 41 COOH. The high equivalent weight of this acid gives these oils high saponification equivalents — e.g., 315 to 330. Glyceryl salts of acids of the ricinoleic series are also present. These oils have a distinct drying tendency, indicating that they contain glyceryl salts of acids more unsaturated than those of oleic acid, a fact borne out by their comparatively high iodine absorptions — e.g., 97 to 105. Their specific gravity ranges from 0*913 to 0*920 ; they form semi-solid elaidins. The chief repre- sentatives are rape oil and mustard oil. (3) Cotton Seed Oil Group. — These are liquid vegetable oils ranging in specific gravity from 0 9 17 to 0-926. They all dry slowly and imperfectly, and are thus distinguished from the true drying oils. As might be expected from the fact that they dry, they have a fairly high iodine absorption (105 to 130), while their saponification equivalent is similar to that of oils of the first group. They yield semi-solid elaidins. The chief members are cotton seed, maize, sesame and sunflower oil. They probably contain glyceryl salts of acids of the linoleic and linolenic series. (4) Linseed Oil Group. — These are the true drying oils ; they are characterised by a high specific gravity, 0-924 to 0-938, and a high iodine absorption, ranging from 133 to 170. The saponification equivalent varies from 268 to 300. They contain glyceryl salts of unsaturated fatty acids, such as linoleic, linolenic and iso-linolenic acids, which are capable of oxidation and the production of varnish-like bodies (this change constituting the drying of the oil). The principal members are linseed, poppy- seed and walnut oils. TALLOW GROUP OF OILS AND FATS. 227 (5) Castor Oil Group. — These oils are distinguished by their great viscosity and high specific gravity (0 937 to 0-970). Certain of these, notably castor oil, contain the glyceryl salt of ricinoleic acid as a characteristic constituent. The group is not otherwise possessed of distinctive qualities ; the following oils are conveniently included here, as not falling into any of the preceding classes : — Castor, croton, curcas, and Chinese wood oil. (6) Palm Oil Group. — These are vegetable oils solid at the ordinary temperature. Their characteristic constituents are the glyceryl salts of saturated fatty acids lower in the series than stearic acid — e.g., palmitic acid. Their iodine absorptions (from the fact that saturated acids are mostly present) are low (34 to 54). Their saponiti cation equivalents are also low (277 to 286). On account of these oils being solid at the ordinary temperature, their specific gravities at 15° C. = 59° F. are not comparable either among themselves or with those of other oils. The deter- mination of the specific gravity of oils solid at the ordinary temperature, is generally made at 100° C. = 212° F., and com- parison is then practicable. Thus, at this temperature the specific gravity of palm oil varies from 0*857 to 0*861. All these oils are liquid above 45° C. = 113° F. The chief members of the group are palm oil, cocoa butter and illipe oil. (7) Coco-nut Oil Group. — These are also vegetable oils solid at the ordinary temperature. Their melting points are all below 30° C. = 86° F. They are characterised by containing the glyceryl salts of acids of the acetic series which are volatile with steam at 100° C. = 212° F. — e.g., lauric acid. Their specific gravity at 100° C. varies from 0-868 to 0-878. The iodine absorption is generally low (7 to 15), and the saponification equivalent is also low (209 to 270). The chief members of the group are coco-nut oil, palm-nut oil and laurel oil. Two vege- table oils, somewhat analogous in respect of the fact that they are solid at the ordinary temperature, are Japan wax and myrtle wax, which are included for convenience in this group. They are not characterised, however, by the presence of glyceryl salts of the lower acids of the acetic series, Japan wax consisting mainly of glyceryl palmitate, and myrtle wax having a similar composition. (8) Lard Oil Group. — These are animal oils, liquid at the ordinary temperature, and consisting chiefly of glyceryl oleate. They do not dry; their specific gravity at 15° C. =59° F. varies from 0-914 to 0*916 ; their saponification equivalent from 290 to 299 and their iodine absorption from 55 to 75. The chief members of the group are neatsfoot oil, bone oil, lard oil and tallow oil, the last-named pair being expressed from lard and tallow respectively. (9) Tallow Group. — These are animal oils, solid at the or- 228 OILS, RESINS AND VARNISHES. dinary temperature. They are all liquid above 58° C. = 136° F. They consist essentially of glyceryl stearate, palmitate and oleate, the proportions of these bodies determining their con- sistency. Their specific gravity at 100° C. = 212° F. varies from 0*856 to 0*870, the latter figure being reached by butter fat, which is otherwise abnormal (v.i.). Their saponification equiva- lents (except that of butter) vary from 283 to 292 ; iodine absorption 33 to 62. The chief members of the group are beef and mutton tallow, lard, horse fat, bone fat and butter fat. (10) Whale Oil Group. — These are marine animal oils con- taining glyceryl salts of fatty acids of the oleic series, although the drying tendency of many members lends probability to the belief in the presence of more easily oxidisable fatty acids ; in this respect they resemble oils of the cotton seed group. Their specific gravity at 15° C. = 59° F. varies from 0*911 to 0*933; their saponification equivalent from 250 to 300, and iodine absorp- tion from 99 to 166. Many oils of this group are distinguished by their content of the monohydric alcohol, cholesterol, C 26 H 43 OH,* occurring either in the free state, or as the salt of a fatty acid. The chief members are whale oil, seal oil, menhaden oil, cod- liver and shark-liver oil. (11) Sperm Oil Group. — These oils (which are liquid at the ordinary temperature) do not contain glyceryl salts, but are essen- tially ethereal salts of such monohydric alcohols as dodecatyl alcohol, 0 12 H 25 OH, and pentakaidecatyl alcohol, C 15 H 31 OH ; the acids forming the salts are oleic and its homologue dceglic. The specific gravity of these oils is from 0*875 to 0*884 at 15° C. = 59° F. Their saponification equivalent varies from 380 to 456 and iodine absorption from 80 to 85. The chief members are sperm oil and dcegling or bottle-nose oil. These oils may be regarded as liquid waxes. (12) Wax Group. — The members of this group do not con- tain glyceryl salts, and thus resemble those included in group (11), but are distinguished from them by being solid at the ordinary temperature. The principal salts contained in these waxes are cetyl and myricyl palmitates, and ceryl and myricyl cerotates. Their specific gravity at 100° C. = 212° F. ranges from 0*800 to 0*842. They are all liquid above 88° C. = 190° F. Their saponification equivalent is high, ranging from 438 to 900. TYPICAL PROCESSES OP WINNING AND REFINING FATS AND OILS. (1) Methods of Winning and Refining Vegetable Oils. — (a) Oils from Seed and Fruit.— The seed is either decorticated * Both this hody and an analogous substance, phytosterol, are found re- spectively in other animal and vegetable oils. EXTRACTION OF OILS BY MEANS OF VOLATILE SOLVENTS. 229 or not according to the quality of oil-cake to be produced, and crushed under stamps or between edge-runners or rollers. The crushed product is then submitted to pressure (generally in an hydraulic press), either cold, when a comparatively small yield of mild-flavoured oil is obtained,* or hot, when the maximum yield possible by pressure results. In the latter case the crushed seed passes from the rollers into a steam-heated kettle where it is sprinkled with water, the moist hot mass then going to the presses. The crude oil, containing debris from the seeds, dis- solved resinous matter, colouring material, albuminous and pectinous substances and free fatty acid, is refined by subsidence, nitration through cloths, ttc, by gravitation or pressure, and treatment with 1 to 2 per cent, of strong sulphuric acid (which chars albuminous matters), followed by alkali to decompose any sulphonic acids that may have been formed, and washing with water. After refining, oils may be improved in colour by filtra- tion through animal charcoal, exposure to sunlight and treatment with oxidants — e.g., potassium permanganate. (b) Vegetable Waxes. — These are often rendered in the manner to be described for animal fats, or are extracted with a volatile solvent. If direct pressure be used, a higher temperature is requisite than is needed for ordinary seed oils, on account of the high solidifying point of vegetable waxes. (2) Methods of Winning and Refining Animal Oils. — The process most generally in use is known as rendering. It is simpler than that necessary for the extraction of seed-oils, the reason being that much fat-containing material from animals is not only richer in oil than are seeds and the like, but also is enclosed in less impervious envelopes, animal membranes being less stable and mechanically resistant than are the cellulose husks and shells characteristic of vegetable oil-bearing materials. It is thus sufficient to boil the fatty matter with water or steam, and collect the oil which comes to the surface. In many cases, notably in winning marine animal oils, it suffices to allow the oil-bearing organ (e.g., the liver) to soften by putrefaction, the oil draining out and the residue being rendered by moist heat. Purification is usually less elaborate than that requisite for seed- oils, and consists in rendering afresh with hot water or brine, or with dilute sulphuric acid. (3) General Method of Extraction by means of Volatile Solvents. — The most rational method of winning oils when a maximum yield is the primary object to be obtained, is that used in the laboratory — viz., the repeated extraction of the oil- bearing materials with a volatile solvent, which is continually recovered by distillation and used again, the whole apparatus being typified by the well-known Soxhlet extractor. The * The oil resulting from this process of extraction is known as " cold- drawn." 230 OILS, RESINS AND VARNISHES. extraction, however, is liable to remove substances other than oil — e.g., unsaponifiable matters of the class of cholesterol, and resinous substances. The process is, therefore, chiefly used for extracting residues from other methods of winning. The material is either extracted systematically in a series of steam- jacketed tanks or discontinuously in an apparatus similar to that shown in Fig. 35. The material— e.g., the residue from olive oil presses — is packed into the extractor, B, and carbon bisulphide is pumped from the tank, A, into the extractor, which it enters beneath the per- forated false bottom, d. It percolates through the matter to be extracted, through the perforated plate d 1 , and passes into the still, D, through the pipe shown at d 1 . The carbon bisulphide, containing oil in solution, is distilled in D by closed steam, the Fig. 35. — Oil extractor. A, tank : B, extractor ; d, perforated false bottom ; d l , perforated plate ; D, still ; C, worm ; k, cock ; /, steam pipe ; e, pipe communicating with the worm, C ; I, pipe leading from the still D. vapour being condensed by the worm, C, and the liquid collecting in the tank, A. The process is continued until a sample of the solvent drawn from the cock, k, is found free from fatty matter. Steam is then injected under the false bottom of the extractor through the pipe,/j and the residual solvent thus distilled through the pipe, e — communicating with the same worm as that fitted to the still — into the tank, A. All the fat will ultimately remain in the still, D, whence it is drawn by the pipe, I. Carbon bisulphide is, in many respects, the best solvent for fats and oils, but its use is somewhat risky on account of its low boiling point (4G° C. = 115° F.) and inflammability. Other solvents are used, notably benzene, ether, and light petroleum. Carbon tetrachloride has also been proposed, but its preparation is some what costly. EARTH-NUT? OIL. 231 PROPERTIES AND USES OF THE CHIEF COM- MERCIAL FATS AND OILS. — Olive oil is obtained from the fruit of several varieties of the Olea Europcea, the quality of the oil varying slightly with the class of tree yielding the fruit. The nearly ripe olives, containing 30 to 50 per cent, of oil, are generally first submitted to slight hand pressure, whereby the "virgin oil" is obtained. The yield of this is very small, the bulk of the oil being obtained by crushing the flesh in edge-runners or between rollers, followed by moderate pressure, the first product being the best. The marc or press-cake is broken up, stirred with boiling water, and then more strongly pressed ; the second marc is similarly treated, the stones also being crushed and very strongly pressed. Each succeeding ex- traction yields an oil inferior to that preceding it ; and the residual oil in the final press-cake may be obtained by extraction with volatile solvents. Inferior olive oil, not fit for dietetic purposes, but used for lubrication, although containing 7 to 8 per cent, of free oleic acid, is known as gallipoli or engine oil. Sometimes the kernels are crushed or extracted separately, yielding olive kernel oil, which is similar to low-grade olive oil. The yield of oil is some 20 to 40 per cent, of the weight of the fruit. Olive oil possesses the colour characteristic of the fruit, its green tinge being due to chlorophyll. It has a mild flavour when fresh, but becomes rancid more readily than true seed oils. It consists of about 70 per cent, of glyceryl salts liquid at the ordinary temperature (chiefly oleate), the remaining 30 per cent, being chiefly glyceryl salts of fatty acids of the acetic series (notably palmitic acid) ; these partially separate on cooling to about 10° C. = 50° F. The specific gravity of olive oil varies from 0-914 to 0*917 at 15° C. = 59° F., its saponification equi- valent is 285 to 296, and iodine absorption 81*5 to 84-5. The oil is often adulterated with cheaper oils of about the same specific gravity, such as cotton-seed and sesame oil. It is used for eating, lubrication, burning, making Turkey-red oil (q.v.), and soap making. Almond oil is obtained from both sweet and bitter almonds, but must not be confused with oil of bitter almonds (benzal- dehyde). It much resembles olive oil, but is generally less coloured. It is used chiefly in pharmacy. Earth-nut oil (arachis oil, ground-nut oil, pea-nut oil) is obtained from the fruit of Arachis hypogcea by drying and press- ing, some 40 per cent, of oil being obtained as the gross yield of several treatments, 45 per cent, being about the content of the seeds. The cold-drawn oil is used for eating instead of olive oil, the remaining portions serving for lighting and soap making. The pressed oil cake, containing some 8 per cent, of oil, is used as cattle food. Earth-nut resembles olive oil in composition, save that a part of the glyceryl palmitate is replaced by glyceryl 232 OILS, RESINS AND VARNISHES. arachidate, and part of the glyceryl oleate by glyceryl hypogseate. Arachidic acid has a melting point as high as 75° C. = 167° F., and its isolation and identification are used as a means of detect- ing and estimating the oil when present as an adulterant. The specific gravity varies from 0*916 to 0*920; saponification equi- valent, 289; iodine absorption, 91 to 105. Rape oil (colza oil) is obtained from varieties of Brassica campestris, the seeds being crushed, heated, and pressed in the manner described as characteristic of seed oils. The crude oil is refined by treatment with sulphuric acid, sometimes followed by alkali to remove traces of sulphuric acid and also free fatty acid resulting from the action of the sulphuric acid on the oil itself. The residual cake is used for manure. The oil-content of the seeds varies from 30 to 45 per cent., the yield from 28 to 36 per cent., and the quantity of oil left in the cake from 7 to 10 per cent. Kape oil contains glyceryl oleate and erucate, stearate and rapate. Its specific gravity is from 0*914 to 0*916 at 15° C. = 59° F. ; saponification equivalent, 314 to 328 ; iodine absorption, 97 to 103. It is chiefly used for lighting and lubri- cation, and as an adulterant for olive oil. It is often adulterated with cotton-seed oil. Its viscosity is greater than that of any ordinary fatty oil, except castor oil, and is therefore taken as an arbitrary standard in viscosimetry. Hape oil becomes gummy on exposure to air, but does not actually dry. Cotton-seed oil is expressed from the seeds of various species of Gossypium after the cotton itself has been removed. The seed and its cortex are cut through and parted by screening in a separator. The decorticated seed is then crushed for oil in the ordinary way. Decortication is particularly necessary for cotton seed, inasmuch as the oil cake left after expression of the oil is used for cattle feeding, a purpose for which it would be unfitted were the hulls suffered to remain. The content of oil in the decorticated seed is from 20 to 25 per cent.; the yield is about 15 to 20 per cent., and the oil cake retains about 10 per cent. The crude oil is dark in colour, and contains much pectinous matter. The colouring constituent is removed by treatment with alkali, and the alkali salt formed becomes blue on oxida- tion (cotton-seed blue). The specific gravity of refined cotton- seed oil varies from 0*922 to 0*924, its iodine absorption from 105 to 109, and saponification equivalent from 285 to 294. It has a slight tendency to dry, and is used as a substitute (ad- mittedly or fraudulently) for olive oil in cooking, as a constituent of margarine, for soap making, and as an adulterant for most dearer oils and for making factitious lard. By freezing cotton- seed oil, the glyceryl salts, which are solid at low temperatures, are separated, constituting cotton-seed stearin, which is used as an ingredient of margarine. Cotton-seed oil consists chiefly of the glyceryl salts of oleic and linoleic acids, the drying pro- perties of the oil being due to the latter. LINSEED OIL. 233 Maize oil is contained chiefiy in the germ of the grain, and is won by removing the germ previous to using the maize for spirit making, and pressing the separated germs in the ordinary manner. About 15 per cent, of oil is obtained, the residue con- stituting feeding cake. Maize oil is a yellow liquid of specific gravity 0*920 to 0-925, iodine absorption 116 to 122, and saponi- fication equivalent of 280 to 290. The oil is used for lighting, lubrication and soap making. Sesame oil is another example of the cotton-seed oil group. It is obtained by crushing the seeds of Sesamum orientate, com- monly called til-seed. The seeds contain 47 to 56 per cent, of oil. The oil has a specific gravity of 0*921 to 0 9 24, an iodine absorption of 103 to 110, and a saponification equivalent of about 294. It is used as a food in place of olive oil, and is sometimes mixed with the latter as an adulterant ; it is also employed for burning, lubricating and soap making. Sesame oil contains some 76 per cent, of glceryl oleate, the remainder containing glyceryl salts of acids of the acetic series. The semi-drying properties of oils of the cotton-seed class are probably due to the presence of glyceryl salts of acids of the linoleic and linolenic series. Linseed oil is by far the most important of the drying oils. It is obtained from the seed of the flax plant, which contains 30 to 35 per cent, of oil, the yield by pressing being about 26 per cent. The seed is crushed in the manner already described, and the oil cake used for cattle food. The oil is refined by treatment with a small quantity of sulphuric acid, with sub- sequent washing. Linseed oil, as obtained by simple pressure and refining, is known as raw oil, but when the oil has been heated to enhance its drying properties it is known as "boiled oil," and in that state is used as a vehicle for pigments. Accord- ing to recent researches, linseed oil consists (disregarding the small quantity of glyceryl salts of acids of the acetic series solid at the ordinary temperature, which it contains) of some 65 per cent, of the glyceryl salt of iso-linolenic acid and 15 per cent, of that of linolenic acid, 15 per cent, of the glyceryl salt of linoleic acid, the remainder (5 per cent.) being glyceryl oleate. Linseed oil is generally yellow, but sometimes has a greenish tinge ; its specific gravity varies from 0*930 to 0*937 ; iodine absorption 155 to 170; saponification equivalent 288 to 300. The characteristic property of linseed oil is that when spread in a thin film it dries to a varnish-like surface. The changes involved in this process are not fully understood. The oxidation of the oil involves the transformation of the acids named above into anhydrides of hydroxy-acids, one of which anhydrides is termed linoxyn. Glycerides of the hydroxy-acids themselves also exist in the dried oil. The precise composition of linoxyn is disputed, but it appears to be the chief constituent 234 OILS, RESINS AND VARNISHES. of the film produced by the drying of linseed oil, and to owe its value largely to its insolubility in most menstrua. What has been said here with regard to linseed oil, applies also to other drying oils, which dry the more readily the more linolenic and iso-linolenic acids they contain. The quality of commercial linseed oil varies considerably, that known as Baltic being esteemed the best, while East Indian or Calcutta is inferior. Generally speaking, oil with a high specific gravity and iodine absorption is of better quality than that in which these analy- tical constants are low. Boiled linseed oil is prepared by heating the raw oil, either by a free flame or by high-pressure steam, to a temperature varying from 130° C. = 266° F. to 200° C. = 392° F. for several hours. Sometimes air is blown through the oil, and in all cases "driers" are added. * These bodies — types of which are litharge and manganous borate — probably act as carriers of oxygen. Only a small proportion of the drier added is dissolved by the oil. The drier is added to the extent of about 5 per cent, of the weight of the oil, and is first ground with oil to allow it to mix readily with the bulk. About 0 3 to 1*5 per cent, remains in the boiled oil produced. The process of boiling is probably one of polymerisation and limited oxidation ; the appearance of ebullition is not due to true boiling, but to the escape of gaseous products of decomposition. Boiled linseed oil is darker than the raw oil, higher in specific gravity (0*937 to 0 952), and lower in its iodine absorption. It is frequently adulterated with rosin oil, which itself dries imperfectly. When the boiling of linseed oil is pushed very far, a much larger amount of polymerisation and oxidation occurs, and the product is viscous, stringy, but not greasy, and forms the basis of printing ink. This process is conducted without the addition of driers, and is sometimes continued until the oil takes fire. Another product of the same type is the oil used for linoleum making. Most of this is prepared by exposing linseed oil already partly " boiled," but without appreciable darkening, to the air on sheets of textile material called "scrim" at a tem- perature of about 21° C. = 70° F. During this change much acrolein i* evolved by the oxidation of the glyceryl radicle of the oil. The product, which is a tough translucent, gelatinous, non-greasy mass, is heavier than w r ater ; it is incorporated with cork powder and gum resins and formed into sheets. Recently, attempts have been made to expedite the oxidation by blowing air through the warm oil, instead of exposing it on scrim. Blown oils are non-drying, or partially drying, oils, rendered very viscous by blowing air through the hot oil. They are used to impart viscosity to mineral lubricants. The change effected by blowing may be judged from the following figures for blown * In the parlance of varnish-makers, a boiled oil is one which has been heated after the addition of driers. It is sometimes customary to add the driers to the heated oil after it has cooled. TUHKEY-RED OIL. 235 rape oil : — Specific gravity at 15° C. = 59° F. 0-967, iodine number 63*6, saponification equivalent 280. Blowing with oxygen has also been suggested. Castor oil is made from the seeds of Ricinus communis, of which there are two kinds, the small and large seeded. The former yields the better oil (used in medicine), and is cold pressed. The refining is performed by adding a pint of water to a gallon of the oil, and boiling until the water is evaporated and the mucilage deposited. The larger seeds are generally roasted, crushed, and boiled in water until the oil rises to the surface and can be collected. The seed contains about 55 per cent, of oil, 50 per cent, being .about the yield obtained by several pressings. Castor-oil seeds contain a nitrogenous prin- ciple, ricin, of marked poisonous and purgative properties ; the presence of a trace of this substance in the expressed oil probably imparts to it its well-known purgative property. Castor oil has a specific gravity at 15° C. = 59° F. of 0*958 to 0*970, a saponifi- cation equivalent of 309 to 319, an iodine absorption of 84 to 85. Its viscosity is very high — viz., 1,100, taking the viscosity of normal rape oil at 60° F. as 100. It is further characterised by its solubility in alcohol and sparing solubility in petroleum spirit. The characteristic constituent of castor oil is glyceryl ricinoleate, with which small quantities of the glyceryl salts of acids of the acetic series are associated. Castor oil, besides its use in medicine, is employed for burning, lubricating and soap making, and for making Turkey-red oil. Turkey-Red Oil. — This is a generic title applied to the products of the action of sulphuric acid upon oils — e.g., olive and cotton, but especially castor oil — which are used in mordanting fabrics to be dyed with alizarin. For making Turkey-red oil, sulphuric acid to the extent of from 15 to 40 per cent, of the weight of the oil is run into a vat containing the latter, in such a manner that the temperature can be readily controlled. After some twenty-four hours, brine is added as a washing agent. The use of brine is necessary, as the main product is soluble in water. A partial neutralisation with alkali follows, and water is added, so that the finished Turkey-red oil may contain some 45 to 50 per cent, of fatty matter. The action of sulphuric acid on the castor oil appears to result in the hydrolysis (p. 224) of the oil, and the formation of polyricinoleic acids and their sulphuric acid derivatives. The condensation of the ricinoleic acid (hydroxy- oleic acid) may be typified by the following equations : — (1) HOC !7 H 32 COOH + H 2 S0 4 = HS0 4 C ]7 H 32 COOH + H 2 0 Ricinoleic sulphuric acid. (2) HOC ]7 H 32 COOH 4- HS0 4 C 17 H 32 COOH = HOC 17 H 32 COOC 17 H 32 COOH + H 2 S0 4 " Diricinoleic acid." 236 OILS, RESINS AND VARNISHES. About 65 per cent, of Turkey-red oil— i.e., the sulphuric acid derivatives — is soluble in water, the insoluble portion consisting largely of unattacked oil and polyricinoleic acid. Palm oil is expressed from the flesh of the fruit of Elais guineensis, a species of palm, after a period of fermentation. It has the consistency of butter, a yellow or reddish colour, and a pleasant smell. Its melting point varies from 25° to 36° C. = 77° to 97° F. ; specific gravity at 15° C. = 59° F. is 0-920 to 0 9 27 ; saponification equivalent 277 to 286 and iodine absorption 48 to 54. It consists of glyceryl palmitate and oleate ; it readily becomes rancid and frequently contains much free fatty acid — e.g., 10 to 25 per cent. It is used for making axle-grease, soap and candles. The oil from the kernel of the same fruit (palm kernel oil) is also of buttery consistency, but contains a large proportion of glyceryl salts of lower fatty acids, and resembles coco-nub oil ; it is used for soap making. Coco-nut oil is obtained from the fruit of Cocos nucifera, the dried pulp (coprah), containing some 65 per cent, of oil, being shredded, fermented and pressed. It is refined by heating it with water until the latter has evaporated, as in the case of castor oil. The yield of oil is about 55 per cent. Coco-nut oil is characterised by consisting chiefly of glyceryl laurate, some glyceryl salts of higher acids of the same series being present. It forms a white buttery mass, often containing a good deal of free fatty acid. When fresh its smell is agreeable and recalls its origin, but the oil easily becomes rancid. It melts at 20° to 28° C. = 68° to 82° F., its specific gravity at 100° C. = 212° F. is 0-868 to 0-874, and its saponification from 209 to 228 ; iodine absorption 7 to 9. The expressed cake is used for cattle food, and the oil for soap making (especially marine soap, Vol. II., Chapter XI.), nightlights, and as a constituent of margarine. Neatsfoot oil is obtained from the feet of cattle, which are washed from blood, boiled, and the oil skimmed off; this forms an inferior grade ; an oil of better quality is obtained by direct excision of fatty deposits. It is refined by subsidence, and then forms a yellowish oil, consisting mainly of glyceryl oleate, and therefore not readily becoming solid on cooling. Its specific gravity is 0-914 to 0-916 at 60° F. = 15*5° C; saponification equivalent 299 ; iodine absorption 66 to 72. It does not easily become rancid, and is useful as a lubricant at low temperatures and for dressing leather. Tallow is the generic name for the rendered fat of cattle and sheep. " Mutton tallow " includes the fat from sheep and goats ; beef tallow that from neat cattle. The process of rendering consists in heating the crude fat by direct fire or closed steam, whereby the tissue is broken up and the fat separated. Dilute sulphuric acid is sometimes used for the same purpose of dis- integrating the membrane enclosing the fat. The roasted tissues BUTTER. 237 from the open process are termed "graves," and are used for feeding pigs and poultry ; the less heated tissues from the steam process are utilised for making ammonia and glue. The rendered tallow is refined by boiling with water and settling, and is often bleached by oxidising agents.* Tallow consists essentially of glyceryl stearate (with some palmitate) and oleate, the former constituent amounting to from J to | of the whole. From this it is obvious that the analytical figures for tallow vary through a tolerably wide range. Thus, it melts at 40° to 45° C. = 104° to 113° F. ; its specific gravity at 15° C. = 59° F. is 0-925 to 0-940, mutton tallow giving the higher value ; saponification equivalent 283 to 290 ; iodine absorption 33 to 46, beef tallow having the higher value. When rancid, tallow often contains a good deal of free fatty acid. It is adulterated with bone fat and sometimes with cotton-seed stearin, as well as with non-fatty organic substances and mineral matter. It is used as a lubricant (Vol. I., p. 115) and for soap and candle making. Lard was a term originally confined to the fat from the omentum of the pig, but is now applied to the whole fat of the animal. The parts containing fat are treated in a manner similar to that used in rendering tallow. Lard consists chiefly of glyceryl oleate and stearate, its softness depending on the proportions of these constituents. "Bladder lard," which is the best variety from the kidney fat of the animal, is hard and melts at 42° to 45° C. = 108° to 113° F. " Keg lard," an inferior quality, melts at 28° to 38° C. = 82° to 100° F. Lard is commonly adulterated by expressing lard oil from it and substituting the cheaper cotton-seed oil. (Lard oil is similar in its properties to neatsfoot oil, and is used for lighting and lubricating.) The specific gravity of lard at 100° C. = 212° F. is 0-859 to 0-860; saponification equivalent 280 to 292 ; iodine absorption 55 to 62. The chief use of lard is as a food stuff. Butter is distinguished from all other fats by the large per- centage of volatile fatty acids which it contains. Butter consists of the fat of milk (cream), agglomerated by breaking down the globules of which the fat is constituted. The collection of the cream is done by hand-skimming, or by the use of a centrifugal machine. Normal butter, not strongly salted, contains about 87 per cent, of butter-fat, 0*5 per cent, casein, 0-3 per cent, salt, and 11*7 per cent, water. Butter-fat itself consists of 60 per cent, of glyceryl oleate, 35 per cent, of stearate and palmi- tate, and 5 per cent, of butyrate, with traces of other low fatty acids of the acetic series. Butter, unless freed from casein, &c, or heavily salted, readily becomes rancid, its objectionable taste and smell, when in this condition, being due to butyric acid. * Tallow is sometimes hardened by the conversion of its olein into elaidin by treatment with nitric acid (p. 226). 238 OILS, RESINS AND VARNISHES. The specific gravity of butter-fat at 100° C. = 212° F. is 0 867 to 0-870 ; melting point 29° to 35° C. = 84° to 95° F. ; saponifi- cation equivalent 241 to 253 ; iodine absorption 19 to 38. Margarine is a substitute for butter, made by exposing beef or mutton suet, preferably the former, to a temperature of about 50° C. = 122° F., and collecting the liquid portion which drains away. This liquid is kept at 25° C. = 77° F. until the glyceryl salts, solid at that temperature, have separated, and the resulting mass is pressed. This last oil becomes buttery in consistency at the ordinary temperature. It is churned up with milk to give it a butter-like flavour. Should the product be too solid, it may be mixed with cotton seed oil ; a yellow tint is imparted by annatto, turmeric or saffron. The main chemical difference between margarine and butter is the absence in the former of the glyceryl salts of lower fatty acids. (Coco-nut oil is sometimes used in making margarine, and supplies a certain amount of glyceryl salts of fairly low fatty acids. The char- acteristic flavour of coco-nut oil is removed by treatment with alcohol and animal charcoal.) The specific gravity of mar- garine is from 0-859 to 0-863; melting point 34° to 40° C. = 93° to 104° F. ; saponification equivalent 285 to 290 ; iodine absorp- tion 50 to 56. Whale oil (train oil) is a typical marine animal oil obtained from the blubber of various kinds of whale by boiling this with water, and skimming off the oil. Glyceryl phj^setoleate, (C 15 H 29 COO) 3 C 3 H 5 , and glyceryl salts of other acids of the oleic series, and of the acetic series, are the chief constituents of this oil. It is a brown liquid with a characteristic fishy odour. Specific gravity 0*920 to 0*931 ; saponification equivalent 250 to 296 ; iodine absorption about 110 or higher. Some marine oils dry rapidly. The chief uses of the oil are for soft soap making and leather dressing. Cod-liver oil is prepared by washing and drying the livers, and putting them into open barrels ; the oil slowly exudes, and is skimmed off the surface ; it is filtered through blotting-paper to refine it. This product constitutes the best medicinal oil. The livers, after this treatment, are heated in sheet-iron pots suspended in boiling water, a further yield of oil being obtained. The older method is to throw the livers into a cask, and allow them to ferment, the resulting oil being ladled off as it rises. The residual livers are boiled in kettles until the water present is evaporated ; the oil is strained, and, being crude and of a brown colour, is used only as tanners' oil. The therapeutic value of cod liver appears to be due rather to its easy assimila- tion as a fatty food, than to the minute quantity of iodine which it contains, that having been alleged to be useful. Cod-liver oil consists chiefly of glyceryl oleate and myristate, palmitate and stearate ; a small percentage of glyceryl salts of volatile acids of BIRD LIME. 239 the acetic series is also present, and a small quantity of choles- terol. The specific gravity of cod-liver oil is from 0*925 to 0*930 ; saponification equivalent 263 to 303 ; iodine absorption 159 to 166. It is adulterated with other liver oils, and with seal oil. Sperm oil is distinguished from all the foregoing oils by containing only small quantities of glyceryl salts. It consists essentially of dodecatyl oleate and physetoleate, and a little cetyl palmitate. It is obtained from the head of the sperm whale {Physeter macrocephalus) from which it is ladled out and drained away from the accompanying spermaceti. It is a yellow mobile oil not easily becoming rancid, and excellent as a lubricant. On account of its peculiar constitution its analytical constants differ notably from those of fatty oils consisting of glyceryl salts. Its specific gravity is 0*875 to 0*884 ; saponification equivalent 380 to 454; iodine absorption 81*3 to 85. The yield of higher monohydric alcohols obtained on its saponification is 38 to 41 per cent. Spermaceti is the solid product associated with sperm oil. It consists essentially of cetyl palmitate. The crude material is of a yellowish colour, and is purified by being boiled with a limited amount of caustic potash, to saponify adhering oil. It has a characteristic crystalline structure ; melts at 48° to 49° C. = 118° to 120° F. ; specific gravity at 100° C. = 212° F. 0-808 to 0*812; saponification equivalent 438. It is liable to be adulterated with stearic and palmitic acids, tallow and paraffin wax. It is used in pharmacy and for candle making. Beeswax is made from honeycomb, after the removal of the honey, by melting in water, allowing the impurities to settle and running off the wax. The yellow wax obtained in this way is often bleached by treatment with chromic acid, or exposure to sunlight, the bleaching being aided by the addition of a little fatty matter. Beeswax consists of about 80 to 85 per cent, of myricyl palmitate, the balance being chiefly free cerotic acid with a little melissic acid. Specific gravity at 100° C. = 212° F. is 0*819 to 0*829; melting point 62° to 64° C. - 144° to 147° F. ; saponification equivalent 584 to 602. It yields 53 to 54 per cent, of myricyl alcohol on saponification. It is adulterated with water, mineral matter, foreign fats, paraffin wax and vegetable waxes. It is used for candle making and in pharmacy. Bird lime may be mentioned here, as it is a substance stand- ing between oils of the sperm oil class and the waxes. It is obtained as an extremely sticky tenacious mass by macerating- the inner bark of the holly. It consists essentially of mochyl palmitate and ilicyl palmitate, both mochyl alcohol (C 96 H 4C 0) and ilicyl alcohol (0 22 H 38 0) being monohydric. 240 OILS, RESINS AND VARNISHES. II. TURPENTINES, RESINS, CAOUTCHOUC. The resinous exudations from the stems of trees of the Coni- ferse class consist of solutions of resins in essential oils, the most familiar example being common turpentine, from which rosin and oil of turpentine are obtained. The resins are compounds of carbon, hydrogen and oxygen, which have the character of acids or anhydrides, being capable of combination with alkalies. The essential oils are volatile hydrocarbons, usually terpenes of the general formula (C-H s )„ and their congeners. Mixtures of hydrocarbons and resins of this type are also known as oleo- resins. When resins occur associated with gums instead of hydrocarbons, the mixed bodies are known as gum resins, while when benzoic acid and its congeners are present, the mixed bodies are called balsams. Oil of Turpentine (spirits of turpentine, "turpentine" "turps"). The crude oleo-resin or true turpentine is an exudation from the barks of various conifers, and upon distillation, alone or with water, yields about 20 per cent, of oil of turpentine consisting of various true terpenes, (0 5 H 8 ) 2 . The oil of turpentine thus ob- tained may be rectified by addition of alkali to saturate resin acids, and redistillation. There are three commercial kinds of oil of turpentine. The American consists chiefly of dextropinene. Its specific gravity varies from 0-864 to 0*870 at 60° F. = 15° C, and it distils between 156° C. = 313° F. and 165° C. = 329° F. It usually contains a little resin in solution. The French variety is mostly laevopinene, but save for its direction of optical rotation is similar to American turpentine. Both are often adulterated with petroleum and rosin spirit. They are used for making varnishes and as a vehicle for paints. On exposure to air they slowly resinify. Russian oil of turpentine has sylvestrene as its main constituent (66 per cent.), the remainder being dextro- pinene and cymene. It has a specific gravity of 0*862 to 0*872 at 15° C. = 60° F., and distils between 160° and 170° C. = 320° F. and 338° F. Russian turpentine is not available for paints and varnishes, for the resin which it leaves (2 to 5 per cent.) on evaporation, remains sticky. It is used for making "Sanitas" a disinfecting proprietary preparation made by blowing air through a mixture of the oil and water. The product appears to contain a peroxide of unknown constitution. Essential oils. — Oil of turpentine, already described, is an example of one type of essential oils ; several other classes exist. They are classified by Allen as terpenes, C 10 H 16 — e.g., oil of tur- pentine and oil of lemon ; cedrenes (sesquiterpenes), C 15 H 24 — e.g., cedar oil ; aromatic aldehydes— e.g., oil of bitter almonds (benzal- dehyde, C r H-COH); ethereal salts— e.g., oil of wintergreen or methyl salicylate, 0 6 H 4 (OH)COOCH 3 . The chief methods of RESINS. 241 winning these comprise extraction by pressure (as for oil of lemon) ; distillation in a current of steam, a generally applicable process, the oil when necessary being first liberated by fermenta- tion (as for oil of bitter almonds) ; extraction with a fat or fixed oil, from which, if necessary, the essential oil can be removed by shaking with alcohol. Oil of lemon is extracted by pressing the rind of the fruit just before ripening. Its chief constituent is a terpene, limonene (boiling point 176° C. = 349° F.). The specific gravity of oil of lemon at 60° F. = 15° C. is 0-870. It is used in confectionery and perfumery. Cedar oil is prepared from red-cedar wood by the method of distillation. It consists largely of cedrene, C ir H 34 (boiling point 266° C. = 511° F.). Oil of bitter almonds (benzaldehyde) is obtained by separat- ing the fixed oil (p. 231) from bitter almonds by pressure, and distilling the residue with water ; HON and benzaldehyde, C 6 H 5 COH, are the products, being formed by the hydrolysis of the glucoside amygdalin, under the influence of an unorganised ferment emulsin which occurs in the almond. The oil is mixed with ferrous sulphate and lime, and redistilled, the hydrocyanic acid being thus fixed as calcium ferrocyanide. Benzaldehyde thus obtained is a colourless liquid boiling at 180° C. = 356° F., and having a specific gravity of 105. It can also be prepared synthetically from toluene, C 7 H 8 , by converting it into benzal chloride, C 6 H-CHC1 2 , by chlorination, and heating the product with an alkali and water under pressure. Oil of Wintergreen is obtained by distilling the leaves of Gaultheria procumbens with water ; the yield is about 1 per cent. It consists essentially of methyl salicylate, often associated with a small quantity of terpene. Artificial methyl salicylate is prepared by distilling salicylic acid with methyl alcohol and strong sulphuric acid. It is a colourless liquid, specific gravity 1-18, boiling point 220° C. = 428° F. It is often adulterated with alcohol, chloroform and sassafras oil. It is used in medicine. Many essential oils are associated with a class of bodies known as camphors or stearoptenes, of which common camphor (C 10 H 16 O) is a good type. Camphor is obtained by distillation of the wood of the camphor laurel with water, the crude product being purified by sublimation. It is a white crystalline solid, subliming without fusion at the temperature of the air. Specific gravity 0*986 to 0-996, melting point 175° C. = 346° F., boiling point 204° C. = 399° F. It is soluble in alcohol and sparingly soluble in water. It is largely used as a domestic insectifuge. Kesins. — Common rosin (Colophony) is— as already stated — the residue from the distillation of oil of turpentine from crude turpentine. American rosin has a darker colour than that from 16 242 OILS, RESINS AND VARNISHES. European turpentine. White rosin owes its opacity to the presence of water. The specific gravity of common rosin varies from 1-04 to 1*10; rosin is soluble in most solvents except water; its melting point varies from 100° to 135° C. = 212° to 275° F., but it softens before melting. It consists essentially of abietic anhydride, C 44 H 62 0 4 , easily transformed into the corresponding acid, C 44 H C4 0 5 , by boiling with aqueous alcohol ; its acid character causes it to dissolve in alkalies, and this solution has the properties of a soap, a fact utilised by employing rosin as an addition to fat in soap making (q-v.). Rosin has a saponification equivalent of 300 to 310, and a bromine absorption of 110 to 112. Rosin is also used for varnishes, and in soldering as a protective coating. Much rosin is also used for the manufacture of rosin spirit and rosin oil by destructive distillation. The former is the more volatile fraction. It amounts to about 3 per cent, of the rosin distilled. The quantity of the latter is about 85 per cent, of the rosin distilled ; rosin oil is denser and has a higher boiling point than rosin spirit. Both consist of hydrocarbons of the olefine, acetylene and benzene series, with some terpenes and certain rosin acids. Eosin oil is a yellow or brown liquid, generally fluorescent, of specific gravity 0-98 to 1*10. It dries to some extent when exposed to air in a thin film, and unites with lime to form a grease (rosin grease) used in the manufacture of rough lubricants for trolley wheels. Rosin oil is used as an adulterant for many oils, especially boiled linseed oil, and also for making lithographic inks. Copal is the rosin exuding from trees of the genus Hymencea and others. Some specimens are soft and dissolve in ether, but good copal is hard and insoluble. It is light yellow or brown ; specific gravity 1*06 to 1*08. On heating it undergoes change and becomes more soluble. It is chiefly used for varnishes. Shellac is prepared from the crude rosin exuding consequent on the puncture of the tree Ficus indica by the insect Coccus lacca. The crude stick-lac is stripped off the twigs, and the seed or grain lac is melted in boiling water and poured on to a stone, when it breaks up on cooling into thin pieces. The aqueous solution on evaporation yields lac dye. For decolorising, bleach- ing with sulphurous acid or chlorine is adopted. Shellac is chiefly used for making varnishes, lacquers and sealing wax. Gum benzoin may be taken as a type of the balsams. It is the exudation of Styrax benzoin. It contains from 10 to 20 per cent, of benzoic acid, the remainder consisting of resins. Its melting point varies from 85° to 95° C. = 185° to 203° F. Peru balsam is a similar substance, containing cinnamic in place of benzoic acid. Its specific gravity is about 1*14. Gamboge is an example of the class of gum resins as distinct from oleo-resins and balsams. It has a reddish-yellow colour and is composed of the resin gambogic acid, C 30 H 3 ^O 0 (64 to 74 CAOUTCHOUC. 243 per cent.), gum constituting the balance. It is used as a pigment, . and, to a certain extent, in medicine. Caoutchouc (Indiarubber). — This resinous substance is the inspissated sap of various genera of the three orders Ajiocynacece, Artocarjmcece, and Eujrfiorbiacece, trees which grow in tropical and sub-tropical countries. Trees of the two last-mentioned orders furnish the best caoutchouc, that from Para (in the Amazon district) being the variety of highest quality. Ceara in Rio Janeiro, Madagascar and Mozambique furnish inferior kinds. The sap of the tree is a milky emulsion, and is collected from incisions in the bark. It is coagulated by evaporation (spontaneous or artificial), or by the addition of acid or saline substances. An alkali (e.g., ammonia) retains it in its liquid state. It is moulded into rough lumps or flask-shaped masses or films (Para rubber), for export. It is frequently very dirty, sticks and stones being added as intentional adulterants, and always contains albuminous matter and resinous substances. The imported rubber is cleansed by boiling it with water and macerating it between rollers over which a stream of water flows. The shredded and cleansed raw rubber is then incor- porated with weighting and vulcanising materials (v.i.\ and moulded into the form of the goods to be made. Commercial caoutchouc (rubber) varies much in composition, but its charac- teristic constituent is a hydrocarbon (a polyprene) of the formula (C 5 H 8 ) n . This is often associated with insoluble albuminous matter and from 1 per cent, upwards of resinous substances, these increasing in amount with the state of oxidation of the material. Common qualities contain much of this resinous matter. Pure rubber is serviceable for only a few purposes on account of its plastic and adhesive character, gently-warmed surfaces readily sticking together. When a strip of pure rubber sheeting is stretched to a comparatively slight extent, it returns slowly and imperfectly to its original dimensions. These pro- perties serve to distinguish it from vulcanised rubber. "When heated to 200° C. = 390° F., pure rubber becomes a sticky viscous mass, which is a product of decomposition, inasmuch as on cool- ing it does not harden to the consistency of the original rubber. When destructively distilled, it yields a mixture of hydrocarbons, including caoutchene, isoprene, heveene, all of the general formula (C 5 H 8 ) n . These products form an excellent solvent for rubber itself. Other solvents are chloroform, carbon disulphide, ben- zene and solvent naphtha, none of which, however, dissolves more than 5 per cent, of its weight of rubber. The utilisation of rubber depends on its remarkable behaviour with sulphur. When heated with 5 to 10 per cent, of sulphur to a temperature above the melting point of the sulphur, about 2 per cent, of the element (reckoned on the rubber) enters into some form of com- bination with the rubber. The product (vulcanised rubber) is 244 OILS, RESINS AND VARNISHES. distinguished from raw rubber by its greater indifference to alterations of temperature — it neither becoming soft and sticky on moderate heating nor rigid on slight cooling — and by the possession of greater " elasticity " * and indifference to cold sol- vents, which, at most, cause it to swell, but do not take it into solution. The method of vulcanisation may be briefly described thus : — The raw rubber, being plastic, is capable both of being intimately mixed with the sulphur for its vulcanisation and with any mineral weighting materials that may be added, and of being moulded by any ordinary mechanical process — e.g., rolling or squeezing through dies into sheet, cord, or tube form. The articles thus fashioned are kept in shape by appropriate moulds, which are heated, generally by high-pressure steam, to about 140° C. = 284° F., at which temperature the process of vulcan- ising takes place. Instead of sulphur, "golden sulphide of antimony" (Sb 2 S 5 ) is sometimes used, which decomposes, afford- ing sulphur for vulcanisation and becoming Sb 2 S 3 , thus imparting a red colour to the finished goods. Various loading materials — e.g., chalk, zinc oxide, barium sulphate and lead oxide — are often added, especially to common goods. Lamp black is used for black goods. The vulcanising of rubber can also be performed by the use of sulphur chloride, S 2 C1 2 , in dilute solution, CS 2 being the ordinary solvent. The solvent swells up the rubber and facilitates the penetration of the sulphur chloride. The process is largely used for waterproofing cloth and making thin rubber tubing ; it cannot be used for thick goods, as the penetration is imperfect. But little is known of the nature of the action of sulphur in the dry process of vulcanisation, but the action of sulphur chloride has been studied by Weber, who is of opinion that the vulcanised rubber consists of two molecules of polyprene united by one or more double atoms of sulphur. The introduc- tion of the sulphur is effected by the formation of polyprene sulphochlorides. Ebonite or vulcanite is rubber vulcanised with so much sulphur (25 per cent.) that it is converted into a hard, horny mass quite different in appearance and mechanical properties from ordinary vulcanised rubber. The deterioration of rubber goods appears to be a process of oxidation, resinous products being formed. Rubber is often largely adulterated with " surrogates " consisting of the products of the action of sulphur and sulphur chloride on oils — e.g., rape and cotton-seed oil. These surrogates are gelatinous substances nearly devoid of mechanical strength, and are simply diluents of the rubber with which they are mixed. The use of these surro- gates makes the determination of the specific gravity of rubber as a means of detecting adulteration altogether illusory. Com- mon rubber goods made by moulding (called " mechanicals ") are * "Elasticity" is not here used in its exact mechanical sense. OIL VARNISHES. 245 also largely prepared from old vulcanised rubber re- worked. Indiarubber overshoes are examples of this class of rubber goods. Gutta percha is a substance, similar in many respects to caoutchouc, obtained from Isonandra gutta, a tree found in the Malay Peninsula. It is collected in a manner similar to that used for caoutchouc. It has lately been proposed to extract gutta percha from the leaves of the tree by means of a volatile solvent. Like caoutchouc, gutta percha consists of a hydrocarbon associated with resinous matter. It is chiefly used as an insulating material in electrical work and for moulding purposes. III. VARNISHES. Varnishes may be divided into two broad classes, namely oil and spirit varnishes. The former class consists of those varnishes which contain a drying oil, capable itself of forming a varnish-like film when exposed to the air in a thin layer. The latter comprises those varnishes which are made up of some resin dissolved in a volatile solvent. The chief resins in use for varnish making have been already described ; most of the other constituents of varnishes — e.g., drying oils and volatile solvents — have been dealt with under appropriate headings ; it remains to consider the methods of preparing varnishes, and such principles as are believed to underlie these methods. (1) Oil Varnishes. — The typical constituents of an oil var- nish are a resin — e.g., copal ; a drying oil — e.g., linseed oil ; and a volatile solvent — e.g., spirits of turpentine. The first process in the manufacture usually consists in rendering the resin, or "gum," as it is technically termed, amenable to the solvent action of the oil. Many resins, prominent among which are copal, amber and anime, are almost insoluble in oil or spirits of turpentine, until they have been fused. Others, such as elemi and common rosin, can be dissolved without previous fusion. The operation of fusing or "running" is carried out by simply heating the resin in a large copper pot over a direct fire, the heating being continued until frothing from the escape of mois- ture or of gases from the decomposition of the resin, has ceased. Ordinary linseed oil of good quality is boiled in a manner similar to that adopted when boiled oil is the product sought (p. 234), and the two materials are then mixed, and heated together at about •500' F. = 260° C. for an hour or two, until the mixture becomes so viscous as to form strings, when a sample is drawn out for testing. The product thus obtained is thinned by the addition of spirits of turpentine, and the finished varnish is allowed to settle and run off into storage vessels. It appears that both the linseed oil intended for varnish making and the finished varnish '246 OILS, RESINS AND VARNISHES. are improved by keeping, though the nature of the changes which they undergo is unknown. Specific directions as to con- stituents and quantities must be looked for in compilations of trade recipes. The process of drying which an oil varnish undergoes, takes place in two stages. In the first instance, the volatile solvent (spirits of turpentine) evaporates spontaneously, leaving a sticky film composed of the resin and drying oil, which have been used for making the varnish. The latter then dries by oxidation, and a film results, containing both the resin and the oxidised products of the drying oil. The quality of this film depends naturally both upon the nature of its materials, and the skill with which the varnish has been prepared. The resins must be chosen so that the film, though hard, is not brittle, but tough enough to resist a fair amount of wear and tear. (2) Spirit Varnishes. — These are of the simplest description, merely consisting of solutions of any suitable resin in any appro- priate volatile solvent. The resins most commonly employed are shellac, sandarac, elemi and mastic, and the commonest solvents are methylated spirit, spirits of turpentine and its various substitutes, and occasionally acetone. The method of preparation consists merely in warming the resin with its solvent, in a vessel heated by steam and provided with an agitator. It is fitted with a still head and worm, to recover any of the solvent which may distil over during the process of dissolution. The drying of spirit varnishes is simply the volatilisation of the solvent, the quality of the film left being dependent on the nature of the resins used. They are greatly inferior to oil varnishes in durability. Recently, varnishes for special purposes, such as the slight or temporary protection of bright metal surfaces, have been made by dissolving the lower products of the nitration of cellulose (see Explosives, Vol. II., Chap. XVII.) in solvents such as alcohol-ether, amyl acetate or acetone. RAW MATERIALS FOR SOAP. 247 CHAPTER XL SOAP AND CANDLES. I. SOAP. — Soaps are the alkali salts of fatty and resin acids, soluble in water and capable of giving a lather. Inasmuch as they are made from vegetable and animal oils, they consist of the alkali salts of such acids as occur in these oils (see p. 223) together with those of the acids of common rosin (see p. 242). Caustic soda is generally employed in the process of soap making, usually yielding hard soaps, while caustic potash gives as a rule soft soaps. For the chemistry of the action of caustic alkalies on fats see p. 225. When free fatty acids are used for soap making, saponification can be effected by alkaline carbonates, which are also capable of acting on neutral fats at high tempera- tures, under pressure. RAW MATERIALS. — The fatty matter most commonly used for good soap is tallow (palm oil and rosin being frequently added). A soda soap from this fat is hard and comparatively insoluble, but complete saponification without excess of alkali is difficult. Non-drying oils — e.g., olive oil — also yield hard soda soaps. Semi-drying and drying oils — e.g., rape, linseed, and fish otls — yield somewhat soft soda soaps, and are, therefore, generally used for making potash soap which is intentionally soft. Some oils containing lower fatty acids, notably coco-nut oil, are easily saponified, even in the cold, and nevertheless produce hard soaps. Waste fatty material from a large number of industries is gener- ally worked up into soap, the product varying according to the character of the fat. The description of the manufacture of caustic soda and potash is to be found elsewhere (see Vol. II, , p. 30, and Potash, Vol. II., Chapter XVIII. ). On account of the fact that saponification is generally conducted with a comparatively weak lye, the solution of caustic soda produced by the action of lime upon sodium carbonate solution suffices for the need of the soap maker, who therefore frequently makes his own lye. It is believed that the detergent property of soap is increased by the addition of certain alkaline substances, such as sodium silicate and aluminate. No such plea can be urged for inert mineral matter — e.g., barium sulphate, kaolin and finely powdered pumice frequently used as filling for common soaps. Sodium sulphate is sometimes similarly 248 SOAP AND CANDLES. used in the manufacture of cold water soap, and water itself is often present in enormous proportion — e.g., 60 to 70 per cent. Sugar is also used in making transparent soaps, and various colouring and scenting ingredients are employed, especially for toilet soap. PROCESSES OF MANUFACTURE. — However the details of soap making may vary with the class of soap to be produced, the first part of the process merely consists in heating the fatty material and running in alkali of about 10 per cent, strength, little by little, so as to first emulsify the fat and then gradually saponify it, the completion of the process being judged by test- ing for the presence of free alkali. Salt is added to the contents of the copper containing the soap, and the soap is thus thrown out of solution, it being insoluble in brine. It rises to the top, and the brine, containing the glycerol of the fat freed by saponifica- tion, is run off. Fresh lye is then run in and the heating re- peated, any residual fat being thus saponified, and the soap, which remains undissolved in the caustic liquor, being washed free from adhering salt. The subsequent treatment varies according to whether "curd," "mottled," or "fitted" soap is to be produced. For curd the soap is taken into solution again and allowed to rest until the dirt has settled ; the surplus water is then evaporated, and the soap is run into frames where it solidifies. The separation of the lye is not quite complete in this process, so that the finished soap is somewhat alkaline, but contains less water than most other varieties. Fitted soap is similarly treated, but is allowed a longer time for subsidence, and the boiling down is omitted. The finished product will obviously contain more water than curd soap, but be more nearly free from unsaturated alkali, the lye being given time to settle out. " Primrose " soap is the commonest example of a fitted soap, the raw materials saponified being about 7 parts of tallow and 1 of rosin. (Rosin soap alone cannot be precipi- tated with salt, but a mixed rosin and fatty soap is readily separated from its solution in this manner.) Mottled soap, if genuine, is manufactured similarly to curd, but is a second time boiled with lye until this has become strong enough to pre- cipitate the soap again. It is then run directly into the frames after the surplus lye has settled. The frames are jacketed and the soap cools slowly, a circumstance which causes the total dirt of the materials to segregate in the lines which are last to solidify, producing a mottled appearance in the finished product. Since more than 20 per cent, of water prevents this segregation, by allowing too rapid subsidence of the impurities before the soap passes to the frames, mottling is generally regarded as an indica- tion of freedom from excess of water. Seeing that now artificially mottled soaps are made in which the addition of sodium silicate solution is found to prevent subsidence even though much water FITTED SOAP. 249 be present, this criterion of purity no longer holds good. Origin- ally ferrous sulphide (from the crude alkali used) was the cause of the mottling ; now manganese dioxide is used for artificially mottled soap. When it is desired to incorporate any particular scenting, colouring or disinfecting material, the soap is usually run into a " crutch-pan " (a tank with an agitator) on its way to the frames, and the selected ingredient here worked in. Fraudulently wet soaps may be externally hardened to conceal their true character, by exposing them in a steam closet to a temperature sufficient to dry the outer skin, the interior remain- ing wet. In soaps of the above-mentioned classes the process of manufacture involves the separation of the glycerin in the lye. Chemically it is practicable to recover this glycerin by precipitating the residual soap by the addition of lime, concen- trating, fishing out the residual sodium chloride and distilling, but the cost of the process is usually too high to allow the product to compete with the glycerin obtained as a bye-product in candle making (q.v.). Much soap is, however, made without separation of the glycerin. Thus, the oil or fat is gently heated (to about 45° C. = 113° F.) and mixed with warm lye. The mixture is covered and the saponification allowed to proceed slowly. The soap usually contains both free fat and free alkali. The addition of sugar solution produces a transparent soap ; an excess of alkali is necessary in this case to ensure a good appearance. Soaps of this class are often sold for toilet use. Soft soap is also made without separation of glycerin, by saponifying drying and semi-drying vegetable oils and fish oils with caustic potash in- stead of soda. The greenish shade of much soft soap is due to the presence of hempseed oil, unless it be artificially communi- cated by the addition of ultramarine or indigo. The white specks sometimes present ("figging") are simply potassium stearate, and are no guarantee of good quality. Toilet soaps are made from best yellow soaps as a stock, and are mixed with perfume, C : O groups) having a ring nucleus — e.g., H H C C C C H H Armstrong has suggested that the colour of coloured substances is dependent upon their possession of a structure analogous to that of quinone ("quinonoid structure"). The oxygen of the ^>0 : 0 groups may be replaced by other elements or groups, pro- vided that the double linking be preserved and the " quinonoid structure " of the product maintained. Another characteristic of the quinonoid structure is the existence in the compound of an unsaturated ring nucleus, such as that of benzene, containing six elements, two of which are the ketone or modified ketone groups. Great difficulty has been experienced in bringing all coloured substances within the limits demanded by a quinonoid structure, and the hypothesis is accordingly still not fully substantiated. A substance such as azobenzene, C 6 H 5 'N : N 0 6 H 5 , needs pro- found alteration of its accepted formula to cause it to conform with the requirements of the theory. Quinones generally are powerful chromogens; the ^>C:0 groups or their equivalents are the chromophores, and the chief auxo- chrome is hydroxy 1, so that hydroxy quinones are the commonest dyestuffs of this class. In quinones derived from the benzene series the hydroxy quinones and the tetrahydroxy quinones act as feeble adjective dyes, but the dihydroxyquinones are incapable ANTHRAQUINONE DERIVATIVES. 279 of dyeing to more than a slight extent. In two-ring derivatives, such as those of naphthoquinone, H C HC C C H 6 and in derivatives of anthraquinone, / CO \^ X CO those hydroxy-derivatives which have an hydroxyl group in a position adjacent to that of the quinonic oxygen are alone capable of acting as dyestuffs, and usually there must be two hydroxyl groups present, adjacent to each other, one of which is adjacent to the quinonic oxygen. The chief members of the group of quinone dyestuffs are given below ; they are mainly used as adjective dyestuffs, for although capable of behaving as substan- tive dyestuffs, the dyes produced are comparatively feeble. Dihydroxynaphthoquinone, C 10 H 4 (OH) 2 O 2 (naphthazarine ; alizarin black), is prepared by heating a-dinitronaphthalene with strong sulphuric acid and zinc. The dyestuff is the sodium bisulphite compound."*" Quinone dyestuffs from benzene or naphthalene are of little importance, but those from the next higher series (anthracene series) are largely used. Hydroxyanthraquinones. — In accordance with the statement already made relative to the influence of the hydroxy-groups in quinonic derivatives of the naphthalene and anthracene series, it follows that only such polyhydroxyanthraquinones as have hydroxyl groups in the 1 : 2-positions f are dyestuffs. The * It is characteristic of the ketones, as of the aldehydes, to form additive compounds with bisulphites. t The orientation of anthracene and its derivatives is expressed by the following scheme : — 1' 1 C C C 280 COLOURING MATTERS, DYEING, AND PRINTING. dihydroxyanthraquinone in which the hydroxyl groups have these positions is alizarin. Alizarin was formerly obtained from madder. Madder is the root of Rubia tinctorum, formerly much cultivated in Italy and France. The roots are allowed to remain in the ground after the leaves have been removed, during which sojourn (frequently lasting for years) a fermentation occurs, whereby alizarin is de- veloped by the hydrolysis of the glucoside ruberythrin, C 26 H 28 0 14 , thus, C 26 H 28 0 J4 + 2H 2 0 = 0 14 H 6 0 2 (OH) 2 + 2C 6 H 12 0 6 . The ferment inducing this change is called erythrozyme. Other glucosides are present which also yield alizarin, in addition to purpurin and isopurpurin. The amount of dried madder ob- tained is about 25 per cent, of the weight of the original root. The total colouring matter is about 3 per cent, of the weight of the madder. The madder is prepared for the market in various forms; thus "garancin" is prepared by soaking the madder in water, adding dilute sulphuric acid to the moist mass, and boiling with steam whereby the glucosides are hydrolysed ; " flowers of madder" is prepared by treating the madder with water or dilute sulphuric acid to remove yellow colouring matters. Madder is still used to a small extent for dyeing wool, but it has been almost driven out of the field (especially for cotton) by artificial alizarin. Alizarin is now made from anthracene C 14 H 10 , which is purified by distillation in a current of steam, and the finely divided product treated with the calculated quantities of sodium bichromate and sulphuric acid, whereby it is oxidised to anthra- quinone 0 HC C CH HC C CH By the use of a regulated quantity of the reagents, oxidation of contaminating hydrocarbons is avoided, and a fairly pure pro- duct obtained. The chrome-alum left by the reaction of the sulphuric acid on the bichromate of soda is precipitated by excess of lime and the mixture of chromium oxide, lime, and calcium sulphate roasted, calcium chromate being formed, which is converted into sodium chromate by treatment with sodium carbonate solution. MANUFACTURE OF ALIZARIN. 281 The anthraquinone is purified by dissolution in two or three times its weight of sulphuric acid at 110° C. = 230° F., and crystallisation by cooling, the residue being precipitated by the addition of water. The impurities in the anthraquinone are converted into sulphonic acids by this treatment, and remain in solution. Sublimation in a current of steam completes the puri- fication process. The anthraquinone is next treated with fuming sulphuric acid, whereby a mixture of mono- and disulphonic acids of anthraquinone, C 14 H 7 0 2 (HS0 3 ) and C 14 H 6 0 2 (HS0 3 ) 2 , results. The temperature of sulphonation is kept low in order to obtain a large yield of monosulphonic acid, which alone yields alizarin, although the disulphonic acid is not useless, since from it are ultimately formed isopurpurin and flavopurpurin. The next step consists in saturating the. sulphonic acids with calcium carbonate, and converting the calcium sulphonates into sodium salts by treatment with sodium carbonate. The intermediate use of calcium carbonate effects a saving of sodium carbonate by neutralising the excess of sulphuric acid with a cheaper material. The sodium sulphonates are mixed with three times their weight of caustic soda (dissolved in water) and some sodium chlorate, in an iron pressure vessel provided with an agitator. The mixture is kept at a temperature of 180° to 210° C. = 356° to 410° F. for some days. During this time the sodium anthra- quinone monosulphonate is converted into sodoxyanthraquinone, thus — C u H r 0 2 (S0 2 ONa) + 2NaOH = C 14 H 7 0 2 (ONa) + Na 2 S0 3 + H 2 0. This body is then oxidised by the sodium chlorate in presence of caustic soda into di-sodoxyanthraquinone (sodium alizarate). C u H 7 0 2 (ONa) + NaOH + O = C 14 H 6 0 2 (ONa) 2 + H 2 0. The sodium anthraquinone disulphonates, which are mixed with the mono-compound, yield respectively the isomerides isopurpurin and flavopurpurin, each having the formula 0 14 H 5 O 2 (OH) 3 . The melt is boiled with water, and the dyestuffs precipitated from the solution by the addition of hydrochloric acid, filter pressed, and made into a paste (containing about 20 per cent, of solid dyestuff) with water. Alizarin when once dried and anhydrous will not redissolve readily in water, whence the practice of selling it as a paste has arisen. Nearly pure alizarin is used for dyeing blue shades of red, whilst an alizarin paste rich in isopurpurin and flavopurpurin is used for yellow shades. Alizarin is most widely used for dyeing and printing cotton. The fabric is mordanted in accordance with the colour required. The metallic mordants form salts (alizarates) containing the metals replacing the hydroxyl hydro- gen. The colours range from red with alumina, to violet black with iron. The mordanted fabric is immersed in a vat containing 282 COLOURING MATTERS, DYEING, AND PRINTING. alizarin paste suspended in water, and the whole slowly boiled. Large quantities of alizarin are used for Turkey-red dyeing. In the original form of this process the fabric is saturated with an emulsion of rancid olive oil (huile tournante) in sodium carbonate solution, and exposed to the air, preferably at a somewhat elevated temperature. Oxidation of the oil ensues, and hydroxy-fatty acids are formed, which remain on the fibre after the superfluous oil has been washed off. The fabric is then treated with tannin in a sumach bath, and with aluminium acetate, when it is ready for dyeing with alizarin. The presence of lime in the alizarin bath is necessary, and, should the water be soft, lime must be supplied in the form of calcium acetate. The preliminary treatment with olive oil emulsion is tedious, and is now generally replaced by the use of Turkey-red oil {q.v.), the necessity for the oxidation of the fatty acids by prolonged exposure to air being thus removed. The rest of the process is similar to that described for the older method. The function of the oxidised oil, however obtained, is stated to be partly the formation of an aluminium fatty salt, which gives a finer red than alumina itself, and partly the protection of the colouring matter by a varnish-like film of oxidised fatty acids — an explana- tion lacking confirmation. Tetrahydroxyanthraquinones, C 14 H 4 0 2 (OH) 4 . — The most im- portant of these is " alizarin Bordeaux " (used for cherry red shades on aluminium mordants) obtained by the action of fuming sulphuric acid on dry alizarin and treatment of the product with hot water. Alizarin cyanine is a pentahydroxyanthraquinone, and gives shades very similar to those of alizarin Bordeaux with alumina, but blue shades on chromium mordants. Alizarin blue S, or soluble alizarin blue, is an alizarin product of some importance as an indigo substitute. It is prepared by nitrating alizarin suspended and partially dissolved in glacial acetic acid. The product, /3-nitroalizarin, C 14 H 5 (N0 2 )0 2 (OH) 2 , is heated to 150° 0. = 302° F., with sulphuric acid and glycerin, whereby it is converted into alizarin blue which is dihydroxy- anthraquinone quinoline, /CO v /CH:CH C.H4< >C 6 (OH) 2 / | The sodium bisulphite additive compound of this, constitutes soluble alizarin blue. The presence of quinolinic nitrogen in alizarin blue gives it a feeble basic character. With chromium oxide as a mordant, the blue colour produced by soluble alizarin blue is comparable with that of indigo. Another class of quinone derivatives consists of the quinone- oximes. These contain an ^>NOH group in place of the O of one TRIPHENYLMETHANE DERIVATIVES. 28^ of the C 0 groups characteristic of a quinone. Thus the naphtho- quinoneoxime, NOH gives a green dye with iron mordants and a red with cobalt. (d) Triphenylmethane Derivatives. — The triphenylme thane colouring matters are oxidation products of certain amido- and hydroxy 1-derivatives of the substituted paraffin triphenylme than e> / C 6 H 5 HC^-C 6 H 5 C 6 H 5 . Thus, paraleucaniline, /C 6 H 4 (NH 2 ) HC<^C 6 H 4 (NH 2 ) ^C C H 4 (NH 2 ), gives rise to pararosaniline, ^/C 6 H 4 (NH 2 ) •C 6 H 4 (NH 2 ) C 6 H 4 = (NH), when two hydrogen atoms are removed by oxidation. The chromophore in this chromogen is the quinonoid group CgH 4 — li in which R is either : NH or O. The formula given above for pararosaniline does not represent an isolated compound, for it only exists in the salts of pararosaniline, of the form /C 6 H 4 (NH 2 ) C^— C 6 H 4 (NH 2 ) ^C 6 H 4 :NH* /\ H CI the acid radicles of which constitute the auxochrome. When * There is some evidence in favour of regarding the salts of pararosaniline and its derivatives as having the form C1"C: (U C H 4 NH 2 )3, in which case they would partake of the nature of ethereal salts derived from the carbinol. This view requires confirmation. 284 COLOURING MATTERS, DYEING, AND PRINTING. the salts are treated with bases, a pararosaniline base, such as triamidotriphenyl carbinol, /C 6 H 4 (NH 2 ) HO-C~-C 6 H 4 (NH 2 ) ^C 6 H 4 (NH 2 ) is obtained. This is a colourless substance, and on treatment with an acid yields a coloured salt, the acid radicle serving as an auxochronie as mentioned above. Differences of colour in the dyestuffs thus produced are caused by the introduction of hydrocarbon radicles as substitutes for the hydrogen of the amido-groups. Rosaniline, the basis of the commonest aniline dyestuff, magenta, differs from pararosaniline in that it contains an amidotolyl group, C 6 H 3 < \nh 2 in place of one of the amidophenyl groups, C 6 H 4 (NH 2 ). Although constitutionally the prefixed " para " refers to the position of the amido-groups in the benzene nuclei with respect to the methane carbon atom, yet the expression pararosaniline is arbitrarily used to distinguish this substance from the methyl substituted body of similar constitution. The starting point for dyestuffs of this class ("aniline dyes ") is benzene or a homologue. Modern practice requires the preparation of approximately pure hydrocarbons, chiefly C 6 H 6 , 0 6 H 5 (CH 3 ), C 6 H 4 (CH 3 ) 2 , whereas formerly, mixtures of these were commonly used, such as " 30 per cent, benzol " and "90 per cent, benzol" (Vol. II., p. 79). The hydrocarbon must first be converted into a nitro-derivative, which is then reduced to the corresponding amido- compound. The descrip- tion of these processes as applied to benzene is as follows : — The benzene (about 1,000 lbs.) is charged into a vertical cast-iron cylinder and a mixture of 1,280 lbs. of nitric acid (specific gravity 1 -39) and 1,790 lbs. of sulphuric acid (95 to 96 per cent.) is run in, in a very slow stream, the charge being agitated and the cylinder cooled until the whole of the acid has been added, when the temperature is allowed to rise to about 80° C. = 176° F. When the mixture has settled, the acid is drawn off and the nitrobenzene, C 6 H 5 (N0 2 ), washed with water. Nitrobenzene is a yellow oily liquid, boiling at 206° C. = 403° F., and having a specific gravity of 1*18. It has a char- acteristic, somewhat fragrant odour, and on this account is used for scenting common soaps, as a substitute for oil of bitter almonds. When it is to be thus employed it is redistilled and termed "essence of mirbane." When dinitrobenzene is required, the benzene is treated with two separate nitrating charges, and the temperature is allowed to rise more rapidly. MANUFACTURE OF ANILINE. 285 The isomeric dinitrobenzenes — bodies crystallising in yellow- needles — are allowed to settle and are washed, first with cold water and finally with hot water. Aniline is obtained by the reduction of nitrobenzene by iron in the presence of water and ferrous chloride, which acts as a carrying agent. When aniline was first made on a commercial scale, sufficient acid was used to supply, by the action upon it of the iron, enough hydrogen to convert C 6 H 5 (N0 2 ) into C 6 H 5 (NH 2 ). In modern practice only enough acid (hydrochloric acid) is used to start the reaction, which then proceeds thus : — The small quantity of hydrochloric acid reacts with the iron to form (potential) hydrogen (which reduces nitrobenzene to aniline) and ferrous chloride, which in its turn reduces a further quantity of nitrobenzene to aniline, hydrated ferric oxide and ferric chloride being formed. The ferric compounds are reduced to ferrous compounds by the metallic iron, and then the ferrous chloride goes through the cycle of reactions already described. The following equations may be taken as representative of the changes involved : — Fe + 2HC1 = FeCl 2 + K> C 6 H 5 (N0 2 ) + H 6 = C 6 H 5 (NH 2 f + 2H 2 0 C 6 H 5 (N0 2 ) + 6FeC] 2 + H 2 0 = C 6 H 5 (NH 9 ) + 2Fe 2 Cl 6 + Fe 2 0 3 Fe 2 Cl 6 + Fe = 3FeCl 2 4Fe 2 0 3 + Fe = 3Fe 3 0 4 . The final products are therefore aniline, hydrated ferroso- ferric oxide and ferrous chloride. The process of manufacture is conducted in a cast-iron still provided with an agitator and a hopper for the gradual intro- duction of the iron (borings). A portion of the iron is first introduced, steam is injected, and the hydrochloric acid run in. The nitrobenzene is then allowed to enter. At first water, aniline, and nitrobenzene distil over, and are pumped back into the still. The rest of the iron is added by degrees, and, when the violence of the reaction has subsided, steam is again turned in. The aniline is thus distilled over without the addition of a base {e.g., lime), which was formerly necessary when excess of acid was used. An ordinary charge consists of about 2,688 lbs. of borings ("swarf," the scrapings of soft castings), 2,350 lbs. of nitrobenzene, and 115 lbs. of hydrochloric acid. The reduction should not be conducted rapidly, or with excess of iron, as the aniline may be converted under such conditions into benzene and ammonia. The distilled aniline subsides to the bottom of the receiving tank, and is drawn off and rectified, the little that remains in the water being re- covered by using this to feed the boilers supplying steam to the still in which the nitrobenzene is reduced. Aniline, when pure, is a colourless oily liquid (the commercial product is generally brown), of specific gravity 1*027, and boiling 286 COLOURING MATTERS, DYEING, AND PRINTING. xit 185° C. = 365° F. Aniline of good quality does not contain more than 0*5 per cent, of water. There are several grades of commercial aniline ("aniline oil") used in making aniline dyes. Thus, there are the grades " pure aniline oil " (" aniline for blue "), " aniline for red " and " toluidine." The first is nearly pure aniline ; the second consists of a mixture of aniline, orthotoluidine and paratoluidine ; the third is a mixture of orthotoluidine and para- toluidine (the latter amounting to about 35 per cent, of the whole). Aniline hydrochloride is known commercially as aniline salt. These bases, as well as xylidine, are made by methods similar in principle to that described for aniline. All triphenylmethane derivatives are obtained by the elimina- tion of hydrogen from phenyl derivatives, in the presence of some methane derivative, which may take the form of a methyl group in one of the phenyl derivatives, or may be brought into play in the form of a simple methane derivative. Thus, triphenylmethane itself was originally prepared by heating benzylidene chloride with mercury diphenyl, thus — C 6 H 5 CHC1 2 + (C 6 H 5 ) 2 Hg = HC^— C 6 H 5 + HgCl 2 CeH 5 In this case it will be noted that the chlorine and mercury both occupy the place of hydrogen, and that their mutual elimination is, therefore, chemically equivalent to the elimination of hydro- gen. The other typical method, involving the use of a simple methane derivative, is exemplified by the reaction (in presence of aluminium chloride) — / CeH 5 3C 6 H 6 + CHC1 3 = HC^— C 6 H 5 + 3HC1 an actual elimination of hydrogen, as HC1, taking place. Since triphenylmethane does not contain a chromophore, it is not a chromogen. Its amido-derivatives, which, as stated above, ^ire capable of becoming chromogens, are prepared by methods analogous to those already mentioned, the amido-derivatives of benzene and its homologues forming the raw materials. Thus, pararosaniline base is prepared by eliminating hydrogen from a mixture of aniline and toluidine by oxidation. In this case, the methyl group of the toluidine affords the methane carbon atom round which the amidophenyl groups are disposed, thus — /C 6 H 4 (NH 2 ) 2C 6 H 6 (NH 2 ) + C 6 H 4 <^ 3 + 0 3 = HO - C C 6 H 4 (NH 2 ) + 2H 2 0 ^C 6 H 4 (NH 2 ) Of the six hydrogen atoms eliminated by the action of the three oxygen atoms, two have been left, together with one oxygen MANUFACTURE OF MAGENTA. 287 :atom, as essential parts of the pararosaniline base (the relation of which to pararosaniline has been already given). The method of oxidation employed is similar to that used in the case of the production of rosaniline (magenta ; fuchsine). Pararosaniline base is only used in the production of "aniline blue " (v.i.). Magenta, the commonest aniline colour, is obtained by a reaction similar to that expressed by the above equation, save that two molecules of toluidine and one molecule of aniline are the proportions of these bases. This alteration is necessary, because the rosaniline base contains an amidotolyl group in place of one of the amidophenyl groups, thus — /C 6 H 3 (CH 3 )(NH 2 ) C 6 H 5 (NH 2 ) + 2C 6 H 4 < + 0 3 = HOC^— C 6 H 4 (NH 2 ) + 2H 2 0 CH 3 NH 2 The treatment of the rosaniline base with an acid induces the formation of the chromophoric group, eliminates water and forms the rosaniline salt — e.g., H CI V C 6 H 3 (CH 3 ) = NH C 6 H 4 (NH 2 ) \c 6 H 4 (NH 2 ) The process is carried out in one of two ways, which differ merely in the nature of the oxidising agent used. The older process consists in heating about 500 kilos, of " aniline for red " with 750 kilos, of arsenic acid solution containing 60 to 70 per •cent, of H 3 As0 4 , in iron pots, the temperature being slowly raised to 180° C. = 356°*F., and the contents of the pots well stirred. The heating is continued until a sample is found to be brittle on cooling. Only about two-thirds of the bases in the aniline for red is converted into rosaniline by this process, the remainder distilling over and being worked up with the next batch. The melt containing rosaniline arsenite and arsenate and arsenious acid, formed by the reduction of arsenic acid, is broken up and boiled out with water, sodium chloride and hydrochloric acid being added to the liquor ; rosaniline hydrochloride is precipitated and is recrystallised from brine. Various other colouring matters are produced in minor amount, and are re- covered from the mother liquor. One of the chief is chrysaniline (C 19 H 15 N 3 ), the hydrochloride of which is known in the pure state as phosphine, a dyestuff used for leather and silk. The arsenious and arsenic acids are recovered by evaporating the liquors and burning the residue with the waste organic (tarry) matter of the process. By this means the arsenic is liberated as As. Its vapour is mixed with air and burnt to arsenious oxide in another chamber. This is converted into arsenic acid by nitric acid, the 288 COLOURING MATTERS, DYEING, AND PRINTING. nitrous fuines from the oxidation being re-oxidised to nitric acid by air in presence of water. Thus nitric acid and arsenic acid serve as carriers of oxygen from the air to the aniline and toluidine to be condensed for the production of rosaniline. Magenta obtained by this process is rarely free from arsenic. Legislative enactments in most countries have enforced the absence of arsenic from pigments and dyestuffs, and in con- sequence nitrobenzene is now largely used as an oxidising agent in place of arsenic acid. Aniline for red (100 parts) and nitro- benzene (40 parts) are heated with a small quantity of ferrous chloride to about 175° C. = 347° F., care being taken not to exceed this temperature. The reaction must not be pushed too far, and the mass on cooling should still contain some aniline and be consequently soft. This aniline is extracted by dilute hydro- chloric acid, and the main mass containing rosaniline is worked up as in the case of that produced by the arsenic method. In the nitrobenzene process, the ferrous chloride acts as a carrier of oxygen to the aniline. It is doubtful whether the nitrobenzene acts in any way other than as an oxidant, for it appears that it does not yield aniline as a product, or, if it does, that this aniline remains as such at the end of the reaction, necessitating the extraction with hydrochloric acid already spoken of. The dyestuff obtained differs in no great degree from that prepared by the arsenic acid process, but is of course free from traces of arsenic, and thus meets legislative requirements. The yield, especially of the best grade of magenta (q.v.), is, however, slightly higher. The total yield is about 33 per cent, of the bases used. The bye-product characteristic of this method is the induline (C 24 H 18 N 4 ) in place of the chrysaniline of the arsenic acid pro- cess. Obviously, the cost of this process varies more greatly with the price of benzene than does that of the arsenic method of preparation. Magenta, as at present met with in the market, is rosaniline hydrochloride, C 20 H 19 N 3 , HC1, 4H 2 0, the manufacture of the acetate and nitrate being obsolete. It crystallises in octahedra or rhombic tables of green lustre, difficultly soluble in cold water. It dyes silk and wool directly from its aqueous solution, and cotton with a tannin mordant. It is brilliant, but not fast to light. When it is required to dye with magenta from an acid dye-bath, the sodium salt of the disulphonic acid, C 20 H l7 N 3 (SO 3 ISra) 2 , is prepared by heating rosaniline hydrochloride with fuming sul- phuric acid at 150° 0. = 302° F., the usual practice of neutralising with chalk and forming the sodium salt by the action of sodium carbonate on the calcium salt (see Alizarins, p. 281) being adopted. The substance thus prepared (acid magenta) is a metallic looking powder easily soluble in water; it is used for dyeing wool and silk. Magenta base (rosaniline base), C 20 H 21 N 3 O, is prepared by precipitating the hydrochloride with lime or ammonia. It METHYL VIOLET. 289 separates from the filtered liquid in crystals, which are colour- less when kept from contact with an acid, but speedily become pink on exposure to air from absorption of C0 2 . It is some- times used for the production of the sulphonate described above, and of other colours (v.i.). Other aniline dyestuffs (blue and violet in colour) are deriva- tives of rosaniline or pararosaniline, containing paraffin or aromatic radicles in place of the hydrogen in the amido-groups. The typical method originally used for preparing them consists in treating rosaniline with a halogen substitution product of methane or ethane — e.g., CH 3 C1 or C. 2 H 5 I — the hydrogen of the amido-groups of the rosaniline being thus replaced by a paraffin radicle. In modern practice it is found preferable to convert substituted anilines into corresponding substituted rosanilines, instead of using the substitution process given above. Thus, in the preparation of methyl violet (a mixture of tetramethyl-, pentamethyl- and hexamethylpararosaniline), dimethylaniline is prepared by heating aniline with excess of methyl alcohol and hydrochloric acid, or sulphuric acid, in enamelled iron digesters at a temperature of 180° to 200° C. = 356° to 392° F. The base is liberated with lime, distilled, and freed from monomethyl- aniline and aniline by freezing artificially. The dimethylaniline, C 6 H 5 'N(CH 3 ) 2 , is heated in a current of air with cupric chloride (from sulphate of copper and common salt), which behaves as an oxidising agent, the cuprous chloride produced acting as a carrier of oxygen (cf. Deacons Chlorine Process, p. 39). Phenol is commonly added, but its function is not clear. The double cuprous chloride of methyl violet is treated with ferric chloride, cupric chloride and ferrous chloride being thus formed, and the hydrochloride of the methyl violet is salted out in the usual way ; the yield is nearly that indicated by theory. The com- mercial salt occurs in amorphous masses of green lustre, giving violet solutions which become bluer the further the substitution of methyl groups for hydrogen has been pushed. As in the case of magenta, sulphonated derivatives are sometimes prepared, the method adopted consisting in reduction to the leuco-com- pound,* sulphonation (p. 288), and subsequent oxidation. This order of treatment is made requisite by the difficulty of directly sulphonating methyl violet. Methyl violet dyes silk and wool directly, and cotton with a tannin mordant. The pure hexamethylpararosaniline constitutes another dye- stuff of this class, and is known as crystal violet. It is prepared by the action of carbonyl chloride on dimethylaniline in presence of zinc or aluminium chloride, the reaction proceeding in two stages, thus — * The term " leuco-compound " is commonly applied to the product of the reduction of organic dyestuffs by means of the action of zinc in acid or alkaline solution (" nascent hydrogen "). 19 290 COLOURING MATTERS, DYEING, AND PRINTING. /C 6 H 4 -N(CH 3 ) 2 (1) 2C,jH a -N(CH3)., + COCl 2 = CO< + 2HC1 ^C 6 H 4 -N(CH 3 ) 2 Tetramethyldiamidobenzophenone. . C 6 H 4 -N(CH 3 ), /C 6 H 4 N(CH 3 ) 2 (2) CO + C 6 H 5 -N(CH 3 ) 2 = HO - C ^— C 6 H 4 N(CH 3 ) 2 ^ C 6 H 4 -N(CH 3 ) 2 \ C 6 H 4 N(CH 3 ) 2 Hexamethylpararosaniline base. The commercial salt is the hydrochloride, and is used in the same way as magenta. The aniline blues are examples of substituted rosanilines containing an aromatic radicle. When aniline is heated with rosaniline no reaction occurs, unless an organic acid be present (benzoic acid for choice) ; a very small proportion is requisite to induce their interaction. The aniline used is pure (" aniline for blue ") in order to avoid the red tones produced by higher bases. The highest substitution product that can be formed in this manner is triphenylrosaniline, C 20 H ]6 (C 6 H 5 ) 3 N 3 , which has the bluest shade of the phenyl derivatives. To ensure its production a considerable excess of aniline is needed. The method of manu- facture consists in heating rosaniline base (50 parts), aniline (300 parts) and benzoic acid (3 parts) to 180° 0. = 356° F. The melt is partly neutralised with hydrochloric acid, and the hydrochloride of triphenylrosaniline crystallises. The aniline blue thus obtained is but little soluble in water, but fairly easily soluble in alcohol, whence its name " spirit blue." It is chiefly used for the preparation of sulphonated derivatives, which are readily formed by the action even of vitriol instead of fuming sulphuric acid, the sodium salts being known by the names of " alkali blue " * and " soluble blues," and being used for dyeing cotton, wool and silk. A class of dyestufts related both to the aniline violets (in their mode of preparation) and to the aniline blues, in respect of the fact that they are aromatic derivatives, may be mentioned here. They include Victoria blue and night blue, and are di- phenylnaphthylmethane derivatives. By the action of COCl 2 on dimethylaniline, as in the preparation of the aniline violets, tetramethyldiamidobenzophenone is produced. This is heated with a dehydrating agent and phenyl-a-naphthylamine, yielding bodies of the form /C 6 H 4 -N(CH 3 ) 2 C^-C 6 H 4 -N(CH 3 ) 2 A H CI * This can be used in an alkaline bath, hence its name. AURINE. 291 These blues dye silk and wool from an acid bath, and cotton with an alumina and oil mordant. The foregoing dyestuffs contain three amido- or substituted amido -groups. Another series of dyestuffs is derived from diamidotriphenylmethane — /C 6 H 4 (NH 2 ) HC^-C 6 H 4 (NH 2 ) C 6 H 5 The principal dyestuff of this class (malachite green or benzal- dehyde green) is prepared by heating a mixture of benzaldehyde and dimethylaniline with hydrochloric acid, whereby water is eliminated, thus — /C 6 H 4 -N(CH 3 ) 2 2C 6 H 5 N(CH 3 ) 2 + C 6 H 5 CHO - HC^C 6 H 4 -N(CH 3 ) 2 + H 2 0 The leucomalachite green thus produced is then dissolved in hydrochloric acid, and oxidised by the addition of Pb0 2 , thus — .C 6 H 4 -N(CH 3 ) 2 /C 6 H 5 HC^C 6 H 4 -N(CH 3 ) 2 + 0 + HC1 = C^-C 6 H 4 -N(CH 3 ) 2 + H 2 0 ^ C 6 H 5 ^ C 6 H 4 =N(CH 3 ) A CH 3 CI The lead, which remains in solution as chloride, is precipitated by means of sodium sulphate, and the dyestuff is salted out with zinc chloride, with which it forms a double salt constituting the commercial product. The oxalate is also prepared. Malachite green forms green crystals of metallic lustre, readily soluble in water, dyeing wool and silk directly, and cotton with a tannin mordant. It is not a particularly fast colour. Amine dyestuffs are triphenylmethane derivatives containing phenolic hydroxyl groups, the parent substance being trihydroxy- triphenylmethane, / C 6 H 4 (OH) HC^C 6 H 4 (OH) ^C 6 H 4 (OH) A method of synthesis of theoretical interest consists in con" verting pararosaniline hydrochloride into triamidotriphenylcar- binol trihydrochloride, /C 6 H 4 (NH 2 )HC1 HO - C^-C 6 H 4 (NH 2 )HC1 ^C 6 H 4 (NH 2 )HC1 292 COLOURING MATTERS, DYEING, AND PRINTING. by the action of hydrochloric acid and water. By treating this with nitrous acid it is diazotised (p. 274) into /C 6 H 4 -N:N-C1 H0-C^-C 6 H 4 -N:NC1 ^C 6 H 4 -N:NC1 which, on hydrolysis, is converted into trihydroxytriphenyl- carbinol, /C 6 H 4 (OH) HO-C^— C 6 H 4 (OH) ^C 6 H 4 (OH) this body at once loses water, and becomes the corresponding inner anhydride (amine), /C 6 H 4 (OH) C^— C 6 H 4 (OH) ^C 6 H 4 =0 The actual members of this class of dyestuffs are substituted- aurines. The commercial product called "aurine" is prepared by heating 3 parts of phenol with 2 of anhydrous oxalic acid (potential formic acid) and 1*5 of strong sulphuric acid, to a temperature of 120° to 130° C. = 248° to 266° F.— /H C 6 H 4 OH 3C 6 H 6 OH + C = 0 + O = C-^- C 6 H 4 OH + 3H 2 0 X OH ^^C 6 H 4 =0 The formic acid represented above is a product of the breaking down of the oxalic acid ; the source of the extra oxygen required is not definitely known, but it is probably the air. The melt is extracted with water, the product being a green lustrous sub- stance, becoming brown on powdering. The commercial product obtained in this way is termed yellow coralline, and consists of a mixture of aurine, rosolic acid — its methyl derivative — and other colouring matters. By the action of ammonia, in alcoholic solution, upon coralline, a mixture of substances (called peonine) intermediate between aurine and rosolic acid on the one hand, and pararosaniline and rosaniline on the other, is obtained. Coralline is not a fast colour, and is chiefly used for colouring wall paper, and as an indicator. Phthalein dyestuffs are a class of triphenylmethane derivatives, of which the chromophore is the lactone ring — i II -Cv >0 They may be regarded as substitution products from phthalo- PHENOLPHTHALEIN. 293 phenone which is the inner anhydride (lactone) of triphenyl- methanecarbinolorthocarboxylic acid : — HO-C^-C 6 H 5 = OC^— C 6 H 5 + H 2 0 ^ C 6 H 4 -COOH ^ C 6 H 4 -CO I ! Triphenylmethanecarbinolortho- Phthalophenone. carboxylic acid. They are obtained by the use of phthalic anhydride.* /C = 0 C 6 H 4 / ^>0 >c = o When this compound is heated with phenols (the OH groups of which act as auxochromes in the final product), water is elimi- nated, and two ring nuclei replace one of the carbonyl oxygen atoms, as will be seen in the following case : — By heating phthalic anhydride with phenol in the presence of a dehydrating agent (e.g., ZnCl 2 ), the following reaction occurs: — sC = O /C = O C 6 H 4 < O + 2C 6 H 5 - OH = C 6 H 4 ° OC^— C 6 H 3 (OH) I ^C 6 H 4 CO ! I Fluorescein, as generally prepared, occurs only as a brown crystalline powder, insoluble in water but soluble in alcohol to a brown solution, showing, particularly when dilute, a green fluorescence. It is too sensitive to light to be used as a dye- stuff; its halogen derivatives, on the other hand, are thus employed. Such are the eosins, alkali salts of halogen sub- stitution products of fluorescein. Ordinary or " soluble " eosin is the potassium salt of tetrabromofluorescein, C 6 HBr 2 (OK) OC i I I EOSINS. 295 It is prepared either by direct bromination of fluorescein sus- pended in alcohol, or by preparing a mixture of sodium bromide and broinate, by dissolving bromine in caustic soda and heating the solution (to decompose hypobromite), mixing this solution with one of fluorescein in caustic soda and acidifying the cooled mixture. The acid liberates bromine by the interaction of hydrobromic acid and bromic acid, and effects the bromination of the fluorescein which, being insoluble in the aqueous liquid, is precipitated. It is dissolved in potassium carbonate solution, and the potassium salt is thus formed. Eosin forms reddish crystals, highly fluorescent in dilute solution. It is not a fast dye, though better in this respect than fluorescein, but is used for wool and silk in an acid bath on account of the brilliant red shade which it yields. It is much used for red inks and for preparing lake pigments (q.v.). Eosins soluble in spirit are also prepared by substituting the group CH 3 or 0 2 H 5 for one atom of K. The sodium salt of tetraiodofluorescein constitutes the dyestufF known as erythrosin. This substance is prepared by the direct action of iodine upon fluorescein in presence of an oxidising agent, which incidentally secures economy of iodine, the hydrogen iodide formed by meta- lepsis * being oxidised to iodine, which is available for further reaction. The product is used to some extent as a dyestuff, as an indicator and for making orthochromatic photographic dry plates. By the substitution of two N0 2 groups for two of the bromine groups in ordinary eosin, eosin scarlet or safrosin can be prepared. By substituting pyrogallol, C 6 H 3 (OH) 3 , for resorcinol in the reaction with phthalic anhydride, gallein is obtained instead of fluorescein. (Both this and similar derivatives of phenols con- taining more than two (OH) groups, yield darker colours than those of the dyestuffs from phenol and resorcinol.) The primary product is pyrogallolphthalein, / C 6 H 2 (OH) 3 OC^-C 6 H 2 (OH) 3 ! ^C 6 H 4 CO | I which, losing two molecules of water, becomes ,C e H 8 (OH) / OC^— C 6 H 2 (OH) ^C«H 4 CO I * Metalepsis is a convenient term for the class of reaction typified by the removal of hydrogen by a halogen, as its hydrogen compound, and the simultaneous substitution of the halogen. 296 COLOURING MATTERS, DYEING, AND PRINTING. and then, by oxidation by air, gallein — C 6 H 2 (OH) OC ~ In the manufacture of the dyestuff, gallic acid, C 6 H 2 (OH) 3 COOH, may be used instead of pyrogallol, as on heating it is converted into that body, C0 2 being eliminated. Commercial gallein is a violet paste, dissolving in alkalies with the production of a blue colour. It dyes chrome-mordanted wool a dark violet. Coerulein is prepared from gallein by heating the latter with 20 times its weight of strong sulphuric acid at 200° C. = 392° F. Its empirical formula is C 20 H 8 O 6 , being gallein minus a molecule of water. Its structure is not definitely known, but it is believed to be an anthraquinone derivative, whence its alter- native names anthracene green and alizarin green. In its com- mercial form it is a black paste soluble in alkalies ; it is much used for dyeing wool and cotton, especially in calico-printing. It yields a fast olive-green colour with various mordants. A soluble form of coerulein is the sodium bisulphite compound, C 20 H 8 O 6 ,2NaHSO 3 . The foregoing phthalein compounds are of an acid character, owing to the presence of phenolic hydroxyl groups. When these are replaced by amido-groups, basic dyestuffs are formed. The simplest method of attaining this end would be, for example, to use metamidophenol, C 6 H 4 (OH)(NH) 2 , instead of resorcinol, as the compound to be heated with phthalic anhydride. The substance thus produced is of no practical value, but on using diethylmetamidophenol the dyestuff known as rhodamine is produced, thus — C fi H 3 \ N(C 2 H S ) S Oil 0C(— C 6 H 3 <^ C2H * )2 + H 2 0 C 6 H 4 C0 Diethylamidophenolphthalein. AZINE COMPOUNDS. 297 This body, losing water, becomes rhodamine, C 6 H 3 -N(C 2 H 5 ^ 0 oc C 6 H 3 -N(C 2 H 5 ) 2 C 6 H 4 CO I The commercial product is the hydrochloride of the base, and is obtained as a red powder soluble in water to a red fluorescent solution. It dyes silk and wool directly, and cotton with a tannic acid mordant. The colour is fairly fast. A dyestuff known as rhodamine S is a condensation product of diethylmetamidophenol with succinic anhydride C 2 H, in place of phthalic anhydride. It is not, therefore, a triphenyl- methane derivative. It is very similar to rhodamine itself in its dyeing properties. (e) Azine Compounds. — The characteristic grouping which distinguishes these compounds is R" R" is a divalent radicle, such as (C 6 H 4 )", or its substituted product (C 6 H 3 *CH 3 )". Thus, the simplest body of this class will be CH N CH HC CH CH CH N CH Diphenylene azine or phenazine. The nitrogen ring is thus seen to be attached to adjacent C atoms ; the nitrogen atoms are therefore in the ortho position. The group < \^^ > * s ^ ne chromophore of these bodies, but they become dyestuffs only on the introduction of the auxo- chrome NH 2 or OH. An example of the formation of an azine is furnished by the 298 COLOURING MATTERS, DYEING, AND PRINTING. reaction between a dihydroxy-derivative and an ortho-diamine, in presence of oxygen, thus :— OH NHjj + OH NH 2 Pyrocatechol (Orthodihydroxybenzene). + 0 N Orthophenylenediamine. + 3H 2 0 N Phenazine. A general method for preparing dyestuffs of azine type, consists, in heating an orthoamidoazo-compound with a monamine. The reaction may be represented as proceeding in two stages : — (1) (NH 2 )(CH 3 )C 6 H 3 • N : N • C 6 H 3 (CH 3 )(NH 2 ) + H 4 Orthoamidoazotoluene . = 2C 6 H 3 (CH 3 )(NH 2 ) 2 Orthotoluylenediamine. (2) C 6 H 3 (CH 3 )(NH 2 ) 2 + C 10 H 7 (NH 2 ) a-Naphthylamine. = (CH 3 )C 6 H 3 <^f ^>C 10 H 6 (NH 2 ) + H 6 Eurhodine (amidotolunaphthazine). It is obvious that the elimination of H in the second part of the reaction more than balances the absorption of H in the first. Thus, the reaction can proceed without the introduction of an external reducing agent. The use of an excess of the azo-com- pound serves to absorb the excess of hydrogen after the above equations are satisfied. The actual method of production con- sists in heating orthoamidoazotoluene with a-naphthylamine hydrochloride, dissolved in phenol, at 130° C. = 266° F. When the melt has become scarlet, the hydrochloride of the eurhodine is precipitated by the addition of toluene. Treatment of the hydrochloride with an alkali yields the free base, which forms yellow prisms or brown needles. Since the salts of eurhodine are decomposed by an excess of water they are not adapted for SAFRANINES. 299 use as dyestuffs, the scarlet shade which they impart to fabrics being bleached by water to the yellow of the free base. Another dye of this class, but distinguished by containing two amido-groups (one of which contains two methyl radicles) is toluylene red, which may be formed thus — C 6 H 4 (NH 2 )[N(CH 3 ) 2 ] + C 7 H C (NH 2 ) 2 + 0 3 Dimethylpara- Metatoluylene- phenylenediamine. diamine. = [N(CHs)2]C 6 H,<^?^C 7 H 6 (NH,) + 3H 2 0. Toluylene red. This dyestuff is also obtained as a decomposition product on heating toluylene blue (p. 303). It dyes cotton with a tannin mordant. It will be seen that the eurhodines are amido-derivatives of azines. By hydrolysis (heating with strong hydrochloric acid under pressure) the amido-group is replaced by hydroxyl, the corresponding eurhodol being the product. The typical com- pound of the class is hydroxytolunaphthazine. It is prepared from eurhodine in the manner indicated above. As in the case of all azines, the / )> group has basic properties, so that \N/ the eurhodols, which contain also phenolic hydroxyl, behave as both acid and basic compounds. Most of the basic dyestutfs hitherto dealt with are referable to ammonia as a type. The safranines, about to be spoken of, are, on the contrary, complex ammoniums, and are called azonium bases, since they resemble the azines in structure, save that one of the chromophoric nitrogen atoms has become pentatomic and therefore capable of fixing a monovalent positive radicle and a monovalent salt-forming element or radicle (e.g., CI). The general mode of preparation of these substances may be typified by the oxidation of a mixture of one molecule of a paradiamine, such as paraphenylenediamine, with two molecules of a monamine (as a salt — e.g., the hydrochloride), such as ani- line. The first stage of the reaction takes place between the diamine, oxygen and one of the molecules of the monamine, to produce an indamine (q.v.), thus — C 6 H 6 NH 2 + 0 2 + NH 2 - NH 2 -( 7 = NH + 2H 2 0 300 COLOURING MATTERS, DYEING, AND PRINTING. It would seem that paraph enylene diamine first becomes quinone di-imide NH = = NH i.e., quinone with (NH)" in place of the O of the quinone 0 = 0 groups, and that this then undergoes condensation with the aniline. In the second stage of the reaction, the indamine and the second molecule of aniline (as hydrochloride) undergo a further condensation and oxidation, hydrogen being again re- moved as water. Indamine. Aniline hydrochloride. Phenosafranine chloride. * NH 2 NH 2 The chlorides of the safranines are red, and become blue in the presence of strong hydrochloric acid and green in that of strong sulphuric acid, from the formation of a diacid and a triacid salt respectively. On dilution with water the acid salts are de- composed, and the red colour is restored. Phenosafranine is prepared by the reaction given above ; the hydrochlorides of the bases employed being dissolved in hot water and oxidised by potassium bichromate or manganese dioxide. The first stage (the formation of the indamine) is indicated by the appearance of a blue colour, which speedily gives place to the red of pheno- safranine. The chromium or manganese oxide and less basic dyestuffs present as impurities, are precipitated by caustic soda, the solution filtered and the dyestuff salted out, after the addition of hydrochloric acid. Phenosafranine dyes wool and silk directly, whilst cotton requires a tannin mordant. The corresponding body, tolusafranine (safranine T), is also a red dyestuff, capable of dyeing wool in an alkaline bath, and having a slight attraction for cotton fibres ; a mordant is, however, necessary for the pro- duction of a fast colour. * This is taken to be the nitrogen of the aniline, t This is the aniline ring. MAUVE. 301 Naphthalene red (Magdala red) is another dyestuff of this class made by reactions similar to those used for phenosafranine, but has naphthalene rings in place of the benzene rings of the last- named dyestuff. It can be produced by heating naphthylene- diamine with a-naphthy] amine and an oxidising agent, an indamine being formed as an intermediate product, but this method is not practicable because of the great ease with which naphthylenediamine is oxidised to a-naphthoquinone. By sub- stituting amidoazonaphthalene, (NH 2 )C 10 H 6 * N : N ■ C 10 H 6 (NH 2 ), for naphthylenediamine the use of an oxidising agent can be avoided, inasmuch as amidoazonaphthalene is readily reduced to naphthylenediamine, C 10 H 6 (NH 2 ) 2 {cf. formation of eurhodine given above). According to modern practice a mixture of 23 kilos, of naphthylenediamine hydrochloride, 26 kilos, of a-naph- thylamine and 59 kilos, of amidoazonaphthalene is heated at 130° to 140° C. = 266° to 284° F. until the blue colour of the mix- ture (due to the indamine first formed) becomes red. The function of the naphthylenediamine is to form some Magdala red (with the a-naphthylamine) with the elimination of hydrogen, which then reduces the amidoazonaphthalene to naphthylenediamine,. the latter continuing the cycle of reactions. Naphthalene red * has the formula (NH 2 )C 10 H 5 <^^C 10 H 6 cn/NcjoHeflra,) and occurs as a dark brown powder sparingly soluble in hot water. It is only used in silk dyeing (imparting a pink fluor- escent colour) as it is a costly material. Mauveine has the empirical formula C 2 7H 25 N 4 , and appears to be a phenyl safranine. Recently it has been classed with the indulines (q.v.). It is made by the oxidation of aniline oil containing toluidine, by bichromate of potash and sulphuric acid. A black mass is obtained from which the mauve may be extracted by water. It was the first dyestuff obtained from aniline. It is sold as a violet paste and dyes silk and wool directly. Among the minor classes (not provided for in the classifi- cation given at the head of this section) of synthetic organic colouring matters, the following groups and individuals may be mentioned. * Eecent investigations seem to show that naphthalene red is an induline (p. 312) dyestuff— HN = C 10 H 7 ^^^>C 10 H 6 (NH 2 ) I C 10 H 7 302 COLOURING MATTERS, DYEING, AND PRINTING. Quinonoximes. — The simplest quinonoxime has the formula O II C HC CH N(OH) It is sometimes regarded as nitrosophenol, C 6 H 4 (NO)(OH). This substance is not used as a dyestuff, but the corresponding body derived from resorcinol, C G H 4 (OH) 2 , viz. — " quinonedioxime " or dinitrosoresorcinol 0 = N(OH) N(OH) is thus used, and is made by adding sulphuric acid to an aqueous solution of resorcinol and sodium nitrite. The commercial dye- stuff, known as resorcin green or solid green, occurs as yellowish- brown or green plates, or as a brownish powder. It is sparingly soluble in cold water and acts as an acid dyestuff. It is used for dyeing cotton on an iron mordant, the dye produced being green. Another dyestuff derived from resorcinol is lacmoid, 0 12 H 9 N0 4 , the constitution of which is not definitely known. It is a dark violet substance, used as an indicator. It is made by heating 100 parts of resorcinol with 5 of sodium nitrite and 5 of water at 120° C. = 248° F. Naphthoquinoximes, O = C 10 H 6 = NOEL — Two isomerides exist; they are obtained by treating the corresponding naphthols with nitrous acid, and are sold under the names of gambine R and gambine Y. They are used in calico-printing, with iron mor- dants, and produce a green shade. The iron derivative of the sodium sulphonate of the oxime obtained from /3-naphthol, S0 3 Na NO\ NO/ SOsNa Fe is sold as naphthol green. It is a dark green powder soluble in water, and dyes wool and silk directly. INDOPHENOLS. 303 The derivatives of the chromophore quinonedi-imide, NH NH obtained by the interaction of the dichloro-derivative of this compound, C 6 H 4 (NC1) 2 ,* with an aromatic amine, are called indamines. They are more conveniently obtained by the oxida- tion of a mixture of equal molecular proportions of an aromatic paradiamine and some other aromatic amine. The equation for this reaction for paraphenylenediamine and aniline has been given above (p. 299). The indamine produced ^C 6 H 4 = NH ^C 6 H 4 (NH 2 ) is known as phenylene blue. It is a basic body, and its salts are greenish-blue, dissolving in water. They are not largely used. Toluylene blue has a similar structure, /C 6 H 4 -N(CH 3 ) 2 N C 6 H 2 = NH t A CH 3 NH 2 and is obtained by oxidising a mixture of dimethylparaphenylene- diamine and metatoluylenediamine. The dyestuff is generally prepared as the hydrochloride. It is very soluble in water. When heated it yields toluylene red (p. 299). The indophenols maybe regarded as derivatives of quinoneimide, NH * Obtained by the action of bleaching powder solution on paraphenylene- diamine hydrochloride. t The relation to quinone di-imide is indicated by the presence of two doubly -linked N atoms. 304 COLOURING MATTERS, DYEING, AND PRINTING. so that they differ from the indamines in that the (NH)" group is replaced by a doubly-linked oxygen atom. They are obtained by substituting phenols for amines in the method already given for preparing indamines. Thus, the oxidation of equal molecular proportions of paraphenylenediamine and phenol gives indo- phenol, the equation being C 6 H 4 (NH 2 ) 2 + C 6 H 5 OH + 0 2 = 0=C 6 H 4 =NC 6 H 4 NH 2 + 2H 2 0. This typical indophenol is of no practical importance. The dimethyl derivative (phenol blue), a greenish-blue substance, is used as a dyestuff. Naphthindophenol* O = C 10 H 6 = NC 6 H 4 [N(CH 3 ) 2 ], is the most important of this class of dyestuffs ; it is known as naphthol blue, and is prepared by oxidising an alkaline mixture of dimethylparaphenylenediamine and a-naphthol by means of air or bleaching powder. It is a dark blue powder with a coppery lustre, resembling indigo, for which it is much used as a substitute. It will be seen that the indophenols have no (OH) group, and are therefore not phenolic. Their leuco-compounds, however, have a phenolic function and are soluble in alkalies, and from the solutions the indo- phenols are precipitated by oxidising agents, again recalling the behaviour of indigo. It follows from this that these dyestuffs can be applied in the reduced soluble state, and then oxidised on the fibre, being, in fact, ingrain colours (see Primuline, Dyestuffs containing Sulphur as an Essential Constituent.— One of these (primuline) has already been considered ; its constitu- tion is not sufficiently settled to bring it into this group, the dyestuffs in which are related to the indamines. This connection is evident from the formula for thionine, viz. : — Compare that for phenylene blue (p. 303). On comparison of this with the formula for the azine dyes, it will be seen that these derivatives may also be regarded as "thiazines" (better termed sulphazines ; also termed thia- The chromophore is the same as in the indamine dyestuffs. The dyestuff, in the form usually prepared, is known as Lauth's violet, which is the hydrochloride of the base thionine. It is of no commercial importance. p. 277). C 6 H 3 NH 2 zimes) having the group * Commercially known simply as indophenol. MANUFACTURE OF METHYLENE BLUE. 305 Methylene blue is an ammonium base, but its structure is otherwise similar to that of thionine, being CH 3 CI V /C 6 H, = N(CH 3 ) \C 6 H 3 -N(CH 3 ) 2 The principle underlying the methods of making this body is the oxidation of dimethylparaphenylenediamine in the presence of sulphur. For making this diamine, dimethyl aniline is treated with nitrous acid which converts it into nitrosodi- methylaniline, and this compound is reduced either by zinc or sulphuretted hydrogen. In the older process, this dimethyl- paraphenylenediamine was treated with H 2 S and ferric chloride in acid solution. The reaction may be represented thus (the ferric chloride acting as an oxidant) — /NH 2 2C 6 H 4 < + H 2 S + 2HC1 + 0 3 ^N(CH 3 ) 2 CH, CI C 6 H 3 = NCH 3 ^>S + NH4CI + 3H 2 0 \c 6 H 3 -N(CH 3 ) 2 The methylene blue thus obtained is thrown out of solution by a mixture of salt and zinc chloride, a compound with zinc chloride being produced. According to modern practice the following process is preferred to that described above, as affording a better yield. It will be seen that whereas in the older process a portion of the dimethylparaphenylenediamine is broken up with the elimination of ammonium chloride, thus causing the consumption of the nitrogen of a costly substance for the production of one of relatively insignificant value, in the later method no such waste occurs. Dimethylparaphenylenediamine is oxidised, and the red product treated with sodium thiosulphate and an acid. The compound thus obtained, dimethylparaphenylenediamine " thiosulphonic " acid (v.i.), is mixed with dimethylaniline hydro- chloride, and oxidised with a solution of potassium bichromate. A green crystalline indamine separates. This is boiled with a solution of zinc chloride, whereupon methylene blue is formed and crystallises as a double chloride. The chemistry of the process will be obvious from the following equations : — 20 306 COLOURING MATTERS, DYEING, AND PRINTING. z NH 2 ^NH (1) 2C 6 H 4 < + 2HC1 + 0 2 = 2C 6 H 4 C + 2H 2 0 X N(CH 3 ) 2 ^NCH 3 CH 3 CI Dimethylparaphenylene- Methylquinonediimide diamine. methochloride. (Red oxidation product.) NH /N(CH 3 ) 2 (2) C 6 H 4 ^f + HS-S0 3 H = C 6 H 3 ^— NH 2 + HC1 ^NCH 3 ^S-S0 2 OH CH 3 CI Dimethylparaphenylene- diamine sulphosulphonic acid.* /N(CH 3 ) 3 (3) C 6 H 3 ^-NH 2 + C 6 H 5 -N(CH 3 ) 2 + 0 2 \s g . go 2 OH Dimethylaniline. = N< 6 £ + 2H 2 0 \ u 2 X C 6 H 4 'N(CH 3 ) 2 Tetramethylindamine sulphosulphonate. (Green compound.) This compound on being boiled with zinc chloride solution in presence of iron is both hydrolysed and oxidised, the reactions being shown in the following stages — ^N(CH 3 ) 2 (1) Nr b g a ' + H 2 0 X C 6 H 4 -N(CH 3 ) 2 rH .^N(CH 3 ) 2 C 6 H 3 -N(CH 3 ) 2 Leucomethylene blue. CI CH 3 (2) HN^ ^>S + HC1 + O = N<^ ^>S + H 2 0 C 6 H 3 -N(CH 3 ) 2 ^C 6 H 3 -N(CH 3 ) 2 Methylene blue. Methylene blue is easily soluble in water. Like ammonium * Loosely termed thiosulphonic acid. OXAZINE DYESTUFFS. 307 bases generally it is not a good dye for wool, but it finds considerable application for dyeing silk directly and cotton with a tannin mordant. It is faster to light than is Victoria blue — another basic blue dyestuff. It is of value as a stain for micro- scopic objects. Methylene violet is prepared by treating dimethylpara-amido- phenol with an oxidising agent in presence of sulphuretted hydrogen. Since the parent substance contains but one amido- group, methylene violet has the structure C 6 H S = 0 \C 6 H 3 -N(CH 3 ) 2 Oxazine colouring matters. — These compounds are analogous to the preceding, for they are similarly constituted save that oxygen replaces sulphur. They may also be prepared by methods similar to those employed for their sulphur congeners. Thus, paradia- mines may be treated with phenols in presence of oxygen, which takes the place of the sulphur used in the process for the manu- facture of the sulphurised dyes, and the phenol supplies the second ring nucleus, which, in the preparation of the sulphazines by the analogous process, is obtained at the expense of a second molecule of the paradiamine broken up by the oxidising agent employed. The preparation of naphthalene blue (Meldolds blue) will serve as a type of the reaction which produces compounds CI CH S of this class. y NH 2 ,HC1 / C6H * = N(CHs) (1) C 6 H 4 < + Ci 0 H 7 OH = N / \ 0 + H 6 \c 10 h/ Diamethylparapheny- /3-Naphthol. Naphthalene blue, lenediamine. To induce the occurrence of this reaction an oxidising agent must be present, and this is conveniently furnished as nitroso- dimethylaniline, which can itself take the place of parapheny lene- diamine as a raw material, undergoing the change /NO (2) 3C 6 H 4 < + 3HC1 + 2C 10 H 7 OH \N(CH 3 ) 2 Nitrosodimethylaniline. fi • Naphthol. CI CH 3 ,C 6 H 8 = N(CH 3 ) /NH 3 ,HC1 2N o + C 6 H/ NH2 + 3H 2 0 C 6 H(OH) ^ u \N(CH 3 ) 2 ^COOH Gallocyanin. Gallocyanin is a greenish paste dissolving in hydrochloric acid with a red colour, and in alkalies with a reddish-violet colour. The methyl salt, containing CH 3 in the place of H of the COOH group, is known as prune, and is bronze-colour in the solid state. These dyes are used in calico-printing on chromium mordants, with which they give violet shades. One other class of oxazines includes the dyestuff resorufin. This is prepared by heating resorcinol with five times its weight of strong sulphuric acid, containing nitrous acid, at 100° C. = 212° F., and precipitating the colouring matter with water. In this process, nitrosoresorcinol is formed by the action of the nitrous acid on one part of the resorcinol, and this undergoes condensation with the remaining resorcinol, water being ab- TARTRAZINES. 309 stracted by the sulphuric acid. The following formula represents the structure of resorufin : — ^C 6 H 3 = 0 This substance is only coloured in neutral or alkaline solutions, which are not suitable as dye-baths. The commercial product is the tetrabromo-derivative (2 atoms of bromine in each ring), prepared by adding bromine to a solution of resorufin in potas- sium carbonate, and acidifying. It is sent into the market as the ammonium salt. The chief remaining synthetic organic dyestuffs may be con- veniently dealt with individually rather than in groups. Auramine. — This compound is a ketoneimide, the chromophore being C = NH. It is prepared from tetramethyldiamidobenzo- phenone, the formation of which is carried out by acting on dimethylaniline with carbonyl chloride /C 6 H 4 -N(CH 3 ) 2 2C 6 H 5 -N(CH 3 ) 2 + COCl 2 = CO< + 2HC1 v C 6 H 4 -N(CH 3 ) 2 Te tramethy ldiamido - benzophenone. This latter body on being heated with a mixture of zinc chloride and ammonium chloride at 150° C. = 302° F. condenses in the following way : — / C 6 H 4 N(CH 3 ) 2 / C 6 H 4 N(CH 3 ) 2 * CO< +NH 4 C1 = HN:C< HC1 + H 2 0 ^ C 6 H 4 N(CH 3 ) 2 \ C 6 H 4 N(CH 3 ) 2 Commercial auramine is generally the hydrochloride, a yellow substance slightly soluble in cold water. It is one of the few basic yellow dyestuffs, and dyes silk and wool directly, and cotton mordanted with a tannin mordant. Tartrazines. — These dyestuffs are the products of the reaction between phenylhydrazine and diketones. The best known, termed simply tartrazine, is prepared by acting on sodium dihydroxytartrate with sodium phenylhydrazine parasulphonate, in the presence of hydrochloric acid. Dihydroxytartaric acid may be regarded as derived from the diketone COOH-CO I COOH-CO * Recently, auramine has been classed with the diphenylmethane deriva- tives, and is alleged to have the formula /C 6 H 4 -N(CH 3 ) 2 ^>C 6 H 4 :N(CH 3 ) A CH 3 CI 310 COLOURING MATTERS, DYEING, AND PRINTING. in which the two oxygen atoms have been replaced by four hydroxyl groups thus — COOHC(OH) 2 I COOH-C(OH) 2 Dihydroxytartaric acid. The reaction between this body and phenylhydrazine may be represented as follows : — COOH-C(OH) 2 ! + 2(H 2 N-NH-C 6 H 4 S0 2 ONa) COOH-C(OH) 2 COOH-C = N— NH •C 6 H 4 SOoONa I + 4H 2 0 COOH-C = N— NHC 6 H 4 S0 2 ONa Compounds of this type are termed osazones. Dihydroxytartaric acid may be prepared by the action of nitrous acid upon so-called nitrotartaric acid, obtained by the action of nitric acid upon tartaric acid. Phenylhydrazine is produced by reducing diazobenzene chloride, thus — C 6 H 5 N : N-Cl + H 4 = C 6 H 5 HN NH 2 'HC1 Diazobenzene Phenylhydrazine chloride. hydrochloride. (The reducing agents used include stannous chloride, zinc and hydrochloric acid and sodium sulphite.) Tartrazine, the sodium salt of the above dicarboxylic acid, crystallises in yellow plates, soluble in water, and giving a fast yellow dye on wool and on cotton with a chromium mordant. Isatin yellow is a hydrazone prepared by heating a mixture of phenylhydrazine sulphonic acid and isatin (q.v.) in water. Isatin. C 6 H 4 <^ J>COK The colouring matter is precipitated by neutralisation with sodium carbonate and the addition of salt. It has the formula yC = N - NH-C 6 H 4 S0 2 ONa C 6 H 4 / ^>COH It is a yellow powder soluble in water, dyeing animal fibres a greenish-yellow in an acid bath. ANILINE BLACK. 311 Phenanthraquinone red is an osazone made from phenanthra- C 6 H 4 CO* quinone | and cc-naphthylhydrazine (sulphonic acid pra- C 6 H 4 CO pared by the reduction of diazotised a-naphthylamine sulphonic acid) and has the formula C 6 H 4 C = N - NHC 10 H 6 SO 2 ONa I I C 6 H 4 C = N - NHC 10 H 6 SO 2 ONa The method of preparation is similar to that given above for isatin yellow. The last three dyes are similar to auramine in respect of their chromophore. Phenanthraquinone red is a brownish-red powder, which dis- solves in water and dyes wool red in an acid bath. Aniline Black. — When a solution containing aniline is treated with an oxidising agent, the aniline loses hydrogen and becomes converted into aniline black, the structure of which is not under- stood, though its percentage composition is identical with that of azobenzene, and it may, therefore, be written (OgH^N),, ; the probable value of n is 3. It is insoluble in nearly all solvents, strong sulphuric acid constituting an exception, so that it can be used with difficulty as a dyestuff ; its preparation may, however, be conducted in situ, a method which is applied in calico-printing and cotton-dyeing. It is less suitable for wool on account of the attack of the fibre by the necessary oxidant. For effecting the oxidation a variety of agents will serve, but potassium chlorate (or more commonly the sodium salt) is preferred, and it is advantageous to use a metallic salt capable of acting as an oxygen carrier. If chlorate without a carrier be used, aniline chlorate is produced ; this is fairly stable in solution, so that the black is only formed when the fabric is dried and the aniline chlorate broken up. For the carrier many compounds capable of readily passing to and fro between two states of oxidation may be used — e.g., those of copper (CuCl 2 , Cu 2 Scy 2 , CuS, CuS0 4 ), vana- dium (NH 4 V0 3 ), cerium (Ce 0 (S0 4 ) 3 ), as well as potassium ferro- cyanide (K 4 FeCy 6 ). Copper salts are most generally used, yielding the most stable blacks. Since soluble copper salts attack the iron and copper of the printing machines, copper sulphide and cuprous thiocyanate are preferable. In cotton printing, a mixture of an aniline salt (100 parts), (generally hydrochloride,! which, how- * Made by oxidising the portion of crude anthracene (containing phen- anthrene) which boils between 310° and 340° C. = 590° and 644° F. , with chromic acid in the manner already described for the manufacture of anthraquinone. t Excess of hydrochloric acid appears to lead to the tendering of the fabric by the formation of " oxycellulose. " Aniline itself may be dissolved in aniline hydrochloride to minimise this difficulty. 312 COLOURING MATTERS, DYEING, AND PRINTING. ever, may be replaced by a double sulphate of potassium and aniline), sodium chlorate (20 parts), copper sulphate (20 parts),* ammonium chloride (10 parts) and 400 parts of water, together with a thickening agent (starch or dextrin), is applied to the fibre, and the goods are aged by exposure to air at a temperature of 30° C. = 86° F. For dyeing, potassium bichromate is used as an oxidant in sulphuric acid solution, and the thickening is omitted, the aniline black being precipitated in the fibre and not in the bath. The bath is heated, after the goods have been introduced, to a temperature of 75° C. = 167° F. The tendency of aniline black to "green," appears to be connected both with the extent of oxidation and with the composition of the salt used. If the goods have been aged or dyed at too low a temperature, the oxidising action, to a certain extent, stops at the formation of the bodies emeraldin and nigrauiline, substances less oxidised than true aniline black. The highly purified aniline oil (aniline for blue, q.v.) now in the market, yields blue-blacks which green easily. The presence of orthotoluidine corrects this tendency, but if excess be present rusty shades are obtained. With wool, it has been proposed to use a somewhat acid bath on account of the greater stability of wool fibre in acid solution. Indulines. — These substances form a class of dyestuffs, the constitution of which is still under investigation. They are allied to the azine dyestuffs, but their two nitrogen atoms are not linked together. They are quinoneimide derivatives, but differ from the indamines and other quinoneimide dyestuffs in that they contain a nitrogen ring. The following formula for the simplest induline (benzene induline) will show the quinone- imide structure : — NH - N I R (Here R represents a benzene ring). The other indulines differ from this in respect of the fact that one of the benzene rings (or both) is replaced by a naphthalene ring. Thus, the rosindulines are naphthoquinoneimide derivatives of the type -N I R NH * A much smaller proportion of vanadium salts will serve this purpose (v.s.). SAFRANINES. 313 The isorosindulines are derivatives of quinoneimide of this form :N- The members of the fourth class of indulines (the naphthindulines) contain two naphthalene rings thus — -N- N I R NH The connection between that class of azines called the safranines (p. 300) and the indulines, is shown by the preparation of the simplest induline from the simplest safranine. The latter com- pound — N NH 2 (aposafranine), on the removal of HC1, yields N NH (Benzene induline. ) an intramolecular transformation taking place. 314 COLOURING MATTERS, DYEING, AND PRINTING. The general method of preparing indulines consists in heating amidoazocompounds with aromatic amines in presence of their salts. Thus, the original method adopted for preparing the dyestufF first known as induline consists in heating a mixture of 100 parts of amidoazobenzene,* 130 parts of aniline hydro- chloride, and 300 parts of aniline in a cast iron still, of ample capacity, at 140° to 150° C. = 284° to 302° F. The mass is run into water and made alkaline with caustic soda in order that induline may be precipitated, and unaltered aniline recovered. The induline base obtained in this way is sulphonated, and the sodium salt prepared. The product is known as induline 3 B. By heating with more aniline it takes up more phenyl (C 6 H 5 ), and is converted into induline 6 B. Besides these indulines, several other benzene indulines are produced by varying the proportion of aniline in the melt, and the temperature at which the reaction is conducted. The nature of the change generally consists in the substitution of phenyl or amidophenyl for hydrogen. Azodiphenyl blue is the hydrochloride of benzene induline Induline B has the formula C 18 H 15 N 3 HC1. f Induline 3 B is re- presented by the formula C 30 H 23 N 5 HC1, and induline 6B by C 36 H 27 N 5 HCl-i.e., By heating this with paraphenylenediamine, a new dyestuff y improperly called by the already appropriated name toluylene blue {q.v.), is obtained. The substance immediately concerned in the production of * Amidoazobenzene is prepared by passing nitrous acid into an alcoholic solution of aniline, whereby diazoamidobenzene, C6H 5 N 2 NHC 6 H5, is formed. This is dissolved in aniline in the presence of a little aniline hydro- chloride, and allowed to remain at a temperature of 30° to 40° C. =• 86° to 104° F. for a few days. Under these conditions it undergoes intramolecular change becoming converted into amidoazobenzene, CeHsNgCc^NHa. tlhe separate existence of this substance is doubtful as its structure is not easily explicable. (V.8.). C 6 H 5 NH NAPHTHINDU LINES. 315 induline 6 B is azophenine, which can be isolated from the melt and has the formula C 6 H 5 N^ /NHC 6 H 5 C 6 H 5 N^ \NHC 6 H 5 The indulines as a class are bluish-black dyestuffs insoluble in water, mostly soluble in alcohol, although induline 6 B is but little soluble in this menstruum. They are good fast dyes with some affinity for cotton, and are sometimes substituted for indigo. Their sulphonated products are sold as " soluble indu- lines " on account of their solubility in water. Both indulines and their sulphonated products are used for colouring varnishes and inks. Another method for preparing dyestuffs of this class consists in heating nitrobenzene with aniline hydrochloride and iron filings. The products are called nigrosines. Their constitution and even their empirical formulae are not known. They are, in comparison with the indulines, somewhat grey in shade, but are otherwise similar. Rosindulines. — Such dyestuffs of this class as have been pre- pared, are for the most part not yet of technical importance. By heating nitrosophenylnaphthylamine with aniline, a compound, phenyl rosinduline, containing a phenyl group substituted for the H of the NH group in the typical rosinduline quoted above, is obtained. These dyestuffs are similar to the indulines, but have a reddish shade. Naphthindulines. — Naphthyl blue * is a new dyestuff of this class, of the formula (of the type given above), An ilidophenylnaphthin duline. It is prepared by heating a mixture of benzeneazo-a-naphthyl- amine hydrochloride, a-naphthylamine hydrochloride and aniline. It dyes silk blue with a red fluorescence. Complex indulines termed fluorindines have been prepared by * This must be distinguished from the older dyestuffs of similar name. 316 COLOURING MATTERS, DYEING, AND PRINTING. heating azophenines with a dehydrogenating agent. They are of the form R — N — N — I R I ■N- Quinoline Derivatives. — One of these (alizarin blue) has already been mentioned. The constitution of the type-substance, quino- line, may be expressed thus — OH CH HC HC CH CH HC N the N being substituted for CH of the ordinary naphthalene ring. Flavaniline is a dyestufF of this class, being para-amido- phenylmethylquinoline CH 3 NH 2 ■and is prepared by heating acetanilide * with a dehydrating agent — e.g., zinc chloride at a temperature of 250° to 260° C. = 482° to 540° F. The product is extracted with hydrochloric acid, and the dyestuff is salted out. The reaction ultimately consists in the elimination of two molecules of water from two molecules of acetanilide, CH 3 CONHC 6 H 5 ; amidoacetophenone, NH 2 C 6 H 4 CH 3 CO (the isomeride of acetanilide), is probably an intermediate product. Flavaniline is not now much used as a dyestufF. It crystallises in colourless needles ; the hydrochloride crystallises in yellowish- red prisms, and dyes wool and silk yellow. The cyanines are basic bodies of the quinoline class, formed by the condensation of two molecules of quinoline, one of which contains a methyl group or one homologous to it {e.g., ethyl or * Prepared by heating glacial acetic acid with aniline till the mass solidifies on cooling. This product is then distilled. QUINOLINE RED. 317 amyl). They are prepared by heating quinoline with methyl quinoline (lepidine),* or a homologue, and methyl iodide or an homologous iodide, and an alkali. HI and H are removed and blue dyestuffs formed. Iso-amyl cyanine, C 29 H 35 lsr 2 T, is the best known cyanine. It forms beetle-green crystals, dissolving in alcohol to a blue solution ; being fugitive it is but little used as a dye. Quinoline red is a derivative of iso-quinoline, and is prepared by heating iso-quinoline with quinaldine, benzotrichloride, C 6 H 5 001 3 , and zinc chloride. Crude coal tar " quinoline," contains both iso-quinoline and quinaldine, and may therefore be used. The constitution of quinoline red is probably expressed by the formula /C 9 H 6 N CI C 9 H 5 (CH 3 )N It is thus of similar structure to the triphenylmethane dyestuffs. It gives a fluorescent red colour (on silk), but is fugitive to light. It finds application in the preparation of " isochromatic " photo- graphic plates. Quinoline yellow or quinophthalone has the constitution C 6 H 4 CHC 9 H 6 N 0 : 0 and is produced by heating phthalic anhydride with quinaldine in presence of zinc chloride. Quinoline yellow crystallises in yellow needles. It is not basic. It dyes wool and silk yellow, and its sulphonic acid gives shades like those produced by picric acid. It is fairly fast to light. * The lepidines are quinolines with the methyl group in 'the benzene nucleus. 318 COLOURING MATTERS, DYEING, AND PRINTING. Acridine Dyestuffs * — Chrysaniline may be taken as a type of these. It is para-amidophenylauaidoacridine, having the formula N NH 2 As has been already mentioned, it is a bye-product in the manu- facture of magenta {q.v). The commercial product is usually a mixture of the substance shown above and its methyl derivative. The mother liquors from the magenta-melt are precipitated by the addition of salt and lime, the latter throwing down various bases, among which is chrysaniline. The following laboratory synthesis indicates how chrysaniline may be formed in the rosaniline melt from triamidotriphenylmethane, produced by the condensation of one molecule of orthotoluidine with two molecules of aniline. Orthonitrobenzoic aldehyde (correspond- ing in respect of its substitutions with orthotoluidine) is heated with aniline and zinc chloride, thus — (1) + 2 COH NH, NO, NH 2 CH + H 2 0 * Acridine bears a relation to anthracene similar to that borne by quino- line to naphthalene, as is evident from its structural formula, INDIGO. 319 The reduction of this compound (orthonitroparadiamidotriphenyl- methane) converts the nitro-group into an amido-group. When the resulting triamido-compound is oxidised it yields chrysaniline — N ■<2) NIL CH NH fl NH< NHo H 4 = NHo The precipitate is treated with nitric acid, and the chrysaniline nitrate being sparingly soluble is thus separated, its separation being aided by the addition of a further quantity of nitric acid. The commercial dyestuff (the nitrate, known as phosphine) is a yellow powder which dyes silk and wool directly, and cotton with a tannin mordant. Acridine orange is tetramethyldiamidoacridine, (CH 3 ) 2 N-C 6 H, N I CH C 6 H 3 -N(CH3) 5 and is obtained by heating tetramethyltetramidodiphenylmcthane with an acid, and oxidising the leuco-compound thus produced. Benzoflavine is diamidodimethylphenylacridine, and is pre- pared by condensing benzaldehyde with metatoluylenediamine and heating the resulting tetramidoditolylphenylmethane with hydrochloric acid under pressure. The product is oxidised by means of ferric chloride to benzoflavine. Benzoflavine is a yellow powder slightly soluble in cold water, dyeing wool and silk directly, and cotton with a tannin mordant. (2) Natural Organic Dyestufifs.— Indigo. — This is the pro- duct of various species of Indigqfera, the most important being /. tinctoria, chiefly cultivated in the East Indies. Several other species are grown elsewhere, the chief of which is /. argentea, the culture of which is practised in Africa (notably in Egypt). Another class of plant, woad, Isatis tinctoria, yields indigo in small quantity, and is no longer used as a source of the dyestuff. It is grown in Europe, however, to prepare the " woad-vat " for indigo dyeing (v.i.). Indigo does not exist as such in these plants, but in the form of a " glucoside," indican, C 26 H 31 NO l7 , a substance which readily undergoes hydrolysis with the formation of in- digotin, the colouring matter of indigo, and indiglucin, which 320 COLOURING MATTERS, DYEING, AND PRINTING. has been termed a glucose, although its formula does not corre- spond with that of the glucoses — 2C 26 H 3 iN0 17 + 4H 2 0 = C 16 H 10 N 2 O 2 + 6C 6 H 10 O 6 Indican. Indigotin. Indiglucin. The preparation of crude indigo from the plant consists in macerating the plant with water, whereby fermentation is set up and hydrolysis of the indican takes place. The indigotin produced by the hydrolysis, however, is reduced during the fermentation process by the indiglucin to hydrindigotin (indigo white), C 16 H 12 N 2 0 2 , which dissolves in the aqueous liquor, alka- line from the products of fermentation. The liquor is run off the macerated plants into a second vat, and by exposure to air r aided by agitation, the hydrindigotin is reoxidised, and indigotin precipitated — being insoluble in the alkaline liquid. The yield is about 0*2 per cent, of the weight of the plant. The addition of ammonia to the vat is frequently practised, with the result that the yield is largely increased, as the formation of ammonia by the fermentative breaking down of the indigo is thus hindered. When the indigo-blue has settled, the bulk of the liquor is run off, and the blue transferred to a cauldron where it is boiled with water to stop fermentation and to extract soluble impurities. It is then filtered, and the residue pressed into cakes and cut into cubes. The indigo obtained in this manner varies greatly in quality. Its content of indigotin ranges from 20 to 90 per cent., the average being 40 to 50 per cent. The remainder consists of ash, 5 to 20 per cent.; water, 2 to 8 per cent.; in- dirubin, 2 to 4 per cent., and various amounts of indigo brown, indigo-gluten, and carbohydrates. The value of the blue depends on its content of indigotin and indirubin. Indigotin is a dark blue crystalline substance with a bronze lustre; its specific gravity is 1-35; it sublimes and partially decomposes at 290° C. == 554° F. It is remarkable for its insolubility, being unaffected by dilute acids and alkalies, and almost completely insoluble in ordinary organic solvents. Chloroform, glacial acetic acid and aniline dissolve it sparingly. It dissolves in strong sulphuric acid, and is reprecipitated on dilution ; if the solution be heated sulphonic acids are formed (v.i.). It is soluble in an alkaline liquid in the presence of reducing agents, such as glucose, ferrous hydroxide, stannous oxide, &c. By oxidising agents it is con- verted into isatin C 8 H 5 N0 2 (i.e. , C 6 H 4 <^ ^ ^> C(OH)) Special attempts have been made to synthesise indigo and to make it as much an artificial colouring matter as is alizarin (q.v.), and thus to displace the indigo plant, just as madder has been driven out of cultivation. Hitherto, but little commercial ARTIFICIAL INDIGO. 321 success has attended these efforts. The most hopeful method of synthesis is that recently devised by Heumann. By heating monochloracetic acid with aniline, phenylglycocine (phenylamido- acetic acid) is formed, thus — C 6 H 5 NH 2 + CH 2 Cl'COOH = C 6 H 5 NH-CH 2 -COOH + HC1 Phenylamidoacetic acid. One part of this product is heated with two parts of caustic soda at 260° C. = 500° F. in a closed retort, the melt is dissolved in water, and the solution oxidised by a current of air. The reaction may be represented as taking place in two stages — / CO ^ (1) C 6 H 5 NH-CH 2 -COOH = C 6 H 4 < >CH 2 + H 2 0 ^ XII / Pseudo-indoxyl. (2) 2(C 6 H 4 <^°^CH 2 ) + 0 2 y co \ / co v = C 6 H 4 < > C= C < > C 6 H 4 + 2H 2 0 NH ' ^KII/ Indigotin. Another process of interest, though at present of little commercial importance, consists of the following steps : — Orthonitrobenzaldehyde, prepared from orthonitrobenzyl chlor- ide (by a process not made public), is heated with acetone and an alkali, the following reaction taking place : — /CtJ(OH)CH 2 CO(CH 3 ) C 6 H 4 (N0 2 )CHO + (CH 3 ) 2 CO = C 6 H 4 < \N0 2 Nitrophenyllactomethyl ketone. By further treatment with alkali, this is converted into indigotin and alkali acetate. It has not been found advisable to prepare indigotin in this way and to separate the product ; by converting the ketone into its sodium bisulphite compound, however, a soluble substance is obtained which can be printed on a fabric and transformed into indigotin in situ by treatment with an alkali. Obviously, goods can be dyed by soaking them in a solution of the ketone compound, and passing them through a bath of caustic alkali. Two or more isomerides of indigotin exist. The most im- portant of these is indirubin the relation of which with indigotin may be shown by the formula / CO \ / CO \ C 6 H 4 < >C:C< >NH It is a red crystalline substance, constantly present in commercial 21 322 COLOURING MATTERS, DYEING, AND PRINTING. indigo, and accompanying it throughout the dyeing process (q.v.). > CO v The chromophoric group in these compounds is 0. X NH 7 As there is no salt-forming group in indigotin, this substance, as has been pointed out at the beginning of the section, owes its fastness as a dye to its insolubility and not to chemical attach- ment to the fibre. This is evident from the fact that it rubs off to a slight extent, although otherwise an extremely permanent colour. All the colouring matters in commercial indigo are capable of conversion, by reduction, into colourless derivatives, soluble in alkalies. Such derivatives of colouring matters are known by the generic prefix " leuco " (white). They generally contain more hydrogen than is present in the colouring matter. Thus, indigo-white (leucindigo, reduced indigo, hydrindigotin) has the formula / C(0H)^ ^C(OH)\ C 6 H 4 < >C- C \ > C 6 H * The application of indigo as a dye depends upon this formation of indigo- white. The principle underlying all processes of indigo "vat" dyeing (as distinct from dyeing with indigo-sulphonic acids — v.i.), is the reduction of indigo to indigo-white and the dissolution of the resulting indigo -white, in an alkali ; the fibre to be dyed is saturated with this solution, and exposed to the air, whereby the indigo- white is rapidly oxidised and indigo-blue formed in the interstices of the fibre. In practice, many kinds of vat can be used. It will suffice to describe three as types, viz. : — The copperas (ferrous sulphate) vat (used for cotton), in which ferrous hydroxide is the reducing agent; the woad vat (used for wool) in which the reducing action of a ferment is employed ; and the hyposulphite vat used for both wool and cotton. An average copperas vat will contain 30 lbs. of finely- ground indigo, 80 lbs. of ferrous sulphate, 60 to 100 lbs. of slaked lime, and 1,000 gallons of water. The slaked lime reacts with the ferrous sulphate, producing ferrous hydroxide and calcium sulphate. The former, in presence of excess of lime, reduces the indigo to indigo-white, which dissolves in the alkaline bath. Several vats are worked in series systematically, the cloth passing from the weaker to the stronger vats. The excess of liquor is squeezed out when the cloth leaves the last vat, and the indigo-white is oxidised to indigo by exposure to air, during passage of the cloth over rollers. This vat is not suitable for dyeing wool, on account of the large quantity of lime which it contains, wool being more susceptible of injury by the attack of alkali than is cotton. The woad vat can be worked with a small quantity of lime, and is therefore to be preferred for wool DYEING WITH INDIGO. 323 dyeing. The woad is used in the form of balls of dried leaves of the woad plant (Isatis tinctoria) which, although containing but little indigo, is said to be valuable in imparting a good shade to the dyed material. Its main use, however, is to excite fer- mentation in the indigo vat. For the same purpose bran and madder are used. The vat is generally composed of indigo 10 to 25 lbs., woad \\ to 5 cwts., bran 20 lbs., madder 5 to 20 lbs., slaked lime 24 lbs., water 1,500 gallons. The woad is first added to the water, which is heated to 60° C. = 140° F.; after some hours the finely -divided indigo, madder and bran are added, together with half the lime. Fermentation sets in, and when a piece of wool dipped into the vat is found to become blue on exposure to air, the rest of the lime is gradually added, the temperature being maintained at 60° C. = 140° F. The organism chiefly concerned in the fermentation is a pathogenic bacillus, resembling that characteristic of pneumonia. Recently, an improved vat, said to avoid loss of indigo, has been prepared by adding a cultivation of the organism Desmobacterium hydro- geniferum, and substituting flour and glucose (as nutrient materials) for the bran, &c, and soda and magnesia for the lime. The general method of dyeing is similar to that described above. The hyposulphite* vat, applicable both to wool and cotton, is prepared as follows : — Zinc sheet is allowed to act on a strong solution of sodium bisulphite, producing zinc hyposulphite (ZnS 2 0 4 ). The operation is conducted in a closed vessel, as the hyposulphites are readily oxidised by air. The solution is mixed with milk of lime and indigo (20 lbs. of indigo, 25 lbs. of slaked lime and 20 gallons of water), and heated to about 70° C. = 158° F., whereby indigo is reduced and dissolved. The strong solution of reduced indigo is added, as required, to a vat containing 60 to 70 lbs. of sodium sulphite, 6 lbs. of zinc dust and 6 lbs. of lime (to complete the reduction of the indigo). The process of dyeing is essentially the same as has been already described. The hyposulphite has a somewhat drastic action on wool, so that the use of this vat with that material requires care. The indigo -sulphonic acids are used in dyeing wool and silk under the name of " indigo-extract " and " Saxony blue," but cotton cannot be dyed by these substances. These dyestufis are not ingrain colours, as is indigo, but dye by direct absorption into the fibre ; cotton fibre, being incapable of exercising this attraction, cannot be dyed with them. The shades produced are not fast to washing. The indigo-extract is generally made in the dye house by stirring finely-powdered indigo with about 6 times its weight of concentrated sulphuric acid and heating to about 60° C. = 140° F. The solution is diluted with water and * Not to be confounded with thiosulphate, commonly called ''hypo- sulphite." 324 COLOURING MATTERS, DYEING, AND PRINTING. the dyestuff is salted out by the addition of sodium chloride,, an acid sodium salt of indigo-sulphonic acid being formed. By repeating the treatment, the neutral sodium salt is obtained. According to the proportion of sulphuric acid used, its strength and the temperature of treatment, indigo- monosulphonic acid, C 16 H 9 N 2 0 2 (S0 2 OH), or indigo-disulphonic acid, C 16 H 8 N 2 0 2 (S0 2 OH) 2 , or a mixture of the two is formed. When the disulphonic acid is specially required, fuming sul- phuric acid is used for dissolving the indigo. The monosulphonic acid has a reddish shade and is known as purple indigo -extract, while the disulphonic acid is blue ; its sodium salt is called indigo-carmine. The monosulphonic acid is soluble in pure water, but insoluble in dilute sulphuric acid. The disulphonic acid is a blue powder soluble in water and dilute acid. Both acids are precipitated by the addition of salt or sodium sulphate. With regard to printing with indigo, it was formerly only possible to produce a pattern by printing a discharge (y.i.) upon the dyed fabric. According to modern practice, a system is adopted equivalent to the formation of a true indigo vat in the fibre itself. This is done by saturating the fabric with a solution of glucose, and printing finely-divided indigo, mixed with strong caustic soda. By steaming, the action between the indigo and the glucose in the printed pattern is accelerated, and the reduced indigo, which results, penetrates the fibre wherever printed. On exposure to air, the indigo white is oxidised and the pattern becomes dyed blue. Logwood is the heart- wood of Hwmatoxylon campechianum, a tree growing in Central America. When freshly cut the wood is nearly colourless, but it soon reddens externally on exposure to air. The colouring matter is an oxidation product of the body haematoxylin, C 16 H 14 0 6 , the constitution of which is un- known. This oxidation product is haematein, C 16 H I2 0 6 , which has a bronze green colour in the mass, but yields a red solution ; it is also of unknown constitution. In order to convert the whole of the haematoxylin of the wood into hsematein, the chipped or rasped wood is exposed in heaps, until fermentation sets in (known as the " ageing " of the wood, and supposed by some to consist in the decomposition of a glucoside, yielding haematoxylin). A small quantity of ammonia is formed during fermentation, and aids the oxidation, haBmatoxylin being readily changed into hsema- tein in the presence of an alkali. The wood is either used in chips to make up the dye-bath, or its aqueous extract is employed. This is prepared by systematic extraction with hot water and concentration of the solution thus obtained, in a vacuum pan. Although itself a red colouring matter, logwood is used for producing other colours, notably blues and blacks. It is not a dye but a dyestuff, and as textile fibres have no affinity for it r DYEWOODS. 325 it must always be used with a mordant, the nature of which modifies the colour produced. Thus, chromium mordants give blue passing to black ; iron, grey passing to black ; aluminium, dull-violet ; copper, greenish-blue; tin, reddish-violet. A mix- ture of mordants may be used and mixed shades produced. The colours are fairly fast, though the blue is not so fast as that produced by indigo. Logwood is used for dyeing cotton, wool and silk, especially for producing black dyes. An iso-hsematein has been prepared from ordinary haematein and is said to be faster than its isomeride, but it is not yet of technical im- portance. Brazil Wood. — This wood, together with a number of other woods — e.g., peach wood, sapan wood and Lima wood, all be- longing to the leguminous genus, Ccesalpinia — contains brazilin, 0 16 H 14 0 5 ,* a colourless substance of unknown constitution, but apparently similar to hematoxylin. This substance is present in the wood as a glucoside, and for the purpose of hydrolysing this, the wood is submitted to a process of fermentation ana- logous to that adopted for logwood. At the same time the brazilin suffers oxidation to brazilein, C 16 H 12 0 5 ,f the change being hastened by the presence of an alkali, as in the case of logwood. The shades produced by brazilein are fugitive to light, and are not fast to soap. The colours obtained by means of brazil wood depend on the mordant — e.g., chromium mordants yield a violet or claret ; aluminium, rose-red ; iron, dull violet or purple ; copper, drab or brown ; tin, crimson. The above woods have an open texture, and are termed " soft or open woods." They readily yield their colouring matters on extraction. Another group of woods of the same class — e.g., santal wood, cam wood and bar wood — are known as " close woods," and are less easy to extract. They yield colouring matters similar to brazilein, and are similar in other respects to the woods already described. Old fustic or Brazilian yellow wood is the wood of Morus tinc- toria, obtained from Brazil and the West Indies. Its colouring matter is morin, C 13 H 8 0 6 '2H 2 0, the constitution of which is not known. Fustic is applied like the woods already mentioned, either as chips or extract, and gives bright yellow shades with tin and aluminium mordants. It is also used as an adjunct to logwood, improving the blacks obtained by means of this dyestuff. Young fustic or fustet wood is the wood of Rhus cotinus, and contains the glucoside fustin, which yields the colouring matter fisetin, C 2 3H 10 O 3 (OH) G , and a sugar on hydrolysis. The wood is used as chips, or an extract (termed colinin) is obtained from it. It is a yellow dyestuff, but is mainly employed together with other dyestuffs — e.g., cochineal — for wool dyeing. * Another formula, C 2 2H 18 07, has been proposed. + Another formula, corresponding with that for brazilin, is C 2 2H 16 0 7 . 326 COLOURING MATTERS, DYEING, AND PRINTING. Quercitron bark is the inner layer of bark from Quercus tinc- toria. The main part of the colouring matter is contained in the yellow powder which is obtained, mixed with woody fibre, when the bark is ground. The glucoside quercitrin, C 36 H 38 O 20 , is the source of the yellow colouring matter quercitin, C 24 H 16 0 11 , which it yields on hydrolysis, together with a pentose, rhamnose, C 5 H 9 (CH 3 )0 5 # H 2 0. Both quercitrin and quercitin are dyestuffs yielding yellow shades with aluminium mordants, and orange shades with tin mordants. The product obtained by acting on the bark with dilute sulphuric acid, commercially known as "flavin," contains both quercitrin and quercitin. It is sold as a concentrated form of quercitron. It is used with cochineal in scarlet dyeing. Weld, the leaves of Reseda luteola, contains luteolin, C 20 H. u O 5 ,* which gives fast yellow colours with aluminium mordants and is used for silk dyeing. Turmeric is the colouring matter obtained from the rhizomes of Curcuma tinctoria. The colouring principle curcumin, 0 14 H 14 O 4 , is capable of dyeing cotton without a mordant; it is used for modifying red shades thereon. It is not fast to light. Besides its use as a dyestuff it is employed as an indicator. Persian berries are the fruit of Rhamnus amygdalinus. They contain the glucoside xanthorhamnin. Hydrolysis converts this into rhamnotin and isodulcitol (rhamnose), thus — C48H 66 0 29 + 5H 2 0 = 2C 12 H 10 O5 + 4C 6 H 14 0 6 . Rhamnotin. When dyed with tin, or tin and aluminium mordants, it gives a fine yellow colour. It is used chiefly as an extract. Safflower is the flower of Carthamus tinctorius, and contains- the colouring matter carthamin, the formula for which is doubt- ful. It is found in commerce as an extract, which is dissolved in soda to form the dye-bath, and then acidified with citric- acid. It produces a pink colour on silk. It is mixed with starch to make toilet rouge. Catechu or cutch is obtained as an extract from various species of acacia. (Gambier is a similar material.) It contains catechin (C 21 H 20 O 9 ,5H 2 O) which is itself colourless, but gives a fast brown on cotton when oxidised, after passage through the dye-bath, by potassium bichromate. Lichen Colouring Matters. — The following are the kinds of lichens which are commercially important from the colouring matters which they yield — Roccella tinctoria, R. fuciformia and Lecanora tartarea. These are commercially known as orchella or orchil weed. The lichens contain orcinol or orcin, a dihydroxy- toluene. This body occurs to a slight extent in the free state, but for the most part results from the decomposition of orcellic * Some authorities give C ]2 H 8 0fi. COCHINEAL. 327 acid polymeric with orcellinic acid ; the latter is dihydroxy- toluic acid of the formula C 6 H 2 CH 3 (OH) 2 COOH. Erythrin, C 20 H 22 O 10 , is another compound which yields orcinol on decom- position. Archil is prepared preferably from Roccella tinctoria by moistening the shredded weeds with ammonia, and keeping the mass at a temperature of about 40° C. = 104° F. for some days. During this process various decompositions occur, one of the products of which is orcinol ; this becomes orcein by oxi- dation in presence of the ammonia. The orcein contains nitro- gen, and has the formula C 28 H 24 N 2 0 7 allotted to it by some authorities. The commercial product is sold either as a liquor or paste. Cudbear (perseo) is similarly prepared, Lecanora tartarea being preferred as the raw material. It is a dark brown or purple powder. For preparing litmus a longer treatment of the lichens and the addition of potassium carbonate are necessary. The concentrated extract is mixed with plaster of Paris and cut into cubes. Lit- mus is not used as a dyestuff, but for colouring wine and as an indicator in the laboratory. The above three dyestuffs are used largely in conjunction with other colouring matters, notably indigo. Archil and cud- bear are dyed on wool and silk from acid baths, yielding bluish- red shades. Cochineal. — This is one of the few dyes of animal origin. The commercial material consists of the bodies of females of the insect Coccus cacti, collected from certain kinds of cactus in Mexico and the Canary Islands. Three grades are known, "silver grain" (the best), "black grain" and the inferior "granilla." These are said by some to be insects in different stages of maturity, but by others it is stated that their difference largely depends on the mode of collection and drying — the black having been killed by boiling water, and the silver stove-dried. The white film on the silver grain cochineal is due to the wax coccerin, C 30 H 60 (C 31 H 61 O 2 ) 2 (cocceryl coccerate), naturally present, and amounting to about 1 to 2 per cent, of the weight of the cochineal. This silvery coating is often imitated by facing the cochineal with talc and other mineral matter. Cochineal contains about 10 per cent, of the red colouring matter " carminic acid," which is a glucoside and splits up on hydrolysis, yielding the true colouring matter carmin, and a sugar, thus — CnHisOjo -f 3H2O = C11H12O7 + CgHiaOg. Carminic acid. Carmin. The dyeing process consists in immersing the goods (generally wool) in a decoction of cochineal containing the appropriate mor- dant, tin for scarlet, chromium for purple, aluminium for crimson. Bluer shades are obtained by the use of ammoniacal cochineal, 328 COLOURING MATTERS, DYEING, AND PRINTING. prepared by moistening ground cochineal with ammonia, leaving the mass for some days, adding precipitated alumina and heating until the ammonia is expelled. The product of the action of the ammonia appears to have the formula C l7 H 17 (NH 2 )0 9 . The alumina-lime lake of carminic acid is used as a pigment under the name " carmine " ; it must not be confounded with carmin, the product of the hydrolysis of carminic acid. Kermes is the insect Coccus ilicis, collected from the Quercus ilex, the habitat of which is Spain and North Africa. Its colouring matter is closely allied to that of cochineal, and it served at one time similar purposes as a dyestufF. Lac-dye. — This is a colouring matter which is dissolved from stick lac (see Shellac) on treatment with water. The colouring matter is precipitated from the solution by addition of an alu- minium salt, and the lake is pressed into cakes. When used as a dyestufF it produces a colour similar to, but faster than, cochi- neal ; it is, however, less brilliant. It is stated that the colouring principle is not identical with that of cochineal, but is laccainic acid, C 16 H 12 0 8 . (3) Mineral Dyes. — But few mineral colouring matters are capable of being advantageously used either as dyestuffs or dyes. Those which are in use are ingrain dyes, comparable with indigo (q.v.) precipitated in the fibre. Chrome yellow (lead chromate, PbCr0 4 ) is applied to cotton, for which alone it is used, by passing the fabric first through a solu- tion of lead nitrate or acetate, precipitating the lead as hydroxide in the fibre by means of an alkaline bath, or as sulphate by means of a bath of sodium sulphate, and converting this into lead chromate by passing through a bath of sodium bichromate. Chrome orange (basic lead chromate) is prepared in the fibre by first impregnating it with chrome yellow as described above, and then immersing it in a bath of boiling lime water. Manganese Brown, "Bistre." — Fabrics may be dyed with manganese peroxide by saturation with manganous chloride and precipitation of manganous hydroxide in the fibre by passage through an alkaline bath. Passage through a solution of chloride of lime converts the manganous hydroxide into the brown hydrated peroxide. Another reddish-brown is obtained from manganese and iron salts, which is more resistant to acids than true iron brown (iron buff — q.v.). Iron Buff— Nankin Yellow. — This is produced in two shades, by passing the fabric (cotton) through a solution of ferrous sulphate and then through one of caustic soda. The ferrous hydroxide is either oxidised by exposure to air or by treatment with chloride of lime. Ferric salts may also be directly used. Prussian blue was formerly of some importance, but has been largely displaced by synthetic organic dyestuffs. There are two APPLICATION OF DYESTUFFS. 329 methods for producing Prussian blue in the fibre. The one con- sists in producing ferric hydroxide in the fibre (v.s.) and converting this into Prussian blue by immersion in an acid solution of potassium ferrocyanide. The other consists in saturating the fabric with an acid solution of a ferro- or ferricyanide, and raising the temperature to boiling point, whereby the hydro- ferrocyanic or hydroferricyanic acid first liberated, is decomposed with the formation of a blue pigment. B. DYEING AND MORDANTS. — The methods of bring- ing the material to be dyed into contact with the dyestuff natu- rally vary according to the nature of the material, and the use to which it is to be put. Thus, if the fabric is to be of one uniform colour it suffices to dye it "in the piece" — i.e., after it has been woven. Where a coloured pattern has to be produced {other than by printing methods) threads of different colour have to be employed in the weaving, and the material is dyed as yarn. In some instances stuff that is ready to be spun into yarn is dyed previously to its being further worked up. The details of the apparatus for bringing the material into contact with a dyestuff are purely matters of mechanical engineering and cannot be considered in detail here. It suffices to say that their main object is to bring the dyeing liquor into rapid and perfect contact with the stuff to be dyed. The processes most used fall into two main groups. In the first the stuff is stationary and the dye liquor is caused to filter through it ; in the second the liquor is stationary and the stuff is made to travel through it, often as an endless band. The various mechanical terms, such as "hank-dyeing," "cop-dyeing," &c, have reference to the form in which the material is made up before being put through the dye-bath, such preliminary fabrication being in many cases an early stage in the process of manufacture. With regard to the constitution of the dye - bath, this depends primarily upon that of the fibre to be dyed. Thus, in general terms, the marked chemical activity of silk and wool permits their being dyed directly (although mordants are often used as auxiliaries), whereas the comparative inertness of cotton and similar cellulosic materials necessitates the use of a mordant, in all but a few cases of dyestuffs which are chiefly of quite recent invention. In the foregoing description of dyestuffs, the structure and mode of formation have served as a means of classification. In the ensuing consideration of the application of these dyestuffs, a broad division into (1) acid dyestuffs, (2) basic, (3) indifferent, will be found more convenient, for it is upon the properties thus connoted that the selection of an appropriate mordant for a given dyestuff depends. In general, an acid dyestuff will require a basic mordant, and thus a classi- fication complementary to that given above will be valid for mordants. Seeing that the application of dyestuffs is also in- 330 COLOURING MATTERS, DYEING, AND PRINTING. fluenced by the nature of the fibre to be dyed, the following classification based on a consideration of both the dyestuff and the fibre will be found convenient : — 1. Direct Dyes, applicable to all fibres. 2. Basic Dyes, also applicable to all fibres. 3. Acid Dyes, applicable to wool and silk. 4. Mordant Dyes, applicable to all fibres. 5. Special Dyes, requiring special processes. The subject of mordants may be dealt with before that of the processes of dyeing. Mordants. — These are a group of bodies which are used in dyeing and printing textile fabrics with the second and fourth of the groups of dyes named above, for the purpose of fixing the colour more firmly on the fabric ; in some cases the mordant aids in the development of the colour as well as in its fixation. (1) Basic Mordants. — The object of these mordants is to impregnate the fabric with a basic oxide capable of uniting with the dyestuff used which has acid properties, to form a chemical compound commonly known as a "colour lake." The constitution of these " colour lakes " will be dealt with later. The salts used to supply the basic oxide, which is to serve as a mordant, are generally those of aluminium, iron, chromium and tin. Of these, the iron mordants have a ''saddening" effect — i.e., give somewhat dark shades (a property possessed also by copper salts). Aluminium Mordants. — The principal salts used are alum and aluminium sulphate. Since aluminium sulphate is a moderately stable salt, it is necessary to convert it into a salt more easily broken up by the influence of the affinity of the fibre. For this purpose, an organic acid, generally tartaric acid in the form of bitartrate of potash (cream of tartar), is used. It is generally supposed, as a working hypothesis, that aluminium tartrate is formed, which is broken up by the action of the fibre and the liberated alumina absorbed by the fibre. This is more particularly applicable for wool, the fibre of which has a slight but definite acid character. In the case of silk, it is necessary to use an actual precipitant for the alumina in the form of calcareous water. Another modification often employed for cotton consists in impregnating the material to be dyed with a solution of aluminium acetate, and "ageing" it, either by exposure in a warm atmosphere whereby a portion of the acetic acid is driven off, or by steaming in a closed vessel. The aluminium acetate may also be decomposed by passage of the fabric through a weak alkaline bath — e.g., of sodium phosphate or arsenate. Aluminium thiocyanate is sometimes used, being, like the acetate, capable of easy decomposition. The cotton fabric may also be first impregnated with tannic MORDANTS. 331 acid or "Turkey-red" oil (q.v.) and subsequently with aluminium sulphate. Sodium aluminate is another form in which aluminium may be applied to cotton, its alumina being deposited by the decomposition of the salt by the carbonic acid of the air. Iron Mordants. — These are mainly ferrous sulphate and acetate, the corresponding ferric salts and the so-called "nitrate of iron " — crude ferric sulphate. The general methods are similar to those for aluminium mordants. In addition, when ferrous salts are used, ageing and consequent oxidation are carried out, the ferric salt produced acting better as a mordant than does a ferric salt directly applied to the fibre. Passage through weak alkaline baths is practised, especially for " nitrate of iron," much used in dyeing cotton. Chromium Mordants. — The salts of chromium (from the oxide, Cr 2 0 3 ) are analogous in their behaviour to those of aluminium. Chromic sulphate can be used for mordanting wool, and the more easily decomposable acetate and thiocyanate for cotton. Another form of chromium mordant for wool is the fluoride, CrF 3 , which is useful on account of the ease with which it is decomposed, and the absence of injurious action of the hydrofluoric acid — liberated by its decomposition — on the fibre and dyestuff. An alkaline solution of chromic hydroxide is also used as a mordant. Weak alkaline baths, to follow those of neutral chromium salts, are used in the case of cotton, the rationale of the proceeding being the same as with aluminium. Sodium or potassium bichro- mate may also be applied as a mordant. The fibre apparently fixes chromic acid from this, the chromic acid being subsequently reduced to chromic hydroxide by passage through a bath containing an organic acid or a bisulphite, or in the dye-bath itself at the expense of the dyestuff, fibre or some other con- stituent. Chromic acid thus used and reduced by an organic acid (e.g., oxalic acid) or an organic salt (e.g., tartar, bitartrate of potash) constitutes what is termed a " non-oxidising mordant" ; should no such reducing agent be employed ad hoc, the phrase "oxidising mordant" is appropriate; when chromic acid is utilised in this manner the dye must be such a one as logwood, upon which an oxidising action is required. Tin Mordants. — Tin is used in the form of both stannous and stannic compounds. Stannous chloride (tin crystals) is used as a fixing agent for tannin mordants in cotton dyeing, and in the dyeing of Turkey reds and wood colours on cotton, and in dyeing wool and silk. Stannic chloride is used in silk dyeing. Stannate of soda is largely used in calico-printing for preparing the cloth for printing many dyes, such as the eosins. The cloth is first passed through a solution of the stannate, and then through a weak bath of sulphuric acid, whereby a deposit of stannic oxide is formed on the fabric. (2) Acid mordants are employed for fixing basic dyestuffs on 332 COLOURING MATTERS, DYEING, AND PRINTING. such materials as do not fix them directly. Wool fixes basic dyestuffs directly (in the absence of any notable addition of acid) and, therefore, needs no external mordant. A small quantity of acetic acid may be added, however, to the dye-bath, if the water be calcareous or the wool alkaline from the washing it has undergone. Soap is sometimes used as an aid to dyeing wool, its function probably consisting in providing a fatty acid capable of union with the basic dyestuff. Silk is also dyed from a feebly acid bath, or the bath may be neutral or alkaline with soap, or " boiled-off liquor" — i.e., the solution of the sericin of silk fibre in soap (see Textiles, Vol. II.). The colours on silk are sometimes made more brilliant by subsequent passage through a feebly acid bath. All these processes are in the highest degree empirical. For cotton, on the other hand, definite acid mordants are required. The mordant may be tannin, or fatty acids or an acid dyestuff. The tannic acid generally requires to be fixed on the cotton in the form of the salt of some feeble base (e.g., antimony or tin oxide), so that a bath of tartar emetic or stannic chloride (or pink salt — q.v.) usually follows that of tannic acid. The acid combined with the basic colour is displaced by the tannic acid held on the fibre, and the dyestuff thus enters into combination with the " tanned " fibre to form a dye upon it. Various forms of tannin (q.v.) — e.g., gall-tannin and sumach — are used in this manner, the purified tannic acid from gall-nuts being preferred for delicate colours. The effect of the tannin is refer- able to the fact that in the presence of sodium acetate all basic colouring matters may be precipitated by tannin solution, a reaction which distinguishes them from dyestuffs of acid charac- ter. The commonest form in which antimony oxide is used is tartar emetic, s COO(SbO) C 2 H 2 (OH) 2 > (syrup) 46-06 45-90 5-06 0-70 2-28 0-90 Extracts are not unfrequently adulterated with molasses. In dealing with both liquor and extracts their liability to ferment- ation and oxidation must be borne in mind. With regard to the mineral salts and the oils used in tannins: it will suffice to say here that for mineral tannage, alum, salt, bichromate, copperas, and a few other chromium and iron salts are used, whilst for oil tannage oils belonging to the fish-oil group, especially cod and whale oils, are applied. PREPARATORY PROCESSES. — Before the hide or skin is tanned it is always submitted to certain preliminary treatment, having for its object the production of a pelt which shall be clean, free from hair, soft and supple in the case of skins for light leather, and well distended in the case of hides for heavy leather. (1) Cleansing and Softening. — Market hides and skins — that is, such as have been sold to the tanner within a few hours of their removal from the animal — only require washing, to remove blood and dirt, before they are unhaired. Since no kind of water can be said to be free from a solvent action on hide fibre, it is obvious that a prolongation of the washing will result in loss of weight to the hide. In the case of salted goods the washing must be more thorough, to ensure the removal of salt, for the presence of this substance in the pelt will not only delay the unhairing process and prevent the proper " plumping " of the hide, but will give rise to the species of efflorescence known as " spueing " and to damaged grain in the finished leather. Inasmuch as salt has a very considerable solvent action on hide fibre (p. 369), that which is washed from the salted goods should not be allowed to accumulate in the washing pit. Actual soaking of the hide for the purpose of bringing it back to its natural, soft condition is only necessary in the case of dried hides. The rapidity with which the soaks will effect this object depends on (1) the temperature at which the hide was dried, (2) the tem- perature of the soak, and (3) the age of the soak. Goods dried at an English summer temperature will sufficiently soften in a 382 MANUFACTURE OF LEATHER, GLUE AND SIZE. few days, whereas heavy South American dried hides may take two or three weeks. That the temperature of the soak should have an influence on the duration of the process is obvious when it is remembered that the softening action is a solvent one ; uniformity of temperature in the soaks is much to be recom- mended, deep well water being in this respect preferable to river water. The age of the soak and its temperature will determine the extent to which putrefaction of the dissolved hide substance will progress, said pa?'i passu the alkalinity (due to ammonia and amines) of the water. It is found that soaks which are swarm- ing with micro-organisms will soften hides very rapidly, but the danger that the micro-organisms will attack the hide substance too vigorously renders such putrid soaks unsafe. The formation of thin places in the hide — sometimes amount- ing to pinholes (so-called "lime specks") in the thinner skins — damage to the grain (inducing it to "frizz" or roughen), and stains (caused by the development of pigmentary matters) are frequently due to the action of micro-organisms in the soaks ; such injuries may to some extent be avoided, and the advantage of the rapidity induced by micro-organisms be retained, by constantly "handling" the hides — i.e., drawing them from and replacing them in the pit — and thus preventing settlement of the organisms in patches on the hides. The introduction of antiseptics to prevent excessive putrefaction in soaks is practised ; that most generally used is salt, which, however, has the objections already indicated. To complete the softening of dried hides they must, when soft enough to be bent without cracking, be submitted to the "breaking" action of a machine called the "stocks." This con- sists of two mallets which are alternately raised by cams and allowed to fall on to the hides in a wooden box. (2) Unhairing. — It was stated on p. 367 that the hair is an appendage of the epidermis; in order that it maybe removed the epidermis must be thoroughly softened, whereupon it is possible to scrape the hair, and with it the rest of the epidermis tissue, from the hide. Almost any alkaline substance will effect the necessary softening, but that almost universally used in this country is lime. In America and on the Continent it is custom- ary to submit the skins to a process known as sweating, which consists in exposing them to conditions favourable to incipient putrefaction, whereby the epidermis is loosened, the action being aided by the alkalinity of the ammonia produced during the process. Other depilatories are used, but generally only as aids to lime. Liming not only effects the loosening of the epidermis, but converts the fat of the hide into a lime soap, which is more easily removed by subsequently scraping the hide, than the grease itself would be. At the same time, the solvent action of the lime on the hide produces a separation of the fibres, which DEPILATORIES. 383 makes the pelt thicker, and is advantageous in the manufacture of heavy leather, owing to the fact that hide plumped in this manner will take up a larger percentage of tannin, and produce a heavier and firmer leather. When the hide is sweated, it has to be plumped either by lime or a dilute acid (which is equally effective) after the removal of the hair. For light leather plumping is not desirable, since suppleness is the great desider- atum ; but liming is none the less a useful method of unh airing: light skins, for the sake of the removal of grease. It is becoming customary now, however, to degrease with volatile solvents, in some such continuous apparatus as is used for extracting oils (see Vol. II., p. 230) ; the perfect neutrality of the solvent, enables such a process to be used at almost any stage of the- manufacture of the leather ; thus the method is replacing the use of hydraulic pressure by which the grease was formerly expressed. The process of liming is conducted in pits, each of which is generally large enough to hold a 50 hide pack. For light skins about J lb. of quicklime per skin, and for heavy hides from 2 to 4 lbs. per hide, are common proportions ; but these amounts are probably wastefully in excess. The lime is best slaked before it is put into the pit. A number of pits, commonly three, is worked systematically, the fresh hides going into the nearly spent limes; the process lasts from 4 to 12 days, and the hides are frequently handled in order that the pit may be "plunged" to agitate its contents, and bring fresh lime into contact with the water (a cubic foot of water dissolves nearly 1^ ozs. of lime). The solvent action of the lime on the hide speedily causes the liquor to become sufficiently rich in organic matter to form a nidus for bacteria, so that old limes are apt to be putrid, and on that account dangerous, as liable to cause the leather to be thin ; much ammonia is present in old limes. Warming the limes to about 90 u F. = 32° C, is found to greatly expedite the unhairing process, but the plumping action of the lime is thereby much diminished. It is an American practice to use a very sharp (i.e., new) lime for three or four hours, and then to transfer the skins to water at about 110° F. = 43° C, to complete the loosening of the hair. Arsenic sulphide (red or yellow arsenic ; rusma), As 2 S 3 , or As 2 S 2 , is frequently added to the limes to the extent of some 10 per cent, on the weight of the lime. The sulphur forms a sulphide (or sulpharsenite) with the lime, and this, like all soluble sul- phides, is a rapid depilatory ; it is claimed that the arsenious acid (calcium arsenite) acts specifically and as an antiseptic ; the improving effect of white arsenic on skin has been asserted in other connections. The use of sodium sulphide as a depilatory, particularly for light skins, is extending. It is generally employed in conjunc- tion with lime ; thus, a solution containing 4 to 5 lbs. of sodium 384 MANUFACTURE OF LEATHER, GLUE AND SIZE. sulphide per gallon of water may be made into a paste with lime and spread on the hair side of the skin, which may then be folded and left for a few hours, by which time the hair can be brushed off, for the action of the sulphide is much more drastic than that of lime. Immersion in a solution of the sulphide, containing J to 1 lb. per hide, is also practised ; it is very difficult, however, to wash out the sulphide completely. Sheep skins are unhaired by being plastered with lime on the flesh side, and then placed, wool to wool, in heaps ; after a short time it becomes possible to pull the wool from the skin. Sweating is effected by suspending the hides or skins in a room — the sweating pit — which is either underground, or com- pletely covered with earth to ensure a constant temperature of 60° to 70° F., = 15° to 21° C. The atmosphere in the room must •be kept saturated with moisture, to which end steam must be admitted in winter, and in summer cold water must be sprayed in. In from three to seven days — during which time the hides have been repeatedly reversed, in order that the more rapid action in the upper, and, therefore, warmer part of the room, may affect all parts of the hides alike — the hair will be sufficiently loosened. By whatever means the epidermis tissue and hair have been loosened, they are actually removed by scraping with a blunt knife. Hides for sole leather are then trimmed or " rounded," the portions which covered the belly, cheeks and shoulders of the animal being removed and tanned apart from the "butt," as the portion which covered the back and sides of the animal is called. The butt is the most valuable portion, since, on account of its greater thickness, it yields a heavier leather than does the "offal" (bellies, cheeks and shoulders). The trimmed hide is washed in water for a day, to remove the greater part of the lime which it still contains. It will be obvious that for this purpose water as free from chalk as possible should be used. The butts are now ready for the tanpits, except that they some- times receive a scraping (scudding) on the grain side with a blunt knife, to remove any remaining epidermis and lime soaps. (3) Softening Processes. — For leather that is to be soft and supple the plumpness produced during the liming process must be counteracted before the skin is tanned ; it is customary, there- fore, to submit all skins which are not destined for sole leather to some process capable of causing them to " fall " — that is, to become thoroughly soft. It was originally observed that the desired effect could be obtained by immersing the skins in some liquid which had become putrid, and thus the custom has arisen <»f using a liquid which is easily capable of undergoing a putre- factive fermentation. An infusion of dogs' dung or birds' dung fulfils this condition, and has long been used under the name of a "bate" or "puer," the process being termed "bating." Since such an infusion is always alkaline, it is not so well fitted for CHEMISTRY OF BATES AND DRENCHES. 385 the removal of lime as an acid liquor would be ; hence, for the lightest leathers the treatment in the bate is followed by immer- sion in an infusion of bran, which is undergoing lactic ferment- ation ; this process is known as the "bran drench." The heavier of the light leather skins are generally bated with pigeons' dung, the bath containing about 1 peck of dung to 30 hides, and the process lasting for some three or four days, according to the prevailing temperature. This bate is reputed to be sharper in its action than the dog-dung bate, which is generally employed for lighter skins. With regard to the rationale of the bating process, what was said concerning the action of bacteria in putrid soaks will apply; there can be little doubt that the feeding of micro-organisms on the hide substance produces the beneficial effect. It must be remembered, however, that dung will contain unorganised ferments, such as trypsin and pepsin • it has been found that these will cause a skin to fall, even in presence of antiseptics, although the leather pro- duced from such skins is not so good as that from bated skins. The action of soluble ammonium salts — which are always present in the bate — as solvents for lime must also be included among the influences of the process. Whatever the chemistry of the bate may be, the operation is objectionable both on account of its offensive character and of its uncertain action. This uncer- tainty is probably due to the dependence of microscopic life on temperature ; it is well known that in warm weather, particularly when a sudden rise of temperature occurs, as in thundery weather, the action of the bate will become so much enhanced that the skins will be speedily riddled with holes. Constant agitation of the skins in a bate, to prevent local action, is essen- tial ; to promote rapid action the bates are sometimes warmed to 30° to 40° C. = 86° to 104° F. Attempts have been made to substitute acids (for the most part feeble organic acids, such as naphthalenesulphonic acid, cresotinic acid, &c.) for the bate; these, however, can only act as lime solvents. . It is claimed that glucose has been successfully used ; if so, its effects are probably due to the fact that the com- mercial article can supply nutriment for bacterial life. A bath of dilute mineral acid (free from iron), followed by the bran drench, appears to be actually in use in some tanneries as a substitute for bating. The bran drench is intended for the completion of the soften- ing of such skins as have been imperfectly softened by the bate, and is more commonly used for the lightest skins. It consists of an infusion of bran in about 200 times its weight of water at 30° to 35° C. = 86° to 95° F. The starch of the bran is speedily converted into glucose and dextrin by an unorganised ferment in the bran, and the glucose undergoes a fermentation similar to, but not identical with, the lactic fermentation (see Minor 25 386 MANUFACTURE OF LEATHER, GLUE AND SIZE. Chemical Manufactures, Vol. EL, p. 417), and resulting in the pro- duction of lactic, formic, acetic and butyric acids. It is desirable that butyric acid fermentation should not take place, since the solvent action of this acid on the skin is considerable. The gases evolved (chiefly hydrogen) during the fermentation serve to distend the skins and render their contact with the liquid more perfect. The following figures (J. T. Wood) show the quantities of acid likely to be produced, in grams per litre : — Formic acid, 0*0306; acetic acid, 0-2402; butyric acid, 0*0134; lactic acid, 0*7907. An artificial mixture in these proportions has been found successful. The time during which the skins are in the drench depends on the amount of previous bating which they have received. TANNING PROCESSES. — (1) Tanning with Tanstuffs.— The varieties of vegetable-tanned leather are so numerous that a description of the system used for each cannot be here given, the more so as the chemical principles involved are the same for many. It will suffice to consider the systems in use for (a) leather for soles, (b) leather for dressing, (c) leather for dyeing. (a) Leather for Soles. — For this kind of leather a process must be adopted which will produce the greatest possible solidity, combined with sufficient flexibility to prevent cracking. To the tanner it is advantageous that the maximum weight should be produced, and for the purchaser also, the weight per unit of area is a criterion of solidity. Hence the tannage for sole leather is conducted with materials which impart the maxi- mum weight — by yielding certain proportions of other matters besides tannin to the hide — and in such a manner that the hide shall be tanned throughout. In order to effect this thorough tannage, it is essential that the hide should not be immersed in a liquor comparatively rich in tannin, until such time as it has become already slightly tanned, lest by the rapid tannage of the surface, the fibres should be so swollen that entry of tannin into the interior be hindered. It may be said that when once a partial tanning has occurred, the completion of the process will be the more rapid the richer the liquor (within limits) in tannin. When oak bark is the sole material employed as a source of tannin, the liquors can never be made strong enough by the method of leaching adopted (p. 380) to produce a rapid tannage. Consequently, until comparatively recently, when valonia, myro- balans, &c, were introduced, the tanning process was a very lengthy one, lasting even as long as two years. With regard to the use of tanstuffs which yield liquors rich in tannin, it must be remembered that, inasmuch as careless tanning with oak bark could originally be detected by the bad colour of the leather, the tanner is now somewhat hampered by the necessity for producing a leather which shall have a colour approaching that of good oak-bark tannage. In English practice, the butts ABSORPTION OF TANNIN BY HIDE. 387 are first suspended in pits (suspenders) containing nearly spent liquors, which have served either in the handlers or layers (see below) ; they should be agitated by some mechanical rocker while completely immersed in the liquor. Several suspenders are generally used, and are worked systematically. The object of this process is, technically, to strike the colour of the leather, and, actually, to effect the partial tanning, to which reference has already been made ; the attainment of this object depends very largely on the degree of acidity which the liquors possess. The function of the acid will be understood from the following considerations. It is only possible to produce thick leather when the hide has been properly plumped — i.e., so swollen that the entrance of the tannin can be effected easily. A hide may be either alkali- plumped or acid-plumped, the former being the case when it has been limed. As might be expected, the entrance of tannin, itself an acid-like compound, into an alkali-plumped hide is more rapid than into one which is acid-plumped. If there be no acid in the suspender, the hide being alkali-plumped, tannage will take place very rapidly ; but owing to the tendency of com- binations of lime with tannins to darken by oxidation, the colour of the leather produced will be bad. If there be sufficient acid to neutralise the lime left in the hide, but not more than this, the hide will fall, and plump leather will not be produced. A third possibility is that there should be enough acid in the liquor to dissolve all the lime from the hide, and to substitute an acid-plumped for an alkali-plumped condition ; in this case the tannage will be slow — i.e., the striking of the colour will take long — but this colour when produced will be good. For the production of the best leather, then, the acidity of the suspender liquors must be considerable, the more so as the hide tends to fall pari passu with the entrance of tannin, at all events during the early stages of tanning. The acids present in these liquors are such as result from the fermentation of sundry of the soluble bark constituents in the earlier stages of the tanning. They are, of course, vegetable acids, acetic, butyric and lactic acids being the chief. Their amount is, to a certain extent, under control, since the materials most liable to fermentation {e.g., myrobalans) may be used in the handlers. In American and German practice hides for sole leather are sweated, so that they have to be plumped with acid before tannage. In America, plumping with dilute vitriol is practised; the Germans prefer to use a very acid liquor from the layers. It may be said that the German system of tanning is a " sour one throughout, since even in the layers the liquor becomes highly acid owing to their degree of dilution and the dustiness of the material employed. A German suspender liquor, made 388 MANUFACTURE OF LEATHER, GLUE AND SIZE. from sour bark, was found to contain, in grams per 100 c.c. : — Tannin, 0*226; non-tannin, 0 - 916 ; total acid (as acetic acid), 0*463; volatile acids (as acetic acid), 0 300; non-volatile acid (as acetic acid), 0*163 ; specific gravity, 1*0059 (5*9° barkometer). From the suspenders the hides pass into the handlers ; these are pits in which the hides are laid flat, in a heap, and from which they are " handled " every day. The series of handlers is worked systematically, the fresh liquor being run into the pit which is to receive the most fully tanned hides. It is advantageous to feed the hides in the handlers with rapidly tanning materials, such as gambier, hemlock extract, &c. After about a month has been spent in the handlers, the pack of hides is moved on to the first layer ; here it is allowed to remain in strong liquor with a layer of tanstuff (bark, myrobalans, valonia) between each hide, the whole being covered with bark, to exclude air. The time of laying away varies considerably, from- one to six weeks, for each layer being quoted as usual. The thickest hides require twelve months for thorough tannage, but an average of eight to ten months is now common. Owing to the fact that the strength of liquors is judged solely by an erroneous criterion, the specific gravity (generally quoted in degrees of the barkometer — i.e., the last two figures of the true specific gravity, water being taken as 1000 *), little is yet known as to the actual content of tannin requisite in the different layers. The last layer should contain the strongest obtainable liquor. In German practice a liquor containing more than 2 per cent, of tannin is seldom used. Up to 6 per cent, of tannin is common in English practice. Systems designed to hasten the tanning of sole leather have been from time to time brought forward. They fall under the following heads: — (1) Keeping the hides in continual motion in the tanpit; (2) circulating the tanning liquor continuously around the hides ; (3) forcing the liquor through the hides by pressure ; (4) tanning with very strong extracts ; (5) passing a current of electricity through the liquor in which the hides are kept in motion. The last of these has alone received attention from experts, and it appears to be established that by suspending hides on a rotating frame in a vat containing a strong (4*25 per cent, tannin) mimosa and gambier liquor, and using a current density of from 0*375 to 1 ampere per square foot of electrode (the electrodes being copper plates on the sides of the vat), at a voltage varying with the strength of the liquor, it is possible to produce the same quality of leather in one-sixteenth of the time taken to produce it when the hides are at rest, and in one-fourth of the time taken when the hides are in motion, but when no electric current is passed. Lack of substance (" hungry leather ") generally characterises goods produced by such rapid processes. * Thus, 15° barkometer indicates a liquor of specific gravity 1*015. LEATHER FOR DYEING. 389 (b) Leather for Dressing. — This class of leather is destined for the uppers of boots, for saddlery, belts, and other purposes where a stout but flexible leather is required ; it is generally curried or dressed, whence its name. The bated hides are frequently shaved with a sharp knife to reduce their thickness (shaved hides) ; sometimes this process is postponed until they have been par- tially tanned, when, however, the shavings are of no use as glue- pieces (see Gelatine, Vol. II., p. 396) ; sometimes thick hides are split, after partial tanning, by a knife consisting of an endless steel band which travels like a driving belt, and works against emery wheels to sharpen it. The tanning of dressing hides and of East India kips is carried out in a manner which is, to a certain extent, the converse of that employed for sole leather, since it is not desired to make a firm leather. Thus, the first treatment of the bated hides consists in handling them or "tumbling" them (in revolving casks) in a comparatively strong liquor devoid of acidity. The object of this "graining" process is to tan the grain of the hide rapidly, and to cause it to shrink into a number of wrinkles. The degree of the shrinkage will depend on the strength of the liquor. Gambier is frequently the material used for graining. The completion of the tannage is effected similarly to that of sole leather, if a bark tannage is employed, the liquor being somewhat weaker; but a much more rapid tannage is now obtained with valonia, mimosa, myrobalans and gambier, the liquors being sometimes heated. It is customary to tumble the leather in sumach as a concluding process, to cor- rect the colour. The currying of the leather is treated of under Finishing Processes. (c) Leather for Dyeing. — Such vegetable tanned leather as is dyed is commonly known as morocco. Genuine morocco is made from goat skins, but there is now a large trade in " roans " and "skivers." The former are sheep skins tanned whole, the latter are the grain sides of sheep skins which have been split for making wash leather and white leather. Both are tanned with sumach which leaves them pale enough for dyeing. When dyed they are called morocco. Bazils are dyed with bark. Goat skins are bated, drenched and tanned in sumach, at first in tubs,, in which they are agitated with paddles, and then in handlers. Sheep skins for roans are sewed into the form of bags into which the sumach liquor is poured and through which it is allowed to drain, the operation being repeated two or three times. Skivers are merely paddled in sumach liquor. After drying for the dye-house, roans and skivers are said to be in the "crust" state. (2) Tanning with Mineral Salts. — The only mineral salts which have as yet been employed for tanning are alum, chromium salts and ferric salts. It is noteworthy that these salts contain very feebly basic oxides, of the type B. 2 0 3 ; the deposition of these 390 MANUFACTURE OF LEATHER, GLUE AND SIZE. oxides, in the form of basic salts, within the skin seems to con- stitute the tannage ; the matter will receive further notice under Theory of Tanning. (a) Alum Tanning. — Alum is never used alone, being always accompanied by salt. White leather, used for bottle coverings, &c, is made by tumbling sheep skin splits (i.e., the flesh sides) with a liquor containing about 4 per cent, of a mixture of alum with | of its weight of salt. The leather is wrung out, and slowly dried. Such leather readily becomes de-tanned in water. In the tanning of kid, whether calf-kid or the true glove-kid, a process is adopted which may be regarded as a cross between alum tanning and oil tanning, and has received the distinctive name of tawing. In both cases particular care is taken to submit the skins to a thorough bating, drenching and scudding, since suppleness is very necessary, and, in the case of kid and lamb skins for gloves, the limes are always sharpened with arsenic, this being mixed with the lime before the latter has had time to cool after slaking. The tannage is effected by tumbling the skins in drums containing alum and salt, drying, and again tumbling in drums with a mixture of oil (generally olive), flour and egg-yolk. The last named mixture appears to fill the inter- fibrillar spaces of the skin, imparting the necessary softness and elasticity. A final stretching (staking) over a blunt knife fixed in a post, and, when necessary, shaving to reduce the thickness, finish the skins for the dye-house, unless a second "stuffing" with the egg-yolk mixture be deemed essential. (b) Chrome Tanning. — This is effected by immersing the skins (goat or sheep), unhaired and bated as usual, in a solution of chromic acid (or bichromate of potash with hydrochloric acid), and subsequently passing them through a bath consisting of a solution of sodium hyposulphite or sulphite and hydrochloric acid. The skins absorb the chromic acid, which is subsequently reduced to a chromium salt in the sulphite bath ; the chromium salt is pro- bably decomposed by the fibre, chromic oxide remaining in the skin to the extent of some 4 to 6 per cent., calculated as K 2 Cr 2 0 7 . Since chromic acid may have too corrosive an action on the hide fibre, it has been suggested to use a chromium chromate, prepared by dissolving chromic oxide in chromic acid. Chrome-tanned leather is used for glazed kid in the United States, for glove leathers, and as a substitute for calf-kid and chamois leather. (c) Iron Tanning. — The use of ferric salts in conjunction with salt, as a substitute for alum and salt, has frequently been sug- gested. The best results are obtained by the use of basic salts, such as a ferric oxychloride, made by dissolving ferric hydroxide in ferric chloride. The patentee of one process suspends the hides from wooden frames and allows the ferric oxychloride and salt solution to flow down each side. Iron tanning is not yet practised to any extent. MANUFACTURE OF WASH LEATHER. 391 (3) Tanning with Oils. — This consists in impregnating the skins with some easily oxidisable oil (most commonly cod oil or whale oil) and allowing them to heat, owing to oxidation of the oil, in heaps. In this way the skin is converted into an exceedingly soft leather, which readily absorbs water, but cannot be easily de-tanned by any agent. Such leathers are wash leather or chamois leather — the applications of which are well known — and huffs, used for soldiers' belting, &c. For wash leather the flesh splits of sheep skins are used. They are very thoroughly limed, fleshed, washed and bated with a bran drench. They are then submitted to hydraulic pressure to remove water and grease, painted with cod oil and stocked (p. 382) for two or three hours. After this preliminary stocking, the skins are hung up in a warm drying room, again sprinkled with oil and stocked. This series of operations is repeated five or six times in order to replace completely the water in the skins by oil. After the final stocking the leathers are thrown into bins, covered with sacking and allowed to heat, great care being necessary to prevent burning ; during the heating much acrolein is evolved. Since only a portion of the oil has been utilised by the hide, a process is necessary for removing the remainder which renders the leather greasy. For this purpose the leather is submitted to hydraulic pressure, when a considerable quan- tity of semi-oxidised oil is expressed ; this constitutes dlgras (moellon), valued as a currying agent. The remainder of the oil is removed by a bath of alkali, which is afterwards neutralised with sulphuric acid to recover the fatty acids ; these constitute sod-oil, which is also used in currying, but is inferior to degras for this purpose. The leathers are finally stretched over a beam and scraped with a circular knife, having a central hole by way of a handle. Sun bleaching, or bleaching with sulphur dioxide, and stretch- ing, complete the manufacture. Shammy (chamois) leather is said to be much improved if frozen while moist. Buffs are made in a very similar manner, from South American calf skins, which have been shaved on both grain and flesh sides, and bated. It is stated above (p. 367) that the complete desiccation of a skin will preserve it from putrefaction, although the product will not be leather, since it will lack pliability. Much dried skin is, however, prepared for parchment and vellum. The former is made from the flesh splits of sheep skins. The skins are limed for two or three weeks, fleshed and split. The splits are again fleshed and are then tightly stretched in frames, scraped and washed with hot water. They are next painted over with a mud of chalk, which absorbs the remaining grease, again scraped and dried. For vellum, Swedish calfskins are employed. They are soaked 392 MANUFACTURE OF LEATHER, GLUE AND SIZE. in putrid soaks for a week, worked on the beam, limed for three or four weeks, unhaired, washed and fleshed. Skins from pie- bald animals will not serve for the best vellum, as they are parti- coloured. The prepared skins are stretched in frames and treated as described for parchment. FINISHING PROCESSES. — No leather is fit for the market in the condition in which it leaves the tanhouse. In the case of sole leather the finishing process is chiefly designed to give the leather a presentable appearance, the drying of the goods, which must take place in any case, constituting the real difficulty in the finishing process. In the case of lighter leather, the final operations consist in stuffing the goods with grease, so as to impart the necessary softness to the leather. • (a) Finishing Sole Leather. — In order to improve the grain of the leather and at the same time to remove the bloom (p. 376), the butts are "struck out" (generally after they have be'en lightly oiled and left in a heap until a slight heating has occurred — a process known as samming) by means of a three- cornered knife, which is capable of stretching the grain without cutting it. A fluted or plain roller passed by power over the grain is now generally substituted for the striking-out pin. The drying of the leather must be gradual and must be effected in the dark ; to these ends the drying shed is generally constructed with slats, which can be placed at such an angle as to exclude light, whilst admitting the maximum volume of air. Such sheds may be heated to about 70° F. = 21° C. in winter. A good sole leather, when cut with a sharp knife, should show a section which is uniform in appearance and free from fleshy or horny streaks. When gradually bent, the grain should not break. It will absorb about 33 per cent, of water when soaked therein. If fully tanned it will have about the following composition : — The percentage of hide substance is calculated from a nitrogen determination, on the basis that the true hide substance contains 17*8 per cent, of nitrogen. Leather is frequently adulterated with glucose, soluble salts and barytes. Market hides should yield about 56 per cent, of their weight * Containing CaO 0*30, S0 3 0*50. t Containing sugar 0*40. X Containing hide substance 39*90, combined tannin 32*00. Water, Fat and ash, * . Soluble tannin, . Soluble non-tannin,+ . Pure leather substance, + 18*00 1*30 5*00 3*80 71*90 100*00 DYLING LEATIIEK. 393 of leather, green-salted hides about 75 per cent., and dry hides about 150 per cent. (b) Currying. — Dressing leather is generally scoured by a machine which moves brushes and stones ("sleekers") over the leather. It is then stuffed, either by hand or in a tumbler, with tallow and oils. The oils preferred are such as readily emulsify with water, which may contain a little soap to improve the emulsion. Those generally used are castor, neatsfoot, cod-liver oil, whale oil, olive oil and sperm oil ; the characteristic features of these have been dealt with in the section on oils (Vol. II., p. 223). Degras (p. 391) is especially valued for currying, and owes its property, according to Eitner, to a nitrogenous substance — the degras-former — which exists to a small extent in the cod oil used in chamoising, but to a greater extent in the degras itself; this substance is insoluble in petroleum ether, and should amount to at least 12 per cent, in degras containing 20 per cent, of water. Fahrion has denied the existence of a degras-former, and attributes the peculiar properties of degras to the presence of hydroxy fatty acids. The iodine absorption of genuine degras should be very similar to that of its parent cod oil. Many imitations are on the market. Russia leather is scented by dressing the flesh side with birch oil obtained by the destructive distillation of birch bark. Light leathers are generally blacked, if not dyed, by a mixture of lampblack and oil. Koans, skivers and kid are nearly always dyed. This is most commonly effected by means of dyewoods (p. 324), but synthetic colours are used to a con- siderable extent, particularly Bismarck brown.* Basic dyestuffs are readily fixed on the leather, since this is already mordanted with tannin ; it is difficult, however, to keep the dye-baths clear, on account of the precipitation of the dye by such tannin as is removable from the leather by water. To remedy this, the leather should be first passed through a bath of tartar emetic to fix the tannin. In dyeing it is customary either to fold the skins grain outwards and immerse them in the dye-bath, or to brush the dye on to the leather as it lies on the table. To whiten leather it may be passed first through a bath of sugar of lead and then through dilute sulphuric acid, whereby lead sul- phate will be precipitated in the leather. Artificial grain may be put on the leather either by folding it and rolling it under a board, or by mechanical rollers or stamps. Japanned or enamelled leather (patent leather) is glazed by being stretched and coated with a varnish of linseed oil, ground with some pigment, commonly lampblack ; this coat is dried by placing the leather, still stretched, in a stove at a temperature * Most leathers are damaged by the high temperature necessary in alizarine dye-baths, but chrome-tanned leather is sufficiently resistant to be dyed with alizarine colours. 394 MANUFACTURE OF LEATHER, GLUE AND SIZE. of 70° to 80° C. = 158° to 176° F., and another coat is applied, the operation being repeated until the desired thickness is ob- tained. A coating of a true black varnish imparts the final glaze. Theory of Tanning. — In attempting to account for the retention of a tanstuff by hide fibre, difficulties are met with which recall those experienced in attempting to account for the retention of a dye by textile fibres (see p. 270), and just as there are those who support a "physical theory," and those who support a "chemical theory" of dyeing, so chemists have long been divided into two camps concerning the physical or chemical nature of the tanning process. There is, however, a further diffi- culty in the way of formulating a theory of tanning, engendered by the fact that the hide fibre is so far altered during the process that it is incapable of putrefaction, and, in the majority of cases, will not become gelatine when boiled with water. Knapp is of the opinion that the tanning process is only due to the coating of the hide fibres with the tanstuff, be this a tannin, a basic salt or an oil. In accordance with this view, he defines leather as hide in which the individual fibres are prevented from adhering together when dry. The definition certainly finds support when a study is made of alumed leather, a product which can be closely imitated by merely dehydrating the skin by •absolute alcohol; in neither case is the "leather" permanent, for boiling water will convert it completely into gelatine. In the case of leather made with tannin, however, the matter is different ; well-tanned sole leather will yield no gelatine when heated with water, nor can more than an inconsiderable per- centage of tannin be extracted from it by water, or even by caustic soda solution. Attempts have been made to apply Witt's solid solution theory of dyeing (p. 271) to the tanning of hide, and the classical silk-magenta-alcohol experiment (loc. cit.) has been quoted in ■support of this theory. It must be remarked, however, that the solvent which will behave to bark-tanned leather in a manner parallel to that in which the alcohol behaves to the magenta-dyed silk, has yet to be found. It has been stated by v. Schroeder and Passler that hide cannot absorb more than its own weight of tannin (calculated on the weight of the anhydrous hide), and it is supposed that this is a saturated solid solution of tannin in hide. According to former statements, upper leather is never completely tanned by bark, but depends for its complete conver- sion into leather on a species of oil tannage imparted during the currying process. The assertion of Stenhouse that upper leather yields 25 per cent, of its weight of gelatine when heated with water, supports this view ; but v. Schroeder has given the following figures, which show that all properly tanned leather contains about the same proportion of tannin calculated on the content of pure hide substance in the hide : — THEORY OP TANNING. 395 100 Parts of Prepared Hide Contain 100 Parts of Prepared Hide give of Leather Water. Hide Substance. Mean. Poor Tannage. Maximum Tannage. Sole leather, . Strap leather (cowhides), Dressing leather (kips, \ horse hides), . . J Calf leather, . Per cent. 71 75 78 81 Per cent. 29 25 22 19 64 57 50 41 55 49 43 35 75 67 59 48 The same chemist has shown that the amount of tannin which hide will absorb depends on the strength of the tanning liquor ; this, he claims, couhi not be the case were the process a chemical one. Tannin in 500 c.c. Tannin Absorbed by 100 Parts of Anhydrous Hide. Grams. Grams. 1-74 33 50 2-61 48-10 435 68-60 871 77-90 It was found that if the hide were placed in a stronger liquor than the last-named, it became so rapidly tanned on the outside that the liquor never penetrated to the inside. By introducing the hide into successively stronger liquors, as in the tanning process, 100 per cent, of tannin was absorbed. Reviewing the whole of the evidence above quoted, it must be admitted that Witt's solid solution theory will not apply to the tanning of leather with tannin, and that in this case the exist- ence of a chemical compound of tannin with hide fibre must be conceded. In the case of mineral-tanned leather, where the whole of the tanstuff can be removed by water, Witt's theory may represent the true state of affairs. In oil tanning a similar dissolution of the oil in the fibre may occur, the oil subsequently becoming fixed by oxidation, much as indigo white is converted into indigo blue in the fibre. II. GELATINE, GLUE AND SIZE.— These are three differ- ent forms of the same material, and are produced by the action of boiling water on collagen, the chemical individual, or indi- viduals, of which hide fibre and the organic matter of bones ("osseine") are composed. Gelatine and glue differ solely in the care with which they are made, and therefore in the purity of the product ; size is an impure gelatine put on to the market in the form of a jelly instead of that of a hard material. 396 MANUFACTURE OF LEATHER, GLUE AND SIZE. Gelatine is now generally made from hide fibre, whilst bones form the raw material for glue, although in some factories both are made from either raw material. The hide fibre used in the manufacture of gelatine is the waste cuttings of the tannery and skins that are not used for leather — e.g., rabbit and dog skins which have been duly unhaired. The hide pieces are first well digested with dilute soda lye for some time in order to saponify completely the fat contained in them, then washed with cold water and bleached by sulphurous acid. The next process is to convert the collagen into gelatine, and to strain the solution from the unattacked elastin, &c. Several methods of doing this are in vogue : the material may be placed on the perforated false bottom of a kettle, into which water and steam are admitted, or it may be heated with a little water in earthenware vessels contained in a steam chest, and the solution of gelatine afterwards strained. It is sometimes customary to add a little albumin in the form of blood to the gelatine solution, in order that by its coagulation it may carry suspended matter to the surface in the form of a scum, which can be skimmed off. Whatever the plan for obtaining the solution of gelatine, it is desirable that this should be strong enough to set to a firm jelly on being run into the cooling troughs, since the subsequent heating to expel water impairs the gelatinising property of the product. The troughs are generally of such a shape that the blocks of gelatine may be directly sliced by wires into layers which are sufficiently thin to dry at the most advantageous speed, for it is in this drying that the greatest difficulty of gelatine manufacture is experienced. The sheets are placed upon netting and exposed to a drying atmosphere in two rooms. The first of these must be heated by closed steam pipes to a temperature not exceeding 20° C. = 68° F., lest the gelatine melt and run through the netting, or soften sufficiently to adhere strongly thereto. The air in this room must not be too dry, because if the sheets dry quickly at this stage they curl up and crack. The second room generally has a current of air forced through it, over the wire nettings, by means of an air propeller. Gelatine contains from 0*5 to 2 per cent, of ash ; its organic matter contains, per cent., C, 49-91; N, 17*72; H, 6-35; S, 0-50; 0, 25-52. Good gelatine will gelatinise in a solution containing only 1 per cent. ; but samples which have been long heated or contain much chondrin (the substance into which cartilage is converted by treatment similar to that which gelatine has under- gone) will not gelatinise so well. Chondrin is precipitated from aqueous solution by acetic acid. All tannins precipitate gelatine solution. Isinglass, used chiefly for clarifying wines, beer, &c, is ob- tained from the dried swimming bladder of various fishes; this membrane is washed, dried by exposure to air, and the inmost GLUE. 397: layer stripped off and further dried. It contains some 86 to 93 per cent, of gelatine, up to 1*5 per cent, of ash, and a small pro- portion of insoluble matter. Much factitious isinglass is made from ordinary gelatine ; it is, however, devoid of the true isin- glass structure. In making glue from bones, these are first steeped in hydro- chloric acid (about 10 per cent. HOI)* until they are thoroughly soft, drained, washed and steamed in iron digesters at a pressure of 30 to 35 lbs. per square inch for three or four hours. The glue and fatty matter are run off from time to time into settling tanks kept hot enough to prevent gelatinisation ; here the fat rises and is skimmed off (see Bone fat, Vol. II., p. 228), and any bleaching, such as with S0 2 , which may be customary is effected. The glue is next filtered through sieves and boiled down by closed steam until it is capable of becoming a firm block when cold. This is cut up and dried as described for gelatine. The refuse in the digesters is sold as a manure material. Size is prepared similarly to gelatine, but generally from much rougher material. It is commonly sent into the market as a stiff jelly. Liquid glues are made by dissolving ordinary glue in acids. These prevent the solution from gelatinising when cold, but do not deteriorate the adhesive power of the dried material. Such a liquid glue is made by dissolving 2 lbs. of glue in a quart of water and adding 7 ozs. of nitric acid (specific gravity 1-35). Acetic acid is also used. Two flat surfaces of wood, glued together, should withstand a shearing stress of 38 to 73 kilos, per square centimetre, and a tensile stress of 14 to 37 kilos, per square centimetre. Various glue substitutes are used as " cements " for china, &c. Solutions ot casein in alkaline liquids, such as borax solution or soluble glass solution, are used for this purpose. * The subsequent neutralisation of the acid with chalk precipitates a calcium phosphate containing 18 to 20 per cent, of P.>0 5 ; it is used as a manure. 398 EXPLOSIVES AND MATCHES CHAPTER XVII. EXPLOSIVES AND MATCHES. I. EXPLOSIVES. — Explosives are bodies which, under a suit- able stimulus, yield suddenly large volumes of gas and evolve heat. Nearly all endothermic compounds are capable of behav- ing as explosives under suitable conditions. Thus, hydrogen peroxide, an endothermic substance, will explode when heated to the boiling point of water, HA = H 2 0 + 0+21-5 Cal., that is, 34 grams (1 gram-molecule) of anhydrous hydrogen per- oxide evolves, by its decomposition into water and oxygen, 21*5 kilogram units of heat. In actual practice, however, the heat of inter-combination of the elements constituting an explosive, provides the greater part, or the whole of the energy evolved by the explosive. Thus, the decomposition of mercuric fulminate into its elements, would be expressed by the equation — HgC 2 NA = Hg + C 2 + N 2 + 0 2 + 62-9 Cal.; but the actual energy evolved by its explosion is much greater, owing to the fact that the carbon and oxygen combine to form CO, with liberation of heat. HgC 2 N 2 0 2 = 2C0 + N 2 + Hg + 114-5 Cal. It will be observed that, in both the cases quoted, the pro- ducts are gaseous at the temperature of explosion. Seeing that the volume of these gases is large compared with the compara- tively dense substances generating them (H 2 0 2 , specific gravity 1*45 ; HgC 2 N 2 0 2 , specific gravity 4*42), the pressure exerted by the gases is great if they be confined in a space previously com- pletely filled by the explosive from which they are derived. For practical purposes the effective pressure exerted by an explosive depends upon — (1) the volume of gas at normal tem- perature and pressure liberated per unit volume of explosive, (2) the temperature attained at the moment of explosion and the coefficients of expansion of the gases, (3) the degree of imperviousness of the walls of the cavity in which the explosion occurs, and the rapidity with which the explosion takes place. When the thermal change accompanying an explosion and the EXPLOSION AND DETONATION. 399 volume of gas are known, the total possible pressure can be cal- culated for an explosion taking place in an impermeable vessel, within the limits of our knowledge of the physical properties of gas at high temperatures. The effective pressure has been directly- measured by performing the explosion in a closed vessel, which is eitheritself capableof permanent distortion (e.^., a cylinderof lead), or communicates with pressure gauges, consisting of plungers bearing upon lead cylinders, the deformation of which serves as a measure of the pressure. A better method consists in firing the explosive from a pendulum mortar of known weight, and measuring the recoil produced. The difference between the calculated pressure and the effective pressure thus measured, depends largely on the rapidity of the explosion, a rapid explosive producing its maximum effect in a space of time suffi- ciently short to make the escape of gas from a not perfectly impervious envelope smaller than that which occurs during the action of a slow explosive. The rapidity of an explosive is the factor of most importance in deciding for what uses it is best fitted. Thus, for severe shattering action where the escape of gases cannot be fully restrained, an explosive like nitro- glycerin, which is so rapid that the atmosphere itself is a sufficiently resistant envelope, is used, while for the slow move- ment of large masses — such as that involved in winning coal and propelling shot — gunpowder, which explodes comparatively slowly, is employed. The rapidity of explosion is influenced by the state of division of the explosive as well as by its composition, whence it follows that, ceteris paribus, a compound will be a more rapid explosive than any mixture, however intimate. No distinction in kind can be drawn between the phenomenon of explosion and that of com- bustion, the difference being essentially one of rate of propaga- tion. Thus it happens that a substance — e.g., gun-cotton (v.i.) — may behave either as a combustible or as an explosive, according to the means used to initiate its decomposition. Loose gun cotton ignited by a source of heat of comparatively low tem- perature — as for example, a flame or red hot wire — merely burns, the hot gases generated by the combustion being able to escape freely, but should the gun cotton be ignited in the centre of a compact mass, the gases will not be able to escape readily, and the pressure rapidly generated will raise the tem- perature and cause approximately instantaneous combustion of the whole mass ; the same effect is produced by the use of a source of initial high temperature and pressure — e.g., a detonator of mercuric fulminate (v.i.). Detonation is, therefore, caused by the high pressure generated by the most rapid combustion that can be attained under any given conditions. It follows from this that the theory that an explosion is necessarily initiated by the vibration of the particular wave 400 EXPLOSIVES AND MATCHES. length generated by the detonator used, is erroneous, and, there- fore, that so-called "sympathetic" explosion (the detonation of one explosive by the shock produced by the explosion of another in its neighbourhood) may be rather due to the setting up of a new vibration, probably identical with the vibration of the temperature of ignition of the second explosive, acted on sym- pathetically. (A) Gunpowder. — Gunpowder is the oldest explosive known. It consists of a mixture of potassium nitrate, sulphur, and char- coal ; its energy of explosion is derived from the exothermic reactions involved in the oxidation of the carbon and sulphur by the potassium nitrate. The original proportions in which these constituents were mixed were, in England, 75 per cent, of potas- sium nitrate, 10 per cent, of sulphur, and 15 per cent, of charcoal, the same proportion being still in use for black rifle powder. The manufacture of gunpowder comprises the preparation of pure potassium nitrate, distilled sulphur, and charcoal from a light -wood such as alder, and the mixing of these to a homogeneous mass. Potassium nitrate was at one time obtained exclusively from East Indian " saltpetre earths," which are natural accumulations of nitrates (the potassium, calcium and magnesium salts) in the surface soil, produced by the nitrification of nitrogenous organic matter through the agency of an organism (see Manures, Yol. II., p. 113). The earth varies in composition, the better kinds con- taining about 8 per cent, of potassium nitrate and some 4 per cent, of calcium nitrate. The earth is leached, and the liquor concentrated and mixed with wood ashes (crude potassium carbonate), whereby the nitrates are converted into the potassium salt, which crystallises, and in its crude state contains from 45 to 70 per cent, of KN0 3 . It is generally recrystallised in India for exportation. The best quality (Bengal ordinary) contains 96 "5 per cent, of KN0 3 . The production of a saltpetre earth has formed an industry in some European countries, where it is made by mixing calcareous soil with putrefying nitrogenous substances, and allowing nitrification (for the mechanism of nitrification see Artificial manures, Yol. II., p. 113) to proceed for months or years. For the manufacture of gunpowder the nitre is dissolved in boiling water and filtered hot. The hot liquid is constantly agitated; when its temperature falls to 32° 0. = 90° P., the saltpetre crystallises in a fine " flour," and is drained and washed with successive small quantities of water; a further draining leaves the flour in a fit condition for the incorporating mill (v.i.). The greater part of saltpetre for gunpowder is now made by the decomposition of sodium nitrate (Chili saltpetre) and potassium chloride (from Stassfurt salts). Commercial sodium nitrate (95 per cent.) is dissolved together with Stassfurt " muriate of CHARCOAL FOR GUNPOWDER. 401 potash " (which contains 80 per cent, of KC1) in the mother liquors of a previous crystallisation. The solution is boiled down and allowed to crystallise. Sodium chloride crystallises first, and the potassium nitrate is deposited on running the mother liquor into crystallising tanks. The flour thus obtained still contains some 8 per cent, of NaCl, and is purified by re- crystallisation and subsequent washing with water. Gunpowder saltpetre must be free from chlorides, which tend to keep it moist, and from sodium nitrate, which is also deliquescent. It is liable to contain potassium perchlorate, derived from Chili saltpetre. Beyond its use for gunpowder and fireworks, potassium nitrate is only employed for minor purposes — e.g., as a preservative for meat. Sulphur for gunpowder making is distilled in an iron retort, which is connected with a sublimation chamber, as well as with the condenser. At the beginning of the distillation the vapour is sent into the sublimation chamber, oxides of sulphur being thus got rid of ; subsequently the vapour is passed through the condensers, and is collected as a liquid. The redistilled sulphur, which should be free from oxides of sulphur, is sent to the incorporating mill. The carbonisation of wood for gunpowder charcoal is effected with or without the collection of the bye- products (see Destructive distillation, Vol. II., p. 90), and at a temperature depending on the kind of powder to be made. The wood of the alder buckthorn {Rhamnus frangula) and that of the true alder and willow are preferred. The wood is stored for some three years before carbonisation, and is carbonised in cylinders fitting in cylindrical retorts. The resulting charcoal is stored for a couple of weeks before grinding, as it is then less liable to spontaneous ignition. The temperature for the manufacture of black gunpowder charcoal ranges from 3G0° to 520° C. = 680° to 968° F., that for brown powder is carbonised at a lower temperature, 280° C. = 536° F., and in some cases is made from cereal straw. The temperature is also regulated according to the grain of the powder of which the charcoal is to form a part. The com- position of some gunpowder charcoals is as follows {Noble and Abel) : — Waltham Waltham Waltham Abbey- Abbey Rifle Abbey Rifle Pebble. Large Grain. Fine Grain. c, 85'26 80-32 75-72 H, 2-98 3-08 3-70 OandN, . 10-16 14-75 18-84 Ash, ..... 1-60 1-85 1-74 26 402 EXPLOSIVES AND MATCHES. A high percentage of carbon corresponds with a high tem- perature of carbonisation. The sulphur and charcoal are ground separately and screened, and mixed with the still moist salt- petre in a rough mixing machine, consisting of a gunmetal drum and stirrer. This "green charge" is sifted, and passed to the incorporating mill, which consists of iron or stone edge- runners working on an iron or stone bed plate, the contact of iron with stone being avoided. During incorporation the mixture is kept moist. The "mill cake" thus produced con- tains from 1 to 6 per cent, of moisture, according to whether the grain to be made is small or large, and is then broken up between grooved gunmetal rollers, and pressed into cakes in gunmetal boxes lined with wood. The next process is "granu- lation," and is effected by passing the "press cake" between toothed rollers. The granulated cake is graded by sieves, and the powder is glazed by rotation in drums, an ounce of graphite to each 100 lbs. of the gunpowder being added for large grain powder. Drying and finishing by a final rotation in a cylindrical frame covered with canvas, for the purpose of removing dust, complete the process. The dust from the various grading pro- cesses is termed meal powder, and is much used in pyrotechny. " Pebble " and " prismatic " powders are cut from the press cake either by rollers provided with knife-like ridges, or by hand. Prismatic powder is generally perforated longitudinally to ensure uniformity of surface during combustion. The main portion of the energy set free in igniting gunpowder is derived from the oxida- tion of the charcoal by the saltpetre. The presence of sulphur is, however, necessary to increase the rapidity of explosion to such an extent as to allow of the exertion of a maximum of effective pressure. The low igniting point of sulphur (248° C. = 478° F.) adapts it for this purpose. The rapidity of explosion also depends on the size of grain, pebble or prismatic powder (v.s.) being used where a comparatively long continued pressure, as distinct from a sudden bursting strain, is required, as in heavy guns. Explo- sions of this type can be produced by powder poor in sulphur, in which class of material the charcoal used has to be carbonised at a low temperature and thus rendered more readily combustible. "Cocoa" powder, containing 79 per cent, of KN0 3 , 2 per cent, of S, 18 per cent, of charcoal and 1 per cent, of moisture, is of this character. The brown colour is due to the lightly carbonised charcoal, which is generally made from straw. Mining powder, from which it is desired to obtain the highest possible effective pressure by generating a large volume of gas in a short space of time, contains about 67 per cent. KN0 3 , 19 per cent, charcoal and 14 per cent. S. The increase in the proportion of sulphur also augments the inflammability of the powder. The chemical changes occurring in the explosion of gunpowder are very com- plex, and differ according to the composition of the powder. HIGH EXPLOSIVES. 403 The following equation (Debus and Berthelot) may be taken as showing the nature of the chief changes : — I6KNO3 + 21C + 7S = 13C0 2 + 3CO + 16N + 5K 2 C0 3 + K 2 S0 4 + 2K 2 S 3 . The salient properties of powders of various kinds are shown in the table below :— Cocoa. Rifle, Large Grain. Mining. Calories (kilogram degrees), Litres of permanent gas at\ 0° C, and 7(30 mm., . / 1 kilogram of Dry Powder. 837 198 725-7 274 2 516-8 360-3 A comparison of the maximum pressure produced (in tons per square inch) by mining and black military powders, gave the figures 44 and 43 respectively, when the explosion was con- ducted in a closed vessel. The rapidity of the explosion of gunpowder is decreased by increase of apparent density, which varies from 1-67 for rifle powder, to 1*87 for brown prismatic powder. The exploding temperature of black powder is given at 300° C. = 572° F. At very low pressures — e.g., 5 mm. — rapidity of explosion becomes very small, the converse being true of high pressures such as those obtaining in a gun. Recently, the exigencies of modern warfare have caused the manufacture of smokeless, or as they are better termed in Germany, "rauchschwache" powders. Inasmuch as the smoke of gunpowder consists chiefly of finely-divided potassium carbonate and sulphate, smokeless powders must not 3-ield such saline products. Gun-cotton (v.i.) yields no solid matter on explosion, and is, therefore, smokeless, but is not adapted in its ordinary state for artillery and small arms, because of its intensely rapid and violent action. Nitrated products of cellulose, containing less N0 3 than gun- cotton, are per se, too feeble, but when formed into a gelatinous solid with nitro-glycerin, give an explosion of the right char- acter. For further information see iV ' tiro-Explosives. (b) Nitro-Explosives — " High Explosives." — These differ from gunpowder in that their explosive basis is a definite chemical compound, containing oxygen and oxidisable elements in unstable equilibrium. The expression nitro - explosive, although convenient, is a misnomer in the case of nitro- glycerin and gun-cotton, these compounds being the nitrates of certain organic radicles. Gun-cotton of ideal purity is cellulose hexanitrate, C 12 H 14 0 4 (N0 3 ) 6 , but as commercially prepared it con- tains various lower nitrates, although these do not exceed 2 to 3 per cent, in the best specimens. 404 EXPLOSIVES AND MATCHES. The manufacture is conducted as follows : — The waste from cotton spinning machines is thoroughly freed from grease and dried at 80° C. = 176° F. It is introduced in charges of about 1 lb. into a cast-iron vessel containing 220 lbs. of a mixture of 1 part by weight of the strongest nitric acid, specific gravity 1*5, with 3 parts by weight of the strongest sulphuric acid. After some five or six minutes the cotton is placed upon a grating provided at the back of the nitrating vessel, and is com- pressed by a plate and lever. The charge, containing in its pores 10 to 15 times its weight of acid, is transferred to a covered stoneware pot, which is placed in a stream of cold water for twenty-four hours, at the end of which time nitration is com- plete. The bulk of the acid is removed from the cotton by a centrifugal machine, and the remainder is washed out by a cascade of water and another treatment in a centrifugal drier. Finally, two boilings by steam are administered. The gun-cotton is then pulped in a " beater," such as is used in paper manufacture. The pulp must be washed in a paddle machine, and after six hours, is tested according to the conventional method by heating 20 grains to 150° F. = 65° C. in a test tube, in which is sus- pended a piece of paper moistened with potassium iodide and starch. This paper must not be blued by the separation of iodine, indicating the evolution of nitrous fumes. Gun-cotton is similar to cotton wool in appearance, but is somewhat harsher to the touch. Its specific gravity is 1 '66 when its pores are freed from air. It is distinguished from the lower products of the nitration of cellulose by its insolubility in a mixture of ether and alcohol. It is soluble in ethyl acetate, and becomes converted into a jelly by nitrobenzene and nitro- glycerin. In common with other explosive organic nitrates, it can be reconverted into the original substance —in this case cellulose — by treatment with potassium hydrosulphide. When kindled (as distinct from detonated) in an unconfined space, it burns fiercely with considerable flame (CO and H being evolved by its decomposition and burning in the air). It ignites spon- taneously at about 150° C. = 302° F., but this temperature varies with the condition of the gun-cotton. It does not explode by percussive shock, but does so with shattering violence, even though saturated with water, when detonated with a cap con- taining mercuric fulminate. When wet, however, a priming of dry gun-cotton is advisable to ensure detonation. Its decom- position on explosion is represented by the following equation : — Ci 3 Hh0 4 (NO s ) 6 = 5CO + 7C0 2 + 8H + 3H 2 0 + 6N. It will be seen, therefore, that gun-cotton does not contain enough oxygen to yield completely oxidised products when exploded per se. If imperfectly washed, and containing a trace of acid, it is liable to spontaneous decomposition and explosion. MANUFACTURE OF NITROGLYCERIN. 405 On explosion it gives more heat and more gas than an equal weight of any kind of gunpowder. Kilo, of gun-cotton yields Calories (kilcgram-degrees), . . . . 1071 Litres of gas, including water vapour, at\ c ~ n 0° C. and 760 mm., / boJ It is not of much industrial importance, as its price is too high; but it is used for loading torpedoes and for military mines. Attempts have been made to supply the oxygen required for its complete combustion by mixing it with nitrate. Thus tonite is made by mixing gun-cotton pulp (100 parts) with barium nitrate (79 parts). For sporting powders cellulose less highly nitrated than true gun-cotton is employed, as well as crude cellulose, such as sawdust, alone or mixed with metallic nitrates. Such substances are E. C. Powder, Johnson's [Powder, and Schultze's Powder. (c) Nitroglycerin Explosives. — Nitroglycerin, C 3 H 5 (N0 3 ) 3 , is glyceryl trinitrate, and is prepared by acting on anhydrous glycerin (specific gravity 1*26) with a mixture of the strongest nitric and sulphuric acids (1 : 2 by volume), as in the prepara- tion of gun-cotton. The mixture of acids is cooled and run into a leaden vessel kept cool by circulation of water through lead coils, and the glycerin is sprayed into the mixture by compressed air. The nitration takes place very rapidly, and the temperature is carefully regulated, so as not to exceed 30° 0. = 86° F., as indicated by a thermometer in the liquid. Should the tempera- ture rise unduly, there is risk of decomposition and even explosion. When the temperature has fallen, the contents of the vessel are run into a settling tank, the nitroglycerin then forming an upper layer ; this is run off and washed, first with water and finally with dilute alkali, as residual traces of acid would cause its spontaneous decomposition. The acid from which the nitroglycerin has been separated is diluted with water, and a further portion of nitroglycerin obtained by allowing it to settle from the diluted acid. The yield is about 2 parts by weight of nitroglycerin from 1 of glycerin. On account of the difficulty of controlling the nitration of glycerin conducted as described above, a method known as the Boutmy-Faucher method has been devised, by which it is attempted to eliminate some of the heat of the reaction by a preliminary conversion of the glycerin into sulphogly eerie acid, C 3 H 5 (HS0 4 ) 3 , with one-half of the sulphuric acid that is used in the direct treatment, thus removing a part of the water which would otherwise be split off during nitration, and evolve heat with the excess of sulphuric acid present. The rest of the sulphuric acid is mixed with the nitric acid, and the mixture cooled before use, as in the ordinary method. 406 EXPLOSIVES AND MATCHES. Nitroglycerin is a colourless (though commercial samples generally have a shade of yellow) oily liquid, specific gravity 1*60, with a sweetish taste and toxic properties, producing faint- ness and headache. It is insoluble in water and solidifies at 8° C. = 46° F., and is volatile at 100° C. = 212° F. It is re- converted into glycerin by treatment with alkaline sulphides. When rapidly heated to 200° C. = 392° F. it inflames, but may detonate below this — e.g., 180° C. = 356° F. Detonation is also caused by a shock or blow, and by the use of mercuric fulminate explosion takes place with certainty. On explosion, nitroglycerin yields the following products : — 2(C 3 H 5 (N0 3 ) 3 ) = 6C0 2 + 5H 2 0 + 6N + O It will be seen, therefore, that nitroglycerin contains more than enough oxygen for the complete oxidation of its carbon and hydrogen, on which account it may be advantageously used in conjunction with explosives, such as gun-cotton, which contain less than the quantity of oxygen requisite for their complete oxidation (see Blasting Gelatine). The quantity of heat evolved, and of gas liberated by the explosion of one kilo, of nitroglycerin is — Calories (kilogram degrees), .... 1,570 Litres of gas at 0° C. and 760 mm., including water vapour, ...... 714 Nitroglycerin, therefore, gives less gas but more heat than does gun-cotton. In practice it is found that its effect is about five times that of an equal weight of blasting powder. The dis- advantages attending the use of nitroglycerin, such as risk in transport, cause it to be little used ; indeed in this country its sale and transport are illegal. When absorbed in a porous medium it becomes less unsafe to handle, and constitutes the class of explosives mentioned below. Dynamite. — This explosive consists of nitroglycerin absorbed by an inert substance. The material generally used as an absorbent is a siliceous earth, kieselguhr, which consists of frustules of diatoms, and contains 95 per cent, of silica. Other absorbents, such as kaolin, chalk, magnesia, mica and cork charcoal, are used to a limited extent, but are less effective than kieselguhr. Kieselguhr is prepared by calcining and sifting the raw earth. It is then mixed by hand with three times its weight of nitroglycerin, forming a plastic mass of dyna- mite containing 75 per cent, of nitroglycerin and 25 per cent, of kieselguhr. The dynamite is then granulated by passage through a sieve, and made up into cartridges by the pressure of a wooden piston in a small metal cylinder, or by being expressed in a continuous rod, which is divided into suitable lengths ; the finished cartridges are enclosed in parchment paper cases. Dynamite is less sensitive to shock than is nitroglycerin, NITROGLYCERIN EXPLOSIVES. 407 but like it, it is rapidly decomposed at 180° C. = 356° F. Small quantities, when kindled, may burn without explosion, but large amounts usually reach their critical temperature of explosion and then detonate. Frozen dynamite cannot be completely exploded when detonated with mercuric fulminate in the usual way, and has to be thawed before being used. Many accidents have occurred by carelessly heating frozen dynamite. As the specific heat of kieselguhr is about 0'2, an appreciable quantity of the energy generated on explosion of the nitroglycerin is uselessly employed in heating the absorbent. The disadvantage of an inert absorbent and the fact that a certain amount of oxygen is set free in the explosion of nitro- glycerin, have led to the manufacture of explosives of which the absorbent base is itself active. The following are the chief members of this class. Blasting Gelatine. — This explosive consists of 93 per cent, of nitroglycerin, absorbed by 7 per cent, of nitrated cotton (col- lodion cotton containing lower products of nitration than the hexanitrate), this quantity sufficing for the surplus oxygen of the nitroglycerin. Blasting gelatine is made by warming nitro- glycerin in a copper vessel, and stirring in the finely-divided nitrated cotton in small quantities at a time, the temperature being kept below 35° 0. = 95° F. In the course of an hour the mass gelatinises to a viscous semi-transparent mass, which freezes at a low temperature. It can be employed under water, whereas dynamite is disintegrated when thus used, the nitroglycerin being washed out. It is somewhat sensitive to shock when frozen, but in its normal state requires a heavier detonating charge than does dynamite ; its detonation also takes place more slowly. One kilo, of blasting gelatine liberates 1,530 Cal. on explosion. Its intensity of blasting effect is given as 160 when that of dynamite equals 100. Gelatine dynamite consists of 65 per cent, of a thin blasting gelatine (containing 2*5 per cent, of nitrated cotton), 26*25 per cent, of potassium nitrate, 8 -4 per cent, of wood meal and 0*35 per cent, of soda. Many other nitroglycerin explosives are made. Cordite, the smokeless powder adopted by the British Government, is of the blasting gelatine order, and is made by incorporating 58 parts of nitroglycerin with 37 parts of gun- cotton and reducing the mixture to a pulp by the addition of a solvent such as acetone (19*2 parts) ; the pulp is mixed with vaseline (5 parts) and manufactured into threads by expression through dies ; the threads are used for loading cartridges. (d) Other Nitro-Explosives. — The idea suggested by Sprengel of avoiding the transport of high explosives by supplying the user with two or more substances, each of which by itself is not explosive, to mix when required and thus yield an explosive composition, has received numerous developments. 408 EXPLOSIVES AND MATCHES. The original explosives proposed by Sprengel were either solu- tions of such substances as nitrobenzene and picric acid dissolved in the strongest nitric acid, or porous cakes of potassium chlorate saturated with combustible liquids. These mixtures, which could be made on the spot, were detonated by mercuric fulminate. Thus, hellhoffite is a solution of nitro- and dinitrobenzene in nitric acid ; panclastite, a mixture of nitrogen peroxide with carbon bisulphide. The objection to the handling of liquid explosives has caused a reversion to mixtures of solid substances, one class of which is oxidising agents and the other combustible materials, functioning in precisely the same manner as gun- powder, but needing a detonator for their explosion. Examples of this class of explosive are roburite, a mixture of dinitro- benzene, chloronitronaphthalene and ammonium nitrate, and rack-a-rock (potassium chlorate and nitrobenzene) ; also picric acid powders consisting of a mixture of a picrate with potassium nitrate or chlorate. Picric acid is itself capable of detonation, and is said to be the main constituent of the French Government explosive, Melinite. For detonators, mercuric fulminate is invariably employed. It is prepared by acting on 1 part by weight of mercury with 10 parts by weight of nitric acid in the cold, the solution being poured into 8 '3 parts by weight of methylated spirit. A very violent action arises, and the fulminate separates in crystals, which are filtered off and washed. The finished product is a white crystalline powder, which is very easily exploded by friction or percussion unless it contains upwards of 10 per cent, of water. The detonation temperature is about 150° to 200° C. = 302° to 392° F. The equation representing the decomposition of mercuric fulminate on explosion, and information concerning the heat evolved, are given at the beginning of the chapter. For use for the caps of military and sporting cartridges, mercuric fulminate is generally mixed with a small quantity of potassium chlorate or nitrate. II. MATCHES. — Phosphorus. — Two varieties of phosphorus of commercial importance are known, a vitreous pale yellow substance, crystallising in the regular system, and a red body, generally supposed to be amorphous, but recently alleged by Retgers to form hexagonal crystals. The former has a specific gravity of 1-83 and melts at 44° 0. = 111° F. and boils at 290° C. = 554° F. ; it is soluble in carbon bisulphide, is easily inflamed by friction, and oxidises spontaneously in air at the ordinary temperature. It is highly poisonous. The latter has a specific gravity of 2*14, and is not affected by heating in air below 290° C. = 554° F. when it becomes converted into the yellow variety. It is not readily inflamed by friction. It is insoluble in carbon bisulphide and is not poisonous. Both varieties 'are used for making lucifer matches. MANUFACTURE OF PHOSPHORUS. 40D In the manufacture of phosphorus the yellow variety is first obtained. The raw material is phosphoric acid, which is prepared from a mineral calcium phosphate (see Manures, Vol. II., p. 107). Formerly, phosphorus was made from bone-ash, but this source of supply is more costly than mineral phosphates. The finely ground mineral is mixed in a wooden vat with sufficient chamber vitriol (see Sulphuric Acid, Vol. II., p. 14) to convert all the lime of the mineral phosphate into calcium sulphate, the liquid being heated with open steam. Ca 3 (P0 4 ) 2 + 3H 2 S0 4 = 3CaS0 4 + 2H 3 P0 4 When the reaction is complete, the coutents of the vat is run into lead-lined filtering pans, and the solution of phosphoric acid, which should have a specific gravity of 1*17, is allowed to run through. The calcium sulphate is washed until the filtrate has a specific gravity of 1 01. The calcium sulphate retains some calcium phosphate, as shown by the following analysis- headman), and is known as phosphatic gypsum : — Calcium sulphate, 71*14 Calcium phosphate, . . . . . 6*56 Siliceous matter, . . . . . 12*10 Ferric oxide, alumina and organic matter, . 5*55 Water, 4 65 100 00 It is used as a " drier " by manure makers. The liquor is evaporated in lead-lined tanks, containing lead worms through which high-pressure steam is passed, and provided with agitators. During the concentration, calcium sulphate is deposited and is removed by filtration. The concentration is pushed until the liquor has a specific gravity of 1*325 to 1*5, according to the reducing agent subse- quently used, the weaker liquor sufficing when sawdust is em- ployed and the stronger being requisite for coke or charcoal, which are less absorbent. The phosphoric acid is now mixed with the reducing agent, which is some form of carbon, in quantity amounting to about 25 per cent., charcoal, coke, or sawdust being used as stated above. The wet mass has to be dried in iron pots or muffle furnaces, and is stored in airtight iron vessels until required for distillation. During the drying, the phosphoric acid loses water and becomes metaphosphoric acid (HP0 3 ). The distillation is carried out in bottle-shaped fireclay retorts about 3 x 1 ft. and 1 inch thick in the walls. The retorts, are placed in two tiers, in a furnace similar to that used in the distillation of zinc by the Belgian method (see Zinc, Yol. I., p. 183). Iron or copper tubes are affixed to the necks of the retorts by clay luting and are connected with the cOndenser, which is a long trough containing water beneath which the 410 EXPLOSIVES AND MATCHES. aforesaid pipes open, and in which the phosphorus collects. The distillation is conducted at a high temperature and frequent breakages of the retorts occur. The chemistry of the distillation may be represented by the equation — 4HP0 3 + C 12 = H 4 + 12CO + P 4 . The average yield of refined phosphorus is not more than 70 per cent, of the theoretical amount. The phosphorus which collects in the troughs, being fused, is ladled into boxes and transferred to the refinery, where it is re-melted, so that the sand and clay, with which it is mixed, separate, and the purified phosphorus is either squeezed through chamois leather or melted in a pan under a dilute solution of potassium bichromate and sulphuric acid. With this liquor it is agitated and heated by steam coils, and is finally washed with hot water, filtered through canvas and re-moulded into sticks or wedges, which are packed in water in tin-plate boxes for the market. On account of the high temperature needed for the reduction and distillation of phosphorus, externally fired retorts, such as have been described, are costly, as the heat has to be transmitted through their walls. Further, advantage cannot be taken of the possibility of dis- placing P 2 0 5 by Si0 2 at high temperatures by using a charge of calcium phosphate, sand and carbon, and thus avoiding the preliminary manufacture of phosphoric acid, as the necessary temperature cannot be attained. On account of these drawbacks .attending the use of retorts, internally fired furnaces present considerable prima facie advantages. An attempt to apply this principle in the form of the electric furnace (see Aluminium, Vol. I., p. 221) has been made by Readman and Parker, whose apparatus consists essentially of an iron box lined with fire-brick, provided with carbon electrodes at its lower part, and a hopper a-nd feeding screw and an exit tube at the upper. The arc is established by small independent electrodes, and maintained by the large electrodes, phosphorus being volatilised in the ordinary manner. The charge consists of mineral phosphate, sand and <3oke, and it is claimed that a yield of 86 per cent, of the total phosphorus is obtained. Red Phosphorus. — The manufacture of red phosphorus is •conducted by heating ordinary phosphorus in a cast-iron pot heated at 240° to 250° C. = 464° to 482° F. by a sand bath. The pot is provided with a screw cover and a tube for the escape of air at the beginning of the operation. This tube is sometimes trapped with mercury or water, and is closed by a cock when the displacement of the air is complete. The conversion of yellow into red phosphorus takes place more rapidly when it is heated under pressure at 300° C. = 572° F., but the risk of the operation is greater than when a lower temperature is employed. By this process the yellow phosphorus is converted into hard LUCIFER MATCHES. 411 lumps of red phosphorus ; grinding under water and extraction of unaltered yellow phosphorus by boiling under caustic soda solution, followed by thorough washing, finish the manufacture. Matches. — The chief use of phosphorus, both yellow and red, is in the manufacture of matches, for which purpose it is adapted by its easy inflammability. The particular explosive mixture which is used for the heads of matches must be of such a nature that it can be ignited by slight friction, either on any rough surface or on one that has been specially prepared. Such sensi- tiveness is most easily attained by the use of phosphorus either for the head composition or for the prepared surface. Matches may be roughly classified as " common " and " safety * matches, according as their ignition is due to the use of yellow or red phosphorus. In common matches phosphorus is the chief oxidisable constituent of the explosive mixture used for their heads, while in safety matches sulphur, generally in the form of antimony trisulphide, takes its place. The essential ingredients in a common match composition are : — (1) yellow phosphorus ; (2) an oxidant, such as potassium chlorate or nitrate ; (3) glue or gum, serving both as an emulsifying agent and as a binding material ; (4) indifferent gritty material — e.g., powdered glass, to increase friction ; (5) colouring matter, such as ultramarine. The number of compositions in use is very great, but the following may be quoted as giving some idea of the proportions of the ingredients : — Yellow phosphorus, Potassium chlorate, Glue, . Powdered glass, 0*5 parts by weight. 4-0 „ ' „ 20 „ 4-0 The colouring matter varies accordin to the preference of the market for which the matches are intended. The mixture is made by dissolving the glue and potassium chlorate in warm water, gradually stirring in the phosphorus to form an emulsion and adding the other ingredients. The com- position is spread out on slabs heated by steam, and the match stem, whether of wood or wax-coated thread (for vestas), dipped therein to form the head. Wooden matches are generally primed by a preliminary dipping in sulphur or paraffin wax, which aids the ignition of the wood, the splints being made in double lengths and dipped at both ends. The dipped matches are allowed to dry, and are then halved and packed. With safety matches red phosphorus is substituted for yellow, but usually on the prepared striking surface only. Head Composition. Antimony sulphide, . 1 Potassium chlorate, . 1 Gum arabic, ... 2 Powdered glass, . . 12 Rubber Composition. Bed phosphorus, . . 2 Gum arabic, ... 1 Powdered glass, . . 1 412 EXPLOSIVES AND MATCHES. As an additional precaution, the stems of wooden safety matches are sometimes prepared by being soaked in a dilute solution of alum, magnesium sulphate or a phosphate, so that the wood may not glow after the match has been extinguished. The finished match is sometimes waterproofed with paraffin wax. On account of the outcry against the risks run by operatives in match factories of contracting necrosis by exposure to the phosphorus vapour, attempts have been made to prepare matches entirely without phosphorus, but with indifferent success. The best composition hitherto proposed contains lead thiosulphate, PbS 2 0 3 , as the oxidisable ingredient, potassium chlorate serving as the oxidiser. Fusees are common matches with wooden or wax stems, provided with enlarged heads consisting of powdered charcoal mixed with potassium nitrate and a binding material, tipped with an ordinary striking composition, the object of the former being to cause the match to burn fiercely in wind. HYDROFLUORIC ACID. 413 CHAPTER XVIII. MINOR CHEMICAL MANUFACTURES. This section is devoted to the chemistry of the manufacture of such acids, salts, = Na 2 Mn 2 0 8 + Mn0 2 + 4NaOH. * Sodium permanganate, thus formed, is not easily crystallised, but the potassium salt, K 0 Mn 2 O s . crystallises readily in red prisms ; it is similarly prepared. The manganates and perman- ganates are used as oxidising agents ; thus sodium manganate, being the cheapest, serves as a disinfectant. When the alkalinity * The whole of the manganese can be obtained as a permanganate by treating the manganate with chlorine or bromine, thus : — 2K 2 Mn0 4 + CI, = 2KC1 + K 2 Mn 2 Q 8 « Compare the production of K 3 FeCy6 from K 4 FeCyc. COPPER SULPHATE. 423 essential to the preservation of a manganate is objectionable, potassium permanganate is substituted for the sodium salt, as it can be prepared in a state of purity. Potassium perman- ganate is also used for producing manganese brown (hydrated 3In0 0 ) on cotton fabrics, and also for staining wood ; both uses depend on the ease with which permanganates are reduced by organic substances. Sulphates.— Blue Vitriol or Blue Stone, Copper Sulphate, CuS0 4 .5H 2 0. — This salt is mainly a bye-product and may be prepared in a variety of ways according to the raw material available. Thus it may be prepared by the direct dissolution of copper in sulphuric acid, as in the parting of gold from silver and copper by the action of boiling oil of vitriol. When silver and gold alone are parted by sulphuric acid, the silver is re- covered by precipitation with copper, an equivalent of copper sulphate being formed ; a considerable quantity of pure copper sulphate is thus obtained. In order to save acid when copper sulphate is the main product, the preparation may be effected by treating granulated copper, spread on the perforated false bottom of a suitable vessel, with a spray of dilute sulphuric acid, which gradually attacks the copper in presence of air ; the copper being oxidised at the expense of the air instead of at that of the sulphuric acid. Advantage is also taken of the ease with which copper sul- phide can be oxidised to sulphate by air at a dull red heat. Thus scrap copper may be heated with sulphur and then oxidised by roasting, or crude sulphide of copper obtained in the dry process of winning copper may be similarly oxidised. Copper sulphate from this source is liable to contain both iron and nickel. When a product free from iron is required, the tempera- ture of the roasting is raised to such a point that any sulphate of iron is decomposed, leaving ferric oxide as an insoluble resi- due easily separated from the copper sulphate. Sulphates other than ferric sulphate— e.g., ZnS0 4 .7H 2 0 — have a strong tendency to crystallise with copper sulphate and form mixed salts. This arises from the fact that the members of the class of sulphates known archaically as the vitriols, tend to crystallise with the same number of molecules of water, either 7H 2 0 or 5H 2 0, and to assume the same form. Since ferric sulphate is not a "vitriol," iron may be separated from copper sulphate by oxidation and crystallisation. The chief uses of copper sulphate are the pre- paration of agricultural germicides, the production of a black dye with logwood, and the preparation of electrolytic baths. Ferrous Sulphate, Copperas, or Green Vitriol, FeS0 4 .7H 2 0. — The chief supply of sulphate of iron is obtained as a bye-product in the manufacture of cement copper, by precipitating this metal from a solution of its sulphate by means of scrap iron (see Copper, Vol. I., p. 165). It is also obtained by the direct treatment of 424 MINOR CHEMICAL MANUFACTURES. iron scrap with sulphuric acid, especially the spent acid left after the process of purifying mineral oils (q.v.). It is, moreover, a bye-product of the manufacture of alum by the oxidation of pyritic shale. The ferrous sulphide left by distilling iron pyrites for the sake of obtaining a fraction of its sulphur (see Sulphur, Vol. II., p. 1) is also weathered and leached for ferrous sulphate. The solution, however obtained, is allowed to crystallise on wooden rods, and is put upon the market as green vitriol. Black vitriol is a term applied to a highly crude sulphate of iron containing the sulphates of copper and nickel and some ferric sul- phate. It is a bye-product in the precipitation of copper in the Mansfeld process. An artificial " black vitriol " is prepared by staining common green vitriol with a little gallo-tannic acid. Green vitriol readily oxidises in air, losing water at the same time and becoming converted into basic iron sulphate, brown in colour and incompletely soluble in water. When crystallised from an acid solution its tendency to oxidise is diminished. The chief uses of ferrous sulphate are as a co-colouring matter for logwood (q.v.), as a sewage preciptant and disinfectant, for making inks and as a reducing agent — e.g., in the preparation of the indigo vat. It is soluble in about one and a-half times its weight of cold water. Ferric sulphate, Fe. 2 (S0 4 ) 3 , is now prepared to some extent by the oxidation of pyrites and treatment with sulphuric acid, the product being used as a substitute for aluminium sulphate for the defecation of sewage. Zinc sulphate, white vitriol, ZnS0 4 .7H 2 0, may be prepared by leaching roasted zinc sulphide or by dissolving zinc scrap in sulphuric acid. It finds a limited use in the preparation of pigments — e.g., Orr's white zinc (q.v.) — in calico-printing and dyeing, and as a drier for oils (q.v.); its use in pharmacy is chiefly as an astringent. Aluminium Sulphate. — This is used both per se and in the form of alum. The name alum primarily applies to potassium al- uminium sulphate, KA1(S0 4 ).,.12H 2 0, but has been extended in significance to all salts of the type R/B/"(S0 4 ) 2 .12H 2 0 which are isomorphous. Alum can be prepared from most minerals rich in alumina, but a few offer special advantages. Particularly is this the case with the mineral known as alum stone (alunite), which contains an anhydrous double sulphate of aluminium and potassium asso- ciated with aluminium hydroxide. An analysis of such material is as follows : — Per cent. SiO.„ 13 4 A1 2 0 3 , 35 5 K 2 0, 12-5 S0 3 , 30 0 Fe 2 0 3 0 05 H 2 0, 8 5 MANUFACTURE OF ALUM. 425 The preparation of alum is effected by roasting this alum stone at a temperature of about 500° 0. = 032° F., and extracting the roasted product with sulphuric acid (specific gravity 1*5), the solution being then allowed to crystallise. When water is used to leach the roasted stone, the basic double sulphate of the form K 0 O.S0 3 . A1 2 0 3 .2S0 8 is formed ; this crystallises in cubes instead of the octahedra characteristic of ordinary alum, and on account of its basic constitution is neutral in reaction, whereas ordinary alum is acid to litmus. On this account it is used in some cases where acidity is objectionable. Pyritic shale is another source from which alum can be pre- pared. Some of this, particularly that of South Lancashire, is sufficiently carbonaceous to serve as its own fuel in the burning process necessary to bring about the oxidation of the pyrites destined to furnish the sulphuric acid which attacks the aluminous material (clay). The sulphate of alumina thus formed is extracted by systematic leaching. As a portion of the sulphur remains in the form of ferrous sulphide, after roasting, long exposure to air before leaching is advisable, so that the oxidation of this ferrous sulphide may yield ferrous sulphate, which is useful in the conversion of the aluminium sulphate into alum (v.i.). The solution of crude aluminium sulphate is evaporated in tanks over which the hot gases of a reverberatory furnace are led, and when sufficiently concentrated (e.g., specific gravity 1*4), the solution is transferred to precipitating tanks and treated with potassium chloride or sulphate, alum being thrown down. Potassium chloride (the cheaper material) can be used when sufficient sulphate of iron is present to yield with it potassium sulphate and iron chloride. The crude precipitate is purified by crystallisation. Alum is chiefly prepared now- adays from aluminium sulphate, which is manufactured by decomposing clay with sulphuric acid. The clay should be free from calcium carbonate, which con- sumes H 2 S0 4 uselessly. When a " fat " clay — e.g., china clay — is used, it should be dehydrated by gentle roasting to render it porous. It is treated with 11,864 (specific gravity 1*5) in lead pans, and the mass allowed to solidify; this is either sold as alum cake, containing the bulk of the silica of the clay, or it may be purified and sold as sulphate of alumina, or used for the prepara- tion of alum. Alum contains about 10 per cent, of alumina ; alum cake contains about 12 per cent, of A1 2 0 3 and 22 per cent. Si0 2 . The chief advantage of alum is that, having been crystallised, it is purer than other aluminous products. For most purposes both alum and alum cake should be as free as possible from iron and uncombined sulphuric acid. Burnt alum is calcined alum. Alum and aluminium sulphate are used chiefly by the dyer as mordants ; they are also employed by the paper maker and the leather dresser. 426 MINOR CHEMICAL MANUFACTURES. Ammonia alum, NH 4 A1(S0 4 ) 2 . 12H 2 0, is similarly prepared, (NH 4 ) 2 S0 4 being substituted for K 2 S0 4 in the process. Chrome alum, potassium chromium sulphate, KCr(S0 4 ) 2 .12H 2 0, is strictly analogous in composition and crystalline form to common alum. It is obtained as a bye-product in the manufac- ture of alizarin by the oxidation of anthracene with potassium bichromate and sulphuric acid (see Alizarin, Vol. II., p. 281). It is used as a mordant, and for rendering substances containing gelatine insoluble. Potash Salts. — The main source of potassium salts, at the present day, is the deposit found at Stassfurt, near Magdeburg. The salts there found appear to have resulted from the evapora- tion of sea water, which has successively deposited the salts it contains in an order determined by their solubility, relative abundance and mutual reactions. The salts last to be separated constitute Stassfurt salts, and their occurrence as an isolated patch in a bed of the commoner salts of sea water, extending over a much more considerable area, is to be accounted for by the escape of the bulk of the mother liquor from the remainder of the area, this having been brought about by geological disturbances. Many double salts occur in the Stassfurt de- posits. The chief are carnallite, KCl.MgCl 2 .6H 0 0, kainite, K 2 S0 4 .MgS0 4 .MgCl 2 .6H 2 0, kieserite, MgS0 4 .H 2 0," anhydrite, CaS0 4 , associated with large quantities of rock salt, NaCl, and various minor salts, viz. : — polyhalite, MgS0 4 ,K.,S0 4 .2CaS0 4 . 2H,0, boracite, 6Mg0.8B 2 O y .MgCl 2 , etc. The general principles of separation adopted for all these salts depend on the alteration of the solubility of each salt by the influence of the accompanying salts, and the separation thus induced either of a simple salt or of some double salt. By varying the conditions, selective separations can be favoured. The chief raw material is crude carnallite, which contains about 60 per cent, of pure carnallite, 20 per cent, of common salt and 15 per cent, of kieserite, the balance consisting chiefly of an- hydrite. The process now generally adopted of obtaining potassium chloride from carnallite, consists in treating the crude material with a solution containing about 20 per cent, of MgCL, (obtained as a mother liquor from previous operations). The carnallite alone is dissolved in considerable quantity, and the solution thus obtained deposits on cooling crystals which are mainly KC1. These are purified by systematic washing, and when dried con- tain from 80 to 90 per cent, of KC1. The mother liquors from the potassium chloride are evapo- rated in pans, having flues passing through the liquid in the manner of a locomotive boiler. Sodium chloride first separates in crusts which settle on the bottom, thus rendering heating from below undesirable, and the mother liquor yields artificial POTASH SALTS. 427 carnallite (returned to the main process) on cooling. The final residual liquid is rich in magnesium chloride, and is worked up for bromine. The residue left in the first extraction of the crude carnallite is mainly common salt (50 to 55 per cent.), with much kieserite (25 per cent.), some potassium and magnesium chlorides and a good deal of anhydrite (10 per cent.). The sludge is chiefly valuable for the magnesium sulphate, which it contains in the form of kieserite, that salt being insoluble in water until it passes into the form of Epsom salts, MgS0 4 7H 2 0, a transition delayed by the presence of magnesium chloride in the water. By washing this sludge with water on to an inclined sieve, the bulk of the water flows away whilst sufficient passes over the surface of the sieve with the sludge to react slowly with the kieserite to form cakes of block- kieserite, containing MgS0 4 .3H 2 0 and some insoluble matter, mainly CaS0 4 . Kieserite sludge is also worked up for Glauber's salts by treating it with an equivalent quantity of NaCl, which at a temperature of about 0° C. = 32° F. enters into double decom- position on account of the sparing solubility of Na 2 SO 4 .10H 2 O (Glauber's salt) at low temperatures. This process can only be carried out in winter, unless it be practicable to cool artificially. The large quantity of magnesium chloride obtained as a bye- product in the manufacture of potash salts, finds little applica- tion, although attempts have been made to use it as a source of chlorine, as in the Pechiney process (q.v.). Potassium sulphate is sometimes prepared from kainite — the chief market for which, however, is in the raw state as a manure — by treatment with KC1, which reacts with the MgS0 4 . forming magnesium chloride and potassium sulphate, this last-named salt being easily crystallised from the liquor. It is used as a manure and a source of potassium salts. The final mother liquor from the working up of the Stassfurt salts is used for the preparation of bromine (q.v.). Although Stassfurt salts yield a large proportion of the potash salts of commerce, yet considerable quantities are obtained from other sources, the chief being wood ashes, residues from beet sugar and suint. Sources of purely mineral character are sea water, orthoclase and potash mica. Potassium chloride is but little used as such, but serves as a starting-point for the preparation of most other potash salts. An example of its use is afforded by the conversion of sodium into potassium nitrate in the manufacture of gunpowder (Vol. II., p. 400). Potassium Carbonate, or Potashes, K 2 CO ;j . — The conversion of KC1 into K 2 CO ;J is effected by the Leblanc process (see Soda ash, Vol. II., p. 19), which is worked in the same manner as that used for soda, with a few modifications, due to the greater 428 MINOR CHEMICAL MANUFACTURES. chemical activity of the base. Thus, muffles (blind roasters) are not used in the conversion of the chloride into sulphate, because of the high temperature requisite. The decomposition of potassium sulphate in the revolver, corresponding with the black-ash process, is less easily effected, and the product attacks the lining more readily than does black ash. The extraction of the roasted product is performed as for soda, and the liquor is evaporated to the point at which K 2 S0 4 separates, followed by K 4 FeCy 6 (resulting from the interaction of the potash, iron — present as an impurity — and the carbon and nitrogen of the coal). The crude ferrocyanide is recrystallised for the market. The mother liquor is evaporated to dryness and calcined in a reverberatory furnace. Sometimes the liquors are carbonated before calcination, when the product contains some 87 percent, of K 2 C0 3 , and is marketable; otherwise the crude potash is leached out and separated from insoluble impurities, and the solution evaporated to dryness. Such refined potash contains about 98 per cent, of potash, calculated as K 2 C0 8 , Caustic potash, KOH, is prepared from K 2 C0 3 by causticising with lime in the same manner as is practised lor caustic soda ; it is used chiefly for making soft soap, and for preparing oxalic acid (q.v.). In America, Russia and Scandinavia much potash is made from wood ashes. The percentage of jjc-tash varies with the nature of the wood, being, for instance, about 0*4 per cent, in pine wood, and 0-15 in oak wood ; in most cases, however, the percentage on the ash is about the same — viz., 10 per cent. The wood ash is systematically extracted in wooden vessels fitted with perfected false bottoms, and the liquor, containing about 25 per cent, of salts, is evaporated in cast-iron pots; the residue is calcined. A good deal of sulphate is removed during evaporation. The crude potash may be purified in the manner described above ; on an average it contains 60 per cent, of K 2 C0 3 , the balance consisting of KC1, K 2 S0 4 , and ]Na 2 C0 3 . A large quantity of potash is obtained from the residues left after the extraction of sugar from beet. The beet molasses con- tain the total potash salts of the root, amounting to 0*5 per cent., calculated on the weight of the root. This material is either ashed directly, yielding schlempekohle, or it is desaccharised or fermented (see Beet Sugar, Yol. II., p. 173), and the final liquors (vinasse or schlempe) from these processes is evaporated to dry- ness and the residue calcined. Instead of this direct conversion into a char, it is sometimes customary to destructively distil the liquor, whereby it is carbonised, and much ammonia, methyl alcohol and trimethylamine come over from the organic con- stituents, which are rich in nitrogen. By further heating the trimethylamine hydrochloride— obtained by absorbing the gas STRONTIUM SALTS. 429 in hydrochloric acid and evaporating the liquor until the less soluble ammonium chloride has crystallised — much methyl chloride is obtained, and is condensed by pressure for the use of the synthetic colour manufacturer. The final char, however obtained, is a black porous mass containing about 30 per cent, of K.,C0 3 and 20 per cent, of Na 9 C0 3 , the remaining soluble salts consisting chiefly of K 2 S0 4 and KOI. The liquor obtained by leaching the char is evaporated in iron pans heated by steam coils, until K 2 S0 4 crystallises, from which the mother liquor is run off; further evaporation causes the crystallisation of KC1, this and the sulphate being sold as such or used for making K. 2 C0 3 by the Leblanc process. The mother liquor is further concentrated until Na 9 C0 3 .H 2 0 separates in the hot liquid, which is run off, and on cooling deposits more KC1. The next salt to separate is the double carbonate, K 9 C0 3 .Na 2 C0 3 . 12H 2 0, which is returned to a fresh quantity of the liquor or is decomposed by a second crystallisa- tion. The final mother liquor is taken to dryness and calcined for potassium carbonate, the product containing about 85 per cent. K 2 C0 3 and 8 per cent. Na 2 C0 3 . Another source of potash is the "yolk" or "suint" of wool, resulting from the sweat of the animal. The raw wool is systematically extracted with cold water, whereby the potash soaps, together with some of the neutral fat and cholesterol, are extracted. The solution is evaporated to dryness and calcined, giving a residue containing about 85 per cent, of K 9 C0 3 , the remainder being Na 2 C0 3 , together with K 2 S0 4 and KCL This •crude potash may be purified in the usual way. Strontium Salts. — Strontium occurs both as carbonate (stron- tianite, SrC0 3 ) and sulphate (coelestine, SrS0 4 ). These minerals are worked up for strontium nitrate and hydrate, the sole com- pounds of this metal which are of technical importance. Strontium nitrate, Sr(N0 3 ) 2 , is prepared by dissolving the carbonate in nitric acid. If the native carbonate can be pro- cured sufficiently free from other bases, which would consume nitric acid, this mineral may be used. The carbonate is some- times made from coelestine by fusing it with soda ash and leaching out the sodium sulphate formed by the double decomposition SrS0 4 + Na 2 C0 3 = SrC0 3 + Na 2 S0 4 . Strontium nitrate dissolves in twice its weight of water at the ordinary temperature, and in its own weight at 100° C. = 212° F. It is much used in pyrotechny for the sake of the red colour which it imparts to a flame. Strontium hydrate, Sr(OH) 2 , is now largely employed in sugar refining (Vol. II., p. 175). Strontium carbonate can be burnt to strontia (strontium oxide, SrO) just as calcium carbonate can be burnt to lime ; but the temperature required is very much .higher than that at which limestone can be burnt. By heating 430 MINOR CHEMICAL MANUFACTURES. the carbonate in superheated steam, it can be directly converted into hydrate at a low red heat. More generally, strontium hydrate is produced from the sul- phate ; the conversion is not easy, and many processes have consequently been devised to effect it. Ccelestine is roasted with equal weights of coal and iron oxide (brown iron ore) ; strontium* sulphide is probably formed, for when the mass is lixiviated with water, ferrous sulphide remains undissolved, whilst the solution contains strontium hydrate. SrS0 4 + C 4 = SrS + 4CO ; Fc.fi & + C = 2FeO + CO. SrS + FeO + H 2 0 = Sr(OH) 3 + FeS. By another process, ccelestine is ground, mixed with coal and roasted to sulphide ; the sulphide is extracted with water, and the solution mixed with caustic soda solution. The reactions involved may be represented by the equations — (1) 2SrS + 2H 2 0 = Sr(OH) 2 + Sr(SH) 2 ; (2) Sr(SH) 2 + 2NaOH = Sr(OH) 2 + 2NaSH. The strontium hydrate crystallises from the liquor, and is recrystallised ; the sodium hydros ulphide is converted into car- bonate by passing C0 2 through the mother liquor, and causticised for further use. Strontium hydrate crystallises from water in the form Sr(OH) 2 .8H 2 0, dissolving in 50 parts of cold water and 2*4 parts of boiling water. It is less poisonous than barium hydrate. Barium salts are prepared from the native carbonate (witherite), and sulphate (heavy spar) by processes analogous to those used for strontium. Barium chloride, BaCl 2 .2H 2 0, is used to a certain extent for softening water for boiler use (see Yol. I., p. Ill), and barium carbonate for decomposing objectionable sul- phates in clay intended for the preparation of tiles and similar goods. Soluble barium salts are strongly toxic. III. HALOGENS.— Bromine. — The chief source of bromine is the end liquors of the separation by crystallisation of the salts from sea water or of the Stassfurt deposits. Sea water contains about 2 ozs. of bromine per ton, whilst the mother liquor from the working up of carnallite in the Stassfurt process contains as much as \ per cent, of bromine or 5 \ lbs. per ton. The preparation from these liquors is dependent upon the fact that bromine is more readily expelled from its salts than is chlorine by a suitable oxidising agent in the presence of an acid. It was at one time customary to distil the liquor with such an oxidising agent — viz., manganese dioxide and sulphuric acid. Nowaday s^ however, chlorine is generated from Mn0 2 and HC1 in a separate still, and the liquors are treated systematically with the gas, the bromine being liberated. The concentrated liquor, contain- ing the bromine chiefly as MgBr 2 , trickles into a tower fitted EXTRACTION OF BROMINE. 431 with a perforated plate, serving to distribute the liquid over a large number of earthenware balls with which the tower is filled ; * this packing is supported by a perforated false bottom, beneath which the chlorine enters. The bromine liberated from the liquor as it meets the ascending chlorine, passes through an exit pipe at the upper end of the tower, and is condensed in a stoneware worm. The partly spent liquor, still containing some bromine and chloride of bromine, passes into another vessel, which remains full of the liquid since the outlet for the completely spent liquor is brought up from the bottom to the level of the top of the vessel. Steam is blown into the bottom of this vessel and is distributed by baffle plates ; by this means the remainder of the bromine is expelled chiefly as bromine chloride, and passes up the tower together with the fresh chlorine, which enters at the top of the heating vessel. By adopting this second vessel, not only is the liquid freed from bromine, but the bromine chloride which it yields is, to a great extent, decomposed by contact with fresh magnesium bromide in the tower. After the main quantity of bromine has been condensed in the stoneware worm, the residual vapour is caught in a small tower packed with iron borings and is thus held in the form of ferrous bromide, from which the bromine can be recovered in a marketable form (potassium bromide) by double decomposition with potassium carbonate. The crude bromine contains chloride of bromine, and generally lead bromide and hydrocarbons, the latter being derived from tar joints. It is shaken with potassium bromide, to decompose bromine chloride, and distilled in glass retorts. Bromine is chiefly used for the production of bromeosins (q.v.) and for the manufacture of bromides. On account of the difficulty of transporting liquid bromine it is sometimes absorbed in kieselguhr, the product being termed " solidified bromine." Potassium bromide, KBr, is prepared by acting on iron with bromine to form an iron bromide, which is then run into a hot solution of potassium carbonate, whereby an oxide of iron is precipitated and C0 2 liberated, while potassium bromide remains in solution and is crystallised. It is used as a sedative and for making silver bromide on photographic plates. Iodine is a characteristic constituent of seaweed, but its production from the ash of such plants (kelp) is now much diminished by the competition caused by the preparation of iodine as a bye-product in the manufacture of nitrate of soda (p. 112). The method of isolating iodine from the mother liquor of the crystallisation of caliche (p. 112) is as follows :-— The mother liquor contains about 0*5 per cent, of iodine, chiefly as sodium iodate *A Lunge plate column (see Vitriol Making, Vol. II., p. 8) would probably be effective. 432 MINOR CHEMICAL MANUFACTURES. (NaI0 8 ).* It is run into wooden vats coated with pitch, and treated with the calculated quantity of a solution prepared by passing S0 2 into sodium carbonate solution until there has been formed a sulphite of sufficiently acid structure to ensure the saturation of the whole of the soda of the iodate with S0. 2 . An agitator is provided in order that the liquids may be thoroughly mixed, whereupon the iodine separates according to the equa- tions — (1) 2NaI0 3 + 2NaHS0 3 = 2Na 2 S0 3 + 2H10 3 . (2) 2HI0 3 + 5Na 2 S0 3 = 5Na 2 S0 4 + I, + H 2 0. The sparing solubility of iodine in water allows of its direct recovery by subsidence ; the iodine which remains in solution is fixed by the addition of a small quantity of sodium bisulphite and sodium carbonate, and the liquor is returned to the boiler in which the caliche is first extracted. The crude iodine is filter- pressed, when it contains about 80 per cent. I, 10 per cent, of water and 10 per cent, fixed matter. It is generally refined by sublimation in iron retorts with stoneware condensers, and comes into the market containing 98 per cent. I. The applications of iodine are not sufficiently numerous to create a demand commensurate with the supply, on which account its price is a conventional one. Iodine is used for the preparation of iodeosins (q.v.) and other synthetic dyestuffs, as well as in medicine and in making iodides, which are also used in medicine and in photography. Potassium iodide, KI, is made, like the bromide, by taking advantage of the direct combination of iodine with iron. The •compound formed appears to be Fe 3 I 8 , which is a better com- pound for the purpose than Fel. 2 , since the iron is more readily ■separated than from the ferrous salt by double decomposition with an alkali carbonate. IV. CYANOGEN COMPOUNDS.— The heat of formation of cyanogen is C 2 ,N 2 — - 65*7 Cal., from which it may be antici- pated that direct union of C and N can only be effected at a high temperature. Since the compound has acidic properties, the presence of a metal capable of forming a powerful base — e.g., K or Ba — favours the production of cyanogen from its -constituents. It is thus possible to produce a cyanide at a temperature below that essential for the formation of free cyano- gen. This circumstance is taken advantage of in a process which has been worked experimentally on a large scale and consists in heating a mixture of barium carbonate with carbon, in the form of pitch, in a fireclay retort through which nitrogen is passed, while the temperature is kept at about 1,400° C. * Highly oxidised substances are characteristic of Chili saltpetre ; thus, in addition to nitrate, iodate and chromate, perchlorate has lately been recognised. CYANOGEN COMPOUNDS. 433 = 2,552° F. by' a producer-gas furnace. Since barium cyanide is acted on by CO., at high temperatures, the nitrogen used must be free from this gas, and may be conveniently obtained as the waste gases from the carbonating towers of the ammonia-soda process (q.v.). The use of ammonia as a source of nitrogen for preparing cyanides has not hitherto proved feasible. Another method of some promise consists in removing the sulphur of a thiocyauate — e.g., NaOyS (v.i.) — by means of zinc or other metal combining readily with S. A fairly cheap source of nitrogen for the formation of cyanides, and one which has the advantage of being already in union with carbon, is waste animal matter — e.g., leather cuttings, blood and the like. When such material is heated with potassium carbonate and iron borings, a cyanogen compound is formed. The potassium carbonate and iron are heated in a cast-iron pan set on the hearth of a reverberatory furnace, the organic matter* being introduced after the fusion of the mass. Oxidation should be prevented by maintaining a reducing atmosphere. The "metal" thus produced is lixiviated with boiling water, and the crude liquor is evaporated until potas- sium ferrocyanide (yellow prussiate of potash), K 4 FeCy 6 . 3H 2 0, crystallises out. The mother liquor is evaporated to dryness and returned to the process, and the crude prussiate is recrystal- lised. The carbonaceous matter left after extraction is used for decolorising paraffin wax and vaseline. The reactions which prevail during this process are somewhat obscure. It appears that sulphur is necessary for their occurrence, and is present in the organic matter and the crude potash used. The potash reacts with the carbon and nitrogen of the organic matter, yield- ing KCN, which in its turn acts on iron compounds, notably FeS, formed in the melt, according to the equation — 6KCy + FeS = K 2 S + K 4 FeCy 6 . The products of the destructive distillation of coal contain cyanogen, which, therefore, forms a bye-product of gas manufac- ture. On the Continent, purification of gas by hydrated ferric oxide is chiefly practised, and the cyanogen is thus fixed, chiefly as Prussian blue (ferrocyanide of iron), while a portion exists as ammonium thiocyanate. The iron oxide mass is worked up as follows : — It is systematically extracted with warm water, and the ammonium thiocyanate recovered by crystallisation. The extracted residue is dried, mixed with caustic lime, and heated in closed vessels by means of steam, calcium ferrocyanide being formed. This salt is extracted with water and treated with KC1 in the boiling solution, whereby the double salt CaK 2 FeCy ( > is precipitated. This is heated with a solution of K 2 C0 3 , when CaCOo and K 4 FeCy G are formed ; the dilute liquors are boiled * This is usually previously charred. 28 434 MINOR CHEMICAL MANUFACTURES. down in a vacuum pan, and crystallised prussiate, K 4 FeCy c .3H 2 0, is obtained. Potassium ferrocyanide is chiefly used for the preparation of potassium cyanide (v.i.), Prussian blue, and potassium ferri- cyanide, K 3 FeCy 6 . Potassium ferricyanide (red prussiate of potash), K 3 FeCy c , is made by removing an atom of potassium from the ferrocyanide by means of an oxidising agent, thus — K 4 FeCy G + CI = KC1 + K 3 FeCy c ; bromine and lead peroxide can also be used. This salt is used in dyeing and calico-printing, chiefly as an oxidant, and in photography. Potassium cyanide, KCN, is generally obtained from the ferro- cyanide, though much is now prepared from the sulphocyanide. When K 4 FeCy G is dehydrated and fused, it is decomposed according to the equation, K 4 FeCy 6 = 4KCy + Fe + C 2 + N 2 . Much cyanogen is thus lost, and a more economical process consists in the addition of potassium carbonate, when the reaction takes place thus — K 4 FeCy 6 + K 2 C0 3 = 5KCy + KCyO + Fe + CO., In this case the product is a mixture of cyanide and cyanate. Since this latter is of small commercial value, attempts are made to suppress it by the introduction of charcoal into the fusion, KCNO + C - KCN + CO. The fused mass is allowed to settle, and the clear melt poured off. Potassium cyanide is chiefly used as a solvent for gold in extracting that metal from ores which contain it in a sufficiently finely-divided condition ; as a solvent for gold and silver in electroplating and gilding baths.* Potassium sulphocyanide or thiocyanate, KCSN, is prepared from the ammonium salt as a raw material, which is obtained as a bye-product in gas manufacture. The insolubility of cuprous thiocyanate is sometimes taken advantage of in separating sulphocyanide from gas liquor. A method proposed for the preparation of sulphocyanides, analogous to that by which they are probably formed among the products of the distillation of coal, is that of allowing ammonia to react with CS 2 , according to the equation CS 2 + 4NH 3 - NH 4 CNS + (NH 4 ) 2 S. V. SOLVENTS. — For purposes where aqueous liquids cannot be employed as solvents, certain liquid compounds of carbon are pressed into service. An ideal solvent must be volatile without change at a moderate temperature, so as to be easily recoverable, * The modern product, said to be made by the process represented by the equation, K 4 FeCy G + Na 2 = 4KCy + 2NaCy + Fe, consists largely of sodium cyanide, and may, therefore, appear to contain more than 100 per cent, of KCy if the Cy alone be used as a basis of assay. 436 MINOR CHEMICAL MANUFACTURES. non-inflammable and non-poisonous. Few solvents fulfil all these conditions. Carbon Bisulphide, CS 2 . — This compound is an excellent solvent for fats and for sulphur, but is both inflammable and poisonous. It boils at 46*5° C. = 116° F., and inflames in air at about 150° C. = 302° F. ; not only is the vapour itself poisonous, but the products of combustion C0 2 and S0 2 are also noxious. CS 2 is an endothermic compound, its heat of formation being C,S 2 = - 26 Cal. On this account its production, by the direct union of its elements, can only be attained at a high tem- perature. The operation is generally conducted in a vertical cast-iron retort, A (Fig. 43), set in a furnace, D, and provided with a side inlet, N, through which molten sulphur is allowed to flow from the vessel O. Charcoal, preferably prepared from waste wood, spent dye wood and the like, is filled into the retort and brought to a cherry red heat before the introduction of the sulphur. The CS 2 formed escapes by the pipe I, which slopes upwards to permit uncombined sulphur to condense and flow back down the pipe K, to the bottom of the retort. Any sulphur which is carried on is caught in the vessel P, whilst CS 2 passes down a long Liebig's condenser, Q, where it is chilled by the water- jacket and is caught in the receiver S. The closed vessel U is employed for forcing the condensed CS 9 , by means of compressed air, into a storage tank. Residual vapours are caught in the apparatus W, being scrubbed out with oil dribbling over a series of trays ; on heating the oil, collected in Y, in a retort, the CS. 2 can be recovered and the oil used again. Permanent gases, such as H 2 S, are suppressed by passage through the lime and iron oxide purifier Z. The crude CS 2 is purified by agitation with lime water, and distillation with a small quantity of any fixed oil and a little lead acetate, the object being to retain objectionable sulphur com- pounds. The process of purification is completed by rectifica- tion. Commercial CS 2 has a nauseous odour, but the pure substance has an ethereal smell. Its specific gravity is 1*29. An apparatus fitted for the obtainment or recovery of oils from seeds and waste products has been shown at p. 230. The solvent is also used in vulcanising caoutchouc (q.v.). Carbon Tetrachloride, CC1 4 . — This liquid is in some ways pre- ferable to CS 2 , as it is uninflammable, less poisonous and has a higher boiling point, 77° C. = 171° F. Its specific gravity is 1-63. It is at present prepared from CS 2 , and is, therefore, more costly than that solvent. It may be obtained by passing a mixture of CS 2 vapour and chlorine through a red-hot tube ; or by the action of chlorine on CS 2 at the ordinary temperature, in the presence of iodine or of CARBON BISULPHIDE. 437 antimony pentachloride. Sulphur chloride, SC1 2 , is a product of the reaction, and remains dissolved in the CC1 4 , from which it is removed by treatment with lime. Commercial CC1 4 constantly contains CS 2 , from incomplete conversion. Other solvents, such as benzene, benzine (benzo- line), other forms of light petroleum and alcohol have already received notice. 438 BIBLIOGRAPHY. MATERIALS OF CONSTRUCTION. Redgrave (G. R.) Calcareous Cements. London. Thurston (R. H.) Materials of Engineering. New York. Thurston (R. H.) Text-book of the Materials of Construction. New- York. Unwin (W. C.) Testing of Materials of Construction. London. Journal of the Iron and Steel Institute. Minutes of the Proceedings of the Institution of Civil Engineers. SOURCES OF ENERGY AND STEAM RAISING. Borehers (W.) Elektro-Metallurgie. Braunschweig. English Transla- tion by W. G. M'Millan. London. Butterfield (W. J. A.) Gas Manufacture. London. Donkin (B.) Gas, Oil, and Air Engines. London. Gore (G.) The Electrolytic Separation of Metals. London. Fischer (F.) Die Chemische Technologie des Wassers. Braunschweig. Jamieson (A. ) Text-book on Steam and Steam Engines. Eleventh edition. Mills (E. J.) and Rowan (J.) Fuel and its Applications. London. Ostwald (W. ) Elektrochemie. Leipzig. Rankine (W. J. M.) A Manual of the Steam Engine and Other Prime Movers. London. Thirteenth Edition. Schoop (P.) Die Secundar-Elemente. Halle. Schwackhofer (F.) and Browne (W. R.) Fuel and Water. London. Thorpe (T. E.) Dictionary of Applied Chemistry. Art. "Fuel." London. 'The Electrician. LUBRICATION. Allen (A. H.) Commercial Organic Analysis. Vol. ii. London. Redwood (B.) and Holloway (G. T.) Petroleum. London. Thurston (R. H. ) Treatise on Friction and Lost Work in Machinery and Mill work. New York. Thurston (R. H.) Friction and Lubrication. New York. BIBLIOGRAPHY. 439 METALLURGY. Bloxam (C. L. ) and Huntingdon (A. K.) Metals. London. Borchers (W. ) Elektro-Metallurgie. Braunschweig. English Transla- tion under the title of "Electric Smelting and Refining," by W. G. M'Millan. London. Eissler (M.) The Metallurgy off Gold. London. Eissler (M.) The Metallurgy of Silver. London. Fischer (F.) Chemische Technolofie. Section "Metallurgie." Gore (G.) The Art of Electrometallurgy. London. Howe (H. ) The Metallurgy of Steel. New York. M'Millan (W. G. ) Electro-Metallurgy. London. Percy (J. ) Metallurgy. London. Phillips (J. A.) and Bauerman (H.) Elements of Metallurgy. London. Roberts-Austen (W. C.) An Introduction to the Study of Metallurgy. London. Third Edition. Rose (T. K.) The Metallurgy of Gold. London. Second Edition. Turner (T.) The Metallurgy of Iron. London. "Williams (M.) The Chemistry of Iron and Steel Making. London. SULPHURIC ACID MANUFACTURE. Lunge (G.) Sulphuric Acid and Alkali. Vol. i. London. Thorpe (T. E.). Dictionary of Applied Chemistry. Art. "Sulphuric Acid." London. ALKALI AND ITS BYE-PRODUCTS. Lunge (G.) Sulphuric Acid and Alkali. Vols. ii. and iii. London. DESTRUCTIVE DISTILLATION. Butterfield (W. J. A.) Gas Manufacture. London. Lunge (G.) Distillation of Coal Tar and Ammonia. London. Mills (E. J.) Destructive Distillation. London. Mills (E. J.) and Rowan (J.) Fuel and its Applications. London. The Journal of Gas Lighting. ARTIFICIAL MANURE MANUFACTURE. Spoil's Encyclopaedia of the Industrial Arts. Art. "Manure." London. Thorpe (T. E.) Dictionary of Applied Chemistry. Art. "Manures, Artificial." London. PETROLEUM. Redwood (B.) and Holloway (G. T.) Petroleum. London. LIME AND CEMENTS; CLAY INDUSTRIES AND GLASS. Benrath (H. E.) Die Glasfabrication. Braunschweig. Chatelier (H. Le). Recherches Experimentales sur la constitution des mortiers hydraulicpies. 440 BIBLIOGRAPHY. Church (A. H.) Pottery and Porcelain. London. Fischer (F.) Chemische Technologie. Section " Thonindustrie." Redgrave (G. R.) Calcareous Cements. London. Shenstone (W. A.) Chemical Glass Blowing. London. Thonindustrie Zeitung. Verein deutscher Portland- cement. Fabrikation der Portland-cement. Berlin. SUGAR AND STARCH. Birnbaum (K.) Die Fabrikation der Starke. Braunschweig. Lock (C. G. W.) and Newlands Bros. Sugar. London. Lock (C. G. W.), Wigner (G. W.), and Harland (R. H.) Sugar Growing and Refining. London. Thorpe (T. E.) Dictionary of Applied Chemistry. Arts. "Sugar" and "Starch." London. BREWING AND DISTILLING. Jorgensen (A.) Micro-organisms and Fermentation. London. Maercker (M.) Handbuch der Spiritusfabrikation. Moritz (E. R.) and Morris (G. H.) A Text-book of the Science of Brewing. London. Otto (F. J.) Die Bierbrauerei, Branntweinbrennerei und Liqueurfabrika- tion. Braunschweig. Thorpe (T. E.) Dictionary of Applied Chemistry. Art. "Brewing." London. OILS, RESINS, AND VARNISHES; SOAP AND CANDLES. Allen (A. H.) Commercial Organic Analysis. Vol. ii. London. Benedikt (R.) and Lewkowitsch (J.) Oils, Fats, and Waxes. London. Cameron (J.) Oils and Varnishes. London. Carpenter (W. L.) and Leask (H.) A Treatise on the Manufacture of Soap, Candles, Lubricants, and Glycerine. London. Groves (C. E.) and Thorp (W.) Chemical Technology. Vol. ii. London. Schaedler (C.) Die Untersuchungen der Fette, Oele, Wachsarten und der technischen Fettproducte. Leipzig. Wright (Alder). Fixed Oils, Fats, Butters, and Waxes. London. TEXTILES AND BLEACHING; COLOURING MATTERS, DYEING AND PRINTING. Duerr (Geo. ) Bleaching and Calico- Printing. London. Gardner (J.) Bleaching, Dyeing, and Calico-Printing. London. Hummel (J. J.) The Dyeing of Textile Fabrics. London. Knecht (E.) and Benedikt (R.) The Chemistry of the Coal-tar Colours. London. Knecht (E.), Rawson (C), and Loewenthal (R.) A Manual of Dyeing. London. Nietzki (R. ) The Chemistry of Organic Dyestuffs. London. BIBLIOGRAPHY. 441 Schultz (G.) and Julius (P.) Systematic Summary of Organic Colouring Matters. London. "Witt (D. N.) Chemische Technologie der Gespinnstfasern. PAPER AND PASTEBOARD. Cross (C. E. ) and Bevan (E. J. ) A Text-Book of Paper Making. London. PIGMENTS AND PAINTS. Church (A. H.) The Chemistry of Paints and Painting. London. Hurst (G.H.) Painters' Colours, Oils, and Varnishes. London. Second Edition. LEATHER, GLUE, AND SIZE. Davis (C.T.) Leather Manufacture. Philadelphia. Dawidowsky (F. ) A Practical Treatise on the Fabrication of Glue. Philadelphia. Heinzerling (C. ) Grundziige der Lederbereitung. Braunschweig. Knapp (F.) Natur und Wesenheit der Gerberei des Leders. Miinchen. Procter (H. R.) A Text-Book of Tanning. London. Trimble (H. ) The Tannins. Philadelphia. EXPLOSIVES AND MATCHES. Guttman(0.) Manufacture of Explosives. London. Thorpe (T. E.) Dictionary of Applied Chemistry. Art. "Matches/'" London. GENERAL REFERENCES. Fischer's Chemische Technologie. Groves and. Thorp's Chemical Technology. London. Spoil's Encyclopaedia of Industrial Arts and Manufactures. London. Thorpe's Dictionary of Applied Chemistry. London. Journal of the Society of Chemical Industry. London. Dingler's Polylcclnische Journal. Stuttgart. 442 INDEX. A Abel's test of flashing point of oils, 121. Abies canadensis, 378, Abietic acid, 242 ; anhydride, 242. Absinthe, 215. Absolute alcohol, 217; strength O.P., 218. Absorbents for nitro-glycerin, 40G. Absorption of gases by charcoal, 92 ; tannin by hides, 395. Acacia catechu, 378. Acer saccharimim, 177. Acetanilide, Preparation of , 316. Acetate, aluminium, Preparation of, 360. Acetate, Amyl, 2! 7; Basic copper, 359 ; of lime, Brown, 95 ; of lime, Grey, 93, 95. Acetic acid, 219 ; Application of, in cotton printing, 340 ; Factitious vinegar from, 222 ; Ferment, 219 ; from spent lye in esparto boiling, 345 ; Percentage of, in vinegar, 221 ; used in bleaching, 267 ; in dyeing, 232 ; Yield of, by distilla- tion of wood, 95. Acetic fermentation, 219 ; Succinic acid produced in, 219. Acetification, 219 ; Conditions of, 221. Aceto-arsenite of copper, 359. Acetone, 94. Acetylene, Action of, on copper, 74 ; Enriching gas by, 74 ; from cal- cium carbide, Yield of, 74 ; Heat of formation of, 74 ; Illuminating value of, 74 ; Liquid, 74 ; Specific gravity of, 74. Acid colours, Dyeing cotton with, 334 ; Dyeing silk with, 339. Acid, "drips" in vitriol chambers, 14; dyes, 330; dyes classified, 336; egg, 8 ; for etching on glass, 160, 413 ; green, 336 ; in tan liquors, 379; magenta, 288, 336; mordants, 331 ; oxalates of potassium, 417 ; "tar," 78. Acids, fatty, Formula} of, 223 ; Melt- ing point of, 223 ; volatile, with steam, 227. Acids, Iso-linolenic series of, 226 : Lin oleic series of, 226 ; Linolenic series of, 226 ; Oleic series of, 226, 228 ; Ricinoleic series of, 226. Acorn galls, 374. Acridine dyestuffs, 318 ; orange, 319. Acrolein, 224, 234 ; from smoulder- ing candles, 251. Acrospire, 191. Adjective dyes, 270 ; dyestuffs de- lined, 270. Aerobic ferments, 190. " After-chroming," 338. " Ageing," 330. " Ageing" of logwood, 324. Air and gas, Explosive mixture of, 70. Air condensers for gas making, 62. Air-gas flame, 70. Air-slaked lime, 130. Albite, 141. Albocarbon light, 73. Albumin, Application of, in calico- printing, 341. Alcohol, 215 (see also Spirit); Abso- lute, 217; Absolute, strength O. P., 218 ; Boiling point of, 218 ; Dena- turing, 218 ; denaturing, Wood naphtha for, 218 ; Oil soluble in, 235; Oxidation of, 219; Specific gravity of, 218. Alcoholic strength, Excise system of, 218. Alcoholometry, 218. INDEX. 443 Alcohols, Higher, 217. Aldehyde, 219. Aldehydes, Aromatic, 240. Ale, Mild, 205 ; Pot, 211 ; vinegar, 221. Algarobilla, 37S. Alizarate, Sodium, 2S1. Alizarates, 281. Alizarin, 296, 334; Artificial, 280; black, 279, 280 ; blue S. (soluble), 282; Bordeaux, 282; colours, Application of, 338 ; cyanine, 282; Manufacture of, 281 ; paste, 281 ; yellow, 338 ; yellows, 337. Alkali, Action of, on wool, 271 ; Act, Regulation of vitriol making, 15 ; blue, 290 ; blues, Application of, 388 ; Electrolytic preparation of, 51; for glass, 151 ; lime glass, Analysis of, 157 ; manufacture, Limestone for, 21 ; Nitrogen in coal for, 22 ; Raw materials for, 19 ; Recovery of, in paper making, 345 ; Refined, 29 ; Small coal for, 22; trade standards, 31. Alkali waste, Analysis of, 32 ; Mac- tear process for, 34 ; Parnell & Simpson's process for, 33 ; Sulphur recovery from, 32 ; Treatment of, 32; Use of, in phosphate manu- facture, 109. Alkaline carbonates, Saponification with, 247 ; water, Effect of, in brewing, 199. Alkalinity, Indicator for, 275. Almond cake, 214. „ oil, 226, 231. Almonds, Artificial oil of bitter, 241 ; Oil of bitter, 231, 241 ; Synthesis of oil of bitter, 241. Alphanaphthylamine, Claret colour from, 335. Alum, 424 ; Ammonia, 426 ; Basic, 425 ; Burnt, 426 ; cake, 425 ; Chrome, 426 ; Manufacture of, from clay, 425 ; Preparation of, 425 ; stone, Analysis of, 424 ; Tanning with, 390. Aluminium acetate, Preparation of, 360 ; Use of, in dyeing, 330. Aluminium mordants, 330. resinate as a size for paper, 344. ,, shavings for filtering beer, 204. sulphate, 424, 425 ; Use of, for sugar recovery, 176 ; Use of, in dye- ing, 330. Aluminium sulphocyanide as a mor- dant, 341. ,, thiocyanate, Use of, in dyeing, 330. Alunite, 424. Amido-acetophenone, 316. iVmido-azobenzene, Formula for, 273 ; Preparation of, 314. Amido-azobenzene dyestuffs, Forma- tion of, 274 ; naphthalene, 301. Amidotolunaphthazine, 29i. Ammonia alum, 426. ,, crude, Composition of, 47. ,, Fixed, 47; in gas liquor, 75. , , Free, 47 ; in gas liquor, 75. ,, from bone distillation, 105; in coal gas, 68 ; in London gas, Statutory limit for, 74 ; in soot, 112. ,, Production of, 47; Re- covery of, 47. , , soda ash, Apparent density of, 47. ,, soda process, 43 ; Carbon dioxide in exit gas from, 46 ; Reactions in, 43 ; Recovery of chlorine in, 49; Salt wasted in, 46. "still," 47. ,, Yield of, from gas coals, 75 ; from Simon-Carves oven, 87. Ammoniacal liquor from shale dis- tillation, 102. Ammoniacal liquor, Valuation of, 76 ; Yield of, from coal, 66. Ammonium chromate, 359. ,, orthosulphamidobenzo- ate, 420. ,, sulphate, as manure, 112; commercial, Im- purities in, 112; Manu- facture of, 76. Amygdalin, 241. Amyl acetate, 217. „ alcohol, 211 ; Active, 217 ; Inactive, 217. Amylan, 192. Anaerobic ferments, 190. Analyser, 212. Analysis of alkali waste, 32 ; alum stone, 424 ; animal charcoal, 104 ; ash of yeast, 201 ; barley, 192 ; basic slag, 110; beet molasses, 173 ; black ash, 27 ; bone, 103 ; brass, 205 ; brick clay, 145 ; brine, 20 ; 444 INDEX. Brunswick green, 358 ; caustic liquor, 31 ; cement clinker, 139 ; cement slurry, 138 ; chalks, 127 ; charbon roux, 92 ; charcoal for gunpowder, 401 ; coal gas, 69 ; cochineal carmine, 365 ; cognac, 210; coke, 83 ; commercial sodium nitrate, 113 ; cotton fibre, 260 ; crude nitrate of soda, 112 ; diastase, 193; distillers' grains, 210; extracts for tanning, 381 ; fire clay, 145 ; flax, 261 ; fortified wines, 208 ; fusel oil, 217 ; gas liquor, 75 ; glass, 157; grape juice, 205; grey chalk, 127 ; hemp, 261 ; hides, 370 ; hydraulic limestone, 126 ; jute, 262 ; leather, 392 ; limestone, 126 ; magnesian limestone, 126 ; malt, 192 ; materials for Portland cement, 13S; molasses, 164 ; native phosphates, 108 ; natural gas, 118; osseine, 105; Oxford ochre, 364; phosphatic gypsum, 409; Portland cement, 138 ; products of cane sugar fermentation, 201 ; puzzuolana, 140; raw silk, 259; rock salt. 19 ; Roman cement, 133 ; smalt, 3.17 ; soda ash, 29 ; sole leather, 392 ; spent beet, 1 67 ; spirit, 216 ; starch-yielding materials, 183; sublimed white lead, 352 ; sugar cane juice, 163 ; tank liquor, 28 ; tanning materials, 379; tanstuffs, 379 ; treacle, 164 ; ultramarine, 356 ; water for brewing, 195 ; white chalk, 127 ; wines, 207 ; wood gas, 95 ; wool fibre, 25S ; wort, 98 ; yea^t, 200. Angelica root, 214. Anhydrite, 426. Anhydro - orthosulphamidobenzoic acid, 420 ; sulphuric acid, IS. Anilidophenylnaphthinduline, 315. Aniline black, 311 ; Dyeing with, 311; "Greening" of, 312 ; Print- ing with, 311. Aniline blues, 290. ,, colours, 287. Dimethyl, 289. dyes, 284. dyestuffs, blue, 289. ,, for blue, 286 ; for blue, Application of, 290 ; for red, 286. ,, hydrochloride, 2S6. ,, Manufacture of, 285. Methylation of, 289. oil, 286. salt, 286. Aniline violet, 2S9. Animal charcoal (see Charcoal, Animal). ,, fibres, distinguished from vegetable fibres, 259. oil, 104. ,, oils, Winning and refining of, 229. Anisidine, 335. Annaline as a loading material, 344. Annealing glass, 156. Antheraea mylitta, 259. Anthracene, Boiling point of, 82 ; brown, 338 ; Conversion of, into anthraquinone, 280 ; from Russian petroleum, 123 ; green, 296 ; Melt- ing point of, 82 ; oil, 81 ; Orienta- tion of, 279 ; Purification of, 82, 280 ; " Thirty per cent.," 82. Anthraquinone, Conversion of, into alizarin, 281 ; Formula for, 279^ Manufacture of, 280 ; Purifica- tion of, 281 ; Sulphonation of , 281; sulphonic acids, 281. Antimoniate, Lead, 361. Antimony fluoride, Use of, in dye- ing, 332. Antimony, Golden sulphide of, 244 ; lactate, 408 ; potass um oxalate, 417 ; potassium oxalate, Use of, in dyeing, 332 ; salts, Use of, in dyeing, 332 ; vermilion, 363. Antiseptic, Hydrofluoric acid as an, 413. Antiseptics, Effect of, on diastase^ 193 ; for beer, 204 ; for vines, 206. Apatite, 106. A/>ocynacea>, 243. Aposafranine, 313. Aqua fortis, 11. Arachidate, Glyceryl, 231. Arachidic acid, 223. Arachis hypogaa, 231. Arachis oil, 231. Archil, Preparation of, 327. Argand burner, 70. Argol, 207, 418. Armstrong's theory of colour, 278. Aromatic aldehydes, 240. Arrowroot starch, 183, 187. Arsenate of soda, Application of, in calico-printing, 341. " Arsenic," 415. Arsenic acid, 415 ; as an oxidant, 287 ; Manufacture of, from white arsenic, 416 ; Uses of, 416. Arsenic glass, 416. ,, in sulphuric acid, 16. „ kips, 372. INDEX. 445 Arsenic, Recovery of, 287 ; Red, 3S3 ; soot, 415. Arsenic sulphide, 361; as a depilatory, 383. Arsenic, Vitreous, 41G. Arsenic, White, 415 ; for curing hides, 37 2 ; Purification of, 416; Uses of, 41d. Arsenic, Yellow, 383. Arsenious acid, 415 ; anhydride, 415. Arsenite, Cupric, 359. Artocarpacete, 243. Asbestos, 262 ; fabrics, Effect of heat on, 263. Ascension pipe, 62. Ascospores, 200. Ash of yeast, Analysis of, 201. Asparagine in beet juice, 165. " Asphalt," 82. Asphalt cement, 125. ,, mastic, 125. rock, 125. ,, substitute, 253. Asphaltum, 124 ; Trinidad, 124. Assimilation of nitrogenfrom air, 114; of phosphate manures, Hate of, 111. Astatki as fuel, 122. Astralene, 122. Attemperators, 199. " Attenuation " of wort, 199. Auramine, 309, 334. Aurantia, 273, 336. Aureolin, 361. Aurine, 292 ; dyestuffs, 291. Autoclave, 253. Auxochrome, 273. "Available oxygen" in manganese, 35. Aventurin, 158 ; Chrome, 159. Axle grease, 236. Azine compounds, 297. ,, Diphenylene, 297. Azo-benzene, Formula for, 273 ; diazo-chloride, Formation of, 276. Azo-blue, 333. Azo-colours converted into mordant dyestuffs, 337. Azo - compounds (dyestuffs), 273; explained, 275. Azo-diphenyl blue, 314. Azo-dyes, Bleaching of, 278 ; dye- stuffs, Application of, 337. Azonium bases, 299. Azophenine, 315. Azophor red P N, 335. B Bacillus viscosus, 204. Backs, 134. Bacteria, 1S9 ; in yeast, 202. Bacterium aceti, 219. Bagasse, 163. Ball clay, 149. Ball mill, 111. Balsam, Peru, 2^2. Balsams, 240, 242. Baltic linseed oil, 234. Barium chloride, 430. ,, chromate, 361. ,, nitrate in explosives, 405. ,, salts, 430. ,, sulphate, 353. ,, ,, asaloadingmaterial, 344. Bark, Oak, 376 ; Hemlock, 378. Barkometer degrees, 388. Barley, Analysis of, 11*2 ; Carbohy- drates of, 192 ; couch, 190 ; Drying malted, 191; Flooring, 190; "Meali- ness "of malted, 191; Necessity for drying malted, 191 ; Proximate composition of, 192 ; Steeping, 190; Unsound, as fodder, 190. Barley for brewing, Character of, 192; for malting, 192; for malt- ing, Character of, 190. Barwood, 325. Baryta used for sugar recovery, 176. Barytes, 353 ; in white lead, 352. Base, Primuline, 277. Basic alum, 425. Basic colouis, Dyeing cotton with, 334; Dyeing silk with, 338; Examples of, 334 ; "Topping" with, 334. Basic copper acetate, 359. ,, ,, carbonates, 360. ,, dyes, 330. ,, dyestuffs, Bottoms for, 332. ,, lead acetate, 350. ,, ,, carbonate, 349. ,, ,, chloride, 351 ,, ,, chromate, 361. ,, ,, chromate, Dyeing with, 328. ,, mordants, 330. ,, slag, 110 (see also Slag, Basic). Bassorah galls, 374. Bast fibres, 260, 262. Bate, 384 ; substitutes, 385. Bating skins, 384. Batswing burner, 70. Battery of cells for sugar diffusion process, 166. "Bay salt," 20. Bazils, 3s 9. Beale's rotatory exhauster, 62. Beard of valonia, 377. Beckton coal tar, Composition of, 77. 446 INDEX. Beech shavings for clarifying wine, '220 ; for vinegar process, 220. Beef tallow, 228, 236. Beehive coke oven, 84. Beer, Aluminium shavings for filter- ing, 204 ; Antiseptics for, 204 ; Bitter, 205 ; Caramel for colour- ing, 182 ; Cleansing system, 203 ; Colouring, 204 ; defined, 190 ; Diseases of, 204 ; Finings for, 204 ; Finishing, 204 ; Lager, 200 ; Liquid carbon dioxide for preserv- ing, 204 ; Pilsener lager, 205 ; Priming, 204 ; Racking, 204 ; Raw materials for, 1 90 ; Ropy fermen- tation of, 204 ; Sour, 204 ; " Stench of," 194. Beeswax, 239 ; Adulterations of, 239; Bleaching of, 239. Beet, Analysis of spent, 167 ; Com- position of juice of, 165 ; Concen- tration of juice of, 167 ; Defecation of juice of, 167 ; Fusel oil from, 217 ; Yield of juice from, 165 ; Yield of sugar from, 172. Beet juice, 165 ; Purification of, by lime, 167 ; Trimethylamine from, 165. Beet molasses, 172 ; Analysis of, 173; Utilisation of, 173, 176. Beet sugar (see Sugar, B^ct). Beilby & Young retort, 97, 99. Bengal ordinary saltpetre, 400. Benzal chloride, 241. Benzaldehyde, 231, 241: green, 291. Benzene, Roiling point of, 79; Enrich- ing gas by, 73 ; Induline, 312 ; Melting point of, 79 ; Nitration of, 284. Benzeneazobenzeneazophenol, For- mation of, 276 ; Formula for, 276. Benzeneazobenzeneazo - (i - naphthol sodium disulphonate, 276. Benzeneazo - /3 - naphthol sulphonic acid, Formula for, 275. Benzeneazophenol, Formation of, 274; Formula for, 274. Benzidine, 277 ; dyestuffs, 277. Benzine from petroleum, 120 ; from shale, 101. Benzoazurin, 333. Benzochrome black, 333. Benzoflavine, 319, 334. Benzoic acid, 242, 419 ; Application of, 290. Benzoin, Gum, 242 ; Styrax, 242. Benzol, "Fifty per cent.," 79; Fractionation of crude, 78; from Russian petroleum, 123 ; "Ninety per cent.," 79; still, Dephlegmator for, 78. Benzolene, 101. Benzopurpurin, 333. Berlin porcelain, 147. Betaine in beet juice, 165. Beta vulgaris, 163. Bicarbonate of soda, 30; Conversion of, into soda ash, 46. Bichromate, Chrome-alum converted into, 280 ; Sodium, 421 ; Potas- sium, 421 ; Preparation of, by electrolysis, 422. Bichromates, 420; as mordants, 331; Recovery of, 280. Biebrich scarlet, 276. Bird lime, 239. Bi-rotation, 181. "Biscuit firing," 146. ,, porcelain, 149. Bistre, 328. Bismarck brown, 275, 334. Bisulphide of carbon, 436 (.see Carbon bisulphide). Bisulphite, Calcium, 6 ; for making wood pulp, 347. Bisulphite compounds (dyestuffs) ,279. ,, Magnesium, for making wood pulp, 347. ,, Sodium, 6. Bisulphites, as antiseptics for beer, 204 ; Manufacture of, 6, 347. Bitartrate of potash, 418 ; Use of, in dyeing, 330. Bitter almonds, Oil of, 231 , 241 ; Arti- ficial, 24! ; Synthesis of oil of, 241. Bitter beer, 205. ,, principles for brewing, 194. Bittern, 21. Black ash, Analysis of, 27 ; furnace, 25; Lixiviation of, 27; Manufac- ture of, 25 ; process, Reactions in, 25, 26 ; revolver, 26. Black beer, Water for, 195. ,, liquor, 95. ,, pigments, 364. ,, salt, 29. ,, sulphur, 355. ,, "tar," 101. ,, vitriol, 424. Blacks, Diazo, 333. "Bladder lard," 237. Blanc fixe, 365 ; as a loading material, 344. Blast furnace slag for cement, 140. Blasting gelatine, 407 (see Gelatine, Blasting). Bleach, 51 ; Electrolytic, Prepara- tion of, 51. INDEX. 447 Bleaching, 263 ; by bleaching powder, 266 ; by chloride of lime, 266 ; by hydrogen peroxide, 264, 265 ; by oxidation, 264 ; by potassium per- manganate, 267 ; by reduction, 264 ; by sodium peroxide, 265 ; by sulphites, 264 ; by sulphur dioxide, 264 ; Electrolytic, 267. Bleaching powder, chambers, 41 ; Manufacture of, 34 ; Production of, 40. Blende, Sulphur dioxide from, 5. Blind roasters, 23. Block gambier, 378. ,, kieserite, 427. ,, printing, 340. Blood albumin, Application of, in calico-printing, 341. Blood, Defecation of sugar by, 178 ; Dried, as manure, 113. Bloom deposited by tannins. 376. Blown oils, 234. ,, rape oil, 234. Blubber of whale, 238. Blue, Aniline, dyestuffs, 289. Blue bricks, 145. „ from anisidine, 335. lias limestone, 132 (see Lime- stone. „ oil, 101. ,, pigments, 354. ,, stone, 423. ,, sulphur, 355. ,, vitriol, 423. Blues, alkali, Application of, 338 ; Aniline, 290. Body of pigments, 348. Boiled-off liquor, 265 ; silk, 265. Boiled linseed oil, 234 (see also Linseed oil). ,, oil, 223. Boiling and mashing, Influence of water used for, in brewing, 199. "Bombonnes," 24. Bombyx mori, 259. Bone, Analysis of, 103. Bone-ash, 111; superphosphate from, 111. Bone black, 365. ,, charcoal, 104. distillation, Ammonia from, 105 ; Gas from, 105. ,, fat, 228 ; an adulterant of tallow, 237 ; Recovery of, 103. ,, flour, 111. ,, meal, 111. ,, oil, 104, 227 ; Specific gravity of, 105. Bones, Destructive distillation of, 103 ; Dissolved, 111 ; for manure, 111; Glue made from, 397 ; Nitrogen in, 111. Boracic acid (see Boric acid). Boracite, 426 ; Stassfurt, 414 ; Turk- ish, 414. Borate, Chromium, 359 ; glass, 160 ; Manganous, as a drier, 234. Borax, 415 ; Californian, 414 ; crude, Composition of, 415 ; Prismatic, 415 ; Octahedral, 415. Boric acid, 414 ; as a preservative, 414 ; Tuscany, 414 ; Uses of, 414 ; Winning of, 414. Boric anhydride, 414. Boronatro-calcite, 414. Bot marks, Prevention of, 372. Bottle nose oil, 228. "Bottom acid," 14. ,, fermentation, 200 (see also Fermentation). ,, yeast, 2i}'2. Bottoms for basic dyestuffs, 332. Bouquet of wine, 207, 208. Boutmy-Faucher method of nitrating glycerine, 405. " B. O. V.," 15. Bowk, Lime, 266. Bran drench, 385 ; Acids in, 386. Brandy, 209 ; Brown, 210 ; Colour of, 210; Grape, 209 ; Marc, Fusel oil from, 217 ; Yield of, from wine, 209. Brass, Analysis of, 205. JJra,ssica campestris, 232. Brazil wood, 325, 334; Colours pro- duced by, 325. Brazilein, 325. Brazilian yellow wood, 325. Brazilin, 325. Breaking flax, 261. hides, 382. " ,, the grain," 253. Breeze, Charcoal, 89. Bremen blue, 358. Bi ewers' grains, 197. Brewing and distilling, 189 ; Bitter principles for, 194 ; Boiling wort in, 197 ; Character of barley for, 192 ; Coolers used in, 198 ; Cooling wort in, 198 ; Effect of alkaline water in, 199 ; Effect of sodium chloride in water for, 199 ; In- fluence of water on mashing and boiling in, 199 ; Proportion of yeast used in, 199; Refrigerators used in, 198 ; Starches for, 193 ; Sugars for, 193 ; Water for, 194 : 448 INDEX. water for, Analysis of, 195; Waters rendered fit for, 1 95. Bricks, Blue, 145 ; Burning of, 145 ; clay for, Analysis of, 145 ; Colour of, 145 ; Fire, 145 ; Glazed, 145. Brilliant green, 334. ,, scarlet, 363. Brimstone, Roll, 2. Brine, Analysis of, 20 ; Boiling point of saturated, 20 ; Pumping, 19 ; Saturated, for ammonia soda pro- cess, 43. British gum, 187 ; Manufacture of, 1S8 ; Uses of, 188. Brix degrees, 169. "Broken baths," 339. Bromination, Method of, 295. Bromine absorption, 225. Bromine, Application of, 295 ; Ex- traction of, 431 ; Impurities in, 431 ; Purification of, 431 ; " Sol- idified," 431 ; Uses of, 431. Brown acetate of lime, 93, 95. ,, oil of vitriol, 15. ,, sugar of lead, 95. ,, vegetable colouring matters, 326. Broxburn shale, Yield of products from, 97. Brunswick black, 105. ,, green, 358. ,, ,, Analysis of, 358. Buff, Iron, 328. Buffs, 391. Burners, 70 ; Efficiency of different gas, 71 ; Illuminating effect of gas burnt in different, 70 ; Typical gas, 69. Burning naphtha, 79. ,, oil from petroleum refining, 121. Burton water, 1 95. Burtonising water, 195. Butane, 120. Butter, 237 ; Casein in, 237 ; Cocoa, 227 ; Composition of, 237 ; de- fined, 237 ; fat, 228 ; fat, Propor- ties of, 238 ; rancid, Butyric acid in, 237 ; substitute, 238. Buttery oils, 236. Butt of hides, 384. "Butts," 371. Butyl alcohol, 217. Butyric acid, 223; in rancid butter, 237. C Cadmium sulphide, 361. Cadmium yellow, 361. Caisalpinia, 325 ; brevifolia, 378 ; coriaria, 378. Cakes, Oil, 233. Calamus root, 214. Calcarone, 1. Calcium bisulphite, 6 ; for making wood pulp, 347. ,, carbide, 73. ,, carbonate, Dissociation of, 127 ; Heat of formation of, 127. ,, chlorate, 42. ,, chloride, Function of, in Weldon process, 38. ,, citrate, 419. ,, manganite, 37. ,, monosaccharate, 167. ,, oxalate, 417. ,, saccharate, 167. ,, sulphate, 131 ; as a loading material, 344. ,, tartrate, 418. thiosulphate. 363. Calcutta linseed oil, 234. Caledonian white lead, 353. Calendering, 345. Calf-kid, 390. Caliche, 112 j Extraction of iodine from, 432. Calico-printing, 340 ; styles of, 340, 341, 342; Thickening agents for, 340. Californian borax, 414. Camomile, a hop substitute, 194. Camphor, 241. Camphors, 241. Camwood, 325. Canaigre, 378. Candle moulds, 251. Candle power of cannel gas, 71 ; coal gas, 68 ; coal gas determined, 67 ; oil gas, 74, 75. Candle, Standard, 67. ,, wick, Function of, 250. ,, wicks, Treatment of, 251. Candles, 250 ; Moulded, 251 ; Ozo- kerite, 252; Paraffin, 251; Poured, 251; Haw materials for, 250; Sperm, 252; Stearin for, 252; Stearin (stearic acid), 255; Wax for, 251. Cane sugar,"162, 163 (see also Sugar, Cane) ; Fermentation of, 201 ; juice (see also Sugar-cane juice). Cannabis sativa, 261. Cannel, Composition of, 57 ; for enriching gas, 71 ; gas, Candle power of, 71 ; Tar from, 71. INDEX. 449 Caoutchene, 243. Caoutchouc, 243 ; Behaviour of, when heated, 243 ; Ceara, 243 ; Para, 243 ; Solvents for, 243 ; Vulcanised, 243. Caput mortuum, 18. Caramel, 181 ; for colouring beer, 182, 204; for colouring sherry, 208 ; for colouring spirits, 182 ; for colouring vinegar, 182 ; made from starch sugar, 182. Carbide, Calcium, 73. Carbohydrates, 162 ; of barley, 192. Carbolate, Sodium, 79. Carbolic acid, 79, 80 ; Specific gravity of crude, 80. Carbolic oils, 79. Carbon bisulphide, 436 ; Boiling point of, 436 ; Heat of formation of, 436 ; Plant for making, 436; Kemoval of, from coal gas, 65 ; Specific gravity of, 436. Carbon black, 119, 364. density, 69. Carbon dioxide from breweries, 205; in exit gases from ammonia-soda process, 46 ; in lime kiln gases, 46; Liquid, for preserving beer, 204. Carbon, Gas, 61 ; Retort, 61. Carbon tetrachloride, 230, 436 ; Boil- ing point of, 436 ; Specific gravity of, 436. " Carbonate vessel," 65. Carbonates, alkaline, Saponification with, 247. Carbonating tower for ammonia-soda process, 44. Carbonation of tank liquor, 28. Carbonic acid from breweries, 205. Carbonising in retorts for gas pro- duction, 58 ; wood in kilns, 90 ; wood in retorts, 90. Carbon yl chloride, Application of, 289, 309. Carburine, Enriching gas by, 73. Cardamoms, 214. Carmin, 327 Carmine, 328 ; Cochineal, 365. Carminic acid, 327 ; Alumina lake of, 328. Carnallite, 114, 426. Carriers, Oxygen, 288, 289, 311. Carthamin, 326. Carthamus tinctoriwi, 326. Casein in butter, 237. Cassava, 187. Cassel yellow, 361. Cassia, 214. Cast-iron vessels, Concentration of vitriol in, 16. Castor oil, 227, 235 ; Action of sulphuric acid on, 235 ; group, Oils of, 227 ; Properties of, 235 ; Refining of, 235 : Viscosity of, 235 ; Yield of, 235. Catechu, 326, 377. Caustic ash, 29. ,, liquor, Analysis of, 31. ,, potash, 427. ,, soda, 30 (see also Soda). Causticising process, 30. ,, soda ash by fusion with ferric oxide, 47. Ceara, caoutchouc, 243 ; rubber, 243. Cedar oil, 241. Cedrene, 241. Cedrenes, 240. Celestine blue, 337. Cells, Battery of, for sugar diffusion process, 166. Celluloid, Solvent for, 217. Cellulose, Destructive distillation of, 56 ; for paper-making, 344 ; hexa- nitrate, 403 ; nitrated, Varnishes from, 246 ; Nitration of, 404 ; Nitro-, 403. Cement, Asphalt, 125 ; burning, Chemistry of, 138. Cement, clinker, Constitution of, 139 ; "Fallen," 139; Proximate analysis of, 139 ; Under-burnt, 139. Cement, Effect of temperature on setting of, 131 ; for china, 397 ; Grinding, 137; Hydraulic, 132; kilns, 135. Cement, Portland, 134; Analysis of materials for, 138 ; clay for, Analy- sis of, 138; Hardening of, 139; Materials for semi- dry process of mixing, 134 ; Materials for wet process of mixing, 134; Setting of, 139. Cement, Puzzuolanic, 140 ; Roman, Analysis of, 133; Scott's 132; Slag, 141 ; slurry, Analysis of, 138. Centrifugal machine, 164. Ceresin, 124, 413. Cerotate, Ceryl, 228 ; Myricyl, 228. Cerotic acid, 223, 239. Ceryl cerotate, 228. Cetyl palmitate, 228, 239. Chalk, Analysis of grey, 127 ; Analy- sis of white, 127 ; Levigated, 353. Chamber acid, 14 ; specific gravity of, 14. crystals, 12 ; method of making white lead, 350. 29 450 INDEX. Chamois leather, 391. Champagne, 208. Chance-Clans process, 32. Charbon roux, Analysis of, 92. Charcoal, Absorption of gases by, 92 ; Analysis of animal, 104. Charcoal, animal, Use of, in oil refining, 229 ; in sugar refining, 178. Charcoal, Bone, 104 ; breeze, 89 ; burning in heaps, 88 ; in meilers, 88. Charcoal for gunpowder, 401; Analy- sis of, 401. Charcoal from straw, 402 ; Specific gravity of, 89 ; Wood, for purify- ing spirit, 216 ; Yield of, from wood, 89, 90. "Char," 104. Char for sugar refining, 178. Char, Reburning, 179 ; Revivified, 179. 4 'Char- water," 178. " Check vessel," 65. Chemicking, 266. Chili saltpetre, Perchlorate in, 432. Chimney gases, Hydrochloric acid in, 24. China, Cement for, 397 ; clay as a loading material, 344 ; grass, 262 ; grass, Bleaching, 267 ; stone, 148. Chinese blue, 353. ,, galls, 374. ,, process for making vermilion, 362. , , wood oil, 227. Chlorates, 42 ; Electrolytic prepara- tion of, 51. Chloride, Benzal, 241 ; of lime, Bleaching by, 266 ; of lime, Pro- duction of, 41. Chlorination, Mordanting by, 264. Chlorine, Liquid, 42; Boiling point of, 42 ; Specific gravity of, 38. Chlorine, Manufacture of, 35; Manu- facturing yield of, 37. Chlorine process, Deacon's, 39. Chlorine, Recovery of, by Weldon- Pechiney process, 50; in ammonia- soda process, 49 ; process, Mond's, 50. Chlorine stills, 35. Chlorosulphite of lead, 353. Cholesterol, 228, 258. Choline in hops, 194. Chondrin, 396. Chromate, Ammonium, 359; Barium, 361 ; Basic lead, 361 ; Lead, 360 ; Mercurous, 359; Sodium, 421 ; Stannic, as pigment for glass, 160; Zinc, 361. Chromates, 420 ; Manufacture of, from chrome iron ore, 420. Chrome, alum, 426 ; alum converted into bichromate, 280. ,, aventurin, 159. ,, brown, 337. ,, green, 359. ,, iron ore, 420 ; Manufacture of chromates from, 420. ,, orange, 360. red, 337. ,, tanning, 390. „ yellow, 337, 360; "pure," 361. Chromic acetate, Use of, in dyeing, 331. Chromic acid, 422 ; as a mordant, 331 ; for purifying spirit, 216 ; for wax bleaching, 239. Chromic anhydride, 422. ,, fluoride, Use of, in dyeing, 331. ,, oxide, 359. ,, sulphate, Use of, in dyeing, 331. .,, thiocyanate, Use of, in dyeing, 331. Chromite, 420. Chromium acetate as a mordant, 341. „ borate, 359. ,, fluoride as a mordant, 338. ,, greens, 359. ,, mordants, 331. ,, phosphate, 359. Chromogen, 273 ; I., Application of, 338. Chromophore, 273. Chromotropic acid, 338. Chromotrops, 337. Chrysamine, 336. Chrysaniline, 287 ; Manufacture of,. 318. Chrysoidine, 274, 334. Chrysophenin, 333. Cider, Composition of, 209 ; vinegar^ 221. Cinnamic acid, 242. Cinnamon, 214. Citrate, Calcium, 419. Citric acid, 418 ; as a resist, 342. Claret, 207. Clarifying wine, Beech shavings for, 220. Claus kiln, 33. Clay, 143 ; Analysis of, 143 ; of brick, 145 ; of fire, 145 ; China, as a loading material, 341 ; Cor- nish, 144 ; for Portland cement, INDEX. 451 Analysis of, 138 ; Gault, 134 ; industries, 143 ; Manufacture of alum from, 425 ; marls, 144 ; Plastic, 144; Porcelain, 144. Clays, Classification of, 144 ; Fire, 144 ; Fusibility related to com- position of, 144 ; Plasticity re- lated to composition of, 144 ; pottery, Analysis of, 143; pottery, Properties of, 143. Clean spirit, 211. Cleansing and softening hides, 381. ,, beer, Systems of, 203. ,, fibres, Principles of, 263. Clichy process for making white lead, 351. Clinker Cement, 139. Close test, Flashing point, 121. Close woods (dyewoods), 325. Cloth brown, 337. „ red, 337. Coal, Destructive distillation of, 56. Coal distillation, Distribution of nitrogen in, 61 ; Influence of tem- perature of, 60 ; Lime used in, 61. Coal, Energy value of gaseous pro- ducts from, 73 ; for alkali manu- facture, Nitrogen in, 22 ; Small, for alkali manufacture, 22 ; Valua- tion of, for gas making, 57 ; Yield of ammoniacal liquor from, 66 ; of coke from, 66 ; of gas from, 66 ; of tar from, 66. Coal gas, Action of lime purifier on, 65 ; Ammonia in, 68 ; Amount of impurities in crude, 66 ; Analysis of, 69 ; Candle power of, 69 ; Composition of, 66 ; Determina- tion of sulphur compounds in, 68 ; Diluents in, 69 ; Enrichment of, 71 ; Enriching, by oil water gas, 72 ; Ferric oxide puri- fier for, 64 ; Illuminants in, 69 ; Illuminating power of, 69 ; In- fluence of temperature of distil- lation on, 67 ; Non-illuminant combustible gases in, 69 ; Removal of carbon bisulphide from, 65 ; "roughed," 64; Standard limits for impurities in, 68 ; Sulphur compounds in, 68 ; Sulphuretted hydrogen in, 68 ; Valuation of, 67. Coals, Composition of gas, 57; gas, Influence of composition of, on yield of coke and gas, 57 ; Yield of ammonia from gas, 75 ; Yield of coke from gas, 60 ; Yield, of gas from gas, 60 ; Yield of tar by different, 76. Coal tar, 76 ; Composition of Beck- ton, 77 ; Constituents of, 76 ; Crude naphtha from, 78; Distilla- tion of, 77 ; First runnings from, 78 ; Light oil from, 78 ; Pitch, 82; Products from distillation of, 77 ; Quinoline from, 317 ; Specific gravity of, 76. Coal washing, 83. Cobalt blue, 358. glass, 159. ,, yellow, 361. Coccerin, 327. Cocceryl coccerate, 327. Coccus cacti, 327. ilicis, 328. ,, lacca, 242. Cochineal, 327 ; Artificial silver grain on, 327 ; black, 327 ; carmine, 365; carmine, Analysis of, 365; Granilla, 327 ; Silver grain, 327. Cocoa butter, 227. „ gunpowder, 402. Coco-nut cake as fodder, 236. Coco-nut oil, 227, 236 ; deflavoured, 238 ; for margarine, 238 ; night lights, 251 ; Properties of, 236 ; Refining of, 236 ; Yield of, 236. Cocos nucifera, 236. Cod-liver oil, 228, 238 ; Adulterations of, 239 ; Medicinal, 238 ; Properties of, 238 ; Tanner's, 238. Ccelestine, 429. Ccerulein. 296, 334, 338. Coffey still, 212, 213. Cognac, 209 ; Analysis of, 210. Coke, Analysis of, 83. Coke from petroleum distillation, 83 ; Gas, 82. Coke oven, 83; Beehive. 84 ; Copp^e, 87 ; Simon-Carves, 86. Coke, Yield of, from coal, 60, 66 ; from Simon-Carves oven, 87. Coking in heaps, 83 ; in modern ovens, 85; with recovery of pro- ducts. 85. Colcothar, 18, 363. Cold drawn oil, 229. ,, press, Oil from, 229. Colinin, 325. Collagen, 369. Colloidal character of starch, 187. Colophony, 241. Colour, Armstrong's theory of, 278 ; correctives, 152, 187, 353. Colour lakes, 330. ,, of mixed pigments, 348. ,, printing, 340. | Colouring matters, 273 ; Mineral, 328. 452' INDEX. Colours, Aniline, 287 ; Developers for, 333 ; Fast, defined, 270 ; In- grain, 277, 335. Column still, 212. Colza oil, 232. "Cooler grounds," 198. Coolers used in brewing, 198. Combustion tube glass, Reason for refractory character of, 157. Condenser, Air, for gas making, 62 ; Guttmann's nitric acid, 10. Cones, Seger's, Temperature measured by, 147. Confectionery flavourings, 217, 241. Congo red, 277, 333. Coniferine in beet juice, 165. Conifers, a source of turpentine, 240. Coniine, 105. Connective tissue, 368. Copal, 242. Cop-dyeing, 329. Coppee coke oven. 87. Copper, Action of acetylene on, 74. Copper acetate, Basic, 359. ,, acetoarsenite, 359. ,, carbonate, Basic, 360. ,, oxychloride, 358. sulphate, Manufacture of, 427 ; Uses of, 423. Copperas, 423 ; vat for dyeing with indigo, 322. Coprah, 236. Coprolites, 107. Coralline yellow, 292. Corchorus, 262. Cordite, 407 Coriander, 214. Coriin, 369. Corium, 367. Cornish clay, 144 ; stone, 149. Correctives of colour for glass, 152. Cosettes, 165. Cotton, 260 ; Action of acids and alkalies on, 260 ; bleaching, 265 ; dyeing, 333, 334. Cotton fibre, 260 ; Analysis of, 260 ; Structure of, 260. Cotton, Flax colder than, 261 ; Flax compared with, 261 ; Relation of, to dyestuffs, 272 ; Scouring, 265 ; Scouring, Chemistry of, 266 ; " Staple " of, 260 ; Yellow colour of bleached, corrected, 267- Cotton-seed blue, 232 ; cake as fodder, 232. Cotton-seed oil, 226, 232 ; an adul- terant of lard, 237 ; group, Oils of, 226 ; Properties of, 232 ; Uses of, 232. Cotton-seed stearin, 232 ; an adul- terant of tallow, 237. Cotton singeing, 265 ; wool, 260. Couch, Barley, 190. Covering power of mixed pigments, 348. " Cracking " of hydrocarbons in gas making, 61 ; petroleum, 119. " Craze," 149. Cream of tartar, Use of, in dyeing, 330. Cream separated from milk, 237. Creolin, 79. Creosol, 93. Creosote for lighting, Use of, 81 ; oils, 80 ; Wood tar, 93. Cresotinic acid, 385. Cresylic acid, 79. Crimson lakes, 328. Crocein orange, 275 ; scarlet, 276. Croton oil, 227. Crucifera, Oils of the, 226. Crust, 289. Crust of wine, 208. Crutch pan, 249. Cryolite, C arbonate of, sodium pre- pared from, 51. Crystal carbonate, 29 ; tannin, 375 ; violet, 289. Crystallisation of salts with each other, 423. Cube sugar, 180 ; gambier, 378. Cullet, 152. Cupric arsenite, 359. Curcas oil, 227. Curcuma tinctoria, 326. Curcumin, 326. Curd soap, 248. Curried leather, 389. Currying leather, 393 ; Oils used in, 393. "Curtains" of vitriol chambers, 7. Cutch, 326, 377. Cuttle fish secretion, 365. Cyanamine, 308. Cyanide, Potassium, 434. Cyanides prepared from gas purifier, 433 ; Production of, 433. Cyanine, 317, 338 ; Iso - amyl, 317. Cyanines, 316. Cyanogen compounds, 432 ; Forma- tion of, from carbon and nitro- gen, 432 ; Heat of formation of, 432. Cylinder oils, 123. Cymene, 240. Cymogene, 120. INDEX. 453 D. Deacon's chlorine process, 39. Dead-burnt lime, 120. Deblooming mineral oils, 122. ,, oils, Nitronaphthalene for, 81. Decortication, 232 ; of seeds, 229. Defecation of juice of beet, 167 ; of sugar by blood, 178. Degras, 391, 393 ; former, 393. Degreasing skins, 383. Deraerara sugar, 177 ; Tin in, 180. Denatured spirit for varnishes, 219. Denaturing alcohol, 218. Denaturing spirit, German system of, 219 ; Oil of turpentine for, 219 ; Pyridine bases for, 219. Denitration of artificial silk, 260. Denitrifying organism, 113. Dephlegmator for benzol still, 78. Depilatories, 3S3. Desmobacteriumhydrogeniferum, 323. Destructive distillation, Principles of, 55 ; Typical products of, 56. Detergent action of soaps, 250 ; pro- perties of soap enhanced, 247. Detergents, 417. Detonation, Explosion contrasted with, 399. Detonators, 408. Developers for ingrain colours, 333. Devitrification of glass, 156. Dextrin (dextrine), 187 ; Achroo, 197 ; Erythro, 197 ; Malto, 196 ; Manufacture of, 188 ; Uses of, 188. Dextropinene, 240. Dextrose, Composition of commer- cial, 182 ; for sweetmeats, 182 ; Properties of, 181 ; Purification of, 182 ; Sweetening power of, 181. Diabetic patients, Sugar for, 182. Dialysis of glycerin, 255. Diamidoazobenzene, Formation of, 274 ; Formula for, 274. Diamidotriphenylmethane dyestuffs, 291. Diamine black, 333 ; blue, 333 ; fast red F, 336 ; red, 333 ; yellow, 337. Diamond black, 119, 364 ; yellow, 337. Diastase, 192 ; Analysis of, 193 ; Effect of antiseptics on, 193; Iso- lation of, 193. Diastatic power of malt, 192 ; Lint- ner's standard of, 193. Diazoamidobenzene, Preparation of, 314. Diazobenzene chloride, Formula for, 274 ; Formation of, 274. Diazo blacks, 333. Diazo-compounds, 274 ; defined, 275. Diazotising, Process of, 274. Dibdin's standard lamp, 68. Dicalcium phosphate, 109. Diethylamidophenolphthalein, 296. Diethylmetamidophenol, 296. Dietzsch kilns, 135. DifFusers for sugar extraction, 166. Diffusion process for extracting beet sugar, 165. Digallic acid, 374. Dihydroxyanthraquinone quinoline, 282. Dihydroxynaphthoquinone, 279. Dihydroxyphthalophenone, 293. Dihydroxy tartaric acid, 310. Dihydroxytoluic acid, Formula for, 327. Diluents in coal gas, 69. Dimethylamidoazobenzene sulphonic acid, Formula for, 275. Dimethylaniline, 289. Dimethylparaphenylenediamine,299; Application of, 305 ; Sulphosul- phonic acid, 306. Diuas fireclay, 144. Dinitro-a-naphthol, 273. Dinitro-benzene, Manufacture of, 284. Dinitrosoresorcinol, 302. Dinsmore process, 74. Diphenylene azine, 297. Diphenylnaphthylmethane dyestuffs, 290. Dippel's oil, 104. Dips, Tallow, 251. Direct colours, Dyeing silk with, 338; dyes, 330 ; dyestuffs, Examples of, 333. Disaccharides, 162. Disazo - compounds defined, 375 ; dyestuffs, Formation of, 276. Discharge pastes, Oxidising, 342 ; Reducing, 341. Discharge, Stannous acetate as a, 341 ; style of calico-printing, 341 ; Zinc dust as a, 341. "Discharging" silk, 265. " Diseased" wool, 257. Diseases of beer, 204. Di-sodoxyanthraquinone, 281. Dissociation of calcium carbonate, 127. Dissolved bones, 111. Distillation, Destructive, 35. Distilled oleic acid, 253 ; verdigris, 360. 454 INDEX. Distillers' grains, Analysis of, 210. Distilling and brewing, 189. Di-strontium saccharate, 175. Divi-divi, 278. Dodecatyl alcohol, 228 ; oleate, 239 ; physetoleate, 239. Dceglic acid, 223, 228. Dcegling oil, 228. Dolomite limestone, 126. "Double superphosphate,'' 109. "Draff"," 210. Drawing gas retorts, 60. Drenching skins, 385. Dressed leather, 389. Dressing leather, 389. Drier for manure manufacture, 409; Litharge as a, 234; Manganese borate as a, 234. Driers, 234. Drips, Acid, in vitriol chambers, 14. Dropping pipe, 212. Drying oils, 226, 234 ; defined, 224 ; Oxidation of, 224 ; Semi-, 233. Drysalted hides, 372. Duncan and Newlaud's process, 176. Dung, Application of, in making white lead, 349. Dust from pyrites burners, 6. Dutch process for making vermilion, 362 ; white lead, 349. Dyeing and mordants, 329 ; bath, Circumstances influencing consti- tution of, 329. Dyeing cotton, 333 ; with acid colours, 334 ; with basic colours, 334 ; with direct dyestuffs, 333 ; with mordant dyes, 334 ; with special dyes, 334. Dyeing, Chemical theory of, 271 ; Cop-, 329 ; General principles of, 270 ; Hank-, 329 ; ingrain, Advan- tage of, 277 ; ingrain, Methods of, 277 ; Jute, 339 ; Leather, 393 ; Methods of, 329 ; mixed fabrics, 336, 338, 339 ; Physical theory of, 271; Theory of, 271; tone produced in, Influence of the fibre on, 335 ; < ' Vat-, " with indigo, 322 ; Water for, 343 ; Witt's theory of, 273. Dyeing silk, 338 ; with acid colours, 339 ; with basic colours, 338 ; with direct colours, 338 ; with mordant colours, 339. Dyeing style of calico-printing, 341. Dyeing with aniline black, 312 ; with basic lead chromate, 328 ; with chrome yellow, 328 ; with cochi- neal, 327. Dyeing with indigo, 322 ; Copperas vat for, 322 ; Hyposulphite vat for, 323; Wood vat for, 322. Dyeing with ingrain colours, 333 ; with lead chromate, 328 ; with manganese brown, 328 ; with orange chrome, 328 ; with Prus- sian blue, 328. Dyeing wool with acid colours, 336 ; with basic colours, 336 ; with direct dyes, 335 ; with mordant colours, 337. Dye, Lac, 242, 328. Dyes, Acid, 330 ; Acid, classified, 336 ; Adjective, 270 ; Aniline, 284 ; Basic, 330 ; Direct, 330 ; distinguished from dyestuffs, 270 ; Mineral, 328 ; Mordant, 330 ; mordant, Examples of, 334 ; Special, 330 ; Substantive, 270; substantive, Examples of, 333. Dyestuffs, Acridine, 318 ; Adjective, defined, 270 ; Application of sul- phonic acid, 336 ; Aurine, 291 ; Azo, converted into mordant colours, 337 ; Azo-compounds, 273; blue, Aniline, 289 ; Classification of, 273 ; classified according to mode of application, 329 ; contain- ing sulphur, 304 ; Diamidotri- phenylmethane, 291 ; Diphenyl- naphthylmethane, 290 ; Disazo, 276 ; distinguished from dyes, 270 ; distinguished from pigments, 270 ; Examples of direct, 333 ; Forma- tion of amidoazo, 274 ; Formation of hydroxyazo, 274 ; from naph- thols, 275 ; Methylation of aniline, 289 ; Natural organic, 319 ; Nitro- compounds as, 273 ; Organic synthetic, 273 ; Oxazine, 307 ; Phthalein, 292 ; Primuline, 277 ; Quinone derivatives as, 278 ; Rela- tion of cotton to, 272 ; Relation of fibres to, 271 ; Substantive, de- fined, 270 ; Trihydroxytriphenyl- methane, 291 ; Triphenylmethane, 283 ; Tetrazo, 275 ; tetrazo, For- mation of, 276 ; Violet aniline, 289 ; Witt's Theory of, 273. Dyewoods, 325. Dynamite, 406 ; Explosion of, 407 ; Gelatine, 407 ; Manufacture of, 406. E Earthenware, 149 ; Kilns for, 150. Earth nut oil, 226, 232 ; cake, 232 ; INDEX. 455 Detection of, 232 ; Iodine absorp- tion of, 232 ; Saponification equivalent of, 232 ; Specific gravity of, 232 ; Uses of, 232 ; Yield of, 232. East Indian kips, 372 ; linseed oil, 234. Eau de Javelle, 41. ,, Labarraque, 41. Ebonite, 244. E.G. power, 405. Edge runner, 360. Egg-yolk, Application of, in tanning, 390. Elaidin reaction, 226. Mais Qumeensls, 236. Elastic fibres, 370. Elastin, 370. Electric furnace for phosphorus manufacture, 410. Electric tanning, 388. Electrolysis of magnesium chloride, 267 ; Preparation of bichromate by, 422. Electrolytic bleaching, 267. Electrolytic preparation of alkali, 51; of bleach, 51 ; of chlorates, 51. Electrolytic process, Greenwood, 52. Ellagic acid, 376. Elution, Sugar recovered from molasses by, 174. Emerald green, 359. Emeraldine, 312. Emulsifying power of lanolin, 258. Emulsin, 241. Encaustic tiles, 145. Endogenous division of yeast, 200. Energy absorbed in production of water gas, 72 ; changes in alkali processes, 53 ; into light, Conver- sion of, 71 ; of explosives, 398 ; value of gaseous products from coal, 73. Engine oil, Olive oil as, 231. English galls, 374 ; soft porcelain, 148 ; sulphuric acid, 17. Enriching coal gas by oil water gas, 72. Enriching gas by acetylene, 74 ; by benzene, 73 ; by carburine, 73 ; by naphthalene, 73 ; by tar, 74 ; Cannel for, 71. Enrichment of coal gas, 71. Enzymes, 189 ; Typical effect of, 189. Eosin scarlet, 295 ; Soluble, 295. Eosins, 294. Epidermis, 367. Epsom salts, 427. Equivalents, Mean, of oils ascertained, 225. Erector muscle, 36S. Erucate, Glyceryl, 232. Erucic acid, 223, 226. Erythrin, 327. Erythro-dextrin, 197. Erythrosin, 295. Erythrozyme, 280. Esparto, 262, 344; boiling, 345; Manufacture of paper from, 345. Essential oils, 240 ; Winning of, 241. Etageofen, 135. Etching glass, 160. Ether tannin, 375. Ethereal salts, 223, 240. Ethylidene lactic acid, 417. Euphorbiaceoa, 243. Eurhodol, 298, 299. Euxanthic acid, 366. Evans photometer, 67. Evaporator, Multiple effect, 170, 346; Triple effect, 170; Wetzel, 164; Yaryan, 170. Excise system of stating alcoholic strength, 218. Exhauster, Beale's rotatory, 62. Exothermic decomposition of wood, 96. Explosion contrasted with detona- tion, 399. Explosive mixture of gas and air, 70. Explosive, Picric acid as an, 408. Explosives and matches, 398. Explosives, Barium nitrate in, 405 ; defined, 398 ; Energy of, 398 ; High, 403 ; Measurement of effective pressure exerted by, 399 ; Nitro-, 403 ; Rapidity of, 399 ; Sprengel's, 408. Extractor for use with volatile solvents, 230. "Extracts" for tanning, 380; Analysis of, 381. F. Fabrics, Effect of heat on asbestos, 263. ' ' Fallen " cement clinker, 139. Falling of skins, 373. Farmyard manure, 114. Fast colours defined, 270. Fastness of indigo, Cause of, 322. Fat from omentum of pig, 237. "Fat" lime, 127, 130. 456 INDEX. Fats, 223; Differences of, from waxes, 225 ; Hydrolysis of, 252 ; Hydro- lysis of, by steam, 253; Hydrolysis of, by sulphuric acid, 253, 224 ; Identification of, 225 ; Render- ing, 229 ; Saponification of, 225. Fats and oils, Classification of, 226 ; Hydrolysis of, 224 ; Preparation of, 226 ; Properties and Uses of, 224, 226, 231 ; Use of, in soap making, 247. Fatty acids applied as mordants, 332. Fatty acids, Formulae of, 223 ; Melting point of, 223 ; Solid, made from oleic acid, 255 ; Table of, 223 ; volatile with steam, 227. "Feeding back," 203. Feet of cattle, Oil from, 236. Fehling's solution, 193. Feints, 211. Felspar, 143. Fennel, Sweet, 214. Ferment, Acetic acid, 219 ; defined, 189. Fermentation, Acetic, 219 ; Analysis of products of cane sugar, 201 ; Artificial cooling for bottom, 200 ; Bottom, 200 ; Bottom of wine, 206 ; Chemistry of alcoholic, 201 ; defined, 189 ; Glycerin produced during, 201. Fermentation of cane sugar, 201 ; of grape juice, 206 ; of milk sugar, 201 ; of molasses, 215 ; of must, 206 ; of sugar, 201 ; of wine, Effect of plaster of Paris on, 208 ; of wort, 199 ; of wort for whiskey, 210. Fermentation, Refrigerating for bot- tom, 198 ; Ropy, of beer, 204 ; Starch separated from gluten by, 185 ; Succinic acid produced in acetic, 219 ; Top, 199 ; Top, of wine, 206. Fermenting tuns, 199. Ferments, Aerobic, 190 ; Anaerobic, 190 ; Organised, 189 ; Organised, classified, 189 ; Typical effects of, 189 ; Unorganised, 189. Ferric chloride as an oxidant, 305. Ferric oxide, 363 ; Causticising soda ash by fusion with, 47 ; purifier for coal gas, 64. Ferricyanides as oxidants, 342. Ferricyanide, Potassium, 434. Ferrite, Sodium, 47. Ferrocyanide, Potassium, 433, 434. Ferrous acetate, Use of, in dyeing,. 331. ,, chloride as a carrier in re- ducing nitrobenzene, 285. ,, chromite, 420. ,, sulphate, Manufacture of, 423 ; Use of, in dyeings 331 ; Uses of, 424. Fibre, Bast, 260, 261, 262. ,, Cotton, 260 ; Analysis of, 260; Structure of, 260. „ Flax, 261 ; Analysis of, 261. ,, Hemp, 261. ,, Silk, 259; Behaviour of, to reagents, 259; Specific gra- vity of, 259. ,, Wool, Analysis of, 258 ; Pro- perties of, 259 ; Specific gravity of, 259. Fibres, Animal, distinguished from vegetable, 259. ,, Mineral, 262 ; Relation of, to dyestuffs, 271. Textile, 257; length of, 257. Fibrin, 192. Fibroin, 259. Ficua indica, 242. " Fifty per cent, benzol," 79. "Figging " in soft soap, 249. Filling materials for soap, 247. Filter press, 168. Filter, Taylor's, 178. Filtration, Twill bags for sugar, 178. Fining beer, Isinglass for, 2(J4. " Finings " for beer, 204. Finishing beer, 204 ; processes in tanning, 392. Firebricks, 145. Fireclay, Analysis of, 145 ; Dinas r 144. Fireclays, 144. Firing gas retorts, Percentage of coal needed for, 58. First jet sugar, 172. First runnings from coal tar, 78. Fisetin, 325. "Fishing salt," 20. Fish-tail burner, 70. Fission of yeast, 200. Fitted soap, 248. " Fixed ammonia," 47 ; in gas liquor, 75. Fixing tannin in leather, 393. Flame, Air-gas, 70. Flashed glass, 158. Flashing point, close test, 121 ; of kerosene, 121 ; open test, 121. " Flare lime," 128. Flavaniline, 316. INDEX. 457 Flavin, 326. Flavopurpurin, 281. Flavourings, 241. Flax, 260; "Breaking," 261 ; colder than cotton, 261 ; compared with cotton, 261. Flax fibre, 261 ; Analysis of, 261. Flax, Tensile strength of, 261 ; "Heckling," 261 ; "Retted," 260 ; "Retting," 260; "Rippling," 260 ; "Scutching," 261; Seed, 223; ' ' Staple " of, 261 ; Structure of, 261 . Flint glass, 158. Flooring barley, 190. Flour, Application of, in tanning, 390 ; Saltpetre, 400. "Flowers of madder," 280; of sulphur, 2. Fluorescein, 293 ; Preparation of, 294. Fluoride, Antimony, 332 ; Chromic, 331 ; Chromium, as a mordant, 338; Sodium, as an antiseptic for beer, 204. Fluorindines, 315. Food, Lard as, 237 ; Oils for, 231, 232, 233. Fore-shots, 211. Forge scale, 158. Formaldehyde, 370. Formaline, 370. Fortified wines, 207. Foul main, 62. Fourners burner, 70. Fractionation of crude benzol, 78 ; of whiskey, 211. "Free ammonia," 47 ; in gas liquor, 75. Freezing, Concentration of glycerin by, 256 ; Purification of benzene by, 79. French process of making white lead, 351. French turpentine, 240. Frit, Porcelain, 148. "Fritting," 148. Frizz, 382. Frothing prevented in whiskey stills by soap, 211. Fruit, Oils won from, 238 ; sugar, 182 Fuchsine, 287. Full bleach, 267. Fulminate of mercury, 408. Fungi, 189. Furfural in brandy, 210. Fusees, 412. Fusel oil, 202, 211 ; Analysis of, 217; Content of, in crude spirit, 216 ; from beet, 217 ; from brandy marc, 217 ; from grain, 217 ; from potatoes, 217 ; in whiskey, 211 ; Removal of, from crude spirit, 216, 217 ; removed from spirit by oxida- tion, 216. Fustet wood, 325. Fustic, 325. Fustin, 325. G Galactose, 162. Galena, Lead sulphate manufactured from, 352. Gall and West-Knight process, 79. Gallein, 296. Gallic acid, 375 ; Application of, 296. Gallipoli oil, 231. Gall-nuts, 374. Gallocyanin, 308. Galloflavine, 338. Gallo-tannic acid, 374. Galls, Acorn, 374 ; Bassorah, 374 ; Black, 374 ; Blue, 374 ; Chinese, 374 ; English, 374 ; Extraction of tannin from, 374 ; Japanese, 374 ; Levant, 374; Oak, 374; White, 374. Gall-tannin, Use in dyeing, 332. Gambier, 326, 377 ; Block, 378 ; Cube, 378. Gambine, 338 ; R, 302 ; Y, 302. Gamboge, 242. Gambogic acid, 242. " Garancin," 280. Gas, Analysis of natural, 118 ; of wood, 95. Gas and air, Explosive mixture of, 70. Gas and Coke, Influence of composi- tion of gas coals on yield of, 57. Gas burner, Incandescent, 70. Gas burners, Typical, 69. Gas burnt in different burners, Heating effect of, 70 ; Illuminating- effect of, 70. Gas, Candle power of cannel, 71 ; of coal, 68 ; carbon, 61 ; coals (see Coals, Gas) ; coke, 82 ; Energy absorbed in production of water, 72 ; enriching (see Enriching gas). Gas from bone distillation, 105 ; from coal, Yields of, 66 ; from shale distillation, 103. Gas, Generator, 72. Gas liquor, 75 ; Analysis of, 75 ;. Fixed ammonia in, 75 ; Free ammonia in, 75 ; Recovery of sulphur from, 76; Valuation of,. 76. 458 INDEX. Gas making, Air condenser for, 62 ; "Cracking" of hydrocarbons in, 61 ; Plant for, 62. Gas, Manufacture of water, 72. Gas, Oil, 74 ; Candle power of, 74, 75; " Hydrocarbon " from, 75 ; Pintsch system for, 74 ; Yield of, per gallon of oil, 74. Gas, Oil-water, Composition of, 72 ; Solar oil for, 72. Gas producer, 72 ; for retort furnace, 59. Gas production, Carbonising in retorts for, 58. Gas purification, Weldon mud for, 66. Gas purifiers, 64; Arrangement of, 65. Gas retort, Dimensions of, 58 ; furnace, 58. Gas retorts, Charging, 60 ; Drawing, 60 ; Mechanical charging of, 60 ; Percentage of coal needed for firing, 58 ; Process of distillation in, 60. Gas, Statutory limit for ammonia in, in London, 75 ; supplied to Scotch towns, Composition of, 71. Gas washer, 64. Gas, Yield of, from gas coals, 60. Gaseous products from coal, Energy value of, 73. Gases, Absorption of, by charcoal, 92 ; in coal gas, non-illuminant combustible, 69. Gasolene, 120 ; from shale distilla- tion, 103. Gaultheria procumbens, 240. Gay-Lussac tower, 8 ; Function of, 13 ; Sulphuric acid for, 13. Gelatine, Blasting, 407 ; Explosion of, 407 ; Manufacture of, 407 ; Thermal effect of explosion of, 407. Gelatine, Characters of, 396 ; Com- position of, 390 ; Drying, 396 ; dynamite, 407 ; glue and size, 395; Manufacture of, 396 ; Properties of, 370; Ultimate' composition of, 369. Gelatinisation of starch, 187. Gemmation of yeast, 200. Gems, Artificial, 158, 159. General manure, Definition of, 106, 114. Generator gas, 72. Gentian, a hop substitute, 194. German method of making white lead, 350. German spirit, 215. Germicides, 423. Germination, Chemistry of, 192. Germ of maize removed, 186. Gin, 212 ; Content of alcohol in, 215; Flavouring matters for, 214; Plymouth, 215 ; Sweetened, 214. Ginger-beer, Composition of, 209. Ginger-beer plant, 200. Glass, 150 ; Action of solutions on, 161 ; Alkali for, 151 ; Analysis of alkali lime, 157 ; Annealing, 156 ; Arsenic, 416 ; Black, 159 ; Blue, 159; Borate, 160; Cobalt, 159; Coloured, 158 ; Colouring, 158 ; Colour of corrected, 152 ; combus- tion tubing, Reason for refractory character of, 157 ; Crown, 155 ; Cut, 158 ; Devitrification of, 156 ; etching, 160 ; etching, Hydro- fluoric acid for, 160, 413 ; Flashed, 158 ; Flint, 158 ; Fluorescent, 159; for thermometers, 160 ; furnace, 153, 154 ; gall, 152 ; Green, 159 ; " Hardening," 156; Highly refrac- tive, 160 ; Influence of composi- tion on index of refraction of, 161 ; Influence of composition on specific gravity of, 160 ; Lead, 157; Lead oxide for, 151 ; Lime for, 151 ; Limits of composition of, 150 ; makers' soap, 152 ; Manu- facture of, 155 ; Opal, 160 ; Orange, 159 ; Oxide of iridium pig- ment for, 160; Oxide of uranium pigment for, 160 ; Painting on, 160 ; Plate, 156 ; Platinum pig- ment for, 160 ; -pot, 152 ; "Potash," 157 ; -pot, Lead, 158 ; Properties of, 160; Raw materials for, 150; Red, 158 ; Ruby, 159 ; Selenium, 159 ; Siemens' toughened, 156 ; Silica for, 151 ; " Soda," 157 ; Sodium sulphate for making, 24 ; Soluble, 141 ; Stannic chromate pigment for, 160 ; stills, Concen- tration of vitriol in, 15 ; Thallium, 160 ; Toughened, 156 ; Uranium, 159 ; Use of oxygen in making, 155 ; vessels rendered resistant by steaming, 161 ; Violet, 159 ; Water, 141 ; wool, 263 ; Yellow, 159. Glauber's salt, 427 ; Use of, in dye- ing, 335. Glazes, Coloured, 148 ; for earthen- ware, 149 ; for porcelain, 147 ; for stoneware, 149. Glazing gunpowder, Graphite for, 402. Glazing, Salt, 149. Glove-kid, 390. INDEX. 459 Glover tower, 7 ; acid, Specific gra- vity of, 15 ; Sodium nitrate in, 14. Glucosan, 181. Glucoses, 181. Glucosides, 241. Glued materials, Mechanical strength of, 397. Glue, Manufacture of, 297 ; Silk, 259. Glues, Liquid. 397. Glutamine in beet juice, 165. Gluten recovered in starch-manufac- ture, 189. Gluten, Starch separated from, by- caustic soda, 1S5 ; Starch separa- ted from, by fermentation, 185. Glycerides, 223. Glycerin, 255 ; Boiling point of, 255 ; Concentration of, by freezing, 256 ; Dialysis of, 255 ; produced during fermentation, 201 ; Recovery of, 255 ; Recovery of, from soap lyes, 249 ; Refining of, 255 ; Uses of, 256. Glyceryl, 223 ; arachidate, 232 ; erucate, 232 ; hypogoeate, 232 ; iso-linoleate, 233 ; laurate, 236 ; linol ate, 233 ; myristate, 238 ; oleate, 224, 225, 226, 227, 228, 231, 233, 236, 237 ; palmitate, 224, 228, 231, 236 ; physetoleate, 238 ; ricinoleate, 235 ; salts, Oils not containing, 228 ; stearate,224, 228, 237 ; sulphuric acid, 253 ; tri- nitrate, 405. Glycocoll, 419. Golden sulphide of antimony, 244. Gold-lined stills for vitriol, 16. Oossypium, 232, 260. " Gradation towers," 21. Grain of leather, 368 ; Artificial, 393. Grain, Fusel oil from, 217. Graining hides, 389. Grain-lac, 242. Grains, Analysis of distillers', 210. Granilla, 327. Granite, 143. Granulation of gunpowder, 402. Grape, Brandy, 209 ; juice, Analysis of, 205 ; juice, Fermentation of, 206. Grapes, Changes in, during ripening, 206 ; Malic acid in, 2i)6 ; Tartaric acid in, 206 ; Treatment of, for red wine, 206 ; Treatment of, for white wine, 206. Grape sugar, 181. Graphite for glazing gunpowder, 402. Grasses as textile fibres, 262. "Graves," 237. Green pigments, 358. Green vitriol, 423. Greens containing copper, 359. Greenwood electrolytic process, 52. Grey acetate of lime, 93, 95. Grey sour, 266. Grist, 196. Ground nut oil, 231. " Ground " paint, 366. " Ground " white lead, 352. Guaiacol, 93. Guano, Nitrogenous, 115; Phos- phatic, 115. Guignet's green, 359. Gum benzoin, 242 ; British, 186. Gum resins, 240, 242. Gums, 245. Gumming of rape oil, 232. Gun-cotton, 403 ; Detonation of, 404; Equation for explosion of, 404 ; Gas produced by explosion of, 405 ; Manufacture of, 404 ; Reconver- sion of, into cellulose, 404 ; Solu- bility of, 404 ; Specific gravity of, 404 ; Thermal effect of, 405. Gunpowder, 400 ; Analysis of char- coal for, 401 ; Apparent density of, 403 ; Character of explosion of, 402 ; Charcoal for, 401 ; "Cocoa," 402 ; Equation for explosion of, 403 ; Exploding temperature of, 403 ; Gas produced in explosion of, 403 ; Granulation of, 402 ; Gra- phite for glazing, 402 ; Meal, 402 ; Mining, 402 ; Pebble, 402 ; Press- cake, 402 ; Pressure produced in explosion of, 403 ; Prismatic, 402 ; Rapidity of explosion of, 403 ; smoke, 403 ; Smokeless, 403 ; Sulphur for, 401 ; Thermal effect of, 403. Guttapercha, 245.' Guttmann's nitric acid condenser, 10. Gypsum, 131 ; as a loading material, 344. H H^matein, 324 ; Iso-, 325. Hematite, 363. Hematoxylin, 324. Hwmatoxylon campechianum, 324. Hair, Structure of, 257. 460 INDEX. Half bleach, 267. Halogens, 430. Handlers, 388. Handling hides, 382, 388. Hank-dyeing, 329. Harcourt's standard lamp, 68. Hard pitch, 82. Hard water, Objections to, in tanneries, 373. Hargreaves process, 23. Heating effect of gasburntin different burners, 70. Heavy spar, 430. "Heckling" flax, 261. Helianthin, 274. Hellhoffite, 408. Hemlock bark, 378. Hemp, 261 ; bleaching, 267. Hemp fibre, 261 ; Analysis of, 261 ; Tensile strength of, 261. Henderson retort for shale distilla- tion, 97, 98. Hermite process, 267. Heveene, 243. Hexamethylpararosaniline, 290. Hexane, 120. Hexanitrodiphenylamine, 273. Hide substance, Ultimate composi- tion of, 371. Hides, Absorption of tannin by, 395 ; Analysis of, 370 ; and skins, Quality of, 371 ; Breaking, 382 ; Butt of, 384 ; Cleansing and soften- ing, 381 ; Defects in, 372 ; defined, 371 ; Dry-salted, 372 ; Green- salted, 372; Handling, 382; Liming, 382; Market, 381; Offal of, 384; Pack of, 383 ; Plumped, 383; "Plumping" of, 370, 372; Round- ing, 3S4 ; Scudding, 384 ; Shaved, 389; Soaking, 381 ; Sweating, 384; Trimming, 384; Unhairing, 382 ; White arsenic for curing, 372. Hippuric acid, 419. Hock, 207. Hoffmann's kiln, 136. Hollands, 215. Holly, Bird-lime from, 239. Honey, 183 ; comb, 239 ; Factitious, 182. Hoofs and horns as manure, 113. Hop substitutes, 194. Hopeine in hops, 194. "Hop-backs," 198. Hop flour, 194 ; meal, 194. "Hopper salt," 20. Hops, 194 ; Bleaching, 194 ; Choline in, 194; Condition in, 194; Hopeine in, 194 ; Manuring, 113 ; Morphine in, 194 ; Proximate constituents of, 194 ; " Sulphur- ing," 194 ; Tannin in, 194. Horns and hoofs as manure, 113. Horse fat, 228. Hot press, Oil from, 229. " Household " soaps, 249. Huile tournante, 282. Ilumulus lupulus, 194. Hyaline layer, 368. Hydrindigotin, 320, 322. " Hydrocarbon " from oil gas, 75. Hydrocarbons, " Cracking " of, in ga^-making, 61. Hydrochloric acid, 24; Imparities in, 25 ; in chimney gases, 24 ; Manu- facturing yield of, 25. Hydrocyanic acid, 241. Hydro-extractor, 164. Hydroferrocyanic acid, 356. Hydrofluoric acid, 413 ; as an anti- septic, 413 ; Bottles for, 413 ; for etching glass, 160, 413 ; Manufac- ture of, 413 ; Use of, in sugar refining, 413. Hydrogen peroxide, Bleaching by, 264, 265. Hydrolysis, 189 ; of fats, 252 ; of fats and oils, 224 ; of fats by steam, 253 ; of fats by sulphuric acid, 253 ; of waxes, 225. Hydroxy oleic acid, 235. Hydroxyanthraquinone, 279. Hydroxyazo-dyestuffs, Formation of, 274. Hydroxystearic acid, 254. Hydroxytolunaphthazine, 299. Hygroscopic character of wool, 258. Hymenma, 242. Hypogajate, Glyceryl, 231. Hyposulphite vat for dyeing with indigo, 323. I Idrian process for making vermilion, 362. Ilicyl alcohol, 239. ,, palmitate, 239. Illipe oil, 227. Illuminants in coal gas, 69. Illuminating effect of gas burnt in different burners, 70. oils, 231, 232, 233, 235, 237. , , power of coal gas, 69. ,, value of acetylene, 74. Incandescent gas burner, 70. INDEX. 461 Indamine, 299. Indamines, 303. Indian red, 363. yellow, 366. Indiarubber, 243. Indican, Hydrolysis of, 319. Indicator for alkalinity, 275. Indicators, 277, 293, 295, 302, 326, 327. Indiglucin, 319. Indigo, 319 ; Artificial, 321. ,, brown, 320. carmine, 324. ,, Cause of fastness of, 322. ,, Composition of, 320. , , Copperas vat for dyeing with, 322. disulphonic acid, 324. ,, Dyeing with, 322. Dyestuff similar to, 282. extract, 323. Purple, 324. „ gluten, 320. ,, Hyposulphite vat for dyeing with, 323. monosulphonic acid, 324. ,, Printing with, 324. „ Reduced, 322. ,, Reducing agents for, 320. ,, Solvents for, 320. ,, substitute, 304, 315. sulphonic acids, Preparation of, 323. Synthesis of, 321. , , vat, Dyeing with, 322. ,, white, 320. ,, Woad vat for dyeing with, 322. Yield' of, 320. Indigo/era argentea, 319. ,, tinctoria, 319. Indigotin, Properties of, 320 ; Syn- thesis of, 321. Indirubin, 320, 321. Indophenol, 304 ; Application of, 335 ; Commercial, 304. Indophenols, 303. Induline, 288. Induline B, 314. 3 P>, 314. 6 B, 314. ,, Benzene, 312. Indulines, 312 ; Manufacture of, 314; Soluble, 315. Ingrain colours, 277, 335; Developers for, 333 ; Dyeing with, 333. Ingrain dyeing, Advantage of, 277 ; Methods of, 277. Ink, Printing, 234. Inks, Lithographic, 242 ; Red, 295. Insecticide, Naphthalene as an, 372. Inulin, 1S2. Invert sugar, 183 ; Lsevulose separ- ated from, 182. Invertase, 189, 201. Iodine, 431 ; absorption, 225 ; Ap- plication of, 295 ; Extraction of, from caliche, 432 ; number, 225 ; Uses of, 432. Iridium oxide pigment for glass, 160. Iron buff, 328. ,, liquor, 95. ,, ,, Use of, in dyeing, 334. ,, mordants, 331. ,, pigments, 363. ,, Pyrolignite of, 95. ,, Red oxide of, 363. ,, tanning, 390. ,, Use of, in reducing nitroben- zene, 285. Isatin, 320 ; yellow, 310. Isatis tinctoria, 319. Isinglass, 396 ; Composition of, 397; for fining beer, 204. Iso-amyl cyanine, 317. Iso-butyl alcohol, 217. Iso-cholesterol, 258. Iso-chromatic photographic plates, 317. Iso-dulcitol, 326. Iso-hsematein, 325. Iso-linoleate, Glyceryl, 233. Iso-linolenic acid, 223. ,, series of acids, 226. Isonandra gutta, 245. Iso-oleic acid, 253, 254. Iso-parafnns as lubricating oils, 102. Isoprene, 243. Iso-propyl alcohol, 217. Iso-purpurin, 2S0, 281. Iso-quinoline, 317. Iso-ricinoleic acid, 223. Iso-rosindulines, 313. Ivory black, 365. J Japan black, 253. ,, wax, 227. Jelly, Starch, 187. Jet photometer, 68. ,, sugar, First, 405. Johnson's powder, 405. Juniper, 214. Jute, 262 ; bleaching, 267 ; dyeing, 339 ; fibre, 262 ; fibre, Analysis of, I 262 ; Staple of, 262. 462 INDEX. K Kainit, 114, 195, 426. Kaolin, 143 ; as a loading material, 344 ; Fusibility related to com- position of, 144 ; Zettlitz, 143. "Keg lard," 237. Kelp, 431. Keratin, 257. Keratins, 369. Kermes, 328. Kerosene, 121 ; Flashing point of, 121 ; Shale, 96 ; Standard white, 121 ; Water white, 121. Kid, 390. Kier, 265. Kiers, 345. Kieselguhr, 406; Specific heat of, 407. Kieserite, 426 ; Block, 427. Kiln, Claus, 33; Hoffmann's 136; Pipe, 179 ; King, 136. Kilns, Cement, 135 ; Dietzsch, 135 ; for earthenware, 150 ; Lime, 128 ; Malt, 191 ; Stage, 135. King's yellow, 361. Kips, Arsenic, 372 ; defined, 371 ; East India, 372. Knapp's theory of the colour of ultramarine, 355. Knoppern, 374. L Laccainic acid, 328. Lac-dye, 242, 328. Lac, Grain, 242 ; Seed, 242 ; Shell, 242 ; Stick, 242. Lacmoid, 302. Lacquers, 242. Lactate, Antimony, 418. Lactic acid, 417 ; Ethylidene, 417 ; from whiskey stills, 211 ; Uses of, 418. Lactose, 180. Lsevopinene, 240. Lsevulose, 182; separated from invert sugar, 182 ; Sweetening power of, 182. Lager beer, 200 ; Pilsener, 205. Lake, Colour, 330 ; Magenta, 365 ; "pitch," 124. Lakes, Crimson, 328 ; Pigment, 365. Lamp black, 364. "Land phosphate," 107. "Land pitch," 124. Lanolin, 258 ; Emulsifying power of, 258. Lanuginic acid, 271. Lapis lazuli, 354. Lard, 228, 237 ; Adulterations of, 237; as food, 237 ; "Bladder," 237 ; Cotton seed oil, an adulterant of, 237; Imitation, 232; "Keg," 237 ; Melting point of, 237 ; oil, 227, 237 ; oil group of oils, 227 ; Properties of, 237. Latches, 380. Laurate, Glyceryl, 236. Laurel oil, 2.27. Laurie acid, 227. Lauth's violet, 304. Leaches, 380. Lead, Antimoniate, 361 ; Brown sugar of, 95 ; Caledonian White, 353 ; Chlorosulphite of, 353. Lead chromate, 360 ; Basic, 361 ; basic, Dyeing with, 328 ; Dyeing with, 328. Lead for vitriol chambers, 7. ,, fume, Composition of, 352. ,, glass, 157. ,, glass-pot, 158. ,, oxide for glass, 151. , , oxide, Preparation of, 362. pans, Concentration of vitriol in, 15. plaster, 250. ,, Quality of, for vitriol pans, 15. „ Red, 361. ,, soap, 250. „ sulphate, 360. ,, sulphate, Manufacture of, from galena, 352. ,, thiosulphate, 412. „ W T hite, 349. Leather, 367 ; Adulterations of, 392; Analysis of sole, 392 ; Artificial grain on, 393 ; Chamois, 391 ; Character of good, 392 ; Colour of, 368, 386 ; Curried, 389 ; Currying, 393 ; Dressed, 389 ; Dressing, 389 ; Oils for, 236, 238 ; Drying, 392 ; Dyeing, 393 ; Enamelled, 393 ; Fixing tannin in, 393 ; for dress- ing, Tanning of, 389 ; for dyeing, 389 ; for soles, Tanning of, 386 ; Grain of, 368 ; Heavy, 371 ; Japanned, 393 ; Light, 371 ; Morocco, 389 ; Patent, 393 ; Russia, 393 ; Scouring, 393 ; Shammy, 391; Striking the colour of, 387; Stuffed, 393 ; Wash, 391 ; White, 390 ; Whitening, 393 ; Yield of, 392. Leathers, Content of tannin in, 395. Leblanc process, 19. ,, soda ash, Apparent density of, 47. INDEX. 463 Lecanora tartarea, 326. 327. Lees, Spent, 211. Lemon, Oil of, 241 ; Salts of, 417 ; yellow, 361. Lepidines, 317. " Letting down " a pigment, 360. Leucindigo, 322. Leuco-com pounds explained, 322. Leucomethylene blue, 306. Levigated chalk, 354. Levigation, 366. .Ley-boil, 266. Lichen colouring matters, 326. Lignin, 262. Ligno-cellulose, 262. Ligroiin, 120. Lima-wood, 325. Lime, 129; Air-slaked, 130; Bird-, 239 ; Bird-, from holly, 239 ; Blue lias, ] 32 ; -boil, 266 ; -bowk, 266 ; Brown acetate of, 93, 95 ; burn- ing, Principles of, 127 ; Dead burnt, 130; "Fat," 127, 130; "Flare," 128; for glass, 151; Grey acetate of, 93, 95 ; Hydrau- lic, 1 32 ; -kiln gases, Carbon dioxide in, 46 ; kilns, Typical, 128 ; Over-burnt, 130 ; pits, 383 ; "Poor," 127, 130; Purification of beet juice by,, 67 ; purifier, Action of, on coal gas, 65 ; Saponification by, 252 ; Slaked, 130 ; Slaking of, 130; Solubility of, 130; sour, 266 ; Sources of phosphate of, 107; specks, 382 ; Sugar recovered from molasses by, 174 ; used in coal distillation, 61. Limestone, 126 ; Analysis of, 126. Limestone, Analysis of blue lias, 132; of hydraulic, 126; of lime from blue lias, 133 ; of magnesian, 126 ; of Theil, 132. Limestone, Blue lias, 132 ; Chem- istry of burning hydraulic, 133 ; Dolomitic, 126 ; for alkali manu- facture, 21 ; Theil. 132. Liming hides, 382. Limonene, 241. Linen-bleaching, 267. Linoleate, Glyceryl, 233. Linoleic acid, 223. ,, series of acids, 226. Linolenic acid, 223. ,, series of acids, 226. Linoleum, Oils used for, 234, Linoxyn, 233. Linum usitatissimum, 260. Linseed oil, 226, 233 ; Adulteration of boiled, 234 ; Baltic, 234 ; cake 1 as fodder, 233; Calcutta, 234; Chemistry of drying of, 233 ; East Indian, 234; Grades of, 234; group of oils, 226 ; Oxidation of, 234 ; Preparation of boiled, 234 ; Properties of, 233 ; Properties of boiled, 234 ; Polymerisation of, in ■ boiling, 234 ; Raw, 233 ; Refining of, 233. Lintner's standard of diastatic power, 193. Liqueurs, 218. Litharge as a drier, 234. Lithographic inks, 242. Litmus, 327. Lixiviation of black ash, 27. Loading materials for paper, 344; for rubber, 244. Loaf sugar, 180. London deep- well water, 195. gas, Statutory limit for ammonia in, 75. Logwood, 324, 334 ; "Ageing" of, 324 ; Colours yielded by, with different mordants, 325. " Low wines," 211. Lubricants, Mineral, rendered vis- cous, 234 ; Rosin grease for, 242. Lubricating oils, 231, 232, 233, 235, 236, 237, 289; from Russian petro- leum, 123 ; Iso-paraffins in, 102. Lubrication, Olive oil for, 231. Lucifer matches, 411. Lunge's bleaching process, 267. Lupulic acid, 194. Lupulin, 194. Lupulus humulus, 194. Luteolin, 326. Lye, Spent, from soap works, 249. Lysol, 79. M Machinery oil, 123. Mactear process for alkali waste, 34. Mactear's salt-cake furnace, 23. "Madder," 280 ; bleach, 265. Madeira, 208. Magdala red, 301 ; Manufacture of, 301. Magenta, 287, 334 ; Acid, 288, 336 ; base, 288 ; Dyeing properties of, 288 ; lake, 365 ; Preparation of, 287; Yield of, 288. Magnesia, Silicate of, 263. Magnesian limestone, Analysis of, 126. Magnesium bisulphite for making wood pulp, 347. 464 INDEX. Magnesium chloride, Electrolysis of, 267. ,, hypochlorite, 267. ,, manganite, 39. ,, silicate as a loading material, 344. Magnetic separator, 196. Main, Foul, 62 ; Hydraulic, 62. Maize, germ cake as fodder, 233. ,, ,, of, removed, 186. Maize oil, 226, 233 ; Properties of, 223 ; Yield of, 233. Maize, Spirit from, 216 ; starch, 186; Starch extracted from, 186. Malachite green, 360, 391. Malic acid in grapes, 206. Malt, 190 ; adjuncts, 193 ; Analysis of, 192 ; Diastatic power of, 192 ; Drying, for whiskey, 210 ; Green, 191 ; Grinding, 196 ; High-dried, 191 ; kilns, i91 ; Mashing, for whiskey, 210 ; Medium, 191 ; Reason of mealiness of, 1 93; Slack, 191 ; Screening, 191 ; screen, " Water-fall," 191 ; vinegar, 221 ; Vinegar from, 220 ; vinegar, White, 222. Malted barley, "Mealiness "of, 191. Malting, 190 ; Barley for, 192 ; Character of barley for, 190 ; Chemistry of, 192 ; difficult in summer, 191 ; Pneumatic, 191 ; Saladin system of, 191. Malto dextrin, 196. Maltose, 181, 197. Manganates, 422 ; decomposed by water, 422. Manganese, " Available oxygen "in, 35 ; borate as a drier, 234 ; brown, Dyeing with, 328 ; dioxide for purifying spirit, 216 ; dioxide in soap, 249. "Manganese," Valuation of, 35; Weldon recovery process for, 37. Manganite, Calcium, 37 ; Magne- sium, 39 ; Manganous, 37. Manganous borate, 234. ,, manganite, 37. Manioc, 187. Manure, Ammonium sulphate as, 112 ; Beet sugar sludge as a, 169 ; Bones for, 111 ; Definition of, 106 ; Dried blood as, 113 ; Drier for, 109; Farmyard, 114; General definition of, 106, 114; Horns and hoofs as, 113 ; Rape cake as, 116, 232 ; salts, 76 ; Sewage as, 115 ; Shoddy as, 1 13 ; Sodium nitrate as, 112; Soot as, 112; Water from starch factory as, 185 ; Wood ashes as, 114. Manures, " Grass," 108 ; Nitro- genous, 112; Organic nitrogenous, 113 ; Phosphatic, 106 ; Potash, 114 ; Rate of assimilation of phos- phatic, 111 ; Special, 106. Maple sugar, 177. Maranta arundinacea, 187. Marble, 126. Marc, 206 ; Fusel oil from brandy, 217 ; Olive, 231. Margarine, 238 ; Coco-nut oil for, 238; Manufacture of, 238; Pro- perties of, 238 ; Yellow colour imparted to, 238. Marine animal oil, 338. ,, ,, oils, 228. „ Winning of, 229. Market bleach, 265. Marls, Clay, 144. Martius yellow, 273. Masher, Steel's, 196. Mashing, 196 ; and boiling, Influence of water on, in brewing, 199 ; Chemistry of, 196 ; Influence of temperature on, 197 ; malt for whiskey, 210. Mash tun, 196. Massecuite, 172, 179. Massicot, 362. Mastic asphalt, 125. Matches, 408, 411 ; Common, 411 ; Composition for, 411 ; Extinction of glow of, 412 ; Head composition for safety, 411 ; Lucifer, 411 ; Rubber composition for safety, 411; Safety, 411 ; Waterproofed, 412 ; without phosphorus, 412. Mather and Piatt process, 266. Maturing of whiskey, 212. Mauve, 301. Mauveine, 301. " Mechanicals," 244. Meilers, Charcoal burning in, 88. Melanin, 366. Meldola's blue, 307, 334. Melinite, 408. Melissic acid, 239. Menhaden oil, 228. Mercuric fulminate, 408. ,, iodide, 363. sulphide, 362. Mercurous chromate, 329. "Metal," 155. Metalepsis, 295. Metaphenylenediamine, Formula for, 274. Metaphosphoric acid, 409, 416. INDEX. 465 Metatoluylenediamine, 299. Methyl alcohol, 94 ; Boiling point of, 9-4 ; Specific gravity of, 94. Methyl chloride, 429. ,, orange, 274. . ,, pyridine, 105. ,, quinonediimide methochlo- ride, 306. ,, salicylate, 241, 419. violet, 289, 334. Methylated spirit, 218. Methylation of aniline dyestuffs, 289. Methylene blue, 305. ,, violet, 307. Methylpararosanilines, 289. Mica, 143. Milk, Cream separated from, 237. Milk sugar, 180, 181 (see Sugar, Milk). Mill-cake gunpowder, 402. Milner's process for making white lead, 351. Mimosa, 378. Minium, 361. Minor chemical manufactures, 413. Mochyl alcohol, 239. ,, palmitate, 239. Moellon, 391. Molasses, 164 ; Analysis of, 164 ; Beet, 172 (see also Beet molasses) ; Fermentation of, 215 ; Scheibler's process for recovery of sugar from, 175; Spirit from, 216. Molasses, Sugar recovered from, by direct removal of potash, 176 ; by elution, 174; by lime, 174; by osmosis, 173 ; by Staffen's pro- cess, 174 ; by strontia, 175. Monazo-compounds defined, 275. Mond s chlorine recovery process, 50. Monocalcium saccharate, 174. " Monohydrate " sulphuric acid, 16. Monosaccharate, Calcium, 167. Monostrontium saccharate, 175. Mordant, Aluminium sulphocyan- ide as a, 341 ; azo-dyestuffs, Ap- plication of, 337 ; Chromium acetate as a, 341 ; Chromium fluoride as a, 33S ; colours, Dyeing silk with, 339 ; colours, Dyeing wool with, 337 ; defined, 270 ; dyes, 330 ; dyes, Examples of, 334 ; dyestuffs, Azo-colours con- verted into, 337 ; Oxidising, 331 ; Non-oxidising, 331. Mordanting by chlorination, 264. Mordants, Acid, 331 ; Aluminium, 330 ; Basic, 330 ; Chromium, 331 ; General consideration of, 330 ; Iron, 331 ; Saddening, 330 ; Tin, 331. Morin, 325. Morocco leather, 389. Morphine in hops, 194. Mortar, 130; Effect of temperature on setting of, 131; "Hardening" of, 130 ; Setting of, 130. Morus tinctoria, 325. Moselle, 207. Mother of vinegar, 219. Moulds, 189 ; in yeast, 202. Mucedin, 192. " Multiple effect," evaporators, 170, 346. Muriate of potash, 400. Muriatic acid, 25. Must, 206 ; Fermentation of, 206. Mustard oil, 226. Mycoderma aceti, 219. Myricyl alcohol, 225. ,, cerotate, 228. palmitate, 225, 239. Myristate, Glyceryl, 238. Myrobalans, 377. Myrtle wax, 227. N Nankin yellow, 328. Naphtha, Crude, from coal tar, 78; from petroleum, 120; "Green," 100 ; Mineral, ior denaturing alco- hol, 21 S ; Solvent, from shale, 101 ; Wood. 93 ; Wood, for denaturing alcohol, 218. Naphthalene, 81 ; as an insecticide, 372 ; blue, 307 ; Boiling point of, 81 ; Distillation of, 81 ; Enriching gas by, 73 ; from Russian pet- roleum, 123; Melting point of, 81 ; red, 301 ; Specific gravity of, 81 ; sulphonic acid, 385; tetrachloride, 293 ; Uses of, 81 ; Yield of, from tar, 81. Naphthazine, 279. Naphthenes in Russian petroleum, 123. Naphthindophenol, 304. Naphthindulines, 313, 315. Naphthol blue, 304; green, 302; yellow, 273, 336. Naphthols, Dyestuffs from, 275. Naphthoquinone, Formula for, 279. Naphthoquinoneoxime, 283. Naphthoquinoneoximes, 302. Naphthylamine, a-, 298. 466 INDEX. Naphthyl blue, 315. Naples yellow, 361. Natural gas, Analysis of, 118. Neatsfoot oil, 227, 236 ; Properties of, 236 ; Refining of, 236. Newlands, see Duncan. Night blue, 290. Nightlights, Coco - nut oil, 251 ; "Stearin," 251. Nigraniline, 312. Nigrosines, 315. " Ninety per cent." benzol, 79. Nitrate of iron, Use of, in dyeing, 331. Potassium, from the osmose process, 174. Sodium, as manure, 112; in Glover tower, 14 ; com- mercial, Analysis of, 113; crude, Analysis of, 112; crude, Purification of, 112. Nitrated cellulose varnishes, 246. Nitration of benzene, 284. Process of, 273. Nitre, 400 ; -cake, 6 ; Causes of loss of, in vitriol making, 13 ; pot, 6 ; Purification of, 400 ; Quantity of, used in vitriol making, 13. Nitric acid, Commercial grades of, 11 ; Condensation of, 9 ; condenser, Guttmann's, 10; Impurities in, 11; in vitriol making, 14 ; manufac- ture, 8 ; still, 8. Nitrification, Process of, 113. Nitrifying organism, 113. Nitrite, Potassium and cobalt, 361. Nitro- alizarin, 2S2. Nitrobenzene as an oxidant, 288. , , Manufacture of, 284 ; Properties of, 284 ; Uses of, 284. Nitro-colouring matters, Applica- tion of, 336. -compounds (dyestuffs), 273. ,, explosives, 403. Nitrogen, Assimilation of, from air, 114; Distribution of, in coal dis- tillation, 61 ; in bones, 111 ; in coal for alkali manufacture, 22; in shale products, Distribution of, 103. Nitrogenous guano, 115. manures, 112, ,, organic manures, 113. Nitro-glycerin, 405 ; Absorbents for, 406 ; Equation for explosion of, 406; explosives, 405; Gas evolved by explosion of, 406 ; Manufacture of, 405 ; Properties of, 406 ; re- converted into glycerin, 406 ; Thermal effect of explosion of, 406 ; Yield of, 405. Nitromonas, 113. Nitronaphthalene for debloomiDg oils, SI. Nitrophenyllactomethyl ketone, 321. Nitroso-dimethylaniline as an oxi- dant, 307. Nitrosyl sulphuric acid, 11. Nitro- tartaric acid, 310. "Nitrous acid," 9; Use of, in making dyestuffs, 274. Nitrous vitriol, 13. Non-drying oils, 224, 226. Non-illuminant combustible gases in coal gas, 69. Non-tannins, 378; in tanstuffs, Char- acter of, 379. Nordhausen sulphuric acid, 17. Nut oils, 231. 0 Oak bark, 376. „ galls, 374. ,, reds, 376. Ochre, Analysis of Oxford, 364. Ochres, 363. (Enanthic ether, 208. Oidium, 206. Oil, Blue, 101 ; Cold drawn, 229 ; Constituents of crude seed, 229 ; Crude, from shale, 100 ; Crude, from shale redistillation, 100 ; Cylinder, 123 ; extractor, 230 ; for oil-water gas, 72 ; from cold press, 229 ; from feet of cattle, 236 ; from hot press, 229 ; gas, 74 (see Gas, Oil); " Green," 101 ; Light, from coal tar, 78 ; Machinery, 123; Mineral, 117 ; from petroleum, 121; Red, 252 ; resins for varnishes, 243 ; Rock, 117 ; soluble in alco- hol, 235 ; Spindle, 123 ; used for linoleum, 234 ; Virgin, 231. Oil, refining, Animal charcoal used in, 229 ; Oxidants used in, 229 ; Permanganate used in, 229 ; Sul- phonic acids formed in, 229 ; Sul- phuric acid used for. 229. Oil-water gas, Composition of, 72. ,, Solar oil for, 72. Oils and fats, Classification of, 226 ; Hydrolysis of, 224 ; Preparation of, 226 ; Properties of, 226 ; Pro- perties and uses of, 231 ; used in soap making, 247. INDEX. 4G7 Oils, Blown, 234 ; Buttery, 236 ; con- taining other than glyceryl salts, 228 ; containing saturated fatty acids, 227 ; containing unsaturated fatty acids, 226 ; Deblooming mineral, 122 ; defined, 233 ; Dry- ing, 233 ; Drying, denned, 224 ; equivalents, Mean of, ascertained, 225 ; Essential, 240 ; Extraction of, by volatile solvents, 229 ; for leather dressing, 236, 23S ; for food, 231, 232, 23:5; Groups of, 226 ; Identification of, 225 ; Illu- minating, 231, 232, 233, 235, 237 ; Lubricating, 231, 232, 233, 235, 236, 237, 239 ; Lubricating, from Russian petroleum, 123 ; lubricat- ing, Iso-paraffins as, 102 ; Marine animal, 228 ; Non- drying, 224, 226 ; of cotton seed oil group, 226 ; of high viscosity, 227 ; of linseed oil group, 226 ; of olive oil group, 226 ; of rape oil group, 226 ; of the castor oil group, 227 ; of the coco- nut oil group, 226 ; of the cruci- ferse, 226 ; of the lard oil group, 227 ; of the palm oil group, 227 ; of the sperm oil group, '228 ; of the tallow group, 227 ; of the whale oil group, 228 ; Oxidation of dry- ing, 224 ; resins and varnishes, 223 et seq. ; Semi-drying, 232, 233; Solid, 227 ; Tanning with, 391 ; used as tans tuffs, 381 ; used in currying, 393 ; Viscosity imparted to, 234 ; which become rancid, 226, 236 ; Winning and refining of animal, 229 ; Winning and refining of vegetable, 228 ; Winning of essential, 241 ; Winning of marine animal, 229 ; won from fruit, 228 ; won from fruit seed, 228. Okonite, 124. Olea Ewopcea, 231. Oleate, Dodecatyl, 239 ; Glyceryl, 225, 226, 227, 228, 231, 233, 236, 237 ; Sodium, 225. Oleic acid, 223, 228 ; converted into palmitic acid, 254; Distilled, 253; Solid fatty acids made from, 255. Oleic series, Acids of the, 226, 228. Olein, 224, 252. Oleo-resins, 240, 242. Olive kernel oil, 231. ,, marc, 231. Olive oil, 231 ; Adulterants of, 231 ; Composition of, 231 ; for lubrica- tion, 231 ; group, Oils of, 226 ; Iodine absorption of, 231 ; Pro- perties of, 231 ; Saponification equivalent of, 231 ; Specific gravity of, 231 ; Uses of, 231 ; Winning of, 231 ; Yield of, 231. Olive press-cake, 231. Olives, 231. Omentum of pig, Fat from, 237. O.P., 218. Open test, Flashing point, 121. " Open woods " (dyewoods), 325. Orange red, 362. Orcein, 327. Orcellic acid, 326. Orcellinic acid, 327. Orchella weed, 326. Orchil weed, 326. Orcin, 326. Orcinol, 326, 327. Organised ferments, 189 ; classified, 189 ; Typical effects of, 189. Organism, Denitrifying, 113 ; Nitri- fying, 113. Orientation of anthracene, 279. Orleans process fcr making vinegar, 219. Orpiment, 361. Orris root, 214. Orr's zinc white, 353. I Orthamidoazotoluene, 298. I Orthochromatic photographic plates, 295. I Orthoclase, 143. 1 Orthonitrobenzoic aldehyde, Formula for, 318. Orthophenylenediamine, 298. Orthotoluylenediamine, 298. Oryza sativa, 185. Osazones, 310. j Osmose process, 173; Apparatus for, 173 ; Potassium nitrate from the, 174. Osmosis, Sugar recovered from molasses by, 173. Osseine, Analysis of, 105. Over-burnt lime, 130. ,, -proof, 218. Oxalate, Potassium antimony, 417 ; use in dyeing, 332. Oxalates, Acid, of potassium, 417. Oxalic acid, 416 ; as a solvent for Prussian blue, 357 ; Impurities in, 417 ; Manufacture of, 417 ; Pro- perties of, 417 ; Use of, in dyeing, 331 ; Uses of, 417 ; Yield of, from wood, 417. Oxazine dyestuffs, 307. Oxford ochre, Analysis of, 364. Oxidant, Arsenic acid as an, 287; Ferric chloride as an, 305 ; Ferri- 468 INDEX. cyanides as an, 342; Nitrobenzene as an, 288 ; Nitroso-dimethylani- line as an, 307. Oxidants used in oil refining, 229. Oxidation, Bleaching by, 2(54; Fusel oil removed from spirit by, 216 ; of alcohol, 219 ; of linseed oil, 234 ; Spongy platinum inducing, 219. Oxide, Ferric, purifier for coal gas, 64 ; Spent, 265 ; Sulphur in spent, 65 ; " vessel," 65. Oxycellulose, 272. Oxychloride of copper, 358. " Oxygen, Available," in manganese, 35. Oxygen carrier, 289. carriers, 288, 311. for making blown oils, 235. ,, Use of, in glass making, 155. Ozokerite, 123; candles, 252; Melt- ing point of, 124 ; Refining, 129 ; Specific gravity of, 124. Ozone for purifying spirit, 216. P Pack of hides, 383. Paint defined, 348. „ "Ground," 366. ,, "Mixed," 366. Paints, 366 ; and pigments, 34S ; Vehicles for, 366. Palmitate, Cetyl, 228, 239 ; Glyceryl, 228, 231,236 ; Ilicyl,239 ; Mochyl, 239 ; Myricyl, 225, 239. Palmitic acid, 223, 227 ; Manufac- ture of, 252 ; Oleic acid converted into, 254. Palmitin, 224. Palm kernel oil, 236. nut oil, 227. ,, oil, 227, 236. oil group, Oils of the, 227. oil, Properties of, 236. ,, pith, 187^ ,, sugar, 177. Pan process of saponification, 252. Panclastite, 408. Pandermite, 414. Paper and pasteboard, 344. Paper, Cellulose for making, 344 ; Loading materials for, 344 ; Manu- facture of, from rags, 344. Para - amidophenylamido - acridine, 318. Para - amidophenylmethylquinoline, Para rubber, 243. " Parachutes," 203. Paraffin candles, 251. oil, 101. ,, oil from petroleum, 121. ,, scale, 102. Paraffin wax, 102; Decolorising, 433; from petroleum, 121 ; in Russian petroleum, 123 ; Melting point of, 102. Paraleucaniline, Formula for, 283. Paranitraniline, Scarlet from, 335. Paraphenylene diamine, 299. Pararosaniline base, Preparation of, 286. Formula for, 283. methylated, 289. Paratoluidine, Condensation with sulphur, 277. Parchment, 391. Parian porcelain, 149. Paris red, 362. Parnell and Simpson process for alkali waste, 33. Pars papillaris, 368. ,, reticularis, 368. Pasteboard and paper, 344. Paste, Manufacture of porcelain, 146; Starch, 187. Patent blues, 336. Pathological tannins, 375. Peach wood, 325. Pea-nut oil, 231. Pearl hardening as a loading mate- rial, 344. Peat, Destructive distillation of, 87. Pebble gunpowder, 402. Pectic acid, 261. Pectin, 261. Pectose, 261. Pentahydroxyanthraquinone, 282. Pentakaidecatyl alcohol, 228. Pentane, 120. Pentoses, 192. Peonine, 292. Perchlorate in Chili saltpetre, 432. ,, Potassium, in saltpetre, 401. Perfumes, 241. Permanganate, Potassium, 423 ; Bleaching by, 267 ; Sodium, 422 ; used in oil refining, 229. Permanganates, 422. Peroxide of hydrogen, Bleaching by, 264, 265 ; sodium, Bleaching by, 264. Perry, 209 ; vinegar, 221. Perseo, 327. Persian berries, 326. INDEX. 469 Peru balsam, 242. Petroleum, 117 ; Anthracene from Russian, 123 ; benzine from, 120; benzole from Russian, 123 ; "Cracking," 119; distillation, Coke from, 122 ; Distribution of, 117 ; ether, 120 ; Lubricating oils from Russian, 123 ; Naphtha from, 120 ; Naphthalene from Russian, 123 ; Naphthenes in, 123; Origin of, 117; Paraffin oil from, 121 ; Paraffin wax from, 121 ; Paraffin wax in Russian, 123 ; Pitch from Russian, 123 ; "reduced oil," 120; Refining burning oil from, 121 ; Refining of, I 119 ; Russian and American, com- pared, 119, 123 ; Solidification of, 123; Transmission of, 119; Vaseline from Russian, 123 ; Winning of, 118 ; Yellow wax from, 122. Phenanthraquinone, 311 ; red, 311. Phenazine, 297, 298. Phenol, 80 ; blue, 304 ; Boiling point of, 80 ; Discoloration of, 80 ; Melting point of, 80 ; Salicylic acid prepared from, 419. Phenolazobenzene sulphonic acid, Formula for, 275. Phenoldisazobenzene, Formula for, 275. Phenolphthalein, 293. Phenosafranine, 300. Phenylene blue, 303. Phenylglycocine, Formula for, 321. Phenylhydrazine, 310. Phenylrosinduline, 315. Phlobaphenes, 376. Phoenix sylvestris, 177. Phosphate, Chromium, 359 ; "Dical- cium,"109; "Land," 107; of lime, Sources of, 107 ; of soda, Applica- tion of, in calico-printing, 341 ; \ of soda. Application of, in dyeing, 338 ; of soda, Rhombic, 416 ; pre- cipitated, 109 ; precipitated, Use of alkali waste in manufacture of, 109 ; Redonda, 107 ; Reverted, 109 ; River, 107 ; Soluble, 107, 108, 109. Phosphates, Analysis of native, 108. Phosphatic guano, 115. , , gypsum, Analysis of, 409. ,, manures, 105. ,, ,, Rate of assimila- tion of, 111. Phosphine, 287, 319. Phosphoric acid, 416 ; Glacial, 416 ; Manufacture of, 409. Phosphorite, 107. Phosphorus, Distillation of, 409 ; Electric furnace for, 410 ; Manu- facture of, 409; Manufacture of red, 410 ; Matches without, 412 ; Properties of red, 408 ; Properties of yellow, 408 ; Readman and L Parker's process for making, 410 ; Refining, 410 ; Yield of, 410. | Photographic developer, 375. ,, plates, Orthochroma- tic, 295. j Photometer, Evans, 67 ; Jet, 68. Photometrv, 68. Phthalein clyestuffs, 292. Phthalic anhydride, Preparation of, 293. Phthalophenone, 293. Phylloxera, 206. Physeter macrocpphalvs, 239. Physetoleate, Glyceryl, 238 ; dode- catyl, 239. Physical theory of dyeing, 271. Physiological tannins, 375. Phytosterol, 228. Picoline, 105. Picric acid as an explosive, 408. ,, Melting point of, 273. ,, Preparation and proper- ties of, 273. Pigment lakes, 365. . , Iridium oxide for glass, 160. ,, " Letting down " a, 360. ,, Platinum, for glass, 160. ,, stannic chromate, for glass, 160. , , stvle of calico - printing, 341. ,, Uranium oxide, for glass, 160. Yellow, 360. Pigments and paints, 348. Black, 364. Blue, 354. Body of, 348. ,, Colour of mixed, 348. ,, Covering power of, .'US. „ defined, 348. ,, DyestufFs distinguished from, 270. ,, Green, 358. Iron, 363. Mineral, 349. Red, 361. ,, Theory of colour of, 348. White, 349. ,, ,, containing lead,352. Pilsener lager beer, 205, Piutsch system for oil gas, 74. 470 INDEX. Pitch, Coal tar, 82 ; Composition of, 82 ; epure\ Composition of, 125 ; from Russian petroleum, 123 ; "Hard,"82 ; "Lake," 124; "Land," 124 ; " Soft," 82 ; Softening point of, 82 ; Stearin, 253. " Pitching" wort, 199. Pith, Palm, 187. Plaster, Lead, 250. Plaster of Paris, 131 ; Effect of, on fermentation of wine, 20S ; Setting of, 131. Plastered wines, 208. Plasticity related to composition of clays, 144. Plate column, 7. Platinum. Corrosion of, by vitriol, 15. pigment for glass, 1G0 ; Spongy, inducing oxidation, 219 ; stills, Concentration of vitriol in, 15. " Ploughing" barley during malting, 191. Plumped hides, 383. Plumping hides, 370, 372. Plumule, 191. Pneumatic malting, 191. Poisoning by white lead, Prevention of, 352. *' Poisoning the pan," 20. Polarimeter, 198. Polyhalite, 426. Polyprene, 243. Polymerisation in boiling linseed oil, 234. Polyricinoleic acid, 235. Poppy-seed oil, 226. Porcelain, 146 ; Berlin, 147 ; Biscuit, 149 ; clay, 144 ; Colouring, 148 ; English soft, 148; frit, 148; Glazed, 147 ; Glazes for, 147 ; Hard, 146 ; Parian, 149 ; paste, Manufacture of, 146 ; Reaumur's, 157 ; Sevres, 148 ; Soft, 148. Port, 208. Portland cement, 134 ; Analysis of clay for, 138 ; Analysis of materials for, 138 ; Hardening of, 139 ; Materials for semi-dry process of, 134 ; Materials for wet process of mixing, 131; Setting of, 139. Pot-ale, 211. Pot, Nitre, 6 ; still, 211. Potash, Caustic, 42S ; from beet sugar residues, 428 ; from suint, 429 ; from wood ashes, 428 ; from yolk, 429 ; glass, 157 ; Manufac- ture of carbonate of, 428; manures, 114; Red prussiate, 434 ; salts, 426; soap, 217; Sugar recovered from molasses by direct removal of, 176 ; Yellow prussiate of, 433. Potashes, 427. Potassium aluminium sulphate, 424. ,, antimony oxalate, Use of, in dyeing, 332. ,, bichromate, 421. ,, bromide, 431. ,, carbonate, 427- ,, chlorate, Manufacture of, 42. ,, ,, Separation of, by cooling, 42. , , chloride, Winning of, 426. ,, chromium sulphate, 426. ,, cyanide, 434. ,, ferrocyanide, 433, 434. ,, ,, Uses of, 434. iodide, 432. ,, nitrate, 400. ,, ,, from the osmose process, 174. perchlorate in saltpetre, 401. ,, permanganate, 433. ,, ,, bleaching by, 267- „ for purifying spirit, 216. ,, salts, Sources of, 427. ,, sulphate, 427. ,, sulphocyanide, 434. ,, thiocyanate, 434. ,, ultramariue, 355. Potato, Saccharitication of starch in, 215; spirit, 215,216; starch, 184. Potatoes, Diseased, used for starch making, 1S5 ; for starch, 184 ; Frost-bitten, 184 ; Fusel oil from, 217 ; Loss of starch in, by frost, 184 ; Loss of starch in, by oxida- tion, 184 ; Specific gravity of, in- dicating starch content, 184. Pottery clays, Analysis of, 143 ; Properties of, 143. Pottery, Kinds of, 146. Poudrette, 115. Precious stones, Imitation, 158. Precipitation processes of making- white lead, 351. Preservative, Salicylic acid as a, 416 ; Saltpetre as a, 401. Press-cake, Gunpowder, 402 ; Olive, 231. Press, Filter, 168 ; Hydraulic, 229. " Pressure bowl," 340. Priming beer, 204. Primuline base, 277. ,, dyestutls, 277. INDEX. 471 Prinmline, Method of dyeing with, 278. , , Photographic application of, 278. ,, yellow, 277. Printing, albumin, Application of, in calico, 341 ; Application of acetic acid in cotton, 340 ; Arsen- ate of soda, Application of, in calico, 341 ; Block, 340 ; blood albumin, Application of, in calico, 341 ; Calico, 340 : Colour, 340 ; Discharge style of calico, 341 ; Dyeing style of calico, 341 ; ink, 234 ; phosphate of soda, Ap- plication of, in calico, 341 ; Pig- ment style of calico, 341 ; Resist style of calico, 342 ; Roller, 340 ; Steam style of calico, 340 ; Styles of cotton, 340 ; Thickening agents for calico, 340 ; with aniline black, 311 ; with indigo, 324.; Wool, 342. Producer gas, 72 ; Composition of, 60 ; for retort furnace, 59. Proof spirit, 218; Specific gravity of, 218. "Proof stick, '' 179. "Proof vinegar," 221. Propyl alcohol, 217. Protocatechuic acid, 376. Prune, 308. Prussian blue. 356 ; Dyeing with, 328 ; Manufacture of, 356 ; Oxalic acid as a solvent for, 357; Solu- bility of, 357 ; Soluble, 357. Prussiate of potash, Red, 434 ; Yel- low, 433. Pseudo-indoxyl, 321. Puer, 3S4. Pugmill, 366 Purifier. Arrangement of gas, 65 ; for coal gas, Ferric oxide, 64 ; Lime, Action of, on coal gas, 65 ; Revivification of spent, 64. Purifiers, Gas, 64. Purpurine, 280. Purre'e, 366. Putrefaction applied in winning oils, 229. Puzzuolana, 140 ; Analysis of, 140. Puzzuolanic cement, 140. Pyridine, 105 ; bases, 78 ; bases for denaturing spirit, 219 ; Methyl, 105. Pyrites, 2. ,, burners, 2; Dust from, 6. ,, gases, Percentage of oxygen in, 3 ; Percentage of sul- phur dioxide in, 3. Pyrites smalls, 2 ; burner, 5. ,, spent, Sulphur in, 3. Pyritic shale, 425. Pyrocatechol, 298. 376 ; tannins, 376. Pyrogallic acid, 375. Pyrogallol, 375; Application of, 295; tannins, 376. Pyrogallolphthalein, 295. Pyrolignite of iron, 95. Pyrrol, 105 ; red, 105. Q QrjANDEL, 88. Quarter bleach, 267. Quassia, a hop substitute, 194. Quebracho, 378. Quercitannic acid, 374. Quercitin, 326. Quercitrin, 326. Quercitron bark, 326. Quercus cegylops, 377. castanea, 376. ,, cerris, 376. ilex, 328. ,, infectoria, 374. robur, 376. ,, tinctoria, 326. Quick vinegar process, 220. Quinaldine, 317. Quinoline derivatives dyestuffs), 316. ,, from coal tar, 317. red, 317. ,, yellow, 317. Quinonedichlorimide, 303. Quinone derivatives (dyestuffs), 278. Quinonedi-imide, 303. Quinonedioxime, 302. Quinone dj'estuffs, Application of, 279. Quinoneoximes, 282, 302. "Quinonoid structure," 278. Quinophthalone, 317. R Rack-a-eock, 408. "Racking-back," 204. Racking beer, 204. Raffinose in beet juice, 165. Rags, Manufacture of paper from, 344. Rancid butter, Butyric acid in, 237. Rancid, Oils which become, 226, 236. Rancidity, Cause of, 224 ; Chemistry of, 224. Rape cake as manure, 116, 232. Rape oil, 226, 232 ; Blown, 234 ; group, Oils of, 226 ; Gumming of, 232 ; Properties, of, 232 ; Uses of, 232 ; Yield of, 232. 472 INDEX. Rapic acid, 223. Rasping machine, 184. Have's treatment of vitriol tar, 101. Headman and Parker process of phosphorus manufacture, 410. Realgar, 361. Reaumur's porcelain, 157. Rectification of crude spirit, 217. Rectified spirit of wine, 218. ,, Specific gravity of, 2 18. Rectifier, 212. Red arsenic, 283. „ lead, 261. „ liquor, 29. ,, Caustic soda from, 31. , , oxide of iron, 363. , , phosphorus, Manufacture of, 110, ,, ,, Properties of, 408. ,, pigments, 361. , , vegetable colouring matters, 326. Redistillations, Crude oil from shale, 100. Redonda phosphate, 107. " Reduced oil," petroleum, 120. Reduction, Bleaching by, 264. Refined alkali, 29. Refrigerators used in brewing, 198. Regenerative burner, 70. Renderiug fats, 229. of tallow, 236. Reseda luteola, 326. Resins, 241 ; defined, 240 ; for var- nishes, 246; Gum, 240,242; Oleo, 242 ; Running, 245 ; varnishes and oils, 223. Resists, 342. Resist style of calico-printing, 342. Resorcin green, 302. Resorcinol, Application of, 293 ; Preparation of, 294 ; Properties of, 294. Resorcinolazobenzene, Formation of, 276. Resorcinoldisazobenzene, Formation of, 276. Resorcinolphthalein, 294. Resorufin, 308. Retort carbon, 61. , , Dimensions of gas furnace, 58. gas furnace, 58. ,, Henderson, for shale distilla- tion, 97, 98. ,, Percentage of coke needed for firing gas, 58. ,, Producer for gas furnace, 59. ,, Scurf, 61. Young & Beilby, for shale distillation, 97, 99. Retorts, Carbonising in, for gas pro- duction, 58 ; Carbonising wood in, 90 ; Charging gas, 60 ; Draw- ing gas, 60 ; Mechanical charging of gas, 60 ; Process of distillation in gas, 60. "Retted " flax, 260. "Retting " flax, 260. Reversion of superphosphate, 109. Reverted phosphate, 109. Revivification of spent purifier, 64. Revolver black ash process, 26. Rhamnotin, 326. Rhamnus amygdalinus, 326. ,, frangula, 401. Rhigolene, 120. Rhodamine, 297, 334 ; S, 297. Rhombic phosphate of soda, 416. Rhus coriaria, 377. ,, colinus, 325. ,, japonica, 374. ,, semialata, 374. Rice starch, 184, 185. Ricinine, 235. Ricinoleate, Glyceryl, 235. Ricinoleic acid, 223, 227. ,, series of acids, 226. Ricinus communis, 235. Rinmann's green, 360. " Rippling ' ; flax, 260. " River phosphate," 107. Roans, 389. Roasters, Blind, 23 ; Open, 23. Roburite, 408. Roccella fuciformia, 326. ,, tinctoria, 326. "Rock," 252. Rocks, Influence of rate of cooling on structure of, 157. Roller printing, 340. Roman cement, Analysis of, 133. Rope, 261. Ropy fermentation of beer, 204. Rosaniline, 287 ; base, 288 ; base, Chemistry of, 287 ; Constitution of, 284 ; hydrochloride, 288 ; salt, Formation of, 287 ; Triphenyl-, 290. Rosin, American, 241 ; Common,. 241. Rosinduline, Phenyl, 315. Rosin grease, 242. „ oil, 242. ,, Properties of, 242. „ spirit, 242. ,, White, 242. Rosolic acid, 292. Rotatory exhauster, Beale's, 62, Rouge, 18, 3(53. Rounding hides, 384. INDEX. Rove, 374. Rubber, Adulterations of, 244 ; Black vulcanised, 244 ; Cause of perishing of, 244 ; Ceara, 243 ; Loading materials for, 244 ; Para, 243 ; Red vulcanised, 244 ; Sol- vents for, 243 ; Surrogates for, 244 ; Vulcanisation of, 244 ; Vul- canised, 243 ; vulcanised, Consti- tution of, 244 ; vulcanised, Pro- perties of, 244. Ruberythrin, 280. Rubia tinctoria, 280. Rum, 215. Rumex hymenosepalum, 378. " Running " resins, 245. Rusma, 383. Russia leather, 393. Russian petroleum, 123 (see also Petroleum). tar, 93. ,, turpentine, 240. s " Sacciiarate," 163 ; Calcium, 167; Distrontium, 175; Monocalcinm, 174 ; Monostrontium, 175 ; Tri- calcium, 174. Saccharates, 174. Saccharatum, Sorghum, 177. Saccharides, 162. Saccharification of starch in potato, 215. Saccharine, Manufacture of, 420. Saccharinum, Acer, 177. Saccharomycetes, 189, 200. Saccharomyces cerevisice, 202. ,, ellipsoldeus, 206. Saccharvm officinarum, 162. Saddening mordants, 330. Safranine, 334 ; T, 300. Safranines, 299. Safety matches, 411 (see also Matches). Safflower, 326. Safrosin, 295. Saggers, 147. Sago, 187. Salad in system of malting, 191. Salicylate, Methyl, 241, 419. Salicylic acid, 419 ; as an antiseptic for beer, 209 ; as a preservative, 420; natural, 419 ; prepared from phenol, 419. Salt, 19 ; Analysis of rock, 19 ; Bay, 20. Salt cake, Composition of, 24 ; fur- nace, 22 ; furnace, Mactear's, 23 ; Manufacture of, 22 ; Yield of, 23. Salt, Calcium sulphate in rock, 19. ''Salt fishing," 20. Salt from sea-water, 21. " Salt gardens," 21. Salt glazing, 149. ,, pans, 20. ,, Rock, 19. Saltpetre as a preservative, 401. ,, Bengal ordinary, 400. ,, earths, 400. ,, flour, 400. ,, Perchlorate in Chili, 432. Potassium perchlorate in,. 401. Salts, 420. Samming, 392. Sandblast, 160. Sanitas, 240. Santal wood, 325. Santorin earth, 140. Sapan wood, 325. Saponification, 225, 247, 248 ; by lime, 252 ; equivalent, 226 ; of fats, 225 ; Pan process of, 252 ; processes, Yield in, 253; with alkali carbonates, 247. Saturated fatty acids, Oils contain- ing, 227. Saucers of vitriol chambers, 7. Saxony blue, 323. "Scale, Crude," 101. Scale, Paraffin, 102. " Scars," 3. Scheele's green, 359. Scheibler's process for recovery of sugar from molasses, 175. Schizomycetes, 189. Schlempe, 428. Schlempekohle, 176, 42S. Schultze's powder, 405. Schweinfurth green, 359. Scott's cement, 132. Scouring cotton, 265. leather, 393. ,, wool, 258. Screening malt, 191. " Scrim," 2.'>4. Scudding hides, 384. Scurf, Retort, 61. "Scutching" flax, 261. Sealing wax, 242. Seal oil, 228, 239. Sea-water, Analysis of, 21 ; Salt from, 21. j Seaweed, 431. Sebaceous glands, 368. I Seed- lac, 242. 474 INDEX. Seed, Oils won from, 228. Seger's cones, 147. Semi-rotation, 181. Separator, Magnetic, 196. Sepia, 365. Sepia officinalis, 365. Septaria nodules, 133. Sericin, 259 ; removed from raw silk, 259. Sesame oil, 226, 233 ; Properties of, 233 ; Uses of, 233. Sesamum orientale, 233. Sesquicarbonate, 30. Sesquiterpenes. 240. Setting of mortar, Effect of tempera- ture on, 131. ,, Portland cement, 139. "Settling back," 204. Sewage as manure, 115. precipitants, 424. Sevres porcelain, 148. Shale, benzine from, 101 ; benzoline from, 101 ; Composition of, 96 ; Crude oil from, 100 ; Crude oil from redistillation, 100 ; Destruc- tive distillation of, 96. Shale distillation, Ammoniacal liquor from, 102 ; Gas from, 103 ; Gaso- lene from, 103 ; Henderson retort for, 97, 98 ; Young and Beilby retort for, 97, 99. Shale "green oil,'' 101. kerosene, 96. Naphtha solvent from, 101. oil, Purifying, 101. oil, Yield of products from crude, 102. Origin of, 96. ,, products, Distribution of nitro- gen in, 103. „ Pyritic, 425. Yield of products from Brox- burn, 97. "Shales, Vitriol," 17. Shammy leather, 391. Shark liver oil, 228. Shaved hides, 3S9. Shellac, 242. Sherry, 208 ; Caramel for colouring, 208 ; cask, Use of, for maturing whiskey, 212. Shoddy as manure, 113. Shot effects in dyed silk, 338. Siemens burner, 70. ,, tank furnace, 144. ,, toughened glass, 156. Sienna, Burnt, 364 ; Raw, 364. Siennas, 363. Silent spirit, 217. Silica for glass, 151. Silicate of magnesia, 263. Silk, 259 ; Analysis of raw, 259 ; Artificial, 259 ; bleaching, 264 ; "Boiled-off," 265; Denization of artificial, 260; "Discharging," 265. Silk dyeing, 388 ; with acid colours, 339 ; with basic colours, 338 ; with direct colours, 338 ; with mordant colours, 339. Silk fibre, 259 ; Behaviour of, to reagents, 259 ; Specific gravity of, 259. Silk glue, 259. ,, Sericin removed from raw, 259. ,, " Stripping," 265. „ " Tussur," 259. ,, " Ungumming," 265. ,, Winding, 259. Silks, Wild, 259. Silver ultramarine, 355. Simon-Carves coke oven, S<>. , , oven, Yield of products from, 87. Simpson and Parnell process for alkali waste, 33. Sintering, 148. Size, 397. "Skimming back," 203. Skimming system of cleansing beer, 203. Skin, Proximate composition of, 369; Structure of, 367. Skin-hardened soaps, 249. Skins and hides, Quality of, 371. ,, defined, 371. ,, Falling of, 373. ,, Ultimate composition of, 371. Skivers, 389. Slack malt, 191. Slag, Analysis of basic, 110; Ball mill for basic, 111; Basic, 110; Cement, 141 ; for cement, Blast furnace, 140 ; wool, 263. Slaked lime, 130. Slaking of lime, 130. Sleekers, 393. Slurry, Analysis of cement, 138; Manufacture of, 134. Small coal for alkali manufacture, 22. Smalls burner, Pyrites, 5. ,, Pyrites, 2. Smalt, 159, 357 ; Analysis of, 357. Smoke, Gunpowder, 402. Smokeless powder, 403. Soaking hides, 381. Soaks, 381. Soap, 247 ; and candles, 247 ; Arti- ficial mottled, 248 ; Cold-water, INDEX. 475 248 ; Curd, 248 ; Detergent action of, 250 ; Detergent pro- perties of, enhanced by alkaline substances, 247; "Figging" in soft, 249 ; Filling materials for, 247 ; Fitted, 248 ; Frothing pre- vented in whiskey stills by, 211 ; Glass-makers', 152 ; Green colour of soft, 249 ; Lead, 250 ; lyes, Glycerine recovered from, 249 ; -making, Fats and oils used in, 247 ; Manganese dioxide in, 249 : Manufacture of, 248 ; Manufacture of soft, 249 ; Mottled, 248 ; Potash, 247 ; Primrose, 248 ; Sodium sulphate in, 247 ; Sugar in, 24S ; Use of, in dyeing, 332 ; Water in, 248 ; Yellowing of wool by, 264. Soaps, defined, 247 ; Household, 249 ; Milling, 249 ; Raw materials for, 247 ; Scouring, 249 ; Soda, 247 ; Toilet, 249 ; Transparent, 249. Soapstone, 344. Soda, Analysis of crude nitrate of, 112; ash, 28; ash, Analysis of, 29 ; Apparent density of ammonia, 47 ; ash, Apparent density of Le- blanc, 47 ; ash, Causticising, by fusion with ferric oxide, 47 ; Bicar- bonate of, 30 ; Caustic, 30; Caustic, from red liquor, 31 ; crystals, 29 ; "glass," 157; Grades of caustic, 31; liquor, Concentration of caustic, 31 ; Purification of crude nitrate of, 112; soaps, 247; Ultramarine, 354 ; Washing, 26. Sod- oil, 391. Sodium alizarate, 281. ,, aluminate, Use of, in dyeing, 331. arsenate, Manufacture of, 416. ,, ,, Use of, in dyeing, 330. „ bicarbonate, Conversion of, into soda ash, 46. ,, bichromate, 421. ,, bisulphite, 6. ,, " carbolate," 79. , , carbonate prepared from cry- olite, 51. ,, chlorate, 43. ,, ,, for alizarin manu- facture, 281. ,, chloride, Effect of, in water for brewing, 199. ,, chromate, 421. ,, citrate as a resist, 342. ferrite, 47. fluoride as an antiseptic for beer, 204 ; as a softening agent, 413. metaborate, 415. nitrate as manure, 112. ,, Commercial analysis of, 113. ,, in'„Glover tower, 14. ,, Use of, in making dyestuffs, 274. oleate, 225. oxalate, 417. permanganate, 422. peroxide, Bleaching by, 264. phenyl carbonate, 420. phosphate, Manufacture of, 416. , , Use of, in dyeing, 330. sesquicarbonate, 30. sulphate for glassmaking,24, ,, in soap, 247. ,, Use of, in dyeing, 335. sulphide as a depilatory, 383. ,, for making wood pulp, 346. ,, sulphite, 6. Sodoxyanthraquinone, 281. Soffioni, 414. Softening processes in tanning, 3S4. "Soft pitch," 82. " ,, woods" (dj^ewoods), 325. Solar oil, 123 ; for oil water gas, 72. " Solid flame burners," 70. ,, green, 302. Solidification of Russian petroleum, 123. Solidified bromine, 431. ,, sulphuric acid, 16. Soluble blues, 290. Solution of metals in glass, 158. Solutions, Action of, on glass, 161. " Solvent naphtha," 79 ; from shale, 101. Solvents, 434 ; Spirit, for varnishes, 246 ; Volatile, 230 ; Volatile, for wool washing, 258. j Soot, Ammonia in, 112; Arsenic, 415 ; for manure, 112. | Sorghum saccharatum, 177. ,, sugar, 177. Sorrel, Salts of, 417. Sour beer, 204. Sour, Grey, 266. ,, Lime, 266. " Sour " process of starch extraction, 186. I ,, tanning, 387. 476 INDEX. Sour, White, 266. Soxhlet extractor, 229. Sparger, 196. Sparging, 196. Speise, 357. Spent beet, Analysis of, 167. ,, lees, 211. ,, lye from soap works, 249. oxide, 2, 63. ,, ,, Sulphur in, 65. ,, purifier, Revivification of, 64. , , pyrites, Sulphur in, 3. ,, tan, 380. ,, Application of, in making white lead, 350. ,, wash, 214. ,, ,, as a fodder, 216. Spermaceti, 239 ; Adulterations of, 239 ; Properties of, 239. Sperm candles, 252. „ oil, 22S, 239. ,, ,, group, Oils of, 228. ,, ,, Properties of, 239. Spindle oil, 123. Spirit, 209 ; Analysis of, 216 ; blue, 290 ; Chromic acid for purifying, 216 ; Clean, 211 ; Commercial, 215; Composition of, 217 ; Content of fusel oil in crude, 216; Denatured, for varnishes, 219 ; from maize, 216 ; from molasses, 216 ; from turnips, 216 ; Fusel oil removed from, by oxidation, 216 ; German, 215 ; German system of denatur- ing, 219 ; Manganese dioxide for purifying, 216 ; Materials for manufacture of, 209; Methylated, 218; methylated, New, 218; methylated, Old. 218; of wine, Rectified, 218 ; oil of turpentine, for denaturing, 219; Ozone for purifying, 216 ; Potassium per- manganate for purifying, 216 ; Potato, 215, 216; Proof, 218; proof, Specific gravity of. 218 ; Purification of crude, 216; Pyridine bases for denaturing, 219 ; Rectifi- cation of crude, 217; rectified, Specific gravity of, 218 ; Removal of fusel oil from crude, 216, 217; Silent, 217; Valuation of crude, 216; varnishes, 246; varnishes, Sol- vents for, 246 ; Wood, 93 ; Wood charcoal for purifying, 216 ; wood, Composition of, 94. Spirits, Caramel for colouring, 182 ; Classification of potable, 209 ; of turpentine, 240. Spray, Water in vitriol making, 11. Sprengel's explosives, 407. Stack process of making white lead, 349. Staffen's process, Sugar recovered from molasses by, 174. Stage kilns, 135. Staining wood, 423. Staking skins, 390. Stannate of soda, Use of, in calico- printing, 331. Stannic chloride, Use of, in dyeing, 231. Stannic chromate, pigment for glass, 160. Stannous acetate as a discharge, ,, chloride as a discharge, 341. ,, Use of, in dyeing, 331. "Staple" of cotton, 260; of flax, 261 ; of jute, 262; of wool, 257. Starch, 183 ; and sugar, 162 ; Arrow- root, 183, 187 ; Colloidal character of, 187 ; converted into sugar, 182; extracted from maize, 1 86 ; extracted from rice, 186 ; extraction, Sour processof, 186; extraction, "Sweet" process of, 186 ; factory, Residue from, as fodder, 185 ; factory, Water from, as manure, 185 ; gelatinisation of, 187 ; granules, Sizes of, 183; "Green," 184 ; jelly, 187; Laundry, 185; Maize, 186; making, Diseased potatoes used for, 185; manufactured from wheat, 1 85; manufacture, Gluten recovered in, 186 ; manufacture of, 184 ; paste, 187 ; Potato, 184 ; Potatoes for, 184 ; Rice, 184, 185 ; Sacchari- fication of, in potato, 215 ; separ- ated from gluten by caustic soda, 188 ; separated from gluten by fermentation, 185 ; solution, Vis- cosity of, 187; Sources of, 183; sugar, 181 ; sugar, Caramel made from, 182 ; sugar, Composition of, 182; sugar, Manufacture of, 182; Uses of, 187 ; Wheat, 185 ; Yellow tint of, corrected, 187 ; yielding materials, Analysis of, 183. Starches, Edible, 187 ; for brewing, 193. Stassfurt boracite, 414. Stassfurtite, 414. Stassfurt salt deposits, 426. Steam style of calico-printing, 340. Stearate, Glyceryl, 228, 237.' Stearic acid, 223 ; Manufacture of, 252. INDEX. 477 Stearin, 224 ; Cotton seed, 232 ; Cotton seed, an adulterant of tallow, 237 ; for candles, 252. •" Stearin " niglitlights, 251. Stearin pitch, 253. ,, (stearic acid) caudles, 255. Stearo-lactone, 255. Stearoptenes, 241. Steatite, 344. Steel's masher, 196. Steeping barley, 190. " Stench" of beer, 194. Sterilised air for refrigerating rooms, 198. Stick lac, 242. Stockholm tar, 93. Stone, Alum, 424 ; Analysis of, 42 1 ; Artificial, 141 ; Blue, 423 ; China, 148 ; Cornish, 149 ; square system of cleansing beer, 203. "Stone, Vitriol," 18. Stones, Imitation precious, 158. Stoneware, 149 ; Glazes for, 149. Stout, 205 ; Water for, 195. "Stoving," 264. Strass, 15S. Straw, Charcoal from, 402. "Striking out" leather, 292. ,, the colour of leather, 287. "Stripping " silk, 265. Strontia, 429 ; burning, 176 ; process, 175 ; Sugar recovered from molasses by, 175. Strontianite, 176, 429. Strontium carbonate, 176. ,, hydroxide for sugar re- fining, 176. ,, ,, Preparation of, 176, 430. nitrate, 429. „ salts, 429. Stucco, 132. Stuffed leather, 393. Stuffing skins, 390. Styles of cotton printing, 240. Styrax benzoin, 242. "Sublimed white lead," 352. Substantive dyes, 270 ; Examples of, 333. ,, dyestuffs defined, 270. Succinic acid, 201 ; produced in acetic fermentation, 219. Sucrates, 174. Sucrose, Hydrolysis of, 183. Sucroses, 162. Sudoriferous glands, 368. Suet, 238. Sugar and starch, 162. Sugar, Beet, 165 ; beet, Diffusion process of extraction, 165 ; Beet, identical with Cane sugar, 177 ; Cube, 180 ; candy, 180. Sugar, Cane, 162. 163 ; Composition of raw, 165 ; Extraction of, 163 ; Hydrolysis of, 183 ; Inversion of, 1S3 ; juice, Analysis of, 163 ; juice, •Composition of raw, 165; juice, Concentration of, 163. Sugar, Caramel, made from starch, 182 ; Composition of raw, 177 ; Composition of refined, ISO ; Com- position of starch, 182; Compounds of, with alkaline earths, 174 ; converted into starch, 182 ; Decolorisation of, 178; Defeca- tion of, by blood, 178 ; defined, 162 ; Demerara, 177 ; diffu- sion process, Battery of cells for, 1 66 ; diffusion process, Cells for, 166 ; extraction, Composition of sludge from beet, 169 ; extraction, Diffusers for, 166 ; extraction from beet, 165 ; Fermentation of, 201 ; Fermentation of cane, 201 ; filtra- tion, Twill bags for, 178 ; First jet, 172 ; for diabetic patients, 182; Fruit, 182: in soap, 248; Invert, 183; Loaf, 180; loaves, 180 ; Lump, 180 ; Manufacture of starch, 182 ; Maple, 177 ; Moist, 177; "Moist" fraudulently col- oured, 179; Milk, 180; milk, Extraction of, from milk, 181 ; milk, Fermentation of. 201 ; milk, Solubility of, 181 ; Minor sources of, 176; of fruits, 181; of lead, Brown, 95 ; Palm, 177 ; Prepara- tion of, for the market, 180 ; Recovered from molasses (see Molasses). Sugar recovery, Aluminium sulphate used for, 176 ; Baryta used for, 176; Strontium hydroxide for, 176. Sugar refining, Animal charcoal used in, 178 ; Char for, 178 ; Evapora- tion of liquor in, 179 ; hydro- fluoric acid, Use of, in, 413 ; Raw, 177. Sugar, Scheibler's process for re- covery of, from molasses, 175 ; Solubility of milk, 181 ; solution, Filtration of, 178 ; Sorghum, 177; Starch, 181 ; Tin in Demerara, 180 ; Utilisation of uncrystallised, 172 ; vinegar, 221 ; White, 180 ; Yellow colour of, corrected, 180 ; Yield of, from beet, 172. 478 INDEX. Sugars classified, 162. ,, for brewing, 193. ,, Nomenclature of, 162. Suint, 258 ; Potash from, 429. Sulphate ultramarine, 354. Sulphates, 423. Sulphazines, 304. Sulphide vessel, 65. Sulphite liquor, Spent, 347. ,, process for making wood pulp, 347. Sulphites, Bleaching by, 264. Sulphocyanide, Potassium, 434. Sulphoglyceric acid, 405. Sulphonation, Process of, 273. Sulphonicacid dyestuffs, Application of, 366. , , acids formed in oil refining, 229. Sulphur, Black, 255 ; Blue, 255 ; burners for vitriol making, 5 ; burners, Percentage of oxygen in gases from, 5 ; burners, Percentage of sulphur dioxide in gases from, 5. Sulphur chloride, 437 ; process of vulcanisation, 244. Sulphur compounds in coal gas, 68 ; Determination of, 68. Sulphur dioxide and oxygen, Combi- nation of, 18. Sulphur dioxide, Bleaching by, 264 ; Boiling point of, 6 ; Conversion of, into sulphuric acid, 11 ; from blende, 5 ; from sulphuretted hydrogen, 5 ; Liquefied, 6 ; manu- facture, 6 ; Percentage of, in gases from sulphur burners, 5 ; Specific gravity of, 6. Sulphur, Distillation of, 401 ; Flowers of, 2 ; for gunpowder, 401 ; Igni- tion point of, 402 ; in spent oxide, 65 ; in spent pyrites, 3 ; Methods of extracting, 1 ; Native, 1 ; Re- covered, 1, 33 ; recovery, from alkali waste, 32 ; recovery from gas liquor, 76 ; sprinkled on hops, 194. Sulphuretted hydrogen in coal gas, 68. ,, Sulphur di- oxide from, 5. Sulphuric acid, Action of, on castor oil, 235 ; Arsenic in, 16 ; Conver- sion of sulphur dioxide into, 11 ; English, 17 ; for Gay-Lussac tower, 13 ; Fuming, 17 ; Hydrolysis of fats by, 253, 254 ; Impurities in, 16 ; in vinegar, 221 ; manufacture (see Vitriol) ; Monohydrate, 16 ; Nordhausen, 17 ; "Solidified," 16; Specific gravity of, 17 ; Use of, for oil refining, 229 ; Uses of fum- ing, 18. Sulphur dioxide, Percentage of, in pyrites gases, 3. Sulphuric anhydride, 18. Sulphuring hops, 194. Sulphurous acid, Antiseptic, for beer, 204. Sumach, 377 ; Use of, in dyeing, 332. Sumachtannic acid, 374. Sunflower oil, 226. Superphosphate, 107 ; " Double," 109 ; Evaluation of, 109 ; from bone ash, 111 ; Reversion of, 109. Surrogates for rubber, 244. Suspender liquor, Composition of, 388. Suspenders, 386. Swarf, 285. Sweat elands, 368. Sweat/Wool, 258. Sweating hides, 384. Sweetened gin, 214. Sweet fennel, 214. Sweetmeats, Dextrose for, 182. Sweet process of starch extraction, 186. Sweet-water, 256. Sylvestrene, 240. Synthetic dyestuffs, Organic, 273. T Tallow, 236 ; Adulterations of, 237 ; Beef, 228, 236 ; Bone fat as adulter- ant of, 237 ; Cotton seed stearin as adulterant of, 237 ; dips, 251 ; group, Oils of the, 227 ; Hardening of, 237 ; Melting point of, 237 ; Mutton, 228, 236 ; oil, 227 ; Pro- perties of, 237 ; Refining of, 237 ; Rendering of, 236. Tan liquors, Acids in, 379. Tan, Spent, 380 ; Application of, in making white lead, 350. Tank liquor, Analysis of, 28; Car- bonation of, 28 ; Evaporation of, 29 ; Purifying, for caustic soda, 30. Tank waste, 28, 32 ; Treatment of, 32. Tanneries, Water for, 372. Tannic acid, Preparation of, 375; Properties of, 375 ; -Use of, in dye- ing, 331. INDEX, 479 Tannin, Absorption of, by hides, 395 ; Alcohol, 375 ; Content of, in leather, 395 ; Crystal, 375 ; defined, 374 ; Ether, 375 ; Extraction of, from galls, 374 ; Fixing, in leather, 393; in hops, 194; Use of, in dyeing, 331 ; Water, 375. Tanning, Chrome, 390 ; Electric, 38S; "Extracts" for, 380; Finishing processes in, 392 ; Function of acids in, 387 ; Iron, 390 ; materials, Analysis of, 379 ; Preparatory pro- cesses in, 381 ; processes, 386 ; processes classified, 367 ; processes, Rapid, 388 ; Softening processes in, 384; Sour, 387 ; Theory of, 394; with alum, 390 ; with mineral salts, 389 ; with oils, 391. Tannins, Bloom deposited by, 37G ; Classification of, 376 ; Nomencla- ture of, 374 ; Pathological, 375 ; Pyrocatechol, 376; Pyrogallol,376; Physiological, 375. Tanstnffs, 373 ; Analysis of, 379 ; classified, 374 ; Extraction of, 380; non-tannins in, Character of, 379; Mineral salts used as, 381 ; Oils used as, 381. Taps, 380. Tar acids, 79. ,, Beckton, Composition of coal, 77. Tar, Black, 101 ; Coal, 76 ; Consti- tuents of coal, 76 ; Crude naphtha from coal, 78 ; Distillation of coal, 77 ; distillation, Products from coal, 77 ; Enriching gas by, 74 ; First runnings from coal, 78 ; from cannel, 71 ; Light oil from coal, 78; Naphthalene yield from, 81 ; Russian, 93 ; Stockholm, 93 ; "Vitriol," 101 ; "vitriol," Rave's treatment of, 101 ; Wood, 92 ; Yield of, by different coals, 76 ; Yield of, from coal, 66 ; Yield of from Simon-Carve's oven, S2. Tartar, 418. Tartar emetic, Use of, in dyeing, 331. Tartaric acid, 418 ; Impurities in, 418 ; in grapes, 206 ; Solubility of, 418 ; Use of, in dyeing, 330 ; Uses of, 418. Tartrate, Calcium, 418. Tartrazine, 310. Tartrazines, 309. Tawing, 390. Taylor filter, 178. Temperature measured by Seger's cones, 147. Terminalia chebula, 377. ; Terpenes, 240. t Terra japonica, 377. Terre verte, 360. , Tetrabromofluorescein, 294. Tetrahydroxyanthraquinones, 282. t Tetraiodofluorescein, 295. Tetraiodopyrrol, 105. ; Tetramethyldiamidobenzophenone, ; 290, 309. ; Tetramethylindaminesulpho - sulpho- nate, 306. Tetrazo-compounds defined, 275. Tetrazodiphenyl chloride, _77. Tetrazo-dyestuffs, 275 ; Formation of, 276. Textile fibres, 257 ; Grasses as, 262. Thallium glass, 160. Theil limestone, 132 ; Analysis of,. 132. Thermometer of constant zero point > 160. Thermometers, Glass for, 160. Thiazines, 304. Thickeningagents for calico-printing,, 340. Thiocarmine, 336. Thiocyanate, Potassium, 434. Thionine, 304. Thiosulphate, Calcium, 363. " Thirty per cent." anthracene, 82. Tiles, 145 ; Encaustic, 145. Til-seed, 233. Tincal, 414. Tin crystals, Use of, in dyeing, 331. ,, in Demerara sugar, 180. ,, mordants, 331. Titan red, 333. „ yellow, 336. Tiza, 415. Toluene a source of artificial oil of bitter almonds, 241. ,, Boiling point of, 79. ,, sulphonic acids, 420. Toluidine, 286. Tolusafranine, 300. Toluylene blue, 303, 314. ,, orange. 333. red, 299. Tonite, 405. Top fermentation, 199 ; of wine, 206. " Topping " with basic colours, 334. Top yeast, 202. Toughened glass, 156 ; Siemens', 156. Tow, 262. Tower, Gay-Lussac, 8 ; Glover, 7. " Towers, Graduation," 21. Train oil, 238. Trass, 140. Treacle, 164, 179 ; Analysis of, 164. 480 INDEX. Triamidoazobenzene, Formula for, 275. Triamidotriphenyl carbinol, 284. Tricalcium saccharate, 174. Trihydroxy-benzoic acid, 375. Trihydroxytriphenvlmethane dve- stuffs, 291. Trillo, 377. Trimethylamine from beet juice, 165. ,, hydrochloride, 428. Trimming hides, 384. Trinidad asphaltum, 124. Trinitrophenol, 273. Triphenylmethanecarbinolorthocar - boxylic acid, 293. Triphenylmethane, Derivatives of, 2S6 ; Derivatives (dyestuffs), 283 ; Formation of. 286. Triphenylrosaniline, 290. Triple effect evaporators, 170. Trisazo-compounds defined, 275. Tropseolin 0, 275. Y, 275. Tufa, Analysis of volcanic, 140. Tumbling hides, 3S9. Turkey-red dyeing, 282 ; Oils applied in, 282. Turkey-red oil, 235 ; Manufacture of, 235. Turkish boracite, 414. Turmeric, 326. Turnbull's blue, 357. Turner's yellow, 361. Turnips, Spirit from, 216. Turpentine, 240 ; Adulterations of oil of, 240 ; American, 240 ; Com- mercial grades of, 240 ; Conifers, a source of, 240 ; French, 240 ; Oil of, 240 ; Oil of, for denaturing spirit, 219 ; Properties of, 240 ; Rectification of, 240 ; Russian, 240 ; Spirits of, 240 ; Yield of oil of, 240. Turpentines, resins, caoutchouc, 240. Turps, 240. Tuscany boric acid, 414. Tussur silk. 259. Twill bags for sugar filtration, 178. u Ultramarine, 354 ; Analysis of, 356 ; Artificial, 354 ; as a colour corrective, 187, 267, 353 ; Bleach- ing of, by acids, 355 ; blue, 354 ; Direct process of making, 354 ; Direct process of production of blue, 355 ; for correcting yellow tints, 344 ; Green, 354 ; Green, converted into blue, 355 ; green, Difference of, from blue, 355; Hue of, 354 ; Knapp's theory of the colour of, 355 ; Potassium, 355 ; Silver, , 355 ; Soda, 354 ; Sulphate, 354 ; Uses of, 356. Umber, Burnt, 364 ; Haw, 364. Umbers, 364. Uncaria gambier, 377. " Underback, " 197. Underburnt cement clinker, 139. " Underlets," 196. "Underproof," 218. " Ungumming " silk, 265. Unhairing hides, 382. " Union goods," 335. Union method of cleansing beer, 203. Unorganised ferments, 1 89. Unsaturated fatty acids, Oils con taining, 226. U.P., 218. Uranium glass, 159. ,, oxide pigment for glass, 160. V Vacuum pan, 171, 172. Valeric acid, 223. Valonia, 377. Valon's process, 65. Valuation of ammoniacal liquor, 76. ,, coal gas, 67. ,, gas licpaor, 76. , , " manganese, " 35. Vanadium compounds, Application of, 311. Vanillin in beet juice, 165. Varnishes, 245 ; Denatured spirit for, 219 ; Drying of, 246 ; Manu- facture of, 245 ; Nitrated cellulose, 246 ; Oil, 245 ; oil, Pvesins for, 245 ; resins and oils, 223 ; Resins for, 246 ; Spirit, 246 ; spirit, Solvents for, 246. " Vat " dyeing with indigo, 322. ,, Copperas, for dyeing with indigo, 322. ,, Hyposulphite, for dyeing with indigo, 323. ,, Woad, for dyeing with indigo, 322. Vats, Vinegar/ 220. Vaseline, 121; Decolorising, 433; from Russian petroleum, 123 ; Spurious, 121. INDEX. 481 Vegetable black, 364. ,, fibres, Animal fibres dis- tinguished from, 259. oils, Winning and refin- ing of, 228. Vehicles for paints; 356. Vellum, 391. Venetian red, 363. Verdigris, 359 ; " Distilled, " 360. Verditer, Blue, 358 ; Green, 360. Vermilion, 362 ; Adulterations of, 362; Antimony, 363; Chinese process for making, 362 ; Dry method of making, 362 ; Dutch process for making, 362 ; Idrian process for making, 362 ; Wet method of making, 362. Vermilionettes, 365. Victoria blue, 290, 307. Vinasse, 428. Vinegar, 219 ; Ale, 221 ; Caramel for colouring, 182 ; Cider, 221 ; eel, 221 ; Factitious, from acetic acid, 222 ; fly, 221 ; from malt, 220 ; making, Conditions of, 221 ; Malt, 221 ; malt, Composition of, 221 ; Mother of, 219 ; Orleans process for making, 219 ; Perry, 221 ; process, Beech shavings for, 220 ; process, Quick, 220 ; process, Slow, 219 ; " Proof," 221 ; Sugar, 221 ; Sulphuric acid in, 221; Trade designation of quality of, 221 ; vats, 220; White malt, 222 ; wine, Composition of, 222. Vines, Antiseptics for, 206. Virgin oil, 231. Viscosimetry, Standard of, 232. Viscosity imparted to oils, 234. Oils of high, 227- Vitreous arsenic, 416. Vitriol, Black, 424; Blue, 423; Brown oil of, 15. Vitriol chamber, reactions in, 11, 12, 13. Vitriol chambers, Acid "drips" in 14; "Curtains" of, 7; Lead for, 7 ; Saucers of, 7. Vitriol, Concentration of, 15. ,, ,, in cast iron, 16. ,, ,, in glass stills, 15. ,, lead pans, 15. ,, ,, platinumstills, 15. „ Corrosion of platinum by, ,, Gold-lined stills for, 16. ,, Green, 423. Vitriol making, Causes of loss of nitre in, 13. ,, „ Plant for, 5. ,, ,, Process of, 2. ,, ,, Nitric acid in, 14. ,, ,, Quantity of nitre used in, 13. ,, ,, Regulation of, by Alkali Act, 15. ,, ,, Water spray in, 11. ,, Nitrous, 13. ,, pans, Quality of lead for, 15. ,, Purification of, 16. ,, Raw materials for, 2. ,, " shales," 17. "stone," 18. „ "tar," 101. ,, ,, Rave's treatment of, 101.' „ White, 424. Vitriols, 423. Volcanic tufa, Analysis of, 140. Vulcanisation of rubber, 244. ,, Sulphur chloride pro- cess for, 244. Vulcanised caoutchouc, 243. ,, rubber, 243 (see also Rubber). Vulcanite, 244. W Walnut oil, 226. Warble marks, Prevention of, 372. Wash, 391 ; Composition of whiskey, 211. Washer, Gas, 64. Washing soda, 29. Wash, Spent, 214 ; as a fodder, 216. Waste, alkali, Analysis of, 32. ,, ,, Sulphurrecoveryfrom, 32. ,, ,, Treatment of, 32. ,, Tank, 28, 32. ,, ,, Treatment of, 32. Water, alkaline, Effect of, in brew- ing, 199. ,, Burton, 195. ,, " Burtonising," 195. "Water-fall" malt screen, 191. Water for black beer, 195. Water for brewing, 194; Advantage of the presence of calcium sulphate in, 199 ; Analysis of, 195 ; Effect of sodium chloride in, 189. Water for dyeing, 343. , , for mild ale, 195. for pale ale, 195. 31 482 INDEX. Water for stout, 195. ,, for tanneries, 372. ,, gas, Energy absorbed in pro- duction of, 72. „ ,, Manufacture of, 72. glass, 141. ,, hard, Objections to, in tanneries, 373. „ Influence of, on mashing and boiling in brewing, 199. in soap, 248. ,, in wood, Percentage of, 88. ,, London deep- well, 195. , , seals prevented from freezing, 256. ,, spray in vitriol making, 11. ,, tannin, 375. Waterproofed matches, 412. Waters rendered fit for brewing, 195. Water- white kerosene, 121. Wattle bark, 378. Wax, Adulterations of, 239 ; Bleach- ing of, 239, 251 ; Chromic acid for bleaching, 239 ; for candles, 251 ; Japan, 227 ; Melting point of paraffin, 102; Myrtle, 227; Paraffin, 102 ; Paraffin, from petroleum, 121 ; Paraffin, in Russian petro- leum, 123 ; Properties of, 239 ; Sealing, 242. Waxes defined, 225. Difference of, from fats, 225. Hydrolysis of, 225. ,, Liquid, 228. „ Solid, 228. ,, Winning of vegetable, 229. Weed, Orchella, 326 ; Orchil, 326. Weld, 326. Weldon manganese recovery process, 37. ,, mud, Composition of, 38. ,, ,, for gas purification, 66. ,, process, Chemistry of, 38. ,, Pechiney process, Chlorine recovery by, 50. , , process, Function of calcium chloride in, 38. Welsbach burner, 70. Wenham burner, 70. West-Knight and Gall process, 79. Wet method of making vermilion, 362. Wetzel evaporators, 164. Whale, Blubber of, 238. ,, oil, 228, 238; group, Oils of, 228. Wheat starch, 185 ; Manufacture of, 185. Whiskey, 210 ; Content of alcohol in, 211; Drying malt for, 210; Fermentation of wort for, 210 ; Fractionation of, 211 ; Furfural in, 212 ; Fusel oil in, 211 ; Irish, 210; Mashing malt for, 210 ; Maturing of, 212 ; New, 211 ; Scotch, 210 ; Still for, 211 ; stills, Frothing pre- vented in, by soap, 211 ; stills, Lactic acid from, 211 ; Use of sherry cask for maturing of, 212 ; wash, Composition of, 211 ; Wort for, 210. White arsenic, 415 ; for curing hides, 372 ; Manufacture of, arsenic acid from, 416 ; Purification of, 416 ; Uses of, 416. . White galls, 374. ,, leather, 390. White lead, 349 ; Adulterants of, 352 ; Analysis of sublimed, 352 ; Barytes in, 352 ; Caledonian, 353 ; Chamber method of making, 350 ; Clichy process of making, 351 ; Composition of, 352 ; Dutch pro- cess of making, 349 ; French pro- cess of making, 351 ; German method of making, 350; "Ground," 352 ; manufacture, Chemistry of, j 350 ; Milner's process of making, 351 ; Precipitation processes of making, 351 ; Prevention of poison- ing by, 352 ; Stack process of making, 349 ; " Sublimed," 352. White pigments, 349. ,, ,, containing lead, 352. „ sour, 266. ,, sugar, 180. ,, vitriol, 424. „ wine, Vinegar from, 220. ,, Zinc, 353 (see also Zinc white). Whitening of leather, 393. Whitewash, 354. Whiting, 354. Wick, Function of candle, 250. Wicks, Treatment of candle, 251. "Wild" silks, 259. Wine, Beech shavings for clarifying, 220 ; Bottom fermentation of, 206; Bouquet of, 207 ; Cause of colour in, 208 ; Coloured, 327 ; Crust of, 208; denned, 205; Effect of plaster of Paris upon fermentation of, 208; Index of genuine, 207 ; Influence of temperature on production of, 206; Top fermentation of, 206; Treatment of grapes for red, 206 ;. Treatment of grapes for white, INDEX. 483 206 ; Vinegar, 221 ; vinegar, Com- position of, 222 ; White vinegar, from, 220 ; Yield of brandy from, 209 ; Young, 206. Wines, Analysis of, 207 ; Analysis of fortified, 208 ; Bouquet of, 208 ; Fortified, 207 ; Keeping proper- ties of red, 207 ; Low, 211 ; Plastered, 20S. Wintergreen, Adulteration of oil of, 241 ; Artificial oil of, 241 ; Oil of, 241, 419. Witherite, 430. Witt's theory of dyestuffs, 273. Woad, 319 ; vat for dyeing with indigo, 322. Wood ashes as manure, 114 ; ashes, Potash from, 428 ; Bar, 325 ; Brazil, 325 ; Cam, 325 ; Carbonis- ing, in kilns, 90 ; Carbonising, in retorts, 90 ; charcoal for purifying spirit, 216 ; Destructive distillation of, 88 ; distillation, Yield of acetic acid by, 95 ; distillation, Yield of products from, 92 ; Exothermic decomposition of, 96 ; Fustet, 325 ; gas, Analysis of, 95 ; Lima, 325 ; Manufacture of paper from, 345 ; naphtha, 93 ; naphtha, Denaturing alcohol by, 218; Peach, 325; Per- centage of water in, 88. Wood pulp, Calcium bisulphite for making, 347 ; Chemical, 345 ; Effect of light on mechanical, 345; Magnesium bisulphite for making, 347 ; Mechanical, 345 ; Sodium sulphide for making,346 ; Sulphite process for making, 347 ; Yield of, 347. Wood rendered fireproof, 142. Wood, Santal, 325 ; Sapan, 325 ; spirit, 93 ; spirit, Composition of, 94 ; Staining, 423 ; tar, 92 ; tar creosote, 93 ; wool, 262 ; Yellow Brazilian, 325 ; Yield of charcoal from, 89, 90 ; Yield of oxalic acid from, 417. Wool, Action of alkali on, 271 ; bleaching, 264; Cotton, 260; "Diseased," 257 ; Dyeing, with acid colours, 336 ; Dyeing, with basic colours, 336 ; Dyeing, with direct dyes, 335 ; Dyeing, with mordant colours, 337 ; fat, 258 ; fibre, Analysis of, 258 ; fibres, pro- perties of, 259 ; fibres, Length of, 257; fibres, Specific gravity of, 259; Glass, 263 ; grease, 258 ; Hygro- scopic character of, 258 ; Moisture in, 258 ; printing, 342 ; Raw, 258; Slag, 263; "Staple" of, 257 ; Structure of, 257 ; sweat, 258 ; washing, 258 ; Wood, 262 ; Yellow- ing of, by soap, 264. Wormwood, 215. Wort, 196 ; Analysis of, 198 ; Attenu- ation of, 199 ; boiling in brewing, 197 ; cooling in brewing, 198 ; Fermentation of, 199 ; for whiskey,. 210 ; for whiskey, Fermentation of, 210; "Pitching," 199. X Xanthorhamntn, 326. Xylene, Boiling point of, 79. Xylidine, 286. Y Y Aryan evaporator, 170. Yeast, 200 ; Analysis of, 200 ; Analy- sis of ash of, 201 ; Bacteria in, 202; Bottom, 202 ; Characteristics of good, 202 ; Condition of must for rapid propagation of, 202 ; Endo- genous division of, 200 ; Fission of, 200 ; for distilleries, 211 ; Gemma- tion of, 200 ; Moulds in, 202 ; Proportion of, used in brewing, 199 ; pure, Cultivation of, 203 - y reproduction of, Conditions in- fluencing, 200 ; Top, 202. Yeasts, 189. Yellow, Alizarin, 33S. ,, arsenic, 383. ,, colour imparted to margarine, 238. ., colour of bleached cotton corrected, 267, ,, phosphorus, Properties of, 408. ,, pigments, 360. ,, prussiate of potash, 433. ,, tint of starch corrected,. 187. Titan, 336. ,, vegetable colours, 326. ,, wax from petroleum, 122. ,, wood, Brazilian, 325. Yellowing of wool by soap, 264. Yolk, 258 ; Potash from, 429. Yolk of egg used in tanning, 390* Yorkshire grease, 258. 184 INDEX. Young and Beilby retort for shale distillation, 97, 99. „ fustic, 325. wine, 208. Z Zaffrk, 357. Zambesi blues, 333. Zero point, Thermometers of con- stant, 160. Zettlitz kaolin, 143. Zinc chromate, 361. ,, dust as a discharge, 341. ,, oxide for hydrolysing fats, 253. ,, ,, Preparation of, 353. ,, sulphate, 424. Zinc white, 353 ; Adulterations of, 353 ; discoloured by cadmium oxide, 353; discoloured by cadmium sulphide, 353 ; Orr's, 353 ; Purifi- cation of, 353. HELL AND BAIN, LIMITED, 1'KINTERS, GLASGOW.