iiffnuiiiiTriwiiiiniviniiiiriijiii'mjimii^ioM = ^Ammonium OMPOUND London S AMPS ON LOW&C? LP BOUGHT WITH THE INCOME FROM THE SAGE ENDOWMENT FUND THE GIFT OF Henrs M. Sage 1891 Aji..SL.S.9..0S. s/j/dX. 9963 Cornell University Library arV19178 Ammonia and ammonium compounds 3 1924 031 273 505 olin,anx A dvertisements. PHILIP HARRIS & Co., Ltd., BIRMINGHAM, Manufacturers and Importers of CYery description of ALLEN'S, BUNTES', ORSAT'S, HEMPEL'S, &c., APPARATUS FOR GAS ANALYSIS. STANDARD PENTANE LAMP. HARCOURT'S COLOUR TEST APPARATUS. SULPHUR TESTING APPARATUS. PRESSURE GA.UGES, MIETERS, &cSO, (NH,)s SO, Potassium nitrate. Sodium nitrate. Ammonium nitrate. KNO3 NaNO, (NHJ NO, {b) Occurrence and Formation. — Ammonia plays a very important part in the economy of nature. It is B 2 Chemistry of Ammonia, invariably formed by the putrefactioa of the nitro- genous constituents of plants and animals, being either given off into the atmosphere, or dissolved in running water. The atmospheric ammonia is absorbed by falling rain, and again brought to the earth's surface, and there taken up by the soil, to serve as one of the chief sources of nitrogen for the vegetable world. Although the atmosphere contains about 80 per cent, of nitrogen, the plants have not the power of absorbing it directly, and are therefore dependent on the more active nitrogen compounds, ammonia and nitric acid, for their supply of this element, which is required especially for the formation of the seeds and fruit. It seems probable, however, that the plants can only assimilate the nitrogen from nitric acid, and that the ammonia is first oxidized to that compound by some as yet unknown process which takes place in the soil. It will be seen, therefore, that ammonium compounds form, either directly or indirectly, a powerful manure, and in fact, their cheapest repre- sentative, ammonium sulphate, is employed almost solely for this purpose. Moreover the value of stable manure depends largely on the amount of ammonia which has been found in it by putrefaction. Ammonium compounds do not occur in large qtiantity in nature. A thin layer of ammonium carbonate is found in the guano deposits on the West Coast of South America. Ammonium sulphate and chloride are also contained in the Tuscan " Suffioni." Sal ammoniac is further found as a sublimate in the craters of active volcanoes. None of these occur- rences have, however, any technical importance. In Ammonia. former times ammonium compounds were obtained almost entirely from decayed nitrogenous matter, camel's excrement being, a few centuries ago, the chief source of sal-ammoniac. ' Later on it was also prepared from human urine, and even at the present time ammonium salts are here and there recovered from sewage. When nitrogenous substances of either animal or vegetable origin are subjected to the process of dry distillation, they are decomposed. Charcoal remains behind, aind combustible gases, tarry matter, and ammoniacal water are evolved. For a long time substances rich in nitrogen, such as bones, horn, leather, &c., were thus distilled for the sake of the ammonium salts they yielded ; at present, although these processes are still carried out, the ammonium compounds have become a merely secondary con- sideration, the chief object being the preparation of animal charcoal, or of potassium ferrocyanide (prussiate of potash). The quantity of ammonia obtained from these bodies forms but a very small fraction of the present production. At the present day the dry distillation of coal, the valuable residue of a past vegetable world, forms the richest and almost inexhaustible source of ammonia. When coal is heated in closed vessels to a tem- perature of iioo°— 1200° C. (2000° — 2200° F.) it de- composes, coal-gas, coal-tar, and ammoniacal liquor are evolved, and a more or less pure form of carbon, termed coke, remains behind. Coal contains on the average about i per cent, of nitrogen, but the Chemistry of Ammonia. amount varies considerably in the different varieties, as the following table shows : — Locality. Percentage of Nitrogen (by weight). Northumberland.., 2'2i Upper Silesia Lancashire S. Staffordshire Westphalia Ohio Wales Scotland ... Saarbriicken Zwickau ... 2'oo I '93 171 1-65 1-50 i-i8 ro4 o'6o o'5o In the process of dry distillation only a com- paratively small quantity of the nitrogen is evolved as ammonia, amounting as a general rule to 15 — 20 per cent. ; about 30 per cent, is given off in the form of cyanides and sulphocyanides, nitrogenous compounds in the tar, and other gaseous bodies, whilst 50 per cent, remains in the coke. According to a recent statement, if steam be passed into the retorts at the close of the distillation, the yield of ammonia can be raised to 70 per cent, of the total nitrogen. The chief purpose of the distillation of coal on the large scale is either the preparation of coal gas for lighting purposes, or the manufacture of coke. In the former case it is absolutely necessary to collect all the liquid products, whereas in the coke manu- facture the condensation is frequently neglected. The relative proportions of the products formed from 2 cwt. of coal in coal-gas manufacture and coking are given in the following table : — Ammonia in Gas-liquor. 7 , lias liquor con- taining l'5— 3'o per cent. NH,. Gas. Tar.' Coke. Gas manufacture. Cokinff Per cent. 5— lo 10—15 Cubic feet. 700—900 700 — 1 100 Per cent. 6-8 2—3 Per cent. 60—70 75 The gas-liquor obtained from these processes has a yellow or brown colour, is mostly turbid, and smells strongly of ammonium sulphide and tarry matter. Its composition is variable, but it contains as a rule I '5 — 3*0 per cent, of ammonia. This exists partly as volatile compounds (including ammonium sulphide and carbonate), and partly as non-volatile compounds, such as sulphate, chloride, thiosulphate (hyposulphite) and thiocyanate (sulphocyanide) . In the coal-gas manufacture a second ammoniacal bye-product, the so-called " spent-oxide," is obtained. After the ammonia gas has been freed from ammonia in the washers and scrubbers, it is passed over hydrated oxide of iron to absorb the sulphuretted hydrogen. When the mass ceases to absorb sulphur, it isi exposed to the action of the air and frequently damped and stirred to promote oxidation. By this means the iron sulphide is reconverted into hydrated iron oxide, sulphur separating out at the same time. When the oxidation is complete, the oxide can again be em- ployed for purification. After this process has been repeated a number of times the quantity of sulphur in the mass may rise to 40 — 50 per cent. Besides sulphur,however,ammonium compounds (sulphate and thiocyanate) are also deposited in quantities varying from S — 10 per cent, and frequently also very consi- derable quantities (5 — 25 per cent) of Prussian blue. 8 Chemistry of Ammonia. Of late years, therefore, the spent-oxide has received a large amount of attention, not only as a source of ammonium compounds, but also of ferrocyanides, and thiocyanates. The ammoniacal liquors obtained from the prepara- tion of animal charcoal and potassium ferrocyanide have at the present time lost most of their importance, notwithstanding the fact that they are exceptionally rich in ammonia, chiefly in the fQrm of carbonate. The liquor from bones is a brown nauseous-smelling liquid, having a density of 7 — 1 5° Tw. On distillation it always gives a yellow distillate, and cannot there- fore be employed for the manufacture of colourless salts. 2. Ammonium Compounds. {a^ Ammonia and Water. — When ammonia dissolves in water a considerable evolution of heat takes place, the volume of the solution increasing at the same time. The solubility of ammonia in water at various temperatures is given in the following table : — One volume of water absorbs : M o°C. (32° F.) ... 1050 vols, ammonia, „ io°C. (50°F.) ... 813 ,. „ I5°C. (59°F.) ... 727 ,, „ 20° C. (68° F.) ... 654 „ 100 grams of water dissolve 50 — 60 grams of ammonia at the ordinary temperature. The aqueous solution of ammonia comes into commerce as caustic ammonia, or liquor ammonice. It has asp. gr. ofo"88o — 0-930 and contains from 35 — 20 per cent, of ammonia. If the Ammonia and Acids. solution be warmed, ammonia gas is evolved ; the more concentrated the solution, the lower the tempera- 'ture at which the evolution begins; If, on the other hand, it be cooled to— 40° white crystals separate out. When a rapid current of air is passed through a cold concentrated solution, the temperature of the liquid falls so low that mercury freezes if placed in it. The solution is decomposed by chlorine with form- ation of nitrogen and hydrochloric acid. If, how- ever, chlorine be in excessj chloride of nitrogen is formed. This is a yellow, extremely explosive oil which is also formed by the action of chlorine on ammonium salts. By the action of acids on ammonia solution, or by passing ammonia gas into aqueous solutions of acids, ammonium salts are obtained. If the acid be re- placed by its anhydride, we get instead of the salt of the corresponding acid, a so-called amido-salt. Thus, for example, by the action of ammonia on sulphuric anhydride, ammonium amidosulphonate is formed. SO3 + 2NH3= SO,[gJJ|j^ From ammonia and carbon dioxide again we ob- tain ammonium carbamate. CO, + 2NH3 = C0{^g^^ All these compounds unite with water, forming salts of the acid corresponding to the anhydride employed. As has already been stated, the ammonium salts bear a remarkable resemblance to the corresponding lo Chemistry of Ammonia. potassium and sodium compounds in their general character, such as solubility, crystalline form, &c. They are, however, distinguished from them by their insta- bility at high temperatures, no ammonium compound being known which is not decomposed at a red heat ; many of them indeed are volatile with steam, and some few evaporate even at the ordinary temperature. When heated with alkalies or alkaline earths, ammonia is at once set free, and may be easily recognized by its characteristic pungent smell. Further, all ammonium salts are decomposed by alkaline hypobromites with evolution of nitrogen. (^.) Ammonium Sulphate. — (NH4)2S04. Thissaltis obtained by neutralizing sulphuric acid with ammonia. It separates from a hot saturated aqueous solution on cooling, in beautiful large rhombic tables, which are very readily soluble in water. According to AUuard, lOO parts of water dissolve at o°C. (32° F.) 7100 parts (NH,)2S04 20° C. (68° F.) 76-30 „ So° C. (122° F.) 84-25 „ 80° C. ri76° F.) 92-20 „ „ 100° C. (212° F.) 97-50 „ It melts at 140° C. (284° F.), and decomposes at a higher temperature with evolution of ammonia, and sulphur dioxide. If its solution be boiled with one of common salt, a double decomposition takes place, sodium sulphate and ammonium chloride crystalling out on cooling. When heated with calcium carbo- nate (chalk), ammonia and ammonium carbonate pass off, and calcium sulphate (gypsum) remains behind. The chemically pure salt finds an application in Ammonium Sulphate. ii analytical chemistry, being employed for standard- izing normal- acid solutions. The sulphate prepared on the large scale is used exclusively as manure. Ammonium sulphate combines also with other sulphates forming double salts. Of these, the most important is ammonium-alym, or aluminium ammo- nium sulphate. Al2(SO,)3(NH,).SO, -(- 24 H,0. ' It is obtained as a crystalline meal by mixing concentrated solutions of the two sulphates, and in all its properties closely resembles the common or potash alum. On ignition, it loses ammonia and sulphuric acid, whilst pure alumina remains behind. 100 parts of water dissolve only 12 parts of the double salt at the ordinary temperature, whereas at the boiling point, 422 parts are dissolved. At the present day, ammonium-alum is not manufactured to the same extent as in former years, when the price of potassium salts was much higher. It is chiefly used in dyeing and calico-printing. Ferrous Ammonium Sulphate. — FeSO^ + (NHi)^ SO4 + 6 H2O is formed when a hot saturated solution of iron vitriol is added to a similar solution of ammo- nium sulphate ; on cooling, the double salt separates in bluish-green monoclinic crystals. It is used instead of iron vitriol in dyeing, calico-printing, and analytical chemistry, as it possesses over the latter the great advantage of undergoing no alteration in the air. Nickel Ammonium Sulphate. — NiSO^ -|- (N 114)3 SO^ -f- 6 H2O can be obtained in a similar manner to the foregoing salt. It crystallizes in dark-blue monoclinic 12 Chemistry of Ammonia. prisms, which dissolve in sixteen parts of cold, and three parts of boiling water, and is employed in nickel- plating. Cuprammonium Sulphate. — CUSO44 NH3 + H2O is not a true double salt. It may be regarded as copper vitriol in which four molecules of water of crystalliza- tion have been replaced by four of ammonia. A so- lution of copper vitriol gives with excess of ammonia a deep blue solution, which on addition of alcohol deposits the above compound in dark blue crystals. These dissolve in rj parts of water, have an un- pleasant metallic taste and slight ammoniacal odour. The pure salt is employed in medicine in nervous diseases and affections of the eye, the crude substance being also employed in the preparation of coloured fireworks, and for the destruction of vermin. {c.) Ammonium Chloride {^Sal-Ammoniac^ — NH^Cl. This, the first known ammonium salt, is obtained by neutralizing hydrochloric acid with ammonia. NH3 + HCl = NH.Cl. It is very soluble in water, the solubility at different temperatures being given in the following table : — 100 parts of water dissolve ato"^C. 20° C. 40° C. 60° C. 80° C. 100° C. 28'4 ZTI 46'2 55*o 63-9 72'8 parts NH4CI. The saturated solution boils at 115°—! 16° C. (239°— 241° F.). It crystallizes from its hot solution in snow-white, feathery aggregates, which are built up of small regular octahedra. It dissolves also to some extent in alcohol. On boiling the solution, a small quantity Sal-ammoniac. 1 3 of ammonia is given off, and the solution becomes slightly acid, and therefore attacks iron. Sal-ammoniac has a sharp, saline taste, and is un- altered in the air, but can be sublimed at a higher temperature. The vapours evolved consist of a mixture of free ammonia and hydrochloric acid, which re- unite on cooling. If the cooling take place quickly, it forms a light, crystalline powder ; if, on the other hand, the vapours are slowly cooled, a semi-trans- parent, fibrous, crystalline mass is obtained. In the middle ages, sal-ammoniac was prepared from camel's excrement. Even at the present time the dried excrement forms the sole available fuel in the desert. The soot deposited on burning it, contains considerable quantities of sal-ammoniac, which may be obtamed by extracting with hot water and evaporating the solution thus obtained. It was brought into commerce by Armenian merchants, and hence obtained the name sat armeniacum. Later on this name was changed to sal ammoniacum, a name which had been originally given to the common salt (sodium chloride) found near the ruins of the temple of Jupiter Ammon in the Libyan desert, and with which this sal armeniacum was confused. In the course of time, sal ammoniacum became contracted to sal- ammoniac, which name forms the source of the word ammonium, of which sal-ammoniac and the numerous analogous compounds are now regarded as derivatives. Sal-ammoniac is largely used in dyeing and calico- printing, and also in brazing and soldering. id) Ammonium Carbonate. — Neutral ammonium carbonate (NH4)iCOs is an extremely unstable body. ]4 Chemistry of Ammonia. It forms fine silky crystals, which contain one mole- cule of water of crystallization, and smell strongly of ammonia. The crystals lose ammonia on standing in the air, and become opaque; forming acid ammo- nium carbonate. Commercial ammonium carbonate {sal-volatile, or salt of hartshorn) is not a true carbonate. It is obtained by heating a mixture of ammonium sulphate with calcium carbonate, and consists of a mixture of acid ammonium carbonate with ammonium carbamate, NH4HCO3 + CO \ QvriLr free ammonia being evolved during its preparation. It is also formed when neutral ammonium carbonate is distilled. When the salt is exposed to the air, it loses amm onia, leaving about 50 per cent, of acid ammonium carbonate. It is readily soluble in water, 4 parts of water dissolving at the ordinary temperature i part of the salt ; the solution contains both neutral and acid salt, and on heating gives off carbonic acid at 75" C. (167° F.), ammonia at 85° C. (185° F.) and at 100° C. (212° F.) the whole is volatilized. If sal-volatile be dissolved in concentrated ammonia solution, crystalline plates of normal ammonium car- bonate are obtained. On treating with alcohol, ammonium carbonate go^s into solution, whilst the acid carbonate remains undissolved. Acid Ammonium Carbonate. — NH4HCO3 is usually prepared from sal-volatile by allowing it to stand in the air, or by passing carbonic acid through its saturated aqueous solution. It forms small crystalline plates, which dissolve in 7 — 8 parts of water. It Ammonium Carbamate. 15 occurs in crystalline and fairly pure condition in the lower layers of the guano deposits in South America. Ammonium Carbamate. — CO -j pvMu- is deposited as a white saline mass, when dry carbonic acid and ammonia are brought together. It smells strongly of ammonia, and volatilizes at 60° C. (140° F.). It is converted by water into ammonium carbonate. («.) Ammonium Sulphide. — (NH4)2S is obtained as a white crystalline mass when one volume of sulphuretted hydrogen and two volumes of ammonia gas are brought together. 2NH3 + ms - nhJ^- It is easily soluble in water, is somewhat volatile at the ordinary temperature and loses ammonia in the air, forming Ammonium Hydrosulphide. — tt'' [ S. This can also be prepared by saturating a solution of ammonia with sulphuretted hydrogen. Like the foregoing compound, it is easily soluble, and undergoes alteration in the air. It occurs in gas-liquor, often in consider- able quantity. Higher ammonium sulphides, such as (N 114)254 and (N 1^4)255 are obtained by the action of sulphur on ammonium sulphide solution. A mixture of these bodies was formerly used in medicine under the name " volatile liver of sulphur." Ammonium Hydrosulphide is largely used in analytical chemistry, but none of these compounds 1 6 Chemistry of Ammonia. have much technical importance. The hydrosulphide is occasionally used for the purpose of etching copper. (/) Ammonium Nitrate. — NH4NO3. To prepare this salt, nitric acid is neutralized with ammonia or ammonium carbonate. It forms, colourless, rhombic crystals, which are somewhat hygroscopic, and dis- solve at the ordinary temperature in half their weight of water. By its solution a considerable absorption , of heat takes place, the temperature of the liquid being consequently lowered. It is also readily soluble in alcohol. It melts at 152" C. (305° F.), and when heated beyond this point, splits up into nitrous oxide and water. NH4NO3 = N2O + 2HA Nitrous oxide or " laughing-gas " is largely u.sed by dentists as an anaesthetic agent. {g) Ammonium Phosphate. — Common phosphoric acid forms three ammonium salts, viz -.—Normal Ammonium Phosphate (NHJaPOi Hydrogen Ammonium Phosphate (NH4)2HP04, and Dihydrogen Ammonium Phosphate {J^Yi^Yi^Oi. The first two salts are rather unstable, losing ammonia in the air and leaving a residue of Dihydrogen ammonium phosphate. This salt can be easily prepared from phosphoric acid and ammonia in the ordinary manner. It crystallizes in colourless quadratic prisms, similar to those of the corresponding potassium salt. It dissolves easily in water, giving a solution which has an acid reaction, (A.) Ammonium. Thiocyanate or Sulpho cyanide. — Ammonium Thiocyanate. 17 NH4CNS has of late years assumed some technical importance. It is often contained in considerable quantities in spent-oxide, from which it is now recovered on the large scale, and also occurs in gas- liquor in varying quantities. English gas-liquors may contain as much as i per cent, but as a general rule the amount does not exceed 2 — 3 grm. per litre. Ammonium thiocyanate can also be obtained by heating ammonium thiocarbonate to 100 C. (212° F.) The latter body is obtained by the action of carbon- bisulphide on an alcoholic solution of ammonia. CS, -H 2NH3= CS{^^^^_ The yield is, however, by no means good. According to Gelis, ammonium sulphide and carbon bisulphide combine together to form am- monium thiocarbonate (NH4)2CS3, which, on heat- ing, likewise splits up into ammonium thiocyanate and sulphuretted hydrogen. It may, moreover, be obtained by the action of hydrocyanic acid on yellow ammonium sulphide. The salt is very easily soluble in water and alcohol, and crystallizes in large colourless deliquescent plates which are somewhat volatile with steam. It melts at 159° C. (318° F.) and decomposes on further heating. {t.) Ammonium Oxalate. Theneutral salt j (-q^vttt' is obtained by saturating a solution of oxalic acid with ammonia, and crystallizes with one molecule of 1 8 Chemistry of Ammonia. water in long rhombic prisms. It is easily soluble in water, insoluble in alcohol, and on heating loses water, forming oxamide ( J^-^2' '^'^^ ^"^^^ ^^^^ r CO2NH1 jg obtained by adding to a solution of I CO2H oxalic acid one half the quantity of ammonia necessary for its complete saturation. It crystallizes in needles which also contain one molecule of water, and is less soluble than the normal salt. On heating it loses water and is converted into oxamic (/&.) Ammonium Metavanadate. — NH4VO3 forms a white crystalline powder, which is very sparingly soluble in water, almost insoluble in sal-ammo- niac solution, and completely insoluble in alcohol. On heating, it loses ammonia, leaving a residue of vanadic anhydride. The solution of the salt gives with tincture of galls, a deep black ink, which is, however, according to Wohler, not permanent. The vanadate is employed in the preparation of aniline black. (/.) Ammonium Molybdate. — (NH4)2Mo.04 is obtained as a white powder by neutralizing molybdic acid with ammonia and precipitating the salt by addition of alcohol. If the solution be evaporated ammonium heptamolybdate (NH4)Mo7024 -t- 4H2O is obtained. The solution of this salt in nitric acid is employed for the detection and estimation of phos- phoric acid. [m!) Ammonixim Chromate. — (NHi)oCrO is pre- Ammonium Dichromate. 19 pared by saturating a solution of chromic acid with ammonia. It crystallizes in yellow needles which are permanent in the air. On ignition it loses ammonia and oxygen, and is. converted into chromium sesquioxide. Ammonium Dichromate. — (NH4)2Cr3 07 which crystallizes in large red crystals, is prepared by adding the requisite quantity of chromium trioxide to the normal salt. Ammonium chromate is employed in calico printing. (m.) Ammonium Thiosulphate or Hyposulphite. — 3(NH4)2S20s + H2O crystallizes in beautiful tables which are permanent in the air. It is formed by the oxidation of ammonium sulphide in the air, and is converted by stronger oxidizing agents into am- monium sulphate. On addition of acids sulphur- dioxide is evolved, and sulphur separates. It is found in considerable quantities in gas-liquor. (» s' Ammonium Sulphide NHiHS 3'03 )) J Carbonate (N H.jjCOa . 39-16 » ) Chloride ■ 14-23 ») * Thiocyanate I -So )» » Sulphate o'lg *} ) Thiosulphate 2-8o » ) Ferrocyanide 0.41 » ) Raw Materials. 29 (2) Analysis of an English gas-liquor by two chemists (Kay and Appleyard) : — Kay. Appleyard Total Ammonia 2-91 % 2-98 % Volatile , » ... 272 J) 2-64 „ Ammonium Thiocyanate 0-I7 0-16 „ Total Sulph ur ... 0-638 )) 0-636,, Ammonium Sulphide NH4HS 0-936 »> 901 „ ») Sulphite 0-156 0-152 „ )) Chloride I -OS I '03 „ ,, Sulphate 0-013 ') 0-013,, ^j Thiosulphate trace trace j» Ferrocyanide 0-947 j» 0-948 „ The sp. gr. of this gas-liquor at 16° C. (61° F.) was I -035 (7° Tw.). Gerlach gives the following table of the composition of various German gas-liquors : — Constituents Chemnitz. % Bonn. Trier. Zurich. Total Ammonia 12-09 940 l8-I2 15-23 3-47 Ammonium Thiosulphate 1-036 •628 5-032 2-072 0296 Ammonium Sulphide 0-^40 646 6-222 2-468 1-428 Ammonium Carbonate 1-050 1-470 2-450 ") Acid Ammonium Car- \ 33763 5-856 bonate 4-560 7-680 33-120 5 Ammonium Sulphate 0-462 0-858 1-320 ] 4-922 1-926 Ammonium Chloride 30'49S (?) 17 120 3745 From these tables the great variation in the com- position of gas-liquors is very apparent. This difference does not depend merely on the coal employed, but also very largely upon the method of working, and on special local circumstances. For the valuation of gas-liquors, the usual plan adopted in England is to determine the number of 30 Manufacture of Ammonium Salts. ounces of pure sulphuric acid (H2SO4), necessary to saturate one gallon of the liquor. For this purpose 16^ oz. of best rectified oil of vitriol (= 16 oz. pure H2S04),are diluted with water to one gallon. The sp. gr. of this solution should be i-o68 at 15° C. (60° F.). This acid is then run into 16 liquid ounces of gas-liquor until the solution is neutral to litmus paper. The quantity of dilute a,cid used corresponds to the number of ounces of pure H2SO4 necessary to neutralize a gallon of gas-liquor. This test only indicates the amount of volatile ammonia. Frequently the strength of gas-liquor is simply estimated by its density, as given by Twaddell's hydrometer. In place of this, Fleischner's densimeter is frequently employed. In the latter, the specific gravity is obtained directly by placing the figure I and the decimal point before the. number of degrees recorded. Thus, 50 degrees on the densimeter corre- spond to a sp. gr. of i'50. All hydrometer measurements must be made at the temperature for which the instrument is graduated (generally 60° F.) In cases where it is impossible to bring the liquor to this temperature, a correction must be made, which should be experimentally determined once for all. As a general rule the higher the density of a gas- liquor, the larger is the amount of ammonia it contains. It is generally assumed that each degree Twaddell corresponds to two ounces of sulphuric acid. It is, however, manifest that with a liquid having such a varying composition as gas-liquor, the results- obtained by measurement of the density will often Raw Materials. 3 1 differ very considerably from those given by analysis. If the accurate composition is required, it is therefore necessary to perform a complete analysis. The method of estimating the total ammonia in gas-liquor has already been given (p. 22), In works where there is no proper laboratory, the following method, proposed by Knublauch, may be employed. The gas- liquor, after being diluted with four times its volume of water, is shaken with an excess of lime. The filtrate, which contains all the ammonia and a certain quantity of dissolved lime, is neutralized with acid of known strength, and from this the quantity of ammonia calculated, correction being made for the amount of acid required to neutralize the dissolved lime. The analysis is actually carried out as follows : 100 cc. gas liquor are diluted with water to 500 cc, and shaken with an excess of quicklime, and allowed to stand for an hour. After filtering, 50 cc. of the filtrate are taken, a little aurine added as an indicator, and the solution titrated with acid. Knublauch has constructed a special cylinder for this purpose, from which the acid is allowed to drop into the liquid. If the acid be of the given strength, and filled to the zero mark on the cylinder before each determination, the percentage of ammonia can be directly read off on the cylinder after the titration. By this method results are obtained which are accurate to O'l — or2 per cent. For a complete analysis of gas-liquor, S. Dyson ' recommends the following method : — > Journ. Soc. Chem. Ind., 1883, p. 231. 32 Manufacture of Ammonium Salts. Total Ammonia. — 25 cc. gas-liquor are distilled with magnesia. Carbonic Acid. — Jo cc. gas-liquor are precipitated with calcium chloride solution, the precipitate filtered, washed, and dissolved in normal acid. The excess of acid is titrated back with alkali. Total Sulphur. — 25 cc. gas-liquor are treated with hydrochloric acid containing bromine. The excess of bromine is evaporated off, and after filtration the boiling solution precipitated with barium chloride. Sulphur in the form of Sulphide. — A portion of the gas-liquor is precipitated with zinc sulphate and ammonium chloride. The precipitate is filtered off, dissolved in hydrochloric acid containing bromine, and the solution precipitated as before with barium chloride. Sulphuric Acid. — 250 cc. gas liquor are evaporated to dryness, the residue taken up and treated with zinc oxide to remove ammonium sulphide, and the filtered solution precipitated with barium chloride. Thio sulphuric, or Hyposulphurous Acid is calculated from the difference between the total sulphur on the one hand, and the amount of sulphur in the form of sulphide, sulphate, and thiocyanate (sulphocyanide). Chlorine. — 50 cc. gas-liquor are evaporated, the residue dissolved in water, and the filtered solution precipitated with a mixture of copper sulphate and iron vitriol, and again filtered. The filtrate is then acidi- fied with nitric acid, and precipitated with silver nitrate. Ferrocyanic Acid. — 250 cc. are evaporated, and the residue dissolved in water and precipitated with ferric Raw Material. chloride. The precipitate is then filtered, washed decomposed with caustic soda, and the residual oxide of iron collected and weighed. Thiocyanic or Sulphocyanic Acid. — 50 cc. are evaporated and the residue heated to 100° C. (2I2°F.) for four hours, extracted with alcohol, the alcoholic solution filtered off, and the alcohol evaporated. The residue is dissolved in water &nd precipitated with a solution of coppersulphate containingsulphurous acid. The precipitate is filtered off and then dissolved in nitric acid and reprecipitated by caustic soda. Thiocarbonic Acid is separated by means of zinc sulphate, the precipitated zinc salt being washed with cold water. On boiling with water this salt is de- composed, forming carbon bisulphide, which may be estimated by means of the compound which it forms with methylphosphine. Carriage and Storage. — In cases where the gas- liquor is not worked up at the place of manufacture, it is conveyed to the works either in iron boiler-shaped railway trucks holding about ten tons, in canal boats, or in specially constructed waggons. For the purpose of storage it is best to employ wrought-iron tanks, which are placed either level with the ground or in elevated positions. The former serve for the general storage of the liquor, whilst the latter are employed to feed the stills, both systems being connected together by iron pumps. The best form for the lower tanks is that of a horizontal cylindrical boiler, these being the cheapest both in construction and in setting up. Where possible, the tanks should not be sunk below the level of the D 34 Manufacture of Ammonium Salts. floor, as in that case leaks may long exist unobserved, and repairs are difficult and tedious to execute. For the upper tanks vertical cylinders of the same height and diameter are employed, as horizontal tanks would be too costly in fixing. In smaller works, reservoirs of wood are frequently met with ; these remain tight for a long time provided that they are always kept full. The cost of erection is much the same as for the iron reservoirs. Gas-liquor gradually attacks iron, the action being especially due to the cyanides, sulphocyanides and sulphides it contains, which form with it ammonium ferrocyanide and iron sulphide. On this account, reservoirs of cement have of late been frequently employed in place of the iron ones, and so far as can at present be learned, these answer the purpose very well. In several quarters Monnier's cement reservoirs have been recommended. These are made from a skeleton of wire network of the required shape by coating it on both sides with cement. Their cost is only half that of iron tanks, and they have the additional advantage of being very light, the thick- ness of the walls being only about two inches. A reservoir holding 500 cubic feet costs approximately 22/. lOJ. A process has recently been patented by Kunheim for the removal of ammonium sulphide from gas- liquor, previous to its employment in the manufacture of ammonium salts. It consists in passing a very strong finely divided stream of air through the cold liquor, which carries all ammonium sulphide along with it, the mixed giises passing through dilute alkali Raw Material. 35 containing iron hydroxide in suspension. The iron sulphide formed is at once reconverted by the air into iron hydroxide, the sulphur separating out in the free state. As yet it is unknown whether any practical application of the process has been made. The separation of sulphuretted hydrogen from the gas-liquor before distillation would be of great advantage in many cases, especially for the prepara- tion of sal-ammoniac. It has frequently been pro- posed to precipitate the sulphur by means of iron, or other metallic salts, but this has always proved too costly. Before distillation the gas-liquor must of course be allowed to settle vyell, and should be quite clear. If it still contains tarry matters in suspension, there is no likelihood of obtaining colourless products. (3.) Sulphuric Acid. — Three varieties of Sulphuric Acid are brought into commerce, (i) Acid of 106° Tw. or I '5 sp. gr., containing 60 per cent. HjSOi- (2) Acid of 142° Tw. or 176 sp. gr., containing 78 per cent. HjSO^. (3) Acid of 168° Tw. or 1-83 sp. gr., containing 92 — 93 per cent. H2SO4. For the preparation of ammonium sulphate, the second variety, (142° Tw^.) is usually employed. It is a colourless,, odourless, oily liquid, mostly rather cloudy from the presence of lead sulphate. The valuation of sulphuric acid is almost invariably performed by taking its density with Twaddell's Hydrometer, or by the above-mentioned densimeter. From the specific gravity the percentage of sulphuric acid can at once be found by means of the table given in the Appendix. D 2 2,6 Manufacture of Ammonium Salts. In taking the density the following precautions must be observed : — (i) The cylinder in which the test is performed must be quite dry ; (2) The acid must not be allowed to stand for any length of time in contact with the air ; (3) The temperature of the acid during the operation must be 15° C. (60° F.) unless the' hydrometer is graduated for a different temperature ; (4) Especial care must be observed that the sample is not taken from the surface of the liquid, but from the bottom by means of a siphon. If the acid is not abnormally impure (which is ascertained by a qualitative examination described later) the results obtained from the determination of its density are quite as accurate as those found by titra- tion. To perform the latter operation about one gram of the acid is weighed out in a stoppered flask, diluted with water, and titrated with normal alkali solution. It should be noted that strong sulphuric acid cannot be measured by means of a pipette without consider- able error, on account of the oily nature of the liquid. The impurities usually occurring in commercial sulphuric acid are arsenic, iron, lead, aluminium, and also sulphurous, nitrous, and nitric acids. The non- volatile impurities are determined by evaporating i — 2 grams of the acid in a platinum dish, igniting and weighing the residue. This should not amount to more than 0"5 per cent. Nitrous and nitric acids are detected by the iron sulphate test. This consists in carefully pouring a solution of ferrous sulphate into the sulphuric acid in a test tube. If either of the two acids named are present, a dark ring is formed where the two layers came in contact. The presence of Raw Material. 2)7 sulphurous acid is shown by adding pure zinc to the acid. If the hydrogen evolved also contain sulphuretted hydrogen, — which is recognized by its property of blackening lead acetate paper, — then sulphurous acid is present. To detect arsenic, the acid is diluted with its own volume of water, and bright copper foil placed in the liquid. In presence of arsenic this assumes a steel-grey colour. . For the transport of sulphuric acid, glass carboys containing 17 — 20 gallons are almost invariably em- ployed in this country. It has frequently been proposed to carry it in iron tanks, but this method has not been used to any great extent in England. In Germany, on the other hand, these tanks, mounted on railway trucks, are largely used. So far as con- venience and safety in loading, transit, and unloading are concerned, there is no comparison between the two methods. The men engaged in loading and un- loading the carboys must always be specially protected in case of accident, whereas the tanks are easily filled and emptied by means of an air pump. The tanks in question are constructed of strong iron plate, and provided with a man-hole, delivery tap and pump. Only the upper portions of the tank, which frequently come in contact with the air, need to be protected by lead, for at the ordinary temperature strong sulphuric acid has no action on iron in absence of air. In the works the acid is stored in covered rect- angular troughs, coated with lead on the inside. The acid is conveyed from these to the place required by means of lead tubes, in which cast-iron taps or plugs are inserted. 38 Manufacture of Ammonium Salts. {c.) Lime, This substance is of great importance as on its action the recovery of the non-volatile am- monia entirely depends. Unfortunately the lime which comes into commerce is ofvery varying quality. Good lime, when moistened with a sufficient quan- tity of water, quickly becomes hot, swells up con- siderably, and falls to fine white powder. The chemical analysis of lime gives very reliable results. For this purpose, a good average sample is finely powdered, and exactly O'S grarri distilled with an excess of ammonium sulphate solution, the vapours being passed into 20 cc. of normal acid. At the close of the operation, the acid is titrated back, the amount of acid neutralized thus obtained. Assuming that 16 cc. of acid were neutralized, then, as I cc. acid corresponds to o"028 grams CaO, the original lime contained i6-|-0'028 grams = 0"448 grams or 89'6 per cent. CaO. {d^ Hydrochloric Acid. The hydrochloric acid of commerce, such as is used in the manufacture of sal- ammoniac, has a density of 32*4° Tw., and contains about 30 per cent. HCl. As in the case of sulphuric acid, its strength is ascertained simply by means of the hydrometer. From the specific gravity observed, the strength is calculated by the table given in the Appendix. The usual impurities of commercial hydrochloric acid are sulphurous and sulphuric acids, chlorine, iron, arsenic, &c. It is stored and transported exclusively in glass carboys containing 17 — 20 gallons. (e.) Nitric Acid. Common nitric acid is a yellowish fuming liquid of 88° Tw. or i'44 sp; gr,, containing Ammonium Sulphate. 39 74 per cent. HNO3. The coloration is due to the presence of lower oxides of nitrogen. A stronger acid of 1 00°^ 1 06° Tw. and 1-50 — 1-52 sp.gr. also occurs in commerce as " fuming nitric acid." The valuation of nitric acid is also performed by determining its density, and calculating the strength from the table in the Appendix. Good nitric acid should only become .slightly cloudy with silver nitrate or barium chloride ; when heated in a flask on the water bath, only small quantities of red fumes should be evolved. The amount of nitrous acid present may be determined by titration with standard potassium permanganate solution. It has been proved by R. Hirsch, and by Jackson and Wing, that an admixture of nitrous acid considerably raises the sp. gr. of nitric acid. Thus if the acid is bought simply from its sp. gr., a considerable loss may occur, an impurity of I per cent, of nitrous acid lowering its value by 4-6 per cent. Storage and transport the same as with hydrochloric acid. 2. Ammonium Sulphate. (^Ammonium Sulfuricum, Sulphate of Ammonia.) («.) Former Methods of Preparation. — Ammonium sulphate is prepared by saturating sulphuric acid with ammonia, the latter being obtained by boiling any ammoniacal solution with lime. It was formerly obtained in England by saturating the raw gas-liquor directly with sulphuric acid, and evaporating the neutral solution thus formed. Con- 40 Manufacture of Ammonium Salts. centrated sulphuric acid was poured into gas-liquor until the yellow solution became milky, and this then evaporated until the salt crystallized out. The salt thus obtained was generally coloured yellow or grey, and frequently also red or blue, and contained besides ammonium sulphate other ammonium salts, such as the sulphite, chloride, and especially sulphocyanide. As sulphate free from the latter impurity commands a much higher price, this method of working has now been given up. The fact that the evaporation of the dilute salt solution consumes considerable quantities of fuel, has also assisted to this end. To obtain the ammonia from gas-liquor the latter is treated in special stills. These are constructed so as to distil off first the volatile ammonium com- pounds, and then, by addition of lime and further heating, to recover the ammonia which is present in the non-volatile condition. The apparatus formerly used was extremely primitive, consisting mostly of an ordinary directly fired boiler. After boiling until all the volatile com- pounds had distilled over, lime was added, and the distillation continued. Frequently indeed the last part of the process was neglected, and the non- volatile ammonia allowed to run to waste. Boilers heated by direct fire were found to wear out very rapidly, chiefly owing to the formation of a hard incrustation of lime, and the first improvement made was the employment of either open or indirect steam, i.e. blowing steam directly into, or passing it through coils placed in the liquor. Moreover, instead of Ammonium Sulphate. 41 using a single boiler, a combination of two or more was made, the system being so arranged that the volatile compounds were driven off in a boiler placed at a higher level, by means of steam from a lower boiler in which the treatment with lime took place ; as soon as all the ammonia was driven off from the lower boiler, it was emptied, and the liquor from the higher boiler run into it, and there treated with lime, the steam evolved being passed into the freshly filled boiler above. The stills proposed by Rose, Mallet, Lunge, Griinewald and Wun- der, are all more or less different com- binations of boilers. (3.) Continuous Working Stills. — At the present time, no one with an exact knowledge of the ammonia- industry would erect one of the above stills. The great advances which have been made in the construction of stills in other chemical industries, especially in the process of rectifying spirits, have exerted a beneficial in- fluence on the ammonia industry. It is to a Frenchman, Savalle, that we owe the idea on which all modern continuous stills are based. Fig. 3 shows a portion of Savalle's apparatus. It is a vertical column divided horizontally into a number of chambers. The liquid to be distilled passes gradually downwards from chamber to chamber, by means of the overflow tubes a. A strong current of steam is blown in at the bottom of Fig 3- 42 Manufacture of Ammonutm Salts. the column, and passes upwards through the per- forated caps d. These cause the steam to blow through the liquid in each chamber, and thus, as all the liquid passes in turn through each of these compartments, it must by the time it reaches the bottom have been very thoroughly boiled. Moreover this arrangement has the advantage that the fresh gas-liquor, entering at the top of the column, encounters the steam which already contains large quantities of ammonia, and as it passes downwards, constantly becoming poorer in ammonia, always meets steam which contains still less, to which it gives up another portion ; until at last after under- going the final treatment with fresh steam, it leaves the apparatus entirely freed from its volatile ammonium compounds. We have thus a current of steam mixed with large quantities of ammonia, con- tinuously passing away from the top of the column, whilst the liquid free from ammonia flows off at the bottom, likewise in a continuous stream. This cannot be claimed even for the very best kinds of boiler-stills. In these, during the latter portion of the process, the steam passing off contains but little ammonia, and the boiling must be continued for hours, wasting immense quantities of steam, unless 0"2 — o'3 per cent, of the ammonia are allowed to pass off with the waste-liquor. The columnar stills are therefore not only regular and continuous, but are also markedly economical. The number of continuous working stills is not at present large ; and here only two of these, both of which have stood the test of experience, will be Ammonium Sulphate. 43 described ; viz. those of Feldmann, and of Griine- berg and Blum. Feldmann's apparatus is represented in Fig. 4. A is the main column, B the vessel in which the liquor is treated with lime, and C the subsidiary column. The gas-liquor flows from the reservoir «, Fig. 4. into the supply tank b, and thence by the tube c through the tubular heating apparatus /, to the top- most chamber of the main column. From here it flows downwards from chamber to chamber through the tubes a, until at last, freed from volatile ammonia, it reaches the decomposition tank B. By means of 44 Manufacture of Ammonium Salts. the pump G, milk of lime is introduced into this tank at certain intervals, its contents being kept in continual agitation by passing into it through /, a small current of live steam. By this treatment, the non- volatile ammonium compounds are completely de- composed, and the liquor then passes through the overflow tube e into the subsidiary column C, where the ammonia which has been set free is completely driven off. The spent-liquor collects in D and flows away continuously through the tap /. The steam re- quired for the process enters the apparatus in the lowest chamber of the column C, and, after passing through all its chambers, reaches the lowest chamber of the main column A, by means of the tube h. After passing through each chamber, in the usual manner, it leaves A by the tube i, charged with the accumu- lated- ammonia, from which it is freed by passing through sulphuric acid in the apparatus E (described later on). The unabsorbed aqueous vapour, mixed with the carbonic acid and sulphuretted hydrogen which are set free are conveyed through / into the apparatus / (termed the economizer), where they give up a large portion of their heat to the gas- liquor passing through the tubes on its way to the column A. This apparatus, therefore, serves the double pur- pose of cooling the waste gases and heating the gas- liquor. The gases pass from here into the nearest convenient chimney. As soon as the sulphuric acid in E is nearly satu- rated, the ammonium sulphate commences to sepa- rate out at the bottom of the vessel in the form of small crystals. These are extracted by copper spoons, Ammonium Sulphate. 45 and fresh sulphuric acid added to replace the amount thus neutralized. Feldmann's apparatus is now in use in a large number of gas and chemical works, and up to the 46 Manufacture of Ammonium Salts. present none but favourable reports have been pub- lished. The largest stills can treat no less than 44,000 gallons in twenty-four hours. According to Feldmann's statement, for every 200 gallons of gas- liquor distilled in twenty-four hours, a boiler-heating surface of about five square feet is required. Griineberg and Blum's still is represented in Fig. 5. The main portion of the apparatus consists of three essential parts ; the column a in which the volatile ammonia is driven off, the tank B, in which the fixed ammonium compounds are decomposed and ex- pelled, and the boiler C in which, by means of a steam coil, the last portions of the ammonia are driven off. The gas-liquor before entering the column a passes through the economizer E, which is heated either by direct steam or by the waste gases. It then flows from chamber to chamber in the usual manner, until it reaches the lime decomposition tank, from which it passes into the boiler C. In this, as shown in the figure, there is a peculiar stepped cone, over the steps of which the liquor flows ; in consequence of the in- creased area of each step, the layer of liquor in flow- ing downwards becomes thinner and thinner, thus permitting the passing steam to act on it very tho- roughly, and to expel the last traces of ammbnia. The milk of lime is introduced into B by means of the pump H. The continuous stills are constructed of cast iron. Copper and brass must never be employed, as ammo- niacal aqueous vapour quickly corrodes all metals containing copper. (c.) Subsidiary Apparatus. — The apparatus em- Ammonium Sulphate. 47 ployed for the absorption of the ammoniacal vapours by sulphuric acid, termed the saturator, is constructed either of wood or iron lined internally with lead, or of stone, with a leaden, bell-shaped cover. The latter construction is more generally employed. Formerly it was the practice to use closed chambers constructed of wood and lined internally with lead, an exit tube being provided for the waste gases. In these, dilute sulphuric acid was placed, and Fig. 6. saturated with ammonia, and the solution thus ob- tained evaporated to the point of crystallization. This method of working has now been given up. In Fig. 6, a modern saturator is represented. The walls E of the outer-chamber A are constructed of granite, the slabs being cemented together by sulphur and glass powder. The bell B is constructed of type metal. The am- 48 Manufacture of Ammonium Salts. monia tube C", the exit tube for waste gases D, are made of lead. After the waste gases have been cooled by passing through the economizer, cast iron or earthen pipes may be substituted for those of lead. After the crystals have been extracted, they are thrown into draining chambers or on to draining boards. The former, which are constructed of wood, are made conical at the bottom, and lined with lead ; the liquid which gradually trickles down passes out through a slit made in the bottom of the apparatus. The draining boards are likewise lined with lead, and are generally placed in such a position that the liquid which drops from the salt flows directly back into the saturator. As soon as the greater part of the liquid has drained from the salt, and the latter also sufficiently cooled, it is thrown on to a stone floor coated with' asphalt, so built that there is a slight fall from both sides to a central channel in which the remaining liquid collects, and is thence conveyed back to the saturator. It is of course understood that no hot salt solution must flow into this asphalted channel, as in that case the asphalt would become soft, and the whole coating be speedily destroyed. After lying in this manner for several days the salt contains only 4 — 5 per cent, of water, and is frequently brought into commerce in this condition. In other cases it is spread out in layers in heated and well-ventilated chambers, by which means the quantity of water is reduced to 2 — 3 per cent. (aT.) Regulation of the Process. — The regulation of the process in the manufacture of ammonium Ammonium Sulphate. 49 sulphate is very simple where the mechanical arrangements are good. The stills, when once set to work, continue to work uninterruptedly, and it is only necessary to regulate the ammonia pump according to the steam pressure ; to keep such a quantity of steam blowing through the still, that the waste-liquor passes off free from ammonia, which can be at once ascertained from its smell ; further to pump the requisite quantity of milk of lime into the decomposition tank at the right time, to add fresh acid to the saturator to compensate for the salt ex- tracted. In tio case should too much steam be blown in, as all excess causes unnecessary expense ; the tubes through which the ammonia passes from the still to the saturator, should never be allowed to become cold, as otherwise they may easily get blocked by condensation of ammonium carbonate, which forms an extremely hard deposit. The quantity of sulphuric acid to be placed in the saturator depends upon the percentage of ammonia in the gas-liquor. It is very rarely necessary to place the whole of the acid required in the saturator at once. The amount to be put in each time is best ascertained by experience. When the acid is nearly saturated, the salt separates out, and then is the best time to add fresh acid. When the process is proceeding regularly, it never happens that a liquid is obtained in the saturator which requires further evaporation. So much heat is set free by the combination of ammonia and sulphuric acid, that the liquid under the bell is kept in a con- tinual state of ebullition, and no condensation of E 50 Manufacture of Ammonium Salts. aqueous vapour takes place. On the other hand, sufficient evaporatioji frequently takes place to neces- sitate the acid beinpj somewhat diluted with water. The lime should always be added in the correct proportion. This depends upon the quantity of non- volatile ammonium compounds in the gas-liquor. Ordinary gas-liquor of 4-5° Tw. requires for every 100 gallons, 6 — 7 lbs. of good fresh lime, or 8 lbs. slaked lime. The addition of 7 — 8 lbs. for each 100 gallons, is quite sufficient under ordinary circumstances. The requisite quantity of sulphuric acid of 142° Tw. (containing 78 percent. pure H2SO4) is four- times the quantity of ammonia contained in the gas-liquor. Thus, in case a gas-liquor containing 2 per cent, of ammonia were being distilled, the requisite quantity of sulphuric acid would be about 80 lbs. for every 100 gallons of liquor. The amount of ammonium sulphate obtained does not differ greatly from the quantity of acid employed. The chemical control consists chiefly in the exami- nation of the raw material (gas-liquor, sulphuric acid, and lime) and of the waste-liquor. The estimation of ammonia in gas-liquor, and the valuation of lime and sulphuric acid have already been fully described. For the examination of the waste liquor, 100 cc. are distilled with a small quantity of quicklime, and the vapours passed into 5 cc. of normal acid and the excess of acid determined by titration. Supposing that it is found that 0'5 cc. of acid have been saturated then as i cc. corresponds to O'oiJ grams NH, the waste liquor must contain o"S -t- 0'0I7 = 0-0085 per cent, of ammonia. Ammonium Sulphate. 5 i {e.) Analysis of Ammonium Sulphate. — Especial care must be taken in obtaining a sample for analysis. It must be taken quickly, intimately mixed, and then immediately placed in a well- stoppered vessel, so that no loss of moisture takes place. For commercial purposes the amount of nitrogen it contains is determined preferably by the distillation method (p. 21). The salt is almost invariably sent out in somewhat damp condition, and very rarely comes into commerce quite dry. On this account it is also necessary to determine the quantity of moisture it contains. A weighed quantity of the salt is heated to 110° C. (230° F.) for several hours in a flat dish, and then again weighed, the loss of weight representing the water contained in the original salt. For the estimation of sulphuric acid the solution prepared for the estimation of the ammonia may be employed. 50 cc. of this solution (corresponding to I gram salt) are acidified with hydrochloric acid, and heated to the boiling point in a beaker. To this an excess of boiling barium chloride solution is added, and the resulting precipitate allowed to settle. The liquid is then filtered, the precipitate well washed with hot water, dried, and ignited in a weighed plati- num crucible to which the air is allowed access. The weight of barium sulphate thus obtained must be multiplied by -Us to obtain the weight of sulphuric acid (H2S04) in i gram of ammonium sulphate. The commercial salt should have a neutral reaction. It is, however, in general slightly acid, as, in order to avoid loss of ammonia, the liquid in the saturator is K 2 52 Manufacture of Ammonium Sails. never allowed to become quite neutral. The amount of free acid is determined by titration with one-fifth normal alkali (methyl-orange or Congo-red as indicator). If 50 cc. of the ammonium sulphate solution are taken (10 grams to 500 cc), then each one-tenth cc. of alkali used corresponds to 0-098 per cent of free sulphuric acid. (/".) Applications of Ammonium Sulphate. — This salt is almost entirely employed as an artificial manure, being used in large quantities for agricultural purposes. It has, however, a very powerful rival, viz. Chili saltpetre, which has become very much cheaper since the " Saltpetre War " between Peru and Chili, by which Chili obtained possession of the chief export harbours. The freights from these ports to Europe being also extremely low, the competition between the two compounds has become very keen. In March, 1889, the price of ammonium sulphate was 1 2 J. per cwt., whilst that of Chili saltpetre was \\s. per cwt. Ammonium sulphate contains about 20 per cent., of nitrogen, and Chili saltpetre 16 per cent. A hundredweight of nitrogen in the form of ammo- nium sulphate costs 3/., whereas in the form of Chili saltpetre it costs 3/. gs. Many agriculturists prefer to add the necessary nitrogen in the form of saltpetre, as it is supposed to act more quickly, and because moreover they appear to have a groundless preference for the foreign product. It often happens, therefore, that ammonia-nitrogen obtains a lower price than saltpetre-nitrogen, and all attempts to increase the employment of the former have been as yet unsuc- cessful. The profits obtained by gas-works from the Ammonium Sulphate. 53 gas-liquor have therefore greatly decreased, and only large manufacturers, who can obtain sulphuric acid cheaply and work in a rational manner, get satis- factory pecuniary results. The keen competition between the two salts is very plainly shown in the following table, which gives the import of ammonium sulphate and of Chili saltpetre into Germany from 1880— 1886:— Year. Ammonium Sulphate, Chili Saltpetre. Import in tons. Appr ximate value. Import in tons. Approximate value. 1880 1881 1882 1883 1884 1885 1886 33.783 34,652 34,147 27,904 35,967 35.070 36,558 675,650 710,350 717^100 488,350 539,500 394.550 420,400 55.078 89,950 126.949 166,185 ' 200,647 156,738 181,115 £ 853.700 1,349,250 1,650.400 1,328,050 2,006,450 1,567,400 1,130500 (g.) Double Salts. — Several of the double salts of ammonium sulphate have a practical application and are manufactured on the large scale (see p. 11). Ferrous Ammonium Sulphate is prepared by dissolving 140 lbs. of iron vitriol in the smallest possible quantity of warm water, acidifying, and allowing the solution to stand for several hours with scrap iron, and then adding a warm saturated solution of 66 pounds of ammonium sulphate. The mixture is stirred until it is cold, when the double salt separates as a bluish-green crystalline powder. This is spread out on draining boards, and dried by allowing it to stand for several days in the air. 54 Manufacture of Ammonhim Salis. Ferrous ammonium sulphate absorbs oxygen from the air much more slowly than iron vitriol, and may be kept for a long time without undergoing alteration. 4 It is employed in photography, dyeing, and in analytical chemistry. Nickel Ammonium Stilphate is obtained by precipi- tating a saturated solution of nickel sulphate with a similar solution of ammonium sulphate. It forms a crystalline powder, which is washed with cold water, and recrystallized from the hot liquid. It is the most suitable salt for nickel-plating, and is largely used for this purpose. Cuprammonium Sulphate. — For the preparation of the pure crystalline compound, copper vitriol is dissolved in caustic ammonia until cupric hydroxide begins to separate ; this precipitate is then dissolved by further addition of ammonia, and an excess of me- thylated spirits added. Under these conditions the double salt separates gradually in dark blue crystals. These are employed in medicine for affections of the eyes and nerves. The crude solution of this salt, obtained by the simple addition of ammonia to a solution of copper vitriol, also occurs in commerce, and is employed for destroying mildew on vines. It will probably be further employed in the future for the extinction of tree-lice, and as a disinfecting solution. Ammonium-Alum, was formerly manufactured in large quantities. Since the discovery of the Stass- furt deposits, and the consequent fall in price of potassium salts, its manufacture has been practically given up, and will therefore not be described here. Caustic Ammonia. 55 3. Caustic Ammonia. {Liquor AmmomcB, or Spirit of Hartshorn) {a.) Manufacture. — Until recently the aqueous solution of ammonia, or caustic ammonia, was obtained by the distillation of an ammonium salt with milk of lime. This process is now, however, given up as being much too costly, and the solution is prepared directly from gas-liquor. Instead of distilling off first the volatile ammonium compounds, and then treating with lime to decompose the non-volatile ammonium compounds, as in the manufacture of sulphate, it is necessary in this case to add lime at the commencement of the process. By this means the ammonia vapours are obtained free from carbonic acid, but not, unfortunately, entirely free from sulphur, for the sulphide of calcium which is first formed by the action of lime on ammonium sulphide, is partially decomposed on boiling in aqueous solu- tion, with evolution of sulphuretted hydrogen. The continuous stills are also employed for the manufacture of this product, and are especially valuable because, when combined with a good dephlegmator or cooler, they yield an ammoniacal gas nearly free from aqueous vapour. The crude gas thus obtained contains besides sulphuretted hydrogen, pyridine bases and other volatile constituents of tar. In order to eliminate these products the gas is first passed through a sim- ple lime-washer, and then through a small washer containing iron hydroxide in suspension ; it is also sufficient to employ a single washer containing 6 Manufacture of Ammonium Salts. a mixture of these two compounds. After this the gas passes through two smaller scrubbers filled with wood-charcoal or coke, then through a washer containing concentrated caustic soda solution, and finally passes into water contained in a well-cooled saturator. Two saturators should always be em- ployed, so that when the water in the one is nearly saturated, the gas can be turned at once into the other. (.The ammonia which is not ab- sorbed in the satu- rators is retained by passing it through a washer contain- ing dilute sulphuric acid. A steam pipe is connected to each of the washers and charcoal filters, by which means all the ammonia they con- tain can be driven off before refilling. Fig. 7 shows the arrangement of the still and -dephlegmator for the preparation of caustic ammonia. The gas-liquor is mixed with lime in a vessel of known size, the bottom of which is provided with a sieve, to prevent the larger pieces of lime, &c.. '^i~> Fig- 7- Caustic Ammonia. 57 passing away with the liquor. The mixture passes by means of the tube a (Fig. 7) into the column A, which is constructed exactly according to the plan shov/n in Fig. 3. Steam is blown in by the tube 0, and forced upwards through the gas-liquor. The ammoniacal vapours leave the column by the pipe m. and pass into the dephlegmator B. This contains a system of parallel tuLes which are kept cool by water. The vapours passing through these tubes, become concentrated from the condensation of the steam, so that the ammonia gas leaves the apparatus mixed with only a small quantity of aqueous vapour, whilst the water formed by con- densation passes back into the column by the tube g. The waste- liquor passes out through the regulator c, and the pipe / into the drain. The object of the regulator is to enable sufficient pressure to be kept up at the bottom of the column to overcome the various resist- ances which the gas meets in the column, dephleg- mator, and washing apparatus. The liquor can only flow away from c when the hollow body m swims, which occurs when c and the lowest chamber of the column are filled to a certain level with water. On this account the steam can never pass away by the pipe /, and the necessary pressure in the column can be got up and maintained. Fig. 8. 58 Manufacture of Ammonium Salts. In Fig. 8 the apparatus for washing and purifying the gas is shown. The latter, after leaving the dephleg- mator, passes into the washer E, which contains a mixture of slacked lime and iron hydroxide (bog iron ore) suspended in water. The gas, thus freed from sulphuretted hydrogen, streams upwards through the cylindrical tower D, which is filled with wood char- coal, and serves to restrain any liquid particles or tarry matters mechanically carried along with the gas. From D, the gas passes into the washer £«, which is filled with a concentrated solution of caustic soda. This washer has likewise a small scrubber containing charcoal attached, which completely filters and purifies the ammonia gas, and allows it to pass by the pipe r into the saturator F. This is filled with pure water, which is introduced from a reservoir by the pipe b. After saturation, the caustic ammonia is let off through d into the vessels in which it is stored. To keep the liquid cool during tho process of saturation, a stream of cold water is continuously passed through the coil i. Towards the end of the operation the whole of the ammonia is no longer absorbed, and streams through the tube e into a second similarly constructed saturator, which is in its turn connected with a washer containing dilute sulphuric acid, which effectually hinders any loss of ammonia. In order to avoid interruptions it is preferable to employ a double set of purifying apparatus. As. soon as the purifying agents cease to work properly, (which is at once evident from the condition of the liquor ammoniae formed,) the reserve washers are Caustic Ammonia. 59 filled and the gas passed through them. The valves R and r are now closed, and steam passed through the washers by opening the steam valve u ; instead of passing away through r into the saturator, the vapours are led from the top of D^ by a special pipe back to the still (pipe s in Fig. 7). The end of the operation is determined by the absence of any ammoniacal smell in the vapours given off, which is easily ascertained by opening a small tap placed for this purpose in the pipe s. The vessels are then emptied. If a duplicate set of purifying apparatus be dispensed with, the pipe s is of course unnecessary. In case it is necessary to stop the whole apparatus, the supply of gas-liquor is cut off, and the steam allowed to blow through until all the ammonia is driven out of the still and purifiers. The saturator F is in this case emptied and the ammonia absorbed solely by the acid washer. The shape of the washers should be such that the increase of pressure caused is as small as possible. On that account a horizontal washer is represented in Fig. 8. The pressure which the ammonia gas has to overcome in such washers is so small in compa- rison with the other resistances that it may be prac- tically neglected. The fact that the apparatus there sketched is very compact and easily inspected also tells greatly in its favour. For the construction of the apparatus, cast and wrought iron are solely employed. The saturators are, however, frequently lined with lead, as it is supposed that caustic ammonia may become yellow in iron vessels. Pure caustic ammonia can, however, 6o Manufacture of Ammonium Salts. certainly be kept in iron vessels without undergoing change, and well-purified ammonia gas may also be absorbed without danger in iron saturators. The regulation of the process is not so simple as in the case of the sulphate manufacture. An active, careful, and conscientious foreman is required, who must see especially that the still works properly and economically. The ammonia-gas must leave the apparatus free from carbonic acid, and should only con- tain small quantities of aqueous vapour ; the purifiers must be refilled at the proper time, so that they perform their work properly, and the saturators must never become hot. The waste-liquor must not smell of ammonia, nor show on analysis the presence of more than ooi per cent. NHg. The amount of lime to be added depends in this case on the total ammonia in the gas-liquor. As a general rule, in every lOO gals, of gas-liquor i8 lbs. of lime should be added for each i per cent, by weight of ammonia that it contains. The lime is slaked with sufficient water to form a thick milk, and added in this form to the gas-liquor in the reservoir. The latter is, as already mentioned, provided with a sieve at the bottom, to prevent the larger pieces of lime and other impurities passing into the still, where they might easily cause stoppages. Dr;. Feldmann (German Patent, 31,237) proposes to add the necessary quantity of lime to gas-liquor, and then filter in a filter-press from the lime mud, and to drive off the ammonia thus set free in a Feld- mann still (p. 43). In Griineberg's apparatus for the manufacture of Caustic Ammonia. 6i caustic ammonia, the gas-liquor is treated just as in the case of the manufacture of ammonium sulphate, and the resulting gases, which contain amiiionium carbonate, sulphide, and aqueous vapour, &c., passed through large lime-washers, and thence into the satu- rators. Two lime- washers must always be ready, and are used alternately. As soon as the lime in one be- comes useless, steam is turned on, and the ammonia it has absorbed driven back into the column and the washer emptied, and refilled with fresh milk of lime. If the column of the still is properly built, i.e. if the overflow tubes are wide enough, and the perforated caps so fixed that the steam boils through each chamber thoroughly, the whole of the necessary lime may be added at the commencement of the operation without any danger of interfering with the process. The filtration of the gas-liquor as in Feldmann's process, or the large lime-washers used by Griineberg can thus be avoided. (^.) Analysis and Application. — Commercial liquor ammonise must be clear and colourless^ and quite free from sulphuretted hydrogen and carbonic acid, Its strength is estimated by its specific gravity. The strongest commercial product, such as is employed for ice and freezing machines, and known as "liquor ammonise fortior," has at 15° C. (60° R), a sp. gr. of 0'885, and contains 35 per cent, of am- monia. The ordinary liquor ammonise has a specific gravity of O'Qi.and contains 25 per cent, of ammonia. A solution of sp. gr. 0-96, containing 10 per cent, is known in the Pharmacopoeia as " liquor ammoniae caustici officinalis." 62 Manufacture of Ammonium Salts. The caustic-ammonia prepared from gas-liquor has frequently the great fault that, on long- continued standing it assumes a yellow, or even a brown colour. This coloration is caused by the presence of certain tarry basic impurities, which gradually undergo decomposition. They can only be removed by a second distillation, preferably with the addition of an oxidizing agent. As one of the strongest basic liquids, liquor ammonise is largely used in the arts. An ammonia solution containing 17 per cent. NH3, is equivalent to a 31 per cent, solution of caustic soda, and it has the further advantage that any excess can be driven off and recovered by distillation, and that the ammonia can be recovered from all waste liquors by boiling with lime. It is chiefly employed in dyeing, calico-printing bleaching, and in the colour manufacture, and also to a smaller extent in medicine, and for household pur- poses. The strongest solution is used in ice-machines. It is transported in tinned iron drums, or in glass carboys. The latter are only used for small quantities and short distances. For calculation of the percentage of ammonia from the specific gravity, see table in Appendix. 4. Concentrated Gas-liquor. This name has been given to a product containing a larger percentage of ammonia than gas-liqour, and which is obtained from the latter by distillation. For its preparation, gas-liquor is distilled in one of the continuous stills previously described. The process may be conducted either in the manner Concentrated Gas-liquor. 63 employed for ammonium sulphate, first expelling the volatile salts, and then by addition of lime, the non- volatile compounds, or, as in the liquor ammoniae manufacture, by adding lime first and then distilling. In the first case, an ammonia-liquor is produced containing 10 — 15 per cent, ammonia, of which by far the greater part is in the form of sulphide and carbonate. More concentrated solutions cannot be obtained in this manner, as with vapours containing more ammonia, the pipes frequently become blocked by a deposit of ammonium carbonate. In the second case, a product containing 20 — 25 percent, ammonia can be obtained, and in this case the ammonia is chiefly present in the free state, mixed, however, with small quantities of ammonium sulphide and other impurities. In the manufacture of concentrated gas-liquor by the first named process, the most suitable apparatus is that of Griineberg or Feldmann (pp. 43, 45), in which, however, the saturatoris replaced by an ordinary iron condenser. The amount of lime required is ex- actly the same as in the manufacture of ammonium sulphate. In the second process, by which in reality a crude caustic-ammonia is obtained, it is preferable to employ the appara,tus shown in Fig. 7, the gases being here likewise passed through a simple condenser. The lime required in this case is the same as for the preparation of liquor ammoniae. Concentrated gas-liquor is a yellowish liquid, which smells of both ammonia and amftionium sulphide. It is chiefly employed in the nianufacture of soda by the ammonia-soda process. The crude caustic 64 Manufacture of Ammonium Salts. ammonia obtained by the second method is fre- quently used in chemical works for the preparation of ammonium salts and other products. The manufacture of concentrated gas-liquor will probably become of greater importance in the future, as it is the best starting-point for the manufacture of valuable ammonium salts, such as the chloride, carbonate, nitrate, &c., the direct preparation of which from gas-liquor is a matter of great difficulty. It may be especially recommended for gas-works, as the process is extremely simple, requires no addition of foreign chemicals, and does not necessarily require to be carried out on a very large scale. The valuation of either of the products is per- formed in the usual way. A known weight of the liquor (about 10 grms.) is diluted to 500 cc. ; 50 cc. of the solution are distilled with caustic soda, and the vapours evolved passed into 15 cc. of normal acid. Supposing that on titration 3 cc. of acid are found to have remained unsaturated, then 12 cc. of acid have been neutralized. As 50 cc. of solution correspond to I grm. of original liquid (assuming that exactly 10 grms. have been taken) it contains 100 x o'Oi/ X 12 = 20'4 per cent, of ammonia. For its transport either tanks on trucks, or iron barrels are employed. 5. Sal-Ammoniac. {Ammonwm Chloride, Chloride of Ammonia, Ammonii Chloridum..') {a.) Manufacture of crystallized Sal-ammoniac. — Sal-Ammoniac. 65 The manufacture of sal-ammoniac is very old. As has already been mentioned, it was obtained in the middle ages from camel's excrement, and came iato Europe under the name "sal-ammoniacum." Until the middle of last century, the whole of the European supply came from Egypt, but at the present time it is obtained exclusively from gas-liquor. The apparatus employed for the manufacture of ammonium sulphate can also be used for preparing sal-ammoniac, with the single exception tliat the saturator must be closed and constructed of stone. Lead is easily attacked by hot hydrochloric acid, and must therefore be avoided as far as possible in the construction of the apparatus.- The saturator is filled with acid of sp. gf. it,* and ammonia passed in until it is completely saturated. The solution formed contains about 25 per cent, of sal-ammoniac, and is pumped into an evaporator, the saturator being then refilled with acid. The evaporator consists of a wooden vessel, about 39 feet long, 6 feet broad, and 18 inches deep, lined internally with lead. Through it passes a coil of stout lead pipe, 20 — 26 yards in length which is con- nected with the steam supply. At the end of the coil a vessel is placed, so arranged as to catch the water which condenses in the pipe, without allowing the steam to escape. As soon as the solution has so far evaporated that a film of salt separates on the surface, it is run by means of a siphon into a leaden vessel, and allowed to crystallize. The salt which separates is fished out * Strenger acid must never be employed, as it then loses hydrochloric acid gas when hot. F 66 Manufacture of Ammonium Salts. by wooden shovels, and spread out on drying-boards, the latter being so placed that the drainings run back into the crystallizing vessel. The mother- liquor is then pumped back into the evaporator, and after filling up with fresh sal-ammoniac solution,, again evaporated. Especial care must be taken that the sal-ammoniac solution never comes in contact with iron, for, as already stated, the solution decomposes slightly on heating, a little ammonia being evolved. The hydrochloric acid thus set free remains behind, and on this account the hot solution has always an acid reaction and attacks iron. Sal-ammoniac containing iron may be obtained white by crystallization, bijtt the crystals become yellow or red on standing in the air. (^.) Other methods of preparation of sal-ammoniac are largely employed in chemical works in which certain metallic chlorides are obtained as bye- products. Thus, for example, gas-liquor is often worked up with calcium, magnesium, and even manganese chloride for the preparation of sal- ammoniac. The gas-liquor contains its ammonia chiefly in the form of carbonate, and therefore on addition of the solutions of any of these chlorides, the carbonate is decomposed with formation of sal-ammoniac, and precipitation of the insoluble metallic carbonate. These are separated by filtration, and the filtrate evaporated to the point of crystal- lization. Occasionally hydrochloric acid is added directly to gas-liquor till the solution is slightly acid. The Sal- A mmoniac. 6 7 very dilute solution thus obtained must be separated from the precipitated sulphur by filtration or by settling. The salt obtained is coloured yellow or red, and has a peculiar unpleasant smell. This rough process is still employed in England, in spite of the fact that the price of the " red " chloride is 1 5 — 20 per cent, less than that of the white crystalline salt. A salt which answers all the commercial require- ments can be obtained by saturating the so-called concentrated gas-liquor or crude caustic-ammonia with hydrochloric acid. This method has been successfully employed in several French and German works. The advantages of the method are easily perceptible when one considers the losses which occur in the preparation of sal-ammoniac by dis- tillation, and especially the fact that the saturators do not long withstand the action of the hot hydrochloric acid. Even though the renewal of such stone saturators is not very costly, the repairs and setting up take considerable time, and cause undesirable interruptions in the process. A plant for the pre- paration of concentrated gas-liquor or crude caustic ammonia, combined with the apparatus for saturating the distillate with hydrochloric acid, is not very costly and seems capable of a wide application. With such a plant a manufacturer is in a position to manufacture at will more or less of the. various ammonium salts, according to the state of the market. It seems also probable that sal-ammoniac might be recovered in the ammonia-soda process. This consists, as is well known, in passing carbonic acid r 2 68 Manufacture of Ammonium Salts. through an ammoniacal solution of common salt, when sodium bicarbonate separates out, and ammonium chloride is also formed. NaCl + NH4 HCO3 = NaHCOa + NH4 CI Proposals in this direction have been made by Gerlach and others, but it does not seem to have been practically carried out up to the present. (c.) Sublimation of Sal- Ammoniac. — Sublimed sal- ammoniac is frequently required in commerce, in place of the crystallized saltj for certain purposes indeed, the crystallized salt cannot be employed at all. The sublimation is carried out in cast-iron pots, lined internally with fire-brick, which are covered with slightly concave plates, likewise of cast-iron. The crystallized salt used for subliming should be well dried before placing in the pots, which hold about 10 cwt. The sublimation lasts about five days, after which the sal-ammoniac is found on the cover in the form of a solid, fibrous crust about four inches thick, which can be easily detached. This crust is broken up, separated from adhering dirt and impurities, and sent direct into the market. W. Hempel has found that crystalline sal- ammoniac can be converted into hard stone-like masses without sublimation, by subjecting it at a temperature of 50°.— 100° C. (120° — 212° F.) to great pressure in a hydraulic press. It is to be hoped that practical application of this observation may soon be made. Pressed cakes of sal-ammoniac do occur in commerce, but these are only in a loose Sal-Ammoniac. 69 state of aggregation, and break to pieces very easily. . Sal-ammoniac is transported chiefly in barrels, but also frequently in sacks. {d.) Applications and Valuation. — The applications of sal-ammoniac are very varied. The sublimed salt is used in soldering, as by its action on the hot surfaces it converts the oxide into chlorides, which latter do not hinder the soldering. The crystalline salt is also employed in the so-called " galvanizing " process, being used in solution for cleansing the articles to be "galvanized '' and in the solid form for keeping the surface of the zinc bath unoxidized ; it is further employed in dyeing and calico-printing, and for filling certain galvanic batteries. It is used in medicine for catarrh of the stomach and bronchial catarrh. The chemical examination of sal-ammoniac gene- rally consists in the estimation of ammonia and chlorine, and also frequently of iron, which is detri- mental to its employment in dyeing. The ammonia is best determined by distillation. 10 grm. sal-ammoniac are dissolved in water, diluted to 500 cc, and 50 cc. distilled as usual with caustic soda, passing the vapours into 20 cc. normal acid and titrating back. The estimation of chlorine is generally made' by titration with decinormal silver solution,* using potassium chromate as indicator. * Decinormal silver solution is obtained by dissolving 17 grms. silver nitrate in i litre of water. For the purpose of stan- dardizing it a decinormal solution of common salt (585 grras. per litre) may be employed. 70 Manufacture of Ammonium Salts. 5 cc. of the above sal-ammoniac solution are taken, and a few drops of potassium chromate solution added, and the liquid titrated with the silver solution. As soon as the whole of the chlorine is precipitated, the further addition of silver causes a deep red precipitate of silver chromate, thus clearly showing the end of the • titration. Suppose 17 cc. silver solution have been used, then, as 5 cc. solution contain 0"i grms. sal- ammoniac, and. I cc. decinormal silver solution corre- sponds to 0'0036S grms. hydrochloric acid, the salt contains-^- ^— ^ =62*05 hydrochloric acid. The moisture is determined as in the case of am- monium sulphate ; care must, however, be taken that the temperature does not rise above 100° C. (212° F.), as in that case loss of sal-ammoniac may take place. The amount of iron present is obtained by treating with a potassium permanganate solution of known strength. The sal-ammoniac solution must pre- viously be treated with a little zinc and hydrochloric acid, to convert all the iron into ferrous salt. 6. Ammonium Carbonate. {Sal-volatile, Ammonii Carbonas, Carbonate of Ammonia, Salt of Hartshorn^ At the present time ammonium carbonate is pre- pared by distilling ammonium sulphate with chalk, or directly from gas-liquor. In its manufacture by the former method an intimate mixture of one part of ammonium sulphate with two parts of chalk is heated in cylindrical iron Ammonium Carbonate. yi vessels, and the vapours evolved led into chambers constructed of stone, where the carbonate is deposited on the walls in crusts. The gases which leave the chamber pass through a small scrubber, where they meet a stream of sulphuric acid, which retains the uncondensed carbonate and free ammonia. For the distillation horizontal cast-iron cylindrical retorts are employed. These are generally from 7 — 10 ft. long, and about i8 inches in diameter, and are furnished at both ends with a movable cover. Several of these are heated in one furnace. When sufficient quantities of the salt have collected in the chamber, the crusts are separated by knocking the walls. The crude salt thus obtained is generally purified by sublimation in pots covered by cylindrical lead caps. To avoid over-heating, the pots are heated in water-baths. The temperature ,(is kept between 70° and 80° C. (158°— 176° F.). For every 100 lbs. of ammonium sulphate 76 lbs. of chalk are required. From this mixture a sublimate of 59 — 60 lbs. of ammonium carbonate is obtained ; 6'4 lbs. of free ammonia (corresponding to 25-6 lbs. of ammonium sulphate) are retained in the scrubber, whilst 105 lbs. of gypsum remain in the residue. From this it is apparent that only three-quarters of the ammonia in the sulphate is obtained as carbonate, the remainder being again converted into sulphate. In order to convert the free ammonia into carbonate, Kunheim (Berlin) passed carbonic acid into the condensation-chambers with very good results. This firm has, however, given up preparing 72 Manufachire of Am^nonium Salts. the carbonate from ammonium sulphate and lime, and now obtains it from pure ammonia gas and carbonic acid. The former is prepared in the same manner as for the manufacture of caustic ammonia, and is passed along with the requisite quantity of carbonic acid into the condensation-chambers, where combination takes place^ and the salt is deposited as before. If the carbonic acid has to be specially manu- factured by the action of sulphuric acid on chalk, this process is by no means cheaper than the distillation of the sulphate with lime. Matters are, however, very different where carbonic acid can be obtained cheaply, whether in the form of natural gas, as a product of combustion, from lime-kilns, or as a bye-product from any other manufacture. Ammonium carbonate is also obtained on the large scale in England from pure ammonia and carbonic acid. The salt thus obtained has, however,- not the ordinary composition, but is really acid ( OH ammonium carbonate CO ■< (-v-m-tt . Whereas the ordinary ammonium carbonate, which is a mixture of ammonium carbamate and acid ammonium carbonate, contains about 31 per cent, of ammonia, the acid salt only contains 21 — 23 per cent. On exposure to the air it decomposes much more slowly than the ordinary salt, and is generally speaking more stable, and may therefore be especially recommended for household purposes. Unfortunately, it has not so far proved very acceptable, for it smells much less strongly of ammonia than the ordinary salt, and loses Ammonium Nitrate. 73 all odour on standing for a short time in the air, and is therefore characterized by the general public as " bad " or " weak." The prices of the acid salt are, of course, much lower, and it is therefore probable that its use will, in spite of the above facts, gradually increase. Pure ammonium carbonate forms a snow-white crystalline mass ; it should dissolve completely in water, forming a colourless solution, and when heated on platinum foil should volatilize without leaving any residue. For its valuation, the percentage of ammonia is determined by the distillation method, 10 grms. of a good average sample being dissolved in water, diluted to .500 cc, and 50 cc. of this solution distilled with caustic soda. The vapours are passed into 20 cc. of normal acid, the excess of acid determined by titra- tion, and the quantity of ammonia calculated from these data in the usual manner. The ammonia may also be estimated by dissolving the salt directly in normal acid and titrating back with normal alkali. Ammonium carbonate is employed in medicine, for household purposes, and for baking powder, and also in dyeing and for washing wool and silk. 7. Ammonium Nitrate. {Ammonii Nitras, Nitrate of Ammonia.) Ammonium nitrate is formed by the double decomposition of Chili saltpetre and ammonium sulphate. On account of its great solubility in water 74 Manufacture of Ammonium Salts. it would be extremely difficult to obtain by this method a salt free from soda, and it is doubtful whether any technical application of this process has been made. Its preparation from ammonia and nitric acid is, how- ever, carried out on the large scale. For this purpose it is best to employ crude caustic-ammonia and the ordinary commercial nitric acid. The vessels used as saturators are constructed of earthenware, and are provided with a flue for waste gases, a pipe for passing in the ammonia solution, and a second pipe for drawing off the saturated liquid. A weighed or measured quantity of nitric acid of known strength is placed in the saturator, and the calculated quantity of ammonia solution allowed to pass in slowly from a simple measuring apparatus, until the liquid in the saturator is slightly alkaline. This solution is then evaporated to the point of crystallization. As the salt is hygroscopic and must not remain long in the air, the mother-liquor is separated by qentrifugal drainers, and the salt at once packed air-tight. For analysis lo grms. are dissolved in 500 cc. of water, and the ammonia determination made in the usual manner by the distillation method. To deter- mine the nitric acid, the residue remaining after dis- tillation is diluted with water, some zinc dust added, and the whole again slowly distilled, the vapours evolved being passed into 50 cc. normal acid. By this means the nitric acid is reduced and given off as ammonia, the amount of which is determined in the ordinary way. The commercial salt frequently also contains con- Ammonium Thiocyanate. 75 siderable quantities of nitrite, the amount of which may be easily ascertained by titration with potassium permanganate solution. The demand for ammonium nitrate has increased of late, on account of its employment in the manu- facture of explosives. Whether this is likely to last or to increase remains yet to be seen. It is also employed in considerable quantity for the prepara- tion of nitrous oxide (laughing-gas). This gas, which is so largely used by dentists, comes into commerce now in the liquid state, being kept in strong iron bottles. According to Professor Hofmann, almost the whole of the liquid nitrous oxide is supplied to dentists by two firms, viz. Barth and Co., London, and Losse, Berlin. The wrought-iron bottles hold, as a rule, about two pounds of liquid, which corresponds to about 100 gallons of gas. Such a flask is sufficient for 50 — 60 operations. 8. Ammonium Thiocyanate, or Sulphocyanide. This salt, which occurs in small quantity in gas- liquor, has of late acquired considerable importance. Its mode of formation from carbon bisulphide and ammonia or ammonium sulphide has already been described (p. 17). Up to the present this method has not been employed on the large scale, although several proposals in this direction have been made. Thus, J. Schulz proposes the following method : — 600 parts of 95 per cent, alcohol are mixed with 800 parts of caustic ammonia of sp. gr. o'pi, and then to these 350 parts of carbon bisulphide added, the 76 Manufacture of Ammonium Salts. alcohol distilled off, and the solution evaporated to the point of crystallization. The yield of dry sulpho- cyanide is 280 parts. On the manufacturing scale, it is chiefly obtained from spent-oxide, by a method which is described later on (p. 98). The recovery of ammonium sulphocyanide or other sulphocyanides from gas-liquor is not largely practised. Experiments on the large scale in this direction have been undertaken in several works, but no important results have been published. R. Gasch has attempted to arouse ammonia manufacturers to pay more attention to this point, for he states that there is no great future before its manufacture from spent-oxide, as the amount which the latter contains is due to faulty condensation, and therefore the more the con- densing apparatus is improved, the less will be the quantity obtainable from this source. By proper working 2*4 lbs. of sulphocyanide can be obtained from every 100 gallons of gas-liquor. In his proposals Gasch appears to favour the process of precipitation by copper vitriol. If any process for the recovery of this compound from gas-liquor has any future before it, this must take the form of precipita- tion ; for when the small quantity it contains is con- sidered, no other method appears practicable. The addition of a solution of copper vitriol con- taining sulphurous acid to one of a sulphocyanide at once precipitates copper sulphocyanide as a fine, white, quickly-settling powder. This precipitate can be easily separated on the large scale by filter presses. If the copper sulphocyanide be then treated Ammonium Phosphate. "JJ with ammonium sulphide, copper sulphide is precipi- tated, and ammonium sulphocyanide formed. The latter is obtained pure on filtration and evaporation, whilst the former is reconverted into copper vitriol by- roasting, and this used for precipitating a fresh quantity of gas-liquor. Ammonium sulphide may be replaced by other soluble sulphides or oxides, and thus the different salts obtained, just as in the manu- facture of these salts from spent-oxide (p. loo). The quantity of sulphocyanides in the different gas- liquors varies considerably, the richest being the English liquors. Apart from differences in the coal employed, the method of working and condensing apparatus also considerably affect the amount. Ammonium sulphocyanide, as well as the other sulphocyanides, is employed in dyeing and calico- printing in increasing quantities. A yellow colouring matter termed " Canarine" has also been obtained from it, but this seems at present to have no great practical value. The use of these salts in the manufacture of explosives, which has recently been proposed, has probably no great future, on account of their hygro- scopic nature. 9. Ammonium Phosphate. {a.) Proposals for its Manufacture. — Up to the present time the practical application of this salt has been very limited. Its manufacture has been attempted at Heilbronn gas-works by Raupp. The phosphoric acid there employed was a thick. 78 Manufacture of Ammonium Salts. milky liquid, containing 50 per cent. P2 O5, of which, however, only one-half was present in the form of free acid, the remainder being combined with lime. 655 lbs. of this acid were placed in a wooden tub, and the ammonia given off by 500 gallons of gas-liquor passed in. At first the liquid frothed up considerably, but after a time the evolution of gas ceased, and a dark, greyish-green thin liquid was formed, which gradually became white, and iinally assumed the appearance of lard. This was dried in shallow lead pans, and thus ob- tained as a greyish-white, extremely hard mass, which required grinding before it could be employed as manure. The yield of the salt, which contained 9*6 per cent, nitrogen and 42*9 per cent, phosphoric acid, was S^S lbs. At first, no purchasers for the product could be found, but finally the Agricultural Institute took it at a price corresponding to the ordinary prices of nitrogen in form of ammonia, and of phosphoric acid. The experiments made to deter- mine its value as a manure had very good results. Unfortunately the price of the salt is extremely high. The fact that it absorbs moisture from the air and balls together is a further hindrance to its employ- ment. It is manifest from these facts, and from the above-mentioned difficulties of preparation, that it is useless to manufacture this salt. (3.) Ammonium Superphosphate. — With ammonium superphosphate matters are quite different. Accord- ing to Bolton and Wanklyn's process, the ammonia in coal-gas is separated by passing it over super- phosphate placed in the ordinary oxide of iron purifiers. The process was first tried in the Munich Ammonium Chr ornate. 79 gas-works, and has been introduced in many other places during the last few years. By this process the ammonia is not only absorbed quickly, but also almost completely. One condition must, however, be fulfilled, viz. that the gas is free from tarry matters, as the latter speedily destroy the absorptive power of the superphosphate. In the Munich gas-works it was found that, whereas by the ordinary process of washing with scrubbers, 260 grains of ammonia per 1000 cubic feet remained in the gas only 10 grains could be found after the purification with superphosphate. This can absorb up to 7*5 per cent, of ammonia, and contains then also 0"46 per cent, sulphocyanide. The fears which were at first expressed that the presence of the latter would be deleterious to the growth of plants have not been verified in the experiments made by the first au- thorities. The advantages of the process are that it causes a more complete separation of the ammonia than the scrubbers, and that a better price can be ob- tained for the ammonium superphosphate than for the gas-liquor. It seems therefore probable that the process has good prospects before it, for though it will probably never replace the scrubbers in large gas- works, it is invaluable as a subsidiary method of purification. 10. Ammonium Chromate. Ammonium bichromate was formerly manufactured 8o Manufacture of Ammonium Salts. on the large scale more frequently than at present, especially in England. The chrome-iron-ore is roasted with soda in a furnace, the process corresponding exactly to the first portion of the manufacture of potassium bichromate. The mass thus obtained is lixiviated with water, and sufficient sulphuric acid added to set free the chromic acid. The free acid is then neutralized with concentrated gas-liquor or crude caustic-ammonia, and the liquid thus obtained evaporated till the salt crystallizes out. In the roasting process lime may be substituted for soda. If hydrochloric acid be employed to set free the chromic acid, then on evaporation of the neutralized liquid common salt separates out, whilst ammonium chromate remains in solution, and may be obtained pure by further evaporation of the liquid. When sulphuric acid is used, it is extremely difficult to separate the chromate from the sulphate also formed. ' According to a patent (No. 8602) taken out by J. Park, calcium chromate is treated with the necessary quantity of sulphuric acid to convert it into bichro- mate, and to this ammonium sulphate is added, the whole filtered, and evaporated to the point of crystallization. Since the price of potash salts has been so much reduced by the discovery of the Stassfurt deposits, there is no probability that ammonium bichromate will ever seriously compete with the corresponding potassium salt. Ammonium chromate is employed in calico-print- ing. Ammonium Oxalate. 8r II. Ammonium Oxalate. For the preparation of the neutral salt a solution of crude oxalic acid is saturated with crude caustic- ammonia, the mixture allowed to settle or filtered through a small filter-press, and the clear solution evaporated to the crystallizing point. The salt thus obtained must be recrystallized from water, the solution being first purified by animal charcoal. From the solution of this salt the acid salt is readily obtained by the addition of the calculated quantity of oxalic acid. It may also be prepared by neutralizing a weighed quantity of the acid with crude caustic-ammonia, and then adding the same quantity of oxalic acid, filtering and evaporating. Ammonium oxalate is used in analysis, medicine, photography, and calico-printing. 12. Ammonium Sulphide. The ammonium sulphide occurring in commerce is not prepared on the manufacturing scale. For its preparation sulphuretted hydrogen is passed into caustic ammonia until it is no longer absorbed. The solution should give no precipitate with a solution of magnesium sulphate, otherwise free ammonia is still present. Beyond its use in analytical chemistry ammonium sulphide has no practical applications. It has been occasionally employed in medicine, and also for etching copper objects. G 82 Manufacture of Ammonium Salts. 13. Ammonium Vanadate. This compound, in which the ammonia plays an un- important part compared with the vanadic acid both as regards price and application, is only mentioned here for the sake of completeness. The price of the salt is more than 4/. \os. per lb. Vanadic acid occurs in several rare minerals, the most important of which is Mottramite (Pb Cu) (V04)2. The Magnesium Metal Company in Patricroft (near Manchester) obtain ammonium vanadate from this on the large scale. The mineral is extracted with hydrochloric acid, and the extract evaporated with an excess of sal-ammoniac, when crude am- monium vanadate separates. This is recrystallized several times, and then ignited, and the residue (V2O5) dissolved in ammonia. The solution is filtered and evaporated. The salt is used in calico-printing and wool-dyeing for the formation of black. One part of ammonium vanadate is sufficient to convert 1000 parts of aniline salt into aniline black, if a sufficient quantity of potassium chlorate is also present. 14. Waste Products from the Gas-liquor. The waste products formed in the manufacture of the above salts from gas-liquor are three in number : (i) the gases evolved from the saturators ; (2) the lime-mud ; (3) the waste liquor. («.) Waste Gases. — The two chief constituents of the waste-gases are carbonic acid and sulphuretted Waste-Products. 83 hydrogen, the former being present in the greater quantity; they also contain smaller quantities of cyanogen, sulphocyanic acid, and other organic sulphur compounds, besides being invariably more or less diluted with steam. It is now compulsory to treat these gases in such a manner that they cause no nuisance or damage when they pass into the atmos- phere.i The plan generally adopted is to pass them into the flues of the nearest convenient boiler, in order to burn them'. A complete combustion of the sulphuretted hydrogen to sulphurous acid very rarely takes place on account of the large quantities of steam and carbonic acid present ; the gases pass therefore, largely unaltered, into the chimney, and thence into the atmosphere, where they speedily become so diluted as to be innocuous. If, however, no tall chimney is available, it may happen that in cool, damp weather the aqueous vapour condenses quickly and falls to the earth, where it may cause consider- able damage and nuisance on account of the sulphuretted hydrogen, &c., that it contains ; in that case it is necessary to get rid of the aqueous vapour by a suitable condenser, and then pass the dried gases under the boiler fires, and burn them properly. The Ammonia-gas Purifying and Alkali Company have patented the following process for recovering sul- phur (to the extent of 90 per cent.) from the waste gases (Claus' process). After condensation of the aqueous vapour, the remaining gas is passed, together with the necessary quantity of air, into a specially con- structed kiln, where it comes in contact with red-hot lumps of oxide of iron and firebricks. Under these G 2 84 Manufacture of Ammonium Salts. conditions sulphuretted hydrogen burns to water and sulphur vapour, which are condensed in a series of air- cooled chambers. The necessary amount of air is ascertained by analysis of the gases passing out of the kiln ; if too little air is present, the gases contain sulphuretted hydrogen, if too much, they contain sulphurous acid. The gases should therefore only contain traces of these compounds, along with nitrogen, carbonic acid, and steam. As a general rule a quantity equal to three-quarters of the volume of the waste-gases is sufficient. The chambers remain continuously at work, except during a few short intervals, for about six months, at the end of which time the deposit is removed. The sulphur obtained in this manner is almost chemically pure. The process is said to yield very good results at Stafford and Belfast. (^.) The Lime-Mud is a useless and troublesome waste-product. If allowed to pass away with the waste-liquor, it would speedily block up all drains, and must therefore be separated by filtration or by allowing it to settle. As a general rule the waste- liquor is run into a large pool, and allowed to stand until it becomes clear. The mud is from time to time dug out and carried away. (c.) The Waste-Liquor is not less troublesome than the foregoing. It contains calcium chloride, cyanide, sulphide, thiosulphate, sulphate, and hydroxide, tarry acids, &c. It has a brown colour and un- pleasant tarry smell, and causes constant complaints from the whole neighbourhood. Even though it does not give off vapours dangerous to health, it Waste Products. 85 makes any small watercourses practically useless for other commercial purposes. In the case of water- courses contaminated with decayed organic matter it is to a certain extent beneficial, inasmuch as it has a disinfecting action. No fish can of course live in water which is strongly contaminated with it. At present no suitable method of rendering the waste-liquor innocuous is known. Lunge has, how- ever, recently proposed to cause a precipitate of alumina or oxide of iron in the clarifying pool, by which means the tarry matters and other impurities would also be precipitated. 86 III. UTILIZATION OF THE "SPENT- OXIDE." I. Chemical Changes in the Purification of Coal- Gas by Ferric-Oxide. (a.) Separation of Sulphur in the Spent-Oxide. — The gas obtained from the distillation of coal, after being freed from tarry matters and ammonia in the air- condensers and scrubbers, still contains considerable quantities of sulphuretted hydrogen and other sulphur compounds, the removal of which is absolutely necessary. The combustion of gas containing these products in inhabited rooms would speedily so contaminate the atmosphere as to make it unbear- able. In order to purify the gas from these products, it was formerly passed through purifiers containing " Laming's mixture." This was prepared by mixing iron vitriol and slaked lime with sawdust, and allowing the moistened mass to stand for some time in the air before placing in the purifiers. When the mass ceased to work effectively, it was again exposed to the air, frequently moistened and stirred, and then, after a further addition of lime, once more used for purifying the gas. It was believed at that time that the sulphuretted hydrogen was decomposed by the Utilization of Spent-Oxide. 87 ferric oxide with formation of sesquisulphide of iron and water. FejOs 3HjO + 3HaS = Fe^Sa + 6HjO. Then on exposure to the air it was supposed that this sesquisulphide was oxidized to iron vitriol with separation of sulphur. FeaSa + 80 = 2 FeSO^-l- S. The further addition of lime was supposed to recon- vert the iron vitriol into hydrated ferrous oxide, which took up oxygen from the air, forming hydrated ferric oxide. In 1866 it was found from a number of analyses made at the Munich gas-works that the quantity of sulphur which is separated by the revivification of the mass is three times as large as is possible according to the ■ above theory. This uhexpected result caused further investigations to be made, and it was found that in Laming's mixture the oxide of iron alone takes part in the reaction. This absorbs sufficient sulphur from the gas to form iron sesquisulphide ; and on ex- posing the saturated mass to the air, this compound is oxidized, ferric oxide being re-formed, arid the whole of the sulphur separated out in the free state. The following simple equations explain the reaction : — Fe^Os. HjO 4- 3HisS = Fe^Ss -I- 4Hi,0 FeaSs -t- 3O -h H»0 = FeaOa H^O -f 3S. As soon as this was proved, the use of lime in the purifying mass was dispensed with, and oxide of iron alone employed. The cheapest form of iron oxide is natural bog-iron ore. This contains 50 — 70 per cent, of ferric oxide 88 Utilization of Spent-Oxide. and is especially suitable on account of its porous nature, as in that condition it offers comparatively little resistance to the passage of the gas. The mix- ture proposed by Lux, which is an alkaline hydrated oxide of iron, is also highly spoken of. A mass of similar composition to this is also obtained in working up bauxite. The treatment with alkali at high tem^ peratures is said to render the oxide more active, so that it absorbs sulphuretted hydrogen more energeti- cally than any other mixture. Certain industrial bye- products, which consist for the most part of ferric oxide, are also employed in coal-gas purification ; among these may be mentioned the spent pyrites from the sulphuric acid manufacture, and the ferric oxide precipitated in the preparation of aniline ; care must, however, be taken that these are not too dense. In order to render the mass more porous, the oxide is frequently mixed with sawdust or small coke. The reactions which take place in the operation are not quite so simple as shown in the above equation ; secondary reactions also invariably take place, but these are very small compared with the chief reaction. Various chemists have found that the ferric- oxide can absorb more sulphur than is accounted for by the theory. Thus, for example, Deike passed sulphuretted hydrogen for 24 hours over 2236 grams of powdered ferric hydroxide, and found that the mass then contained 10 per cent, more sulphur than demanded by theory. Cox and others assume that the sesquisul- phideof iron can be to some extent decomposed, even in absence of oxygen, by the action of moisture. The Reparation of Nitrogen Compounds. 89 spent mass taken from the purifier is in fact found to contain not only the sulphide of iron, but also consi- derable quantities of sulphur, even before exposure to the air. In revivifying the mass in the air, besides the oxidation of iron sulphide to sulphur and ferric oxide, a certain amount is converted into basic ferrous sulphate. The importance of the separation of the sulphur in the purifiers is shown by the following statement of Knublauch : — Total weight of coal used per annum . . . 40,000 tons. Sulphur separated in gas-liquor .... 16 „ » » „ the spent-oxide . . . 1 14 „ For every ton of Westphalian coal used, 6-3lbs. of sulphur are deposited in the purifiers. (^.) Separation gf Nitrogen Compounds in the Puri- fiers. Composition of certain Spent-Oxides. — Besides sulphur, other substances are retained by the oxide in the purifiers. Considerable quantities of cyanogen are absorbed, and remain in the form of ferrocyanides, and ammonium sulphocyanide and sulphate also occur in varying quantities. Although the processes by which the separation of sulphur takes place are fairly clear, the formation of ferrocyanides and sulphocyanides is at present quite inexplicable. It can hardly be assumed that the ammonium sulphocyanide reaches the purifiers in the form of vapour and is there deposited, for it is not particularly volatile. It is therefore probably more correct to' assume that it is formed by reactions taking place in the purifier itself, which require further investigation. It is as yet unknown from what original constituent or constituents of the gas the go Utilization of Spent-Oxide. ferrocyanides are formed. It is certain that the gas contains no hydrocyanic acid or ammonium cyanide, for on passing the gas through an acidified solution of ferric chloride no trace of Prussian-blue is obtained ; only when the free acid is neutralized by the ammonia contained in the crude gas is Prussian-blue pre- cipitated together with iron sulphide. It should also be noted that the substance occurring in the spent-oxide is not pure Prussian-blue, but an insoluble compound of the latter with ammonia. The ammonia contained in the mass cannot be completely extracted with water; a certain amount always remains behind, and must be set free by alkali. Moreover, sulphocyanides occur both in soluble and insoluble form. It is well known that Prussian-blue, when obtained by precipitation, frequently carries down with it other salts from which it cannot be separated by washing, and it is not improbable that in the spent-oxide it unites with a portion cf the sulphocyanide in a similar manner. According to Knublauch the composition of the spent-oxide depends not merely on the condition of the original mass, but also to a large degree on the purification in the wet way, i.e. the removal of ammonia in the condensers and scrubbers. If this is faulty, the ferrocyanides are only formed in small quantity. In the gas-works at Cologne, where the wet purification is in very good order, the spent- oxide contains as much as 25 per cent, of Prussian- blue, an amount which is probably equalled at no other works. It is interesting to note the relative quantities Composition of Spent-Oxide. 91 of nitrogen obtained as ammonia and as cyanogen in the dry distillation of coal. According to W. Foster : — o'l^ija of the coal = I4'5i% of the nitrogen form ammonia. 0027,, „ „ = 156,, „ „ „ cyanogen o'6io„ „ „ = 35"26„ „ „ remain in the gas 0-842 „ „ „ = 48-67,, ,, „ „ „ coke According to Knublauch : — 31 — 36% of the nitrogen remain in the coke. 10 — 14,, „ „ form ammonia. i'5— 2„ „ „ „ cyanogen. I — 1-3,, „ „ remain in the tar. The following table shows the quantity of sulphur, Prussian-blue, ammonium sulphocyanide, and the total ammonia, contained in various dried spent- oxides : — Per cent. Per cent, of sulphur. Per cent, of Prus- of ammo- nium sul- Per cent, of total sian-blue. phocya- ammonia. nide. I 31-0 6-0 trace VI 2 42-1 ■ 5'2 2-8 0-8 3 40-5 4' I o'S 1-5 4 37-3 6-4 0-4 07 5 36-4 4-0 OS 10 6 50-6 4-5 20 04 7 25-1 3'3 trace 0-9 8 38-8 2-1 37 V2 Eunte gives the following analysis of a spent-oxide which had been used eight times : — o 77% ammonium sulphate. 4-40 „ „ ferrocyanide and cyanide. 14-08 „ „ sulphocyanide. 16-82 „ hydrated iron oxide. 11-12,, Prussian-blue. 33-50,, sulphur. 19-31 „ saw-dust, tar, &c. 92 Utilization of Spent-Oxide. A. Wagner found in a frequently used spent- oxide : — 217 % iron oxide, 45 '5 „ sulphur, 4"35 „ ammonium sulphocyanide, trace of Prussian-blue. From these examples the varying composition of the spent-oxide is very manifest. (c.) Revivifying the Spent-Oxide. — This is of especial importance, not merely for the gas purification, but also for the subsequent processes in working up the spent-oxide ; for the amount of valuable substances formed in the latter depends largely upon the number of times it has been used and revivified. The general method of revivifying consists in shovelling the mass out of the purifiers on to special floors, where it is frequently turned over and moistened. Here and there this process has been replaced by revivifica- tion in the purifiers themselves. For this purpose the used-up purifiers are disconnected, and a stream of air forced through them for several hours by means of a steam ejector or other draught. The purifiers can then be immediately put into action again. The cover of the purifier must, however, be occasionally removed in order to stir up the mass, which becomes caked together from the separation of sulphur. It is manifest that this process is very much simpler and more convenient than the first named. A process which promises to become of the greatest importance is the continuous x&V\v\^zz.\}ion of the spent- oxide " in situ." For this purpose oxygen is mixed with the crude gas before it reaches the purifiers, in sufficient quantity to oxidize to ferric oxide all the sulphide of iron formed by the sulphur compounds in Preliminary Treatment. 93 the gas. The mass can then be allowed to remain in the purifiers and in the gas, until the quantity of sul- phur deposited causes considerable diminution in the absorptive power of the mass. To judge from experi- ments made on the large scale in certain English gas works, the process promises to be successful. 2'S cubic feet of oxygen* for every 1000 cubic feet of gas were found to be sufficient ; the spent oxide formed contained 50 — 60 per cent, of sulphur, and the illuminatingpowerofthegaswasin no way diminished. 2. Treatment of the Spent-Oxide. (3.) The Raw Material. — The different varieties of spent-oxide show not only great chemical but also great physical differences. From the larger works the mass is, as a rule, free from all those mechanical impurities, such as sawdust and small coke, which are frequently added in smaller gas works, to render the mass more porous. Now and again varieties are found which contain large quantities of lime, for which many gas- engineers have still unfortunately a great preference. Fresh varieties, which have not lain long in the gas- works, frequently contain naphthalene, and possess its characteristic penetrating smell ; other kinds are quite odourless, having lo.st their volatile tarry con- stituents by lying for a long time in the open air, and these have also too frequently had a portion of their soluble salts washed away by the rain. This dis- similarity in the spent-oxides is a great source of inconvenience to those engaged in its treatment * Brin's oxygen, which can now be cheaply obtained, was employed. 94 Utilization of Spent-Oxide. It is to be hoped that in the course of time all gas works will find it to their advantage to prepare it in as homogeneous a form as possible. The mechanical impurities, which frequently amount to 50 per cent, of the whole, should especially be got rid of, as they not only lower its value, but often cause great additional difficulty in the recovery of the various products. A preliminary treatment of the spent-oxide is only necessary when the ferrocyanides are to be recovered. In this case the oxide must be powdered, as it con- tains lumps from ^ to i inch in diameter, which are held together by the deposited sulphur, and are not penetrated by the agents employed. It is quite sufficient to pass the damp mass between grooved cast-steel rollers. For the extraction of sulphur the mass must be quite dry. To this end it is allowed to lie under cover in the air for considerable time, under which conditions not only the moisture, but also the naph- thalene and tarry impurities are given off. The Analysis 0/ Spent-Oxide is of great importance ; as by this alone is it possible to ascertain its value, and to determine the method by which it shall be treated. Estimation of Moisture. — A weighed quantity of a good average sample is dried in a dessicator over calcium chloride. Estimation of Sulphur. — This is estimated as raw sulphur by extraction with carbon bisulphide. Any glass extracting apparatus may be employed which is sufficiently large to extract about 100 grms. From a good average sample 50 — 100 grms. are taken and extracted with carbon bisulphide, until the Analysis of Spent-Oxide. 95 liquid passing off is no longer coloured. After eva- porating off the solvent the residual sulphur is melted and weighed. Estimation of Sulphocyanides. — 50 grms. of the spent oxide, after freeing from sulphur, are extracted with warm water, and the solution partially evapo- rated on the water-bath, acidified with sulphurous acid, and precipitated with an excess of copper sulphate solution. The white precipitate is collected on a weighed filter, dried, and weighed. 121.5 grms. of copper salt correspond to ']6 grms. of ammonium sulphocyanide. If no chloride, cyanide, or ferro- cyanide is present, this estimation may be very quickly made with decinormal silver solution. 10 cc. of this are taken and mixed with a few drops of nitric acid and ferrous ammonium sulphate solution, and titrated with the solution of sulphocyanide diluted to a known volume, till a red coloration is produced. Suppose that the aqueous extract of 50 grms. spent- oxide has been diluted to 500 cc, and that 20 cc. of this solution are required for the titration of 10 cc. decinormal silver solution ; then the whole liquid ioxo'0076x 500 ,„ J . . contains — = rp grms., and the spent- 20 oxide contains 2Xi"9=3"8 percent, of ammonium sulphocyanide. Estimation of Ferrocyanides. — The residue from the extraction of the sulphocyanide, corresponding to 50 grms. spent-oxide, is warmed for some time with an excess of caustic soda. Too large an excess should be avoided, and the whole well stirred. The mixture is then filtered, the residue washed with hot water, and the filtrate boiled with pure ammo- 96 Utilization of Spent'Oxide. nium chloride or sulphate solution until no further smell of ammonia is perceptible. In this manner the alumina dissolved by the caustic soda is precipitated. Its elimination is necessary, as it is precipitated to- gether with Prussian-blue even in slightly acid solu- tions ; moreover, by its precipitation dark tarry matters are likewise carried down, and the solution thus becomes clearer. After filtering off the alumina, the solution is slightly acidified with hydrochloric acid, heated to boiling and poured into a hot dilute solution of ferric chloride. The Prussian-blue pre- cipitated is allowed to settle, the dark red liquid poured off, and the precipitate well washed by decan- tation. It is then brought on to a filter and washed with hot water till the filtrate is free from iron, dried, and ignited in a platinum crucible to which the air has access. It is thus converted into ferric oxide, which is weighed, and the quantity of ferrocyanide calcu- lated from the weight found. 560 parts of ferric oxide correspond to 636 parts ferrocyanogen (Fe(CN)6) and to 860 parts of Prussian-blue. The composition of Prussian-blue varies according to the conditions under which it is precipitated. If iron be not present in excess, a compound of Prussian- blue with potassium or sodium ferrocyanide separates. Moreover, under certain conditions, the precipitate contains also potassium or sodium sulphate. It is therefore necessary to adhere exactly to the method of precipitation given above. In many cases a volumetric method, which the author has employed for a long while, is quite sufficient. 42'2 grms. of pure dry potassium ferro- Analysts of Spent- Oxide. 9 7 cyanide (K4Fe(CN)6 + 3H2O = 422) are dissolved in water and diluted to a litre. A dilute, slightly acid ferric chloride solution is placed in a burette, and 10 cc. of the ferrocyanide solution titrated with it. So long as an excess of ferrocyanide remains in solution, no Prussian-blue is precipitated. If a drop of the dark blue liquid be placed on filter paper, it spreads out to a uniform blue spot. As soon, however, as all ferrocyanide is converted into Prussian-blue, the spots do not spread uniformly, but give a blue patch in which the particles of precipitated Prussian-blue are easily seen. The end of the titration may be accu- rately detected by employing filter paper previously soaked in ammonium sulphocyanide solution. The slightest excess of iron is then recognized by the fact that the blue particles no longer appear on a white, but on a yellow or red ground. The strength of the iron solution having thus been ascertained, it is diluted to correspond with the ferrocyanide solution, and again compared with the latter in the manner above described. With this iron solution, all liquids containing ferrocyanides can be titrated with fairly ac- curate results. The liquids must, however, be neutral and free from alumina. Let us suppose that 20 cc. of the neutralized caustic soda extract (diluted pre- viously to 500 cc.) require 30 cc. of ferric chloride solu- tion, thenas 1000 cc. ferric chloride solution correspond to 2i'2 ferrocyanogen (Fe(CN)6) the whole extract 21-2 X in enn contains -1::^ f^_500 _ j.^ grms. =2x5-3 = 106 20 per cent, of ferrocyanogen. Estimation of Ammonia. — This estimation is best II 98 Utilization of Spent-Oxide. performed by the azotometric method (p. 25). For the total ammonia 3 — 4 grms. of the spent-oxide are weighed out and placed in the inner cylinder of the apparatus, and the analysis performed in the usual manner. To determine the quantity of soluble am- monia, 50 grms. of spent-oxide are extracted with water, the extract diluted to 200 or 250 cc, and 10 cc. analyzed by the azotometer. (^.) Recovery of Sulphocyanides. — The recovery of sulphocyanides from spent-oxide forms at the present time a small but flourishing industry, the process being carried out by about ten different firms. Until recent years, the .epent-oxide was used ex- clusively for sulphuric acid manufacture. It was roasted in the ordinary kilns, thus converted into sulphurous acid, and this oxidized to sulphuric acid by the usual process. The residue was then again employed for gas purification. The increase in the demand for sulphocyanides, due to their employ- ment in dyeing and calico-printing, caused manu- facturers to turn their attention to the recovery of the ammonium salt from the spent-oxide, the first attempts being made in England. The process, which has in the meantime been improved and ex- tended to the recovery of other sulphocyanides, is still being successfully worked. Only such varieties of spent-oxide as are fairly rich in sulphocyanides are worked up. They are directly extracted with water, in an apparatus constructed in a similar manner to that used for the lixiviation of black- ash, and known as Buffand Dunlop's or Shank's appara- Recovery of Sulphocyanides. 99 tus. It consists of a number of wooden tanks arranged in a series, and so connected that the tank containing the fresh spent-oxide is extracted with a liquor which has already passed through several other tanks. After treatment with the fresh spent-oxide, this liquor is pumped offand evaporated. The oxide is next washed with a more dilute liquor from another tank, and the liquor thus obtained pumped into a vessel containing fresh spent-oxide, and then evaporated. The first quantity of spent-oxide is then washed for the third, fourth, and fifth time with liquors which are each time more dilute, and finally with pure water, the liquors formed being in each case conveyed into tanks contain- ing richer spent-oxide. The thoroughly extracted mass is then removed from the tank, and the latter re-filled with fresh spent-oxide. The liquor thus obtained is by no means very concentrated, and rarely contains more than 2 per cent, of ammonium sulphocyanide. The strength, of course, depends largely upon the amount originally contained in the spent-oxide. Besides ammonium sulphocyanide, the liquor always contains more or less ammonium sulphate, gypsum, and ferrous sulphate. If the liquor is sufficiently pure, it is directly evaporated, and the ammonium sulphate allowed to crystallize out, and then the mother-liquor further evaporated until the ammonium sulphocyanide also separates. In many cases, however, this method of treatment would yield very unsatisfactory results. The method of precipitation with copper vitriol already described (p. ^G) might then be employed. Unfortunately, this method is somewhat indirect, and requires a large plant, H 2 loo Utilization of Spent-Oxide. on which account it can scarcely be employed, except in large works. A simpler method is the following : — The liquors are so far evaporated that the gypsum and the greater portion of the ammonium sulphate separate out, and the mother-liquor then boiled with baryta in a boiler lined with lead, the requisite quantity of baryta being previously ascertained by analysis of the liquor. Steam is now blown through the liquor, until no more ammonia is given off. (The ammonia gas thus set free may be used for the pre- paration of caustic ammonia). The solution of barium sulphocyanide formed in this manner should still contain a slight excess of baryta, which is removed by passing carbonic acid through the liquid until it has a neutral reaction. The milky liquid is then filtered from the precipitated barium carbonate, sulphate, and ferrous hydroxide by means of a filter-press. The filtrate has frequently a deep yellow or brown colour, which may be to a large extent removed by the addition of animal charcoal and re-filtration. The filtered and decolorized liquid is then evaporated in a wooden vessel lined with lead, and heated by means of a steam-coil. The evaporation is continued until large bubbles form on the surface, which are covered with a film of salt. The contents of the evaporator are then run into a wooden barrel, likewise lined with lead, and provided with a tight-fitting cover. In the bottom of the barrel is an opening, which can be closed by a wooden plug. When the liquid is quite cold, the plug is knocked out, the mother- liquor allowed to run off, and the salt at once thrown on to centrifugal draineis, and quickly packed air-tight. Recovery of Ferrocyanides. loi The product obtained in this way crystallizes in beautiful needles, and though generally slightly yellow, is almost pure. Barium sulphocyanide is preferred to the other salts for dyeing purposes, and therefore obtains a higher price. The spent-oxide after the extraction of the sulpho- cyanides, is employed for the sulphuric acid manu- facture in the usual manner, unless the sulphur has been previously extracted according to the method described later on, in which case the ferrocyanide can also be recovered. (^.) Recovery of Ferrocyanides. — The recovery of ferrocyanides from spent-oxide is not yet carried on to any great extent. The chief information on the point is found in the German Patent records. The most important process is that of Kunheim and Zimmermann. (German Patent, No. 26,884). The spent-oxide is first freed from sulphur by treatment with carbon bisulphide or light petroleum-ether, and afterwards extracted with water to remove sulpho- cyanides. The mass, after being allowed to dry in the air, is intimately mixed with powdered lime, and heated in a closed vessel to a temperature of 40° — 100° C. (104° — 212" F.), in order to drive off all ammonia present in the form of insoluble compounds. The resulting mass is then systematically extracted. The calcium ferrocyanide solution, which still contains ammonia, is neutralized and boiled, when the difficultly soluble double ferrocyanide of calcium and ammonium Ca (NH4)2 Fe Cye, is precipitated. This salt on boil- ing with milk of lime yields a pure solution of calcium ferrocyanide, which may be converted into I02 Utilization of Spent-Oxide. Prussian-blue by treatment with iron salts. In order to obtain from it potassium ferrocyanide (prussiate of potash), the solution is partially evaporated, and sufficient potassium chloride added to the' solution to form the difficultly soluble potassium calcium ferro- cyanide. On boiling this with a solution of potassium carbonate, it is converted into, potassium ferrocyanide- The corresponding sodium ferrocyanide may be obtained by substituting sodium carbonate (soda) for potassium carbonate (potash). In Hempel and Sternberg's process (G. P. 33,936), the spent-oxide is first extracted with water, and then treated with three to four times the theoretical quantity of caustic ammonia at the ordinary tempe- rature. The solution of ammonium ferrocyanide obtained is then converted into either Prussian-blue or potassium ferrocyanide. S. Marasse (G. P. 28,137) utilizes the ferrocyanides by converting them into sulphocyanides. The spent- oxide, from which the soluble ammonium salts have been extracted with water, is heated in closed vessels with an excess of lime to over 100° C. (212° F.). The end products of the reaction are calcium sulpho- cyanide and iron sulphide, which are separated from one another by filtration. Wolfrum's process (G. P. 40,215) combines the working up of the spent-oxide and of the gas-liquor, and these again with the purification and washing of coal-gas. The process can therefore only be carried out in a gas-works. The spent-oxide is first extracted with dilute sul- phuric or hydrochloric acid, and the solution, which Recovery of Ferrocyanidez. contains considerable quantities of iron, mixed with gas-liquor, the free acid- being, however, first neutralized by ferric oxide or iron ochre. By the treatment with acid the ammonium sulphocyanide contained in the spent-oxide is eliminated, whilst the double compound of ammonium ferrocyanide and Prussian-blue is converted into ammonium sulphate or chloride and Prussian-blue free from amtnonia, which latter remains in the residue. The sulphur in the residue is extracted by means of carbon bisulphide. The precipitate formed on mixing the iron solution with gas-liquor contains about 30 per cent, of sulphur recoverable by carbon bisulphide, and 40 per cent, of ferric oxide, partly as basic ferric sulphate, and partly as Prussian-blue. After the extraction of sulphur, this residue may be mixed with the iron ochre and used for the gas purification. The desulphurized liquor is freed from excess of ammonia by distillation, and then returned to the scrubbers, and the process repeated until the liquor contains sufficient ammonium sulphate and sulphocyanide to pay for their recovery by evaporation. The residue from the spent-oxide after extraction with acid and carbon bisulphide is utilized for the preparation of potassium ferro- cyanide. The only process which is at present used is that of Kunheim and Zimmermann, for although it is some- what roundabout, it suits the present requirements better than the other. Hempel and Sternberg's pro- cess has the advantage of obtaining the ferrocyanide without previous extraction of the sulphur ; the de- composition of the Prussian-blue by ammonia is, how- I04 Utilization of Spent-Oxide. ever, incomplete, and the yield of ferrocyanides would be very unsatisfactory. Marasse's process has no great prospects, for the sulphocyanide market would soon be overstocked if all the ferrocyanide of the spent-oxide could be converted into that substance. Moreover, the further treatment of the calcium sulphocyanide solution would not be easy on account of the calcium sulphide which it must inevitably contain. Wolfrum's process is on a sound basis, but the time has not yet come for the management of the gas-manufacture to pass into the hands of chemists, and for the process to be conducted throughout in such a scientific manner as Wolfrum's process demands. Prussian-blue can only be extracted from spent- oxide by milk of lime and by caustic soda. Caustic potash can hardly come into consideration on account of its price. The extraction with milk of lime does not give by any means good yields. The desulphurized mass must be boiled with milk of lime until no more ammonia is evolved, as otherwise the double salt of calcium and ammonium is formed, which is difficultly soluble, and therefore not readily extracted. This fact alone makes the milk of lime extraction almost impossible in practice, for the thick liquid must be treated for hours with steam before the ammonia is all driven off. In one case an attempt was made to extract the spent-oxide with the waste- liquor from the gas-liquor distillation, but with no great success. Caustic soda solution decomposes Prussian-blue quickly and completely, and the sodium ferrocyanide formed can be easily extracted. Unfortunately the Extraction of Sulphur. 105 larger quantity of the caustic soda is absorbed by the sulphuric acid in the spent-oxide (chiefly present as basic ferrous sulphate), even when the mass has been previously desulphurized and extracted with water. Spent-oxide which does not contain at least 10 per cent, of Prussian-blue, does not pay for treatment with caustic soda. For example, a mass containing 3 per cent, of Prussian-blue requires theoretically i '67 per cent, of caustic soda for its decomposition. It is found, however, that even when the spent-oxide has been carefully extracted with carbon bisulphide and hot water, no less than 5-^6 per cent, of caustic soda are required. The quantity of basic sulphate in spent- oxide is fairly constant, whether they contain large or small quantities of Prussian-blue. With spent-oxide containing large quantities of ferrocyanides, the loss of caustic soda is therefore much less in proportion, and only in such cases does the extraction pay. The liquors obtained must always be slightly alkaline, as they contain also large quantities of sodium sulphate, which it would otherwise be a matter of impossibility to separate from the sodium ferrocyanide by crystal- lization. Sodium ferrocyanide is now being prepared on the large scale by two German firms. (d^ Extraction of the Sulphur. — The weakest point in the process for the recovery of the ferrocyanides lies in the fact that the sulphur must be previously extracted. That this . is unavoidably necessary, is very clear from the foregoing pages. Kunheim and Zimmerman's process requires that the sulphur should be absent, and any treatment with caustic soda whilst I o6 Utilization of Spent" Oxide. the sulphur is still present, is, of course, out of the question. Unfortunately, a grey sulphur contaminated with tarry matters is thus obtained, which has but little value. Matters would be very different if the extraction paid its own way, or, better still, was a source of profit. As the matter stands at present, all profits must be obtained from the ferrocyanides, and this is therefore an additional reason why only spent- oxides rich in ferrocyanides are worth extracting. To desulphurize the spent-oxide without at the same time deconiposing the ferro- and sulphocyanides, is by no means an easy matter. High temperatures must be avoided, on which account the sulphur cannot be driven out by roasting or by superheated steam. The only method which can be employed is that of extracting the sulphur with liquids at tempe- ratures under ioo° C. (212° F.). Suitable liquids for the purpose are, light-petroleum ether, benzene, and carbon bisulphide. Light-petroleum ether dissolves about 5 per cent, of sulphur at a medium temperature, and 10 — 12 per cent, at its boiling point. Benzene {B.P. 80° to 100° C. (186—212° F.)} dissolves at the ordinary temperature 2 — 3 per cent, at 100° C. (212° F.) IS per cent, of sulphur, whilst carbon bi- sulphide takes up 40 — 50 per cent, at the ordinary temperature, and 180 per cent, at 55° C. (131" F.). The latter solvent is therefore the one usually em- ployed, and it has the further advantages of being cheap, and easily prepared. Unfortunately very few details can be obtained concerning this extraction of sulphur, as the process is rarely worked on the large scale. It is true that large plants for the extraction of oils and Extraction of Sulphur. 107 fats have been built, and are working successfully, but it must be borne in mind that the two processes are essentially different, for whereas in the case of oils and fats we have to deal with bodies which are either liquid or melt below the boiling point of water, we have in sulphur a substance which is still solid at that temperature ; moreover, in the first case the oils and fats can be easily freed from the last traces of the solvent by steam, whilst with sulphur the slightest con- densation of moisture causes the whole liquid mass to solidify. Different forms of extractor have been proposed by Wegelin and Hiibner, Biittner, and Hirzel. A description of Wegelin and Hiibner's apparatus, which is known to work well and economically, is given below. The extractor A (Fig. 9), which is provided with a perforated false bottom, is filled with carefully dried spent-oxide. The solvent (in this case carbon bisulphide) is contained in R. After the spent- oxide has been placed in the extractor, the manholes are tightly closed, all taps communicating with the outer air shut, and the carbon bisulphide allowed to flow from R into the extractor. The liquid trickles through the spent-oxide, and flows through the three- way cock Z, directly into the evaporator C, which is heated by a steam coil. The carbon bisulphide distils off, and the vapour passes into the condenser B, the condensed liquid running into R, and from there again to A and to C. The vessel R is in communication with the outer air by means of a tube closed with a valve ; through this tube is evolved the air contained io8 Utilization of Spent-Oxide. in the apparatus at the commencement of the opera tion. When the spent-oxide becomes fairly free from sulphur, the three-way cock is placed in such a posi- tion that the liquid, in order to pass from A to C, must Fig. 9. A. Extractor — B. Condenser. — C. Evaporator. — D. Regulator. — E.E.E. Manholes.— E.G. Spy-glasses.— H. Air-cock. — K. Steam inlet-valve.^ — L. Three-way cock. — M. Steam inlets to coils. — N. Cocks for testing purposes. — P. Cocks for emptying the vessels. — Q. Inlet for carbon bisulphide. — R. Reservoir for Solvent. — S. Inlet for condensing water. — T. Overflow pipe for condensing water. — ^V. Gauge-glass. first go through the upright tube D. By this arrange- ment the level of the liquid in A rises to the same height as the overflow pipe in the vertical tube. Extraction of Sulphur. log Small portions of the liquid which runs off are taken from time to time by means of a small tap provided for the purpose, and tested. When it is found to be nearly free from sulphur, the whole of the liquor is allowed to run from the extractor, the communication between A and R closed, and the carbon bisulphide distilled from C into R. The carbon bisulphide still retained by the extracted mass is driven off by live steam. As soon as the whole of the carbon bisulphide has passed off from C, the liquid sulphur is quickly run out into flat, four-cornered vessels, made of cast iron, where it is allowed to solidify. It contains almost invariably small quantities of carbon bisulphide. Steam cannot be employed to drive the last traces of the solvent from C, and care must also be taken that no water runs into C during the treatment of the extracted mass with steam, for if the sulphur contains moisture it solidifies on the surface, and is then only remelted with difficulty. The mass in A after the treatment with steam, is raked out, find extracted with water. The taps and valves are easily corroded by the carbon bisulphide, and to this fact most of the draw- backs and inconveniences of the process are due. On account of this corrosion leakage frequently takes place, and may cause considerable loss of the solvent. If the taps, which can only be constructed of cast iron, be well ground, frequently inspected, and smeared with graphite, this loss may be reduced to a minimum. For the purpose of caulking, it is best to use asbestos or flour-paste ; oils and fats must be avoided. The losses from leakage may also be materially reduced by I lo UHlization of Spent-Oxide. taking care that during the extraction the pressure does not rise too high. The Residues. — The residual mass, after the ex- traction of sulphur, ferrocyanides, and sulphocyanides, may be again employed for the purification of coal gas, provided that it is left in the form of iron oxide, and free from such impurities as lime, etc. The residue obtained in Kunheim's process can only be used as refuse, or at best, forwarded to iron-works for use as an iron-ore. It is, therefore, an additional argument in favour of the extraction of ferrocyanides by the caustic soda process, that it yields residues having the same value as the original material. Ill APPENDIX. Specific Gravity of Ammonium Sulphate Solutions AT 15° C. (59" F.). (Schiff). Specttic Percentage Specific Percentage (NH.), SO. Specific Percentage Gravity. (NH.),SO. Gravity. Gravity. (NHOa SO. 1-0057 I I -1035 18 1-2004 35 1-0115 2 1-1092 19 1-2060 36 1-0172 3 1-1149 20 I-2116 37 1-0230 4 1-1207 21 I-2172 38 1-0287 5 1-1265 22 1-2228 31 i"034S 6 1-1323 23 1-2284 40 10403 7 1-1381 24 1-2343 41 1-0460 8 I -1439 25 1-2402 42 I -05 18 9 1-1496 26 1-2462 43 I-057S 10 I-ISS4 27 1-2522 44 1-0632 II 1-1612 28 1-2583 45 1-0690 12 1-1670 29 1-2644 46 1-0747 13 1-1724 30 1-2705 47 1-0805 14 1-1780 31 I 2766 48 1-0862 IS 2-1836 32 1-2828 49 1-0920 16 1-1892 33 1-2890 50 1-09/7 17 1-1948 34 Specific Gravity of Sal- Ammoniac Solutions at 15° C. (59° F.). (Gerlach). Specific Percentage Specific Percentage .Specific Percentage Gravity. NH. CI. Gravity. NH. a. Gravity. NH. C). 1-00316 I I -0308 1 10 1-05648 19 1-00632 2 1-03370 II 1-05929 20 1-00948 3 1-03658 12 I -06204 21 1-01264 4 1-03947 13 1-06479 22 . I -01 580 5 1-04325 , 14 1-06754 23 I -01 880 6 1-04524 IS 1-07029 24 I -02 1 80 7 1-04805 16 1-07304 25 I -02481 8 1-05086 17 I-0757S 26 I -02781 9 1-05367 18 1-07658 26-297 112 Appendix. Specific Gravity of Caustic Ammonia containing DIFFERENT QUANTITIES OF NH3 TeMP. 14° C. ($7° R). (Carius). Specific Percentage Specific Percentage Specific Percentage Gravity. NH, Gravity. NH, Gravity. NH, 0-8844 36-0 0-9021 28-2 0-9239 20-4 0-8848 35-8 0-9026 ' 28-0 0-9245 20-2 0-8852 35-6 0-9031 27-8 0-9251 20-0 0-8856 3S-4 0-9036 27-6 0-9257 19-8 0-8860 3S'2 0-9041 27-4 0-9264 19-6 0-8864 35-0 0-9047 27-2 0-9271 19-4 0-8868 34-8 0-9052 27-0 0-9277 19-2 0-8872 34-6 0-9057 26-8 0-9283 19-0 0-8877 34-4 0-9063 26-6 0-9289 18-8 0-8881 34-2 0-9068 26-4 0-9296 18-6 0-8885 34-0 0-9073 26-2 0-9302 18-4 0-8889 33-8 0-9078 26-0 0-9308 18-2 0-8894 33-6 0-9083 25-8 0-9314 18-0 0-8898 33-4 0-9089 25-6 0-9321 17-8 0-8903 33-2 0-9094 25-4 0-9327 17-6 0-8907 33-0 0-9100 25-2 0-9333 17-4 0-8911 32-8 ,0-9106 25-0 0-9340 17-2 0-8916 32-6 0-91 11 24-8 0-9347 17-0 0-8920 32-4 0-9116 24-6 0-9353 16-8 0-8925 32-2 0-9122 24-4 0-9360 16-6 0-8929 32-0 0-9127 24-2 0-9366 16-4 0-8934 31-8 0-9133 240 0-9373 16-2 0-8938 31-6 0-9139 23-8 0-9380 160 0-8943 31-4 0-9145 23-6 0-9386 15-8 0-8948 31-2 0-9150 23-4 09393 15-6 0-8953 31-0 0-9156 23-2 0-9400 15-4 0-8957 30-8 . 0-9162 23-0 0-9407 15-2 0-8962 306 0-9168 22-8 0-9414 15-0 0-8967 30-4 0-9174 226 0-9420 , 14-8 0-8971 30-2 0-9180 22-4 0-9427 14-6 0-8976 30-0 0-9185 22-2 0-9434 14-4 0-8981 29-8 0-9191 22-0 0-9441 14-2 0-8986 29-6 0-9197 21-8 0-9449 14-0 0-8991 29-4 0-9203 21-6 0-9456 13-8 0-8966 29-2 0-9209 21-4 0-9463 13-6 0-9001 29-0 0-9215 21-2 0-9470 13-4 0-9006 28-8 09221 21-0 0-9477 13-2 0-9011 28-6 0-9227 20-8 0-9484 13-0 0-9016 28-4 09233 20-6 0-9491 12-8 Appendix. 113 Specific Percentage Specific Percentage Specific Percentage Gravity, NH, Gravity. NH, Gravity. NH, 0-9498 12-6 0-9654 8-4 0-9823 4-2 0-9505 12-4 0-9662 8-2 0-9831 4-0 0-9512 12-2 0-9670 8-0 0-9839 3-8 0-9520 12-0 0-9677 7-8 0-9847 3-6 0-9527 11-8 0-9685 7-6 0-9855 3-4 0-9534 11-6 0-9693 7-4 0-9863 3-2 0-9542 11-4 0-9701 7-2 0-9873 30 0-9549 11-2 0-9709 7-0 0-9882 2-8 0-9556 li-o 09717 6-8 0-9890 2-6 09563 10-8 0-9725 6-6 0-9899 2-4 0-9571 10-6 0-9733 6-4 0-9907 2-2 0-9578 10-4 0-9741 6-2 0-9915 2-0 0-9586 10-2 09749 6-0 0-9924 1-8 0-9593 lO-Q 0-9757 S-8 0-9932 1-6 0-9601 9-8 0-9765 5-6 0-9941 1-4 0-9608 9-6 0-9773 S-4 0-9950 1-2 0-9616 9-4 0-9781 S-2 0-9959 i-o 0-9623 9-2 09790 5-0 0-9967 0-8 0-9631 9-0 0-9799 4-8 0-9975 0-6 0-9639 8-8 0-9807 4-6 0-9983 04 0-9647 8-6 0-9815 4-4 0-9991 0-2 Specific Gravity of Sulphuric Acid at 15° C. (59° F.) (Kolb). 100 parts by weight I litre contains in >• P3 £ 1 H correspond to kilos. Per cent. it ,£.■2 So -1 Chemically pure acid. It SO, H,SO, m SO, H,SO. <%. I -000 _ 0-7 0-9 1-2 1-4 0-007 0009 0-012 0-014 1-007 1 1-4 1-5 1-9 2-4 3-0 0-015 0019 0024 0-030 I -014 2 2-8 2-3 2-8 3-6 4-5 0-023 0-028 0-036 0-045 I -022 ^ 4-4 .n 3-8 4-9 6-1 0-032 0-039 0-050 10-062 1-029 4 5-8 ^-9 4-8 6-1 7-7 0-040 0-049 0-063 0-078 1-037 7-4 4-7 5-8 7-4 9-3 0-049 0-060 0-077 0-096 1-045 6 9-0 5-6 6-8 8-7 10-9 0-059 0-071 0-091 0-114 1-052 7 10-4 6-4 7-8 lo-o 12-5 0-067 0-082 0-105 0131 114 Appendix. 100 parts by weight I I litre contains in '>. n U •a I correspond to kilos. O Per cent. Chemically pure acid. "0.0 'n^ •u I a in •cm 0) <\ 8 SO., H,SO. ^1 SO, H,SO.. I -060 I2-0 7-2 8-8 1 1-3 14-0 0-076 0-093 0-120 0-149 1-067 9 13-4 8-0 9-8 12-6 15-7 0085 0-105 0-134 0-i68 1-075 10 15-0 8-8 10-8 13-8 17-3 0-095 o-ii6 0-148 o-i86 1-083 II 16-6 9-7 11-9 15-3 19-0 0-105 0-129 0-164 0-206 I -09 1 12 18-2 10-6 13-0 16-7 20-8 O-I16 0-142 0-182 0-227 i-ioo 13 20-0 ii-S 14-1 18-1 22-6 0-126 0-155 0-I99 0-248 i-io8 H 21-6 12-4 15-2 19-5 24-3 0-137 0-168 0216 0-268 1-116 15 23-2 13-2 i6-2 20-7 25-9 0-I47 0-181 0231 0-290 1-125 16 25-0 14-1 17-3 22-2 27-1. 0-159 0-I9S 0-250 0-312 1-134 17 26-8 15-1 18-5 23-7 29-6 0-172 0-210 0-269 0-336 1-142 18 28-4 16-0 19-6 25-1 31-4 0-183 0-224 0-287 0-359 1-152 19 30-4 17-0 20-8 26-6 33-3 0-196 0-239 0-306 0-383 1-162 20 32-4 18-0 222 28-4 35-3 0-209 0-258 0330 0-413 i-iyi 21 3+-2 19-0 23-3 29-8 37-3 0-222 0-273 0-349 0-437 i-i8o 22 36-0 20-0 24-5 31-4 39-3 0-236 0-289 0-370 0-463 1-190 23 38-0 21-1 25-8 33-0 41-3 0-251 0-307 0-393 0-491 1-200 24 400 22-1 27-1 34-7 43-4 0-265 0-325 0-416 0-520 1-210 25 42-0 23-2 28-4 36-4 45-4 0-281 0-344 0-440 0-550 1-220 26 44-0 24-2 29-6 37-9 47-4 0-295 0-361 0-463 0-579 1-231 27 46-2 25-3 31-0 39-7 49-5 0-3 II 0-382 0-489 0-610 1-241 28 48-2 26-3 32-2 41-2 51-5 0-326 0-400 0-511 0-639 1-252 29 50-4 27-3 33-4 42-8 53-S 0-342 0-418 0-536 0-670 1-263 30 52-6 28-3 34-7 44-4 55-5 0-3S7 0-438 0-561 0-702 1-274 31 54:8 29-4 36-0 46-1 57-6 0-374 0-459 °'l^l 0-735 1-285 32 S7-0 30-S 37-4 47-9 59-9 0-392 0-481 0-616 0-709 1-297 33 ,59-4 31-7 38-8 49-7 62-1 0-411 0-503 0-645 0-805 1-308 34 61-6 32-8 40-2 Si-5 64-3 0-429 0-526 0-674 0-841 1-320 35 64-0 33-9 41-6 53-3 66-6 0-447 0-549 0-704 0878 1-332 36 66-4 35-1 43-0 55-1 68-8 0-468 0-573 0-734 0-917 1-345 37 69-0 36-2 44-4 56-9 71-0 0-487 0-597 0-765 0-955 1-357 38 71-4 37-2 45-5 58-3 72-8 0-505 0-617 0-791 0-987 1-370 39 74-0 38-3 46-9 600 75-0 0-525 0-642 0-822 1-027 1-383 40 76-6 39-5 48-3 61-9 77-3 0-546 0-668 0-856 1-069 1-397 41 79-4 40-7 49-S 63-8 79-7 0-569 0-696 0-891 I-II7 1-410 42 82-0 41-8 SI-2 65-6 82-0 0-589 0-722 0-925 1-155 1-424 43 84-8 42-9 S2-6 67-4 84-2 0-6 1 1 0-749 0-960 1-198 1-438 44 87-6 44-1 54-0 69-1 86-4 0-634 0-777 0-994 1-243 1-453 45 90-6 45-2 55-4 70-9 88-6 0-657 0-805 1-030 1-288 Appendix. ^15 100 parts by weight I litre contains in >. c 1 1 correspond to ' kilos. a Per cent. a« ^ Chemically s 1 1 Q pure acid. It It. 1 SO3 HjSO, SO3 H, SO. 1-468 46 .93-6 46-4 56-9 72-9 91-0 0-681 0-835 1-070 1-336 1-483 47 96-6 47-6 58-3 74-7 93-3 0-706 0-864 i-io8 1-382 1-498 48 99-6 48-7 596 76-3 95-4 0730 0-893 1-143 1-429 1-514 49 I02-8 49-8 61-0 78-1 97-6 0-754 0-923 1-182 1-477 1-530 50 106-0 51-0 62-5 80-0 loo-o 0-780 0-956 1-224 1-530 1-540 51 io8-o 52-2 64-0' 82-0 102-4 0-807 0-990 1-268 1-584 1-563 52 1 12-6 53-s 65-5 83-9 104-8 0836 1-024 1-311 1*638 1-580 53 116-0 54-9 67-0 85-8 107-2 0-867 1-059 I-35S 1-694 1-597 54 119-4 560 68-6 87-8 109-7 0894 1-095 1-402 1-752 1-615 55 1230 57-1 70-0 89-6 II2-0 0-922 1-131 1-447 1-809 1-634 56 126-8 58-4 71-6 91-7 114-6 0-954 1-170 1-499 1-872 1-652 57 130-4 59-7 732 93-7 1171 0-986 I-210 1-548 1-936 1-671 58 134-2 61-0 74-7 95-7 119-5 1-019 1-248 1-599 1-996 1-691 59 139-2 62-4 76-4 97-8 122 2 I -055 1-292 1-654 2-037 1-711 60 142-2 63-8 78-1 100-0 125-0 1-092 1-336 I-7I1 2-118 1-732 61 146-4 65-2 79-9 102-3 127-8 I-129 1-384 1-772 2-294 1-753 62 150-6 66-7 81-7 104-6 130-7 1-169 1-434 1-838 2-284 1-774 63 154-8 68-7 84-1 107-7 134-0 i-2ig 1-492 1-911 2-387 1-796 64 159-2 70-6 86-5 11 0-8 138-0 1-268 I-5S4 1-990 2-416 1-819 65 163-8 73-2 89-7 114-8 I43'S 1-332 1-632 2-088 2-671 1-842 66 168-6 8r6 loo-o 128-0 149-4 1-523 1-842 2-358 2-872 The numbers given for 65° and 66° Be are inexact. I 2 ii6 Appendix. Specific Gravity, of Hydrochloric Acid at 15° C. (59° F.) fKOLB). >^ va =s 100 parts by weight I litre contains in e E •0 contain grams. n I 00 % w °o N °S So (3\ \ M « "0 \ S D O'® '0*© *osc 'o:s oS U "o-j ■SS OS OS °S CL Sf »> a .-«» .■5" 3^ .■2" .-3" B .-2* ■h" T.» -2" •oO Cfi p « a -Q -D '0 -3 -3 -3 ■3 Q < < < -1 10-2 19-3 16-5 92 107 202 173 1-067 9 13-4 9-8 11-4 21-S 18-5 105 123 232 200 J -075 10 15-0 10-9 127 24-0 20-5 117 136 268 220 1-083 II 16-6 12-0 14-0 26-S 22-7 130 152 287 246 I-09I 12 18-2 13-1 15-3 28-9 248 143 167 315 270 I-IOO 13 20-0 14-4 16-8 317 27-2 158 182 344 295 I-I08 14 21-6 15-4 18-0 34-0 29-2 170 198 374 321 i-ii6 IS 23-2 i6-6 1-9-4 367 31-4 185 216 408 350 I-I2S 16 25-0 17-8 20-8 39'4 33-6 200 233 440 378 i'i34 17 26-8 190 22-2 42-0 36-0 215 251 474 406 I- 143 18 28-6 20-2 23-6 44"S 382 231 270 510 437 1-152 19 30-4 21-3 24-9 47-1 40-4 245 281 531 454 1-161 20 32-2 22-5 26-3 49-6 42-6 261 305 576 493 1-171 21 34-2 23-8 27-8 52-5 4S'o 279 32s 614 527 i-i8o 22 36-0 25-0 29-2 SS-2 47-4 295 344 650 557 I-I9P 23 380 26-3 30-7 58-0 49-8 313 365 690 591 1-199 24 39-8 27-5 32-1 6o-7 52-0 330 385 728 624 I -210 25 42-0 28-9 33-8 63-9 54-8 35° 408 771 661 1-221 26 44-2 30-4 3S-S 67-1 57-5 371 433 818 701 1-231 27 46-8 317 37-0 69-9 599 390 455 860 737 1-242 28 48-4 33-1 38-6 72-9 62-5 411 480 907 778 1-252 29 50-4 34-5 40-2 76-0 65-1 434 506 956 819 1-261 3° 52-2 35-6 41-5 78-4 67-2 449 523 988 847 1-275 31 55-0 373 43-S 82-2 70-5 475 553 1045 896 1-286 32 57-2 38-6 450 85-1 72-9 496 578 1092 9l(> 1-298 33 59-6 40-4 47-1 890 76-3 524 611 1 154 990 1-309 34 61 -8 41-7 48-6 91-9 78-7 5i5 635 1200 1029 ii8 Appendix. . 100 parts by weight I litre contains in >^ 1 4 contain grams. 2 O t "S-* -n-if ;, •s.,; -^ r& 1 1 iz; a 1-321 35 64-2 43-5 50-7 95-8 82-1 575 670 1266 1085 1-334 36 66-8 4S-3 52-9 loo-o 85-7 604 704 1330 1 140 I '346 37 69-2 47-1 ■^ro 104-0 89-1 634 739 1397 1197 J -3 =59 3« 71-8 49-1 57-3 108-3 92-7 667 777 1469 1259 1-372 39 74-4 51-2 59-6 112-6 96-5 702 818 1546 1325 i-.3«4 40 76-8 52-9 61-7 ii6-6 loo-d 732 «53 1612 1382 i-39« 41 79-6 55-3 64-5 121-9 104-5 773 901 1703 1460 1-412 42 82-4 57-9 67-5 127-6 109-4 818 954 1803 1545 1-426 43 85-2 bo-5 170-6 133-4 114-4 863 1006 1903 1630 1-440 44 88-0 63-8 74-4 140-6 120-5 919 107 1 2024 1735 1-454 45 90-8 67-2 78-4 148-2 127-0 977 "39 2153 1845 1-470 4b 94-0 71-1 83-0 156-9 134-5 1045 1218 2302 1973 1-48S 47 97-0 74-7 87-1 164-6 141-1 1 109 1292 2442 2093 1-501 48 ICO-2 79-4 92-6 175-0 150-0 1 192 1388 2623 2249 1-516 49 103-2 82-3 96-0 181-4 155-5 1247 1454 2748 2355 1-524 49-5 104-8 84-0 98-0 185-4 158-8 1280 1492 2820 2417 1-530 49-9 io6-o 85-71 1 00-0 189-0 1620 1311 1530 2892 2479 Strengtb or Caustic Soda Solution at 15° c (59° F.). I cubic metre con- Sp. Gr. Baume Twaddell. Per cent. NaaO. Per cent. Na OH tains in kilos NasO. NaOH. 1-007 I 1-4 0-47 o-6i 4 6 1-014 2 2-8 0-93 I -20 9 12 I 022 3 4-4 1-55 2-00 16 21 1-029 4 5-8 2-10 2-71 22 28 1-036 5 7-2 2-60 3-35 27 35 1-045 6 9-0 3-10 400 32 42 1-052 7 10-4 3-60 4-64 38 49 1-060 8 12-0 4-10 5-29 43 56 1-067 9 13-4 4-55 5-87 49 63 1-075 10 15-° S-08 6-55 55 70 1-083 II 16-6 S-67 7-31 61 79 1-091 12 18-2 6-20 8-00 68 87 i-ioo 13 20-0 6-73 8-68 74 95 I -108 14 21-6 7-30 9-42 81 104 Appendix. 119 Strength of Caustic Soda Solution at 15° C. (59° F.). I cubic metre con- Sp. Gr. Baum^. Twaddell. Per cent. Na. 0. . Per cent. NaOH. tains in kilos. Na, 0. NaOH. I'Il6 IS 23-2 7-8o io-o6 ^1 112 I-I2S 16 25-0 8-50 10-97 96 123 1-134 17 26-8 9-18 11-84 104 134 I'I42 18 28-4 9-80 12-64 112 144 1-152 19 30-4 10-50 13-55 121 156 1-162 20 32-4 11-14 14-37 129 167 I-I7I 21 34-2 11-73 15-13 137 177 i-i8o 22 36-0 12-33 15-91 146 188 i-igo 23 380 13-00 16-77 155 200 I '200 24 40-0 13-70 17-67 164 212 1-210 25 42-0 14-40 18-58 174 225 1-220 26 44-0 15-18 19-58 .85 239 1-231 27 46-2 15-96 20-59 196 253 1-241 28 48-2 16-76 2 1 42 208 266 1-252 29 50-4 17-55 22-64 220 283 1-263 30 52-6 18-35 23-67 232 299 1-274 31 54-8 19-23 24-81 245 316 1-285 32 57-0 20-00 25-80 257 332 1-297 33 59-4 20-80 26-83 270 348 1-30S 34 61-6 21-55 27-80 282 364 1-320 35 64-0 22-35 2883 295 381 1-332 36 66-4 23-20 29-93 309 399 I-34S 37 69-0 24-20 31-22 326 420 1-357 38 71-4 25-17 32-47 342 441 1-370 39 74-0 26-12 33-69 359 462 1-383 40 76-6 27-10 34-96 375 483 1-397 ,41 79-4 2810 36-25 392 506 1-410 42 82-0 29-05 37-47 410 528 1-424 43 84-8 3008 3880 428 553 1-438 44 87-6 31-00 39-99 446 575 1-453 45 90-6 32-10 41-41 466 602 1-468 46 93-6 33-20 42-83 -487 629 1-483 47 96-6 34-40 44-38 510 658 1-498 48 996 35-70 46-15 535 691 1-514 49 102-8 36-90 47-60 559 721 1-530 5° 106-0 38-00 49-02 581 750 120 Appendix. Solubility of Sulphur in Carbon Bisulphide at 15° C. (59° F.). Sp. gr. Per cent S. Sp. gr. Per :ent. S. Sp. gr. , Per cent. S. Sp. gr. Per cent. S. Sp. gr. Per cent. S. 1-271 1-296 6-0 1-321 12-1 1-346 181 1-371 25-6 1-272 0-2 1-297 6-3 1-322 12-3 1-347 18-4 1-372 26-0 1-273 0-4 1-298 6-5 1-323 12-6 1-348 i8-6 1-373 26-5 1-274 0-6 1-299 6-7 1-324 12-8 1-349 18-9 1-374 269 1-275 0-9 1-306 7-0 1-325 I3-I 1-350 190 1-375 27-4 1-276 1-2 1-301 7-2 1-326 13-3 1-351 19-3 1-376 28-1 1-277 I '4 1-302 7-5 1-327 13-5 1-352 19-6 1-377 28-s 1-278 1-6 1-303 7-8 1-328 13-8 1-353 199 1-378 29-0 1-279 1-9 1-304 8-0 1-329 14-0 1-354 20-1 1-379 29-7 1-280 2-r i-3°S 8-2 1-330 14-2 1-355 20-4 1-380 30-2 I -28 1 2-4 1-306 8-5 1-331 14-s 1-356 20-6 1-381 30-8 1-282 2-6 1-307 8-7 1-332 14-7 1-357 21-0 1-382 31-4 1-283 2-9 1-308 8-9 1-333 15-0 1-358 21-2 1-383 31-9 1-284 3-1 1-309 9-2 1-334 15-2 1-359 21-5 1-384 32-6 1-285 3-4 1-310 9-4 1-335 15-4 1-360 21-8 1-385 33-2 1-286 3-6 1-311 9-7 1-336 15-6 1-361 22-1 1-386 33-8 1-287 39 1-312 9-9 1-337 15-9 1-362 22-3 1-387 34-5 1-288 4-1 1-313 10-2 1-338 i6-i 1-363 22-7 1-388 35-2 1-289 4"4 1-314 10-4 1-339 16-4 1-364 23-0 1-389 36-1 1-290 ^1 1-315 10-6 1-340 16-6 1-365 23-2 1-390 367 1-291 4-8 1-316 10-9 1-341 16-9 1-366 23-6 1-391 37-2 1-292 1-293 5-0 S-3 1-317 1-318 ii-i 11-3 1-342 1-343 17-1 17-4 1-367 1-368 24-0 24-3 Saturated. 1-294 5t 1-319 11-6 1-344 17-6 • 1-369 24-8 1-295 S-8 1-320" 11-8 1-345 17-9 1-370 25-1 Appendix. 121 RECENT LITERATURE. Lunge, G. " Coal-tar and Ammonia." 2nd Edition, 1887. Muspratt's " Theoretical, Practical, and Analytical Chemistry." Wanklyn, J. A. "The Gas Engineer's Chemical Manual." 2nd Edition, 1888. Sadler, P. S. " Recovery of Tar and Ammoniacal Liquor." Schilling, N. H. " Handbuch der Steinkohlengas- Beleuchtung." Fleck, H. " Die Fabrikation Chem. Producte aus Thierischen Abfallen." Stutzer, A. " Der Chilesaltpetre, seine Bedeutung und Anwendung als Dungemittel." Bearbeitet und herausgegeben von P. Wagner. Schering. " Preparation of Pure Liquor Ammoniae." Polytechn. Centralblatt, 1881. p. 1456. Gerlach. " Solway's Still for Concentrating Gas- Liquor." Ing. Zeitschr. Vol. 21, p. 15. Knublauch, O. " New Method of Determining Sulphur in Illuminating Gas." Zeitschr. Analyt. Chemie., 21, p. 335. (Abstract in Journ. Soc. Chem. Ind., 1882, p. 383.) Feldmann, A. " Apparatus for the Distillation of Ammonia-Liquors." Dingler's Polytech. Journ., 248, p. 462, (Abstract J. S. C. I., 1883, p. 380.) Lauber & Haussmann. "Aluminium Sulpho- dyanide." Dingler's Polytech. Journ. 1882, 306. {Abstract J. S. C. I., 1882, p. 364.) 122 Appendix. Bunte. " Removal of Ammonia from Coal Gas." Dingler's Polytech. Journ. 245, p. 40. (Abstract J. S. C. I., 1882, p. 314.) Mond, L. " Preparation of Cyanogen Compounds and Ammonia." Dingler's Polytech. Journ., 248, 366. (Abstract in J. S. C. I., 1883, p. 328.) Tervet, R. " Ammonia from Coke." Journ. S. C. I., 1883, p. 445. Scheurer-Kestner. " On the Destructive Distilla- tion of Coal, and' Transformation of its Nitrogen into Ammonia." Comptes Rendues, 97, p. 3. (Abstract J. S. C. I., 1883, p. 407O Marcker, M. " The Injurious Action of Ammonium Thiocyanate (Sulphocyanide) in Plant Growth." Bie- derman's Centralblatt fiir Agric. Chem., 12, p. 471. (Abstract J. S. C. I., 1884, p. 184.) Cox, J. H. "Notes 'on Ammoniacal-Liquor." J. S. C. I., 1884, p. 158). Otto, C, & Smith, Watson. " Manufacture of Coke with and without Recovery of Bye-Products." J. S, C. I., 1884, p. 505. Winkler, C. " Recovery of Ammonia from Coke- oven Gases." Chemiker Zeitung, 1884, p. 691. (Abstract J. S. C. I., 1884, p. 512.) Leidler, P. " Working up Gas-Liquor and other Products from Gas Purification." Dingler's Polytech. Journ., 252, p. 476. (Abstract J.S. C. I., 1885, p. 112.) Wollny, E. " Crude Ammonium Superphosphate as a Manure." Biederman's Centralblatt, 1884, p_ 167. (Abstract J. S. C. I., 1885, p. 126.) James, W. "Tar and Ammonia from Blast Fur- naces." Engineering, 1885, pp. 387 and 409. Appendix. 123 Schmitz, S. " Determination of Nitrogen in Coal and Coke." Zeitschr. Anal. Chem., 25, 314. (Ab- stract J. S. C. I., 1886, p. 506.) Claus's "Ammonia Process of Gas-Purification." Journ. Gas Lighting, 1886, p. 1181. Gasch, R. "Manufacture of Sulphocyanides." Chem. Zeitung, 10, p. 274. (Abstract J. S. C. I. 1886, p. 379.) Nafzger, F. "Manufacture of Sulphocyanides." Chem., Zeitung, 10, p. 376- Abstract J. S. C. I., 1886, p. 370.) Wright, Lewis, T. "Notes on Gas-Liquor and Ammonia Purification." Journal of Gas Lighting, 48, pp. 280, 329, 373. 5"- Reitmair & Stutzer. " Determination of Nitrogen in Manures containing Saltpetre." Rep. Anal. Chem., 7, p. 4. (Abstract J. S. C. I., 1887, 4S7-) Schmidthorn, K. "Manufacture of Ammonium Chloride and Potassium Sulphate, from Potassium Chloride and Ammonium Sulphate." Chem. Zeit., 10, p. 1499. Abstract J. S. C. L, 1887, i39-) Schilling, E. "Nitrogen in Coals." Dingler's Polytech. Journ., 265, 218. Abstract J. S. C. I., 1887, p. 652.) Ruffle, J. " Analysis of Ammoniated Superphos- phate." J. S. C. L, 1887, p. 491. Raupp. "Production of Ammonium Phosphate from Gas-Liquor." (Abstract J. S. C. I., 1888, p. 114.) Wagner, Prof., " Nitrogenans Manure " (published by Whittaker) . 1 24 Appendix. RECENT PATENTS. English Patent. 3208. 1870. P. Spence. Pre- paration of Prussian-blue from spent-oxide. E. P. 3908. 1874. G. Valentine. Preparation of Prussian-blue from waste-products in coal-gas manufacture. E. P. 5504. 1880. W. L. Wise (from Grouven, H.). Production of ammonium sulphate from nitrogen in coal, peat, &c. German Patent 12,889. 1880. M. Honigmann. Stills and saturators for ammonia. G. P. 13,395. 1880. Strohner & Scholtz. Am- monia, &c., from coke-oven gases. G. P. 13,429. 1880. Society anonyme des produits chemiques, des Sud-Ouest. Paris. Improvements in the apparatus for the distillation of ammoniacal liquids. G. P. 13,594. 1880. T. Richters. Process for recovering ferrocyanides, ammonia, tar, and gas, from nitrogenous organic bodies. G. P. 14,210. 1880. T. Richters, & L. Hagen. Purification of ammoniacal liquors, with recovery of ammonia and manures. G. P. 15,206. 1880. T. Richters. Process for recovery of ammonia from spent-oxide before revivi- fication. E.- P. 5173. 1880. F. J. Bolton & J. A. Wanklyn. Improvements in manufacture of artificial manures and ammoniacal products. E.P. 1148. 1881. F.J Bolton & J. A. Wanklyn. Appendix. 1 2 ; Improvements in the manufacture of coal gas for illuminating purposes. E. P. 2423. 1881. W. L. Wise, & H. Grouven. Ammonia from organic compounds. E.P. 2709. 1882. F.J.Bolton&J. A.Wanklyn. Improvements in treatment of gas containing ammo- nia, for production of artificial manures, and ammo- niacal salts, and in apparatus for that purpose. G. P. 21,252. 1882. C. Schneider. Apparatus for the recovery of ammonia. G. P. 21707. i88!2. Gareis. Apparatus for distillation of ammoniacal liquids. E. P. 433. 1882. L. Mond. Manufacture of cyanogen compounds and ammonia. E. P. 440. 1882. G. Neilson. Extracting am- monia from furnace gases. E. P. 3643. 1882. A. Feldmann. Improve- ments in the manufacture of ammonia and apparatus therefor. E. P. 4644. 1882. C. F. Glaus. Purification of coal-gas, and recovery of ammonia. F. P. 3342. 1883. H. Kunheim & H. Zimmer- man. Extraction of ferrocyanides. E. P. 4871. 1883. H. Simon & Watson Smith. Production of ammonia and its compounds during the process of making coke or gas. G. P. 28,137. 1883. S. Marasse. Preparation of sulphocyanides from spent-oxide. E.P. 11,449- 1884. C. Brisons. Improvements in apparatus for distilling nitrogenous liquids. e". p. 11711- 1884. A. Feldmann. Improve- ments in the process of manufacturing ammonia. 126 Appendix. G- P- 33,936. 1884. M. Hempel & A. Sternberg. Preparation of ferrocyanides from spent-oxide. E. P. 381. 1885. E. W. Parnell & J. Simpson. Process for preparation of ammonia from the ammo- nium chloride obtained in the ammonia-soda process by heating it with alkali waste. E. P. 2578. 1885. H. Simon. Stills for am- monia liquor. E. P. 4902. 1885. A. Neilson & J. Snodgrass. Obtaining ammonia in connection with the distillation of oil-yielding and carbonaceous minerals. E. P. 8973. 1885. L. Mond. Separation of ammoniacal products and tar from producer and other furnace gases. E. P. 10,700. 1885. J. Hood. Manufacture of ammonium bichromate. G. P. 33,320. 1885. J. Griineberg & E. Blum. Improvements in stills for ammonia and other liquids. E. P. 8602. 1886. J. Park. Manufacture of ammonium bichromate. G. P. 40,215. 1886. C. Wolfrum. Process for the simultaneous treatment of gas-liquor and spent- oxide. E. P. 970. 1887. E. W. Parnell & J. Simpson. Improvements in the treatment of ammonium sulphide solutions with carbonic acid gas for the purpose of obtaining ammonium carbonate and strong sulphu- retted hydrogen. E. P. 17,050. 1887. Manufacture of ammonium sulphite. 127 INDEX. A. Acid ammonium carbonate, 14, 72. Amido-salts, 9. Ammonia : — Composition and properties, I. Estimation of, 20, 23. Occurrences and formation, 3. Solubility in water, 8. Sp. gr. of solutions, 112. Ammonium alum, 11, 54. bichromate, 19, 79. carbamate, 15, 71. carbonate, 13, 70. chloride (see sal-ammoniac), chromate, 18, 79. cyanide, 19. hyposulphite, 19. metavanadate, 18, 82. molybdate, 18. nitrate, 16, 73. oxalate, 17, 81. phosphate, 16, 77. sulphate, 10, 39. Analysis of, 51. Applications, 52. Imports into Germany, 53. Relative value as manure, 52. Sp. gr. of solutions, iii. sulphide, 15, 81. sulphocyanide, 16, 75, 98. superphosphate, 78. thiocarbonate, 17. thiocyanate, 16, 75, 98. thiosulphate, 19. Azotometer, 23. 128 Index. B. Barium thiocyanate or sulphocyanide, loo. Bog-iron ore, 87. Bolton and Wanklyn's gas-purification process, 78. BuiFand Dunlop's extraction apparatus, 98. C. Canarine, 77. Caustic ammonia, 8, 55. „ „ sp. gr. of different strengths, 112. Caustic soda : — Normal solution of, 26. Sp. gr. of solutions, 118. Chloride of nitrogen, 9. Chili-saltpetre, 52. Coal, percentage of nitrogen in, 6. Concentrated gas-liquor, 62. Crude caustic ammonia, 63. Cuprammonium sulphate, 12, 54. D. Densimeter, 30. Dephlegmator, 55, 56. Distillation method of estimating ammonia, 20. Dry distillation of coal, 5. „ „ bones, 8. Evaporators, 65. Extractors, 98, 107. Feldmann's still, 43. Ferrocyanides, 90, 95, loi. Ferrous ammonium sulphate, n, 53. G. Gas-liquor : — Analysis, 30, 32. Carriage and storage, 33. Composition, 28. Formation, 7. Removal of ammonium sulphide from, 34 Griineberg and Blum's still, 45. Index. 129 H. Hydrochloric acid, 38. >, „ sp. gr. of solutions, 116. Hydrometer, 30. L. Laming'S mixture, 86. Laughing-gas, 16, 75. Lime, 38. Lime-mud, S4. Literature, 121. Liquor-ammoniffi, 8, 55. „ „ fortior, 61. M. Methyl-orange solution, 27. N. Nessler's reagent, 27. Nickel ammonium sulphate, 11, 54. Nitric acid, 38. „ „ sp. gr. of solutions, 117. Nitrogen compounds in coal-tar products, 91. Normal sulphuric acid solution, 26. „ caustic soda solution, 26. O. OXAMIC acid, 18. Oxamide, 18. Patents, 124. Prussian-blue, 90, 96. „ „ volumetric estimation of, 97. R. Recent literature, 121. „ patents, 124. Residues from spent-oxide, no. Revivification of spent-oxide, 92 . K 1 30 Index. S. Sal-ammoniac, 12, 64. „ „ applications, 69. „ „ sp. gr. of solutions, III. „ „ sublimation, 68. Saturators, 47, 65. Sodium ferrocyanide, 104. „ hypobromite solution, 27. Spent-oxide : — Analysis of, 94. Composition of, 91. Separation of nitrogen compounds in, 89. Separation of sulphur in, 86. Revivification of, 92. Standard solutions, preparation of, 25. Stills for ammonia, 40, 41, 43, 45, 56. Sulphur : — Extraction from spent-oxide, 89, 105. „ „ gas-liquor, 89. ,, „ waste-gases, 83. Solubility in carbon bisulphide, 120. Sulphuric acid, 35. „ „ analysis of, 36. ,, „ sp. gr. of solutions, 113. „ „ transport and storage, 37. Tincture of litmus, 27. V. Volatile liver of sulphur, 15. W. Waste-gases, 82. „ „ sulphur from, 83. Waste-liquor, 84. „ „ clarification of, 85. Advertisements. JOHN J. 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This Balance, which I have introduced into this Country, is supplied by me to the Government, and to a great number of the leading Institutions. Price of Balances which are most in use in the Lahoratory : Balance to carry 200 Gramme, £15 15s. 500 „ £19 19s. iVlaker of Mr. Halse's Sugar Balancei also maker of Specific Gravity Balances and instruments. IlirPOEMATIOW OS APPLIOATIOIir. LONDON PRINTED BY GILBERT AND RIVXNGTON, LIMITED, ST. John's house, clerkenwell road. A dvertisements. 8vo. 740 pages, with 191 Working Drawings to Scale, £1 lis. 6d. COAlL,-TAR & ILNLNLGJSTIL, Being the Second and Enlarged Edition of "A Treatise on the distillation of Coal Tar and Ammoniacal Liquor." BY GEORGE LUNGE, Ph.D., Professor of Technical Chemistry in the Federal Polytechnic School, Zurich, Sfc. "Several new chapters have been added, embracing the recovery of Coal-Tar and Am- monia from olher sources than the manufacture of illuminating fas, the burning of tar as tuel, &c.; others have been completely re-written ; and few pages have been taken nnchan^ed from the former edition— so that this is to all intents and purposes a new book. It has been about doubled in size, both as regards letter-press and illustrations."— /i>»r>;a/ of Cas Lighting. 3 Volumes, 8vo, witli more than 700 Illustrations drawn to Scale, £4 16s. SULPHURIC ACID & ALKALI MANUFACTURE, A THEORETICAL AND PRACTICAL TREATISE ON. By Professor GEORGE LUNGE, Ph.D., &c., Formerly Manager of the Tyne Alkali Works, South Shields. " To the best of our knowledge it is the most complete, practical, and thorough-going treatise on the subject to be met with in any language." — Chemical News, GUKNEY & JACKSOIT, 1, PATEENOSTER ROW, lOSDOS (Successors to Mr. VAN VOOBST). OF IMPORTANT WORKS ON THE MANUFACTURING INDUSTRIES CAN BE HAD OF SAMPSON LOW, MARSTOB, SEAELE, & EIYIKGTOK, Ltd., ST. DUNSTAN'S HOUSE, FETTER LANE, LONDON. A dvertisements. C & W. WALKER, Chemical lEnoineers, C. & W. WALKER'S PATENT SULPHATE OF AMMONIA APPARATUS, unequalled for simplicity, economy, and remarkable efficiency. GLAUS' PATENT SULPHUR RECOVERY PLANT for extracting pure Sulphur from the waste gases of Saturator of Sulphate Plant, and destroying all noxious fumes. MIDLAIJD IRON WORKST DONNINGTON, NEAR NEWPORT, SALOP. 8, FINSBURT dRCUS, LONDON, E.C. WILLIAM METCALF, MANUFACTURER OF NAPHTHA, PREPARED OIL, PARANAPHTHALINE, BRIGK-PRESS OIL, POT OIL, DIPPING OILS, Creosote for Preserving Timber, Black Var- nish, Pitch, Asphalt, Carbolic Oil, Corfe Oil, &c., &c., SHEFFIELD TAR WORKS, WASHFORD ROAD, ATTERGLIFFE, SHEFFIELD; And at CHURCH, jearJCCmNGTON, LANCASHIRE. TAR AND LIQUOR PURCHASED. A dvertisements. Sulphate of Ammonia Plant. Messrs. Cutler are now giving special attention to this Appara- tus. They have recently most successfully erected at Dublin a Plant=i20 tons per day, and are prepared to supply the very best Plant on most favourable terms. Messrs. Cutler make a speciality of Gas Work Plant, and have constructed Gasholder and all other description of Gas Apparatus of the very largest dimensions, both at home and abroad. They have now in hand for the Imperial Continental Gas Association at Vienna, a Treble Lift Holder 200 ft. dia. x 123 ft. high, the largest on the Continent of Europe. Messrs. Cutler manufacture, amongst others, the following specialities : — Cutler's Patent Guide Framing for Gasholders. Cutler's Patent Freezing Preventer for Gasholder Cups. Cutler's Improved Sight Boxes for Betort Bench Flues. Cutler's Patent Mouthpiece Supports, to relieve Hetorts of weight of Mouthpieces. Cutler's Patent Ketnovable Seal, to remove pressure from Eetorts. Livesey & Tanner's Patent Differential Tar and Iiiquor Overflows. Brett's Patent Coke Barrow. Richmond's Patent Coke Barrow. "Wate's Patent Combined Shoot and Platform. Morris & Cutler's Patent " Perfect Condenser." Cutler's Patent " Simplex Distributer." Cutler's Improved Jet Distributer. Cutler's Patent Water Valves for Purifiers, &c. Cutler's Patent Iron Sieves for Lime Purifiers. Church's Patent "Wood Sieves, very light and durable. Cutler's Patent Top Sheeting for Gasholders. Cutler's Patent Adjustable Outlet for Tar and Liquor Tanks. Dougall & Cutler's Patent Furnace Frame and Doors. SAML. CUTLER & SONS, jenaincere, ac. Works : Offlees : PROVIDENCE IRONWORKS, 16, GT. GEORGE STREET, MILLWALL, E. WESTMINSTER, S.W.