^Volume I.— 
 
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 insthuctions 
 
 I FOR SliKtNO THB 
 
 CHEMICAL AND Pk^LOSOPlIlCAL 
 
 INS'lRUMENTS 
 

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TH^ 
 
 ART OP GLASS-BLOWING, 
 
 OE 
 
 PLAIN INSTRUCTIONS 
 
 FOR MAKING THE 
 
 CHEMICAL AND PHILOSOPHICAL 
 INSTRUMENTS 
 
 WHICH ARE FORMED OF GLASS; 
 
 BAROMETERS, THERMOMETERS, HYDROMETERS, 
 Hour-Glasses, Funnels, Sypho7is, 
 
 TUBE VESSELS FOR CHEMICAL EXPERIMENTS, 
 TOYS FOR RECREATIVE PHILOSOPHY, &C. 
 
 BY A FRENCH ARTIST. 
 
 ILLUSTRATED BY ENGRAVINGS. 
 
 CoKi 
 
 TP 
 
 0,1- O) 
 
 LONDON : 
 
 PUBLISHED BY BUMPUS AND GRIFFIN, 3, 8KINNER-STRE ET J 
 AND RICHARD GRIFFIN AND CO. GLASGOW : 
 
 SOLD ALSO BY SULLIES, BROTHERS, EDINBURGH. 
 
 1831. 
 
POLYTE CHNIC L IBRARY. 
 
 The design of the Publishers of the Polytechnic Library 
 in ^ Series of highly-instructive Works, which 
 
 the Public may be tempted to buy, because they will be 
 cheap, be induced to redd, because they will be brief —be 
 competent to understand, because they will be clearly writ- 
 ten,— and be able to profit by, because they will be works 
 OF PRACTICAL UTILITY. Every volume, therefore, will 
 contain a complete Treatise relating to one of the useful arts 
 or sciences, or the chemical or mechanical trades. 
 
 JUST PUBLISHED, PRICE HALF-A-CROWN, 
 
 VOL. I. OP THE POLYTECHNIC LIBRARY, 
 
 Neail;, printed in 18mo. and bound in Cloth, containing 
 
 THE ART OF GLASS-BLOWING, 
 
 Or Plain Instructions for Making the 
 
 CHEMICAL <5f PHILOSOPHICAL INSTRUMENTS 
 
 WHICH ARE FORMED OP GLASS; 
 
 Such as 
 
 barometers, thermometers, hydrometers, 
 
 Hour-Glasses, Funnels, Syphons, 
 
 TUBE-VESSELS FOR CHEMICAL EXPERIMENTS, 
 toys fob RECREATIVE PHILOSOPHY, &C. 
 
 BY A FRENCH ARTIST. 
 
 illustrated by upwards op one hundred figures 
 Elegantly engraved on Copperplates. ’ 
 
 Science, will tod ,M. 
 
 Of their Apparatus' 
 
 their leisure hours ’in nw willingly occupy 
 
 Glass and Enamels with working 
 deterred by the anticinated have hitherto been 
 
 ginary difficulties of^the the ima- 
 
 plesJmosTexSit^^ are taught herein the sim- 
 
 of working Glass into ever^^var^^ 
 
 I UBLISHED BY BUMPUS & GRIFFIN, SKINNER-STREET, LONDON; 
 R. GRIFFIN AND CO. GLASGOW; 
 
 AND STILLIES, BROTHERS, EDINBURGH. 
 
THE FOLLOWING WORKS, INTENDED TO FORM PART OF 
 
 THE POLYTECHNIC LIBRARY, 
 
 Are nearly ready fur Publication. 
 
 THE 
 
 DOMESTIC CHEMIST; 
 
 Comprising Instructions for 
 
 THE DETECTION OF ADULTERATIONS 
 
 In numerous Articles employed in 
 
 DOMESTIC ECONOMY <Sf THE ARTS. 
 
 To which is prefixed, 
 
 THE AET OF DETECTING POISONS IN FOOD AND 
 .. ORGANIC MIXTURES. 
 
 Contents. 
 
 PART I.— Instructions for the Detection of Mineral 
 Poisons in Vegetable or Animal Mixtures.— Copper, Lead, 
 Antimony, Arsenic, Mercury, Iron, Barytes, Alumina, 
 
 Potash, Soda, Sulphuric Acid, Nitric Acid, Muriatic Acid. 
 
 PART II.— Instructions for the Examination op Articles 
 
 SUPPOSED TO BE ADULTERATED .—Alcoliol, Ale, Anchovy Sauce, 
 Arrow-Root, Beer, Brandy, Bread, Calomel, Carmine, Cayenne 
 Pepper, Cheese, Chocolate, Chrome Yellow, Cinnamon, Cloves, 
 Cochineal, Coffee. Confectionery, Crabs’ Eyes, Cream, Cream ot 
 Tartar, Epsom Salts, Flour, Gin. Gum Arabic, Spirits of H“«s- 
 horn, Honev, Hops, Ipecacuanha, Isinglass, Ketchup, LaKes, 
 Leeches, Lemon Acid, Litharge, Magnesia, Milk, Mushrooms, 
 Mustard, Olive Oil, Parsley, Pepper, Peruvian Bark, Pickles, 
 Porter, Red Oxide of Mercury, Rhubarb, Sal Aminoniac, Salt, 
 Saltpetre, Soap, Soluble Tartar, Spanish Liquorice, opirits, 
 .Sugar, Sulphur.Tamarinds, Tapioca.Tartaric A ci d, Tartar (5metic, 
 Tea, Ultramarine, Verdigris, Vermilion, Vinegar, Volatile Oils, 
 Wax, White Lead, Wine, Water, (including directions for testing 
 the purity of all descriptions of Rain, River, or Spring Water. i 
 PART III.— Instructions for the Preparation of the Tests 
 EMPLOYED IN DOMESTIC CHEMISTRY AND FOR THE ^RFORM- 
 ANCE OF VARIOUS ChEMIC.AL OPERATIONS; WITH DESCRIP 
 TiON OF the Glasses and Apparatus properto be employed. 
 *»* The work is written in a popular manner, and intended for the uw^^ 
 Families, Publicans, Wine and Spirit Merchants, n’en. 
 
 Apothecaries, Physicians, Coroners, and Jurynien.-Pttce Three S/nUings. 
 
 THE PERFUMER’S ORACLE. 
 
 The object of this work is to present “ comprehen^ve and ^ 
 tical account of the Preparation of PERF UMES and ■ J 
 
 according to the newest, most successful, and most econo 
 processes. It will he adapted either for Professional Persons, 
 for Ladies who may wish to amuse themselves w th this elegant 
 branch of experimental science.— Price Three dliUUngs. 
 
TRANSLATOR’S PREFACE. 
 
 The scientific instruments prepared by the glass- 
 blower are numerous and highly useful: barome- 
 ters, .thermometers, syphons, and many other 
 vessels constructed of tubes, are indispensable to 
 the student of physics or chemistry. Some of these 
 instruments are high in price, and liable to frequent 
 destruction ; and those by whom they are much 
 employed are subject to considerable expense in 
 procuring or replacing them. It is therefore ad- 
 visable that he who desires to occupy himself in the 
 pursuit of experimental science, should know how 
 to prepare such instruments himself; that, in short, 
 he should become his own glass-blower. The 
 attainment of a ready practice in the blowing and 
 bending of glass,” says Mr. Faraday, is one of 
 those experimental acquirements which render the 
 chemist most independent of large towns and of 
 instrument-makers.” 
 
 Unquestionably the best method of learning to 
 work glass is to obtain personal instructions from 
 one who is conversant with the art : but such in- 
 structions are not easily obtained. The best ope- 
 rators are not always the best teachers ; and to 
 find a person equally qualified and willing to teach 
 the art, is a matter of considerable difficulty. In 
 large towns, workmen are too much engaged with 
 their ordinary business to step aside for such a 
 purpose ; and in small towns glass-blowers are 
 
IV 
 
 translator’s preface. 
 
 seldom to be found. In most cases, also, they are 
 too jealous of their supposed secrets to be willing 
 to communicate their methods of operating to 
 strangers, even when paid to do so. 
 
 The following Treatise is a free translation of 
 JjArt du Soitffleiir a la Lampe, par T. P. 
 Danger. The author is employed, in Paris, in 
 preparing glass instruments for sale, and in teach- 
 ing others the art of preparing them. He has pre- 
 sented in this work the most minute instructions 
 for the working of glass which have ever been 
 offered to the public. The general processes of 
 the art are so fully explained, and the experimental 
 illustrations are so numerous, that nothing remains 
 except the reducing of these instructions to prac- 
 tice to enable the student to become an adept in 
 the blowing of glass. I trust that, in publishing 
 this work in an English dress, I may be considered 
 as aiding in some degree the progress of physical 
 science. 
 
 This work contains a description of a cheap blow- 
 pipe and a very convenient lamp ; both of them 
 the invention of the author : but any other kind 
 of lamp or blowpipe may be employed instead of 
 these. The reader who wishes for a description of 
 the blowpipes generally employed in England, may 
 consult Mr. Griffin’s Practical Treatise on the 
 Use of the Blowpipe in Chemical and Mineral 
 Analysis. 
 
 London, September 1831 , 
 
AUTHOR’S PREFACE. 
 
 The flame of a lamp, or candle, condensed and 
 directed by a current of air, is exceedingly useful 
 in a great number of arts. The instrument which 
 is employed to modify flame is the Blowpipe. This 
 is an indispensable agent for jewellers, watch- 
 makers, enamellers, glass-blowers, natural philoso- 
 phers, chemists, mineralogists, and, indeed, for all 
 persons who are occupied with the sciences, or 
 their application to the ar(s. Its employment 
 ofi'ers immense advantages in amultitude of cir- 
 cumstances ; and the best method of making use 
 of so powerful an agent ought to be well known to 
 every person who is likely to be called upon to 
 adopt it. 
 
 Students, especially those who desire to exercise 
 themselves in chemical manipulation, must feel the 
 want of a simple and economical process, by means 
 of which they could give to glass tubes, of which 
 they make great use, the various forms that are 
 necessary for particular operations. How much 
 reason have they to complain of the high price of 
 the instruments of which they make continual use ! 
 The studies of a great number are shackled from 
 want of opportunity to exercise themselves in 
 
VI 
 
 author’s preface. 
 
 manipulation ; and many^ not daring to be at the 
 expense of a machine of which they doubt their 
 ability to make an advantageous use, figure to 
 themselves the employment of the glass-blower’s 
 apparatus as being beset with diffictilties, and so 
 rest without having even an idea of the numberless 
 instruments which can be made by its means. 
 
 Many persons would very willingly occupy 
 their leisure time in practising the charming art of 
 working glass and enamels with the blowpipe ; 
 but the anticipated expense of the apparatus, and 
 the difficulties which they imagine to foresee in the 
 execution of work of this kind, always repels them. 
 
 The new species of blowpipe which we have 
 offered to the public, and which has received the 
 approbation of the Society for the Encouragement 
 of Arts, obviates all these inconveniences : its 
 moderate price, its portability, and the facility 
 with which it can be used, adapt it to general 
 employment. 
 
 But we should not believe that we had attained 
 the end which we had proposed to ourselves if we 
 had not placed young students in a situation to 
 repeat at their own houses, at little cost, and with 
 the greatest facility, the experiments which are 
 necessary to familiarise them with the sciences. 
 It is with such a view that we present to them this 
 little Treatise, which is destined to teach them the 
 simplest, the most expeditious, the least expensive. 
 
author’s preface. 
 
 vii 
 
 and the most effectual methods of constructing 
 themselves the various instruments which they re- 
 quire in the prosecution of their studies. 
 
 The word glass-hlower, generally speaking, 
 signifies a workman who occupies himself in 
 making of glass and enamel, the instruments, 
 vessels, and ornaments, which are fabricated on a 
 larger scale in the glass-houses : but the domain of 
 the sciences having laid the art of glass-blowing 
 under contribution, the artists of the lamp have 
 divided the labours thereof. Some apply them- 
 selves particularly to the construction of philoso- 
 phical and chemical instruments ; others occupy 
 themselves with little ornamental objects, such as 
 flowers, &c. ; and, among the latter, some manu- 
 facture nothing but pearls, and others only artificial 
 eyes. Finally, a few artists confine themselves 
 to drawing and painting on enamel, which sub- 
 stance is previously applied to metallic surfaces 
 by means of the fire of a muffle. 
 
 As we intend to treat separately of these dif- 
 ferent branches of the art, we commence with that 
 of which the manipulation is the simplest. 
 
 Paris, 1829 . 
 
CONTENTS. 
 
 Page 
 
 1 .— Instruments employed in Glass-Blowing ... 1 
 
 The Blowpipe 
 
 The Glass-Blower’s Table " «? 
 
 The Eolipyle 5 
 
 Blowpipe with Continued Current .... 5 
 
 The Lamp 
 
 The Candlestick i 1 9 
 
 Combustibles ! * ! * ' 9 
 
 Oil, Tallow, &c J * Q 
 
 The Wicks | jq 
 
 Belation between the Diameter of the 
 Beaks of the Blowpipe and the Wicks 
 of the Lamp 12 
 
 II. PreliminaryNotionsof the Art of Glass-Blowing 16 
 
 The Flame 
 
 Places fit to work in 19 
 
 Means of obtaining a Good Fire ..... 19 
 Choice and Preservation of Glass .... 22 
 Preparation of Glass Tubes before heating them 25 
 Method of presenting Tubes to the Fire, and 
 of working them therein 26 
 
 III. Fundamental Operations in Glass-Blowing 
 
 1. Cutting, . . 
 
 2. Bordering . , 
 
 3. Widening . , 
 
 4. Drawing-out . 
 
 5. Choking . . 
 
 31 
 
 34 
 
 36 
 
 36 
 
 37 
 
 6. Sealing 
 
 7. Blowing . 
 
 8. Piercing . 
 
 9. Bending . 
 10. Soldering 
 
 30 
 
 38 
 
 39 
 46 
 
 48 
 
 49 
 
 IV . Construction of Chemical and Philosophical In- 
 struments 
 
 Adapters 
 
 Apparatus for various Instruments .... 
 Archimedes’s Screw 
 
 54 
 
 55 
 55 
 57 
 
CONTENTS. 
 
 IX 
 
 Page 
 
 Areometers 
 
 Barker’s Mill 
 
 Barometers ...• 
 
 Cistern Barometer 
 
 Dial Barometer 
 
 Syphon Barometer 
 
 Stop-cock Barometer 
 
 Compound Barometers 
 
 Gay-Lussac’s Barometer 
 
 Bunten’s Barometer 
 
 Barometer pierced laterally for Demon- 
 strations 
 
 Bell Glasses for Experiments 
 
 Blowpipe 
 
 Capsules 
 
 Cartesian Devils 
 
 Communicating Vases 
 
 Cryophorus 
 
 Dropping Tubes 
 
 Fountains 
 
 Fountain of Circulation 
 
 Fountain of Compression 
 
 Intermitting Fountain . ' 
 
 Hero’s Fountain 
 
 Funnels 
 
 Hour Glasses 
 
 Hydraulic Ram 
 
 Hydrometers 
 
 Baume’s Hydrometer 
 
 Nicholson’s Hydrometer 
 
 Hydrometers with two, three, or four 
 
 branches 
 
 Manometers 
 
 Mariotte’s Tube 
 
 Phosphoric Fire-bottle 
 
 Pulsometer 
 
 Pump 
 
 Retorts for Chemical Experiments . . . . 
 
 Rumford’s Thermoscope 
 
 Syphons 
 
 Sjtoons 
 
 Spirit Level 
 
 Test Glass with a foot 
 
 Thermometers 
 
 Ordinary Thermometer 
 
 71 
 
 57 
 
 58 
 58 
 
 58 
 
 59 
 59 
 
 59 
 
 60 
 61 
 
 61 
 
 61 
 
 62 
 
 63 
 
 64 
 
 65 
 55 
 
 65 
 
 66 
 66 
 
 67 
 
 68 
 68 
 68 
 70 
 
 70 
 
 71 
 71 
 
 73 
 
 74 
 
 74 
 
 75 
 75 
 
 75 
 
 76 
 
 76 
 
 77 
 
 78 
 80 
 80 
 80 
 81 
 81 
 
X 
 
 CONTENTS. 
 
 Page 
 
 Dial Thermometer 93 
 
 Chemical Thermometer 
 
 Spiral Thermometer ! 1 85 
 
 Pocket Thermometer ! 86 
 
 Maximum Thermometer gg 
 
 Minimum Thermometer gg 
 
 Bellani’s Maximum Thermometer . ! *. 87 
 
 Differential Thermometer g^ 
 
 Thermoscope ! 77 
 
 Tubes bent for various purposes ... 89 
 
 Vial of the four Elements ! ! 90 
 
 Water Hammer ! * 91 
 
 Welter’s Safety Tubes .' ! ! 92 
 
 V. Graduation of Chemical and Philosophical In- 
 struments gg 
 
 Of the substances employed in the prepara- 
 tion of these instruments 93 
 
 Of Graduation in general i 94 
 
 Examination of the Bore of Tubes . ! ! * 95 
 Division of Capillary Tubes into parts of 
 
 equal Capacity 
 
 Graduation of Gas Jars, Test Tubes," &'c. ." .* 97 
 
 Graduation of Hydrometers 99 
 
 Graduation of Barometers J 03 
 
 Graduation of the Manometer . ....*! 105 
 
 Graduation of Thermometers 105 
 
 Graduation of Rumford’s Thermoscope . ! 112 
 
 Graduation of Mariotte’s Tube 112 
 
THE 
 
 ART OP GLASS-BLOWING. 
 
 I . — Instruments employed in Glass-Blowings 
 
 On seeing, for the first time, a glass-blower at 
 work, we are astonished at the multitude and 
 the variety of the modifications to which he can 
 make the glass submit. The small number and 
 the simplicity of the instruments he employs, is 
 also surprising. The blowpipe, or, in its place, 
 the glass-blower’s bellows and a lamp, are in- 
 deed all that are indispensable. 
 
 THE BLOWPIPE. 
 
 Originally, the blowpipe was only a simple, 
 conical tube, more or less curvedtowardsits poin<„ 
 and terminated by a very small circular opening. 
 By means of this, a current of air was carried 
 against the flame of a candle, and the inflamed 
 matter was directed upon small objects, of 
 which it was desirable to elevate the tempera- 
 ture. Workers in metal still derive immense 
 advantages from the use of this little instrument : 
 they employ it in the soldering of very small 
 articles^ as well as for heating the extremities 
 
 B 
 
2 
 
 THE ART OF GLASS-BLOWING. 
 
 of delicate tools, in order to temper them. 
 But since the blowpipe has passed into the 
 hands of mineralogical chemists, its form has 
 been subjected to a series of very curious and 
 important modifications. In spite, however, 
 of these ameliorations, which rendered the in- 
 strument better adapted for the uses to which 
 it was successively applied, we are far from 
 having drawn from it all the advantages to 
 which we might attain, were its employment 
 not as fatiguing as it is difficult. We require 
 no other proof of this than the small number 
 of those who know well how to make use of 
 the blowpipe. 
 
 The most economical blowpipe is a tube of 
 glass, bent near one end, and pointed at its 
 extremity. A bulb is blown near that part of 
 the tube which corresponds with the curvature 
 (pi. 3, fig. 7.) This bulb serves as a reservoir 
 for moisture deposited by the air blown into 
 the tube from the mouth. If you employ a 
 tube without a bulb, the moisture is projected 
 in drops into the flame, and upon the objects 
 heated by it — an effect which is very incon- 
 venient in practice. To put this instrument 
 into action, accustom yourself to hold the mouth 
 full of air, and to keep the cheeks well inflated, 
 during a pretty long series of alternate inspi- 
 rations and expirations 5 then, seizing lightly 
 with the lips the mouth of the blowpipe, suffer 
 the air compressed by the muscles of the cheeks, 
 w'hich act the part ot a bellows, to escape by 
 the beak of the blowpipe, which you vyill be 
 able to do without being put to the least incon- 
 
THE ART OF GLASS-BLOWING. 
 
 3 
 
 venience with regard to respiration. When 
 the air contained in the mouth is pretty nearly 
 expended^ you must take advantage of an in- 
 spiration, to inflate the lungs afresh ; and thus 
 the operation is continued. You must never 
 blow through the tube by means of the lungs ; 
 first, because air which has been in the lungs 
 is less proper for combustion than that which 
 has merely passed through the nose and mouth ; 
 secondly, because the effort which it would be 
 necessary to make, to sustain the blast for only 
 a short time, would by its frequent repetition 
 become very injurious to your health. 
 
 The jet of flame produced by the mouth- 
 blowpipe can only be used to heat small ob- 
 jects : when instruments of a considerable bulk 
 have to be worked, it is customary to employ 
 the lamp, or glass-blower' s table, 
 
 THE glass-blower’s TABLE. 
 
 Artists give this name to an apparatus which 
 consists of the following articles : — 
 
 1. A Table, below which is disposed a 
 double bellows, capable of being put in motion 
 by means of a pedal. This bellows furnishes a 
 continued current of air, which can be directed 
 at pleasure by making it pass through a tube 
 terminating above the table in a sharp beak. 
 The bellows with which the glass-blower’s 
 tables are commonly furnished have very great 
 defects. The irregular form which is given to 
 the pannels diminishes the capacity of the in- 
 struments, without augmenting their advantages. 
 If we reflect an instant on the angle, more or 
 
4 
 
 THE ART OF GLASS-BLOWING. 
 
 less open^ which these pannels form when in 
 motion^ we instantly perceive that the weight 
 with which the upper surface of a bellows is 
 charged, and which always affords a vertical 
 pressure, acts very unequally on the arm of a 
 lever which is continually changing its position. 
 This faulty disposition of the parts of the ma- 
 chine has the effect of varying every instant 
 the intensity of the current of air directed upon 
 the flame. All these inconveniences would dis- 
 appear, were the upper pannel, like that in the 
 middle, disposed in such a manner as to be 
 always horizontal. It ought to be elevated and 
 depressed, in its whole extent, in the same man- 
 ner ; so that, when charged with a weight, the 
 pressure should be constantly the same, and the 
 current of air uniform. 
 
 2. A lamp, of copper or tin plate. — The 
 construction of this article, sufficiently imperfect 
 until the present time, has varied according to 
 the taste of those who have made use of it. 
 We shall give, farther on, the description of a 
 lamp altogether novel in its construction. 
 
 3. The glass-blower’s table is generally fur- 
 nished with little drawers for holding the tools 
 employed in modelling the softened glass. 
 Careful artists have the surface of their table 
 coated with sheet iron, in order that it may not 
 be burned by the hot substances that fall, or 
 are laid upon it. As glass-blowers have fre- 
 quent occasion to take measures, it is convenient 
 to have the front edge of the table divided into 
 a certain number of equal parts, marked with 
 copper nails. This enables the workman to 
 
THE ART OF GLASS-BLOWING. 
 
 5 
 
 take, at a glance of the eye, the half, third, or 
 fourth of a tube, or to give the same length to 
 articles of the same kind, without having perpe- 
 tual recourse to the rule and compasses. But 
 w'hen it is desirable to have the tubes, or the 
 work, measured with greater exactness than it 
 can be measured by this method, the rule and 
 the compasses can be applied to, 
 
 THE EOLIPYLE. 
 
 We shall merely make mention of this in- 
 strument. It is a globular vessel, commonly 
 formed of brass. If filled with a very com- 
 bustible liquor, such as alcohol, and strongly 
 heated, it alFords a rapid current of vapour, 
 which, if directed by means of a fine beak info 
 the middle of a flame, produces the same effect 
 as the air which issues from a blowpipe. The 
 eolipyle is a pretty toy, but not a good instru- 
 ment for a workman, its action being too 
 irregular. 
 
 BLOWPIPE WITH CONTlNUEir CURRENT. 
 
 It is after having, during a long period, made 
 use of the instruments of which we have spoken, 
 and fully experienced their inconveniences, 
 that, aware of the indispensable necessity for 
 such instruments in the arts and sciences, we 
 have thought it our duty to make known to the 
 public a Neiv Apparatus, which is, not only 
 calculated to fulfil the same purposes, but 
 presents advantages which it is easy to appre- 
 ciate. The price of it is only tlie sixth part of 
 
6 
 
 THE ART OF GLASS-BLOWING. 
 
 that of the glass-blower’s table*. It is very 
 portable, and capable of being attached to any 
 table w-hatever. It unites the advantages of 
 not fatiguing the workman, of leaving his hands 
 free, and of rendering him absolute master of 
 the current of air, which he can direct on the 
 flame either of the lamp or the candle, — advan- 
 tages which are not offered in the same degree 
 even by the table of the glass-blower. 
 
 The instrument which we have presented is, 
 properly speaking, nothing but a simple blow- 
 pipe, C, (pi. 1, fig. 19) communicating with a 
 bladder, or leather bag, fixed on E, which is 
 kept full of air by means of a bent tube, D, 
 through which the operator blows occasionally 
 with the mouth. This tube is closed at its in- 
 ferior .extremity, F, by a valve, which permits 
 the passage of air into the reservoir, but not of 
 its return, so that the air can only escape by 
 the beak of the blowpipe. 
 
 The valve at F is constructed in the follow- 
 ing manner; — A.t about two inches from the 
 end of the tube a contraction is made, as repre- 
 sented at a, pi. 1, fig. 24. This reduces the 
 internal diameter of the tube about one-third. 
 A small conical piece of cork or wood is now 
 introduced into the tube in the manner repre- 
 sented by c. The base of the cone must be 
 large enough to close the tube at the point where 
 it is contracted ; it must, however, not be so 
 
 * In Paris, the blowpipe which is here described is 
 sold for six francs ("five shillings English) ; or, with the 
 improved lamp and candlestick, twelve francs. 
 
THE ART OF GLASS-BLOWING. 7 
 
 large as to close the tube at the wide part. A 
 brass pin is inserted in the' poin^f the cone, as 
 is shewai in the figure. Between the cone and 
 the end of the tube, the piece of wood, b, is 
 fixed ; the shape of this piece of wood is best 
 shewn by figure 25, on the same plate. There 
 is a hole in the centre, in which the pin of the 
 cork cone can move easily. The cone or valve 
 is therefore at liberty to move between the con- 
 traction «, and the fixture b. Consequently, 
 when air is blown into the tube at e, the valve is 
 forced from the contraction, falls into the posi- 
 tion indicated by the dotted lines d, and allows 
 the air to pass by its sides. When, on the 
 contrary, the operator ceases to blow, the valve 
 is acted upon by the air in the bladder, which, 
 pressing back at f, drives the valve . close 
 against the contraction, and efiectually closes 
 the aperture. A slight hissing is heard, but 
 when the contraction is well made, and the 
 cork is good, an extremely small quantity of 
 air escapes. 
 
 The workman, seated before the table where 
 he has fixed his instrument, blows from time to 
 time, to feed the reservoir or bladder, which, 
 being pre.ssed by a system of strings stretched 
 by a weight, produces an uniform current of 
 air. The force of this current of air can be 
 modified at pleasure, by pressing the reservoir 
 more or less between the knees. (Fig. 22 re- 
 presents a blowpipe complete, formed not of 
 glass, but of brass tubes. Fig. 22, bis, repre- 
 sents the bladder or reservoir appertaining to 
 tliis blowpipe.) 
 
8 
 
 THE ART OF GLASS-BLOWING. 
 
 M. Gaultier de Claubry, who was charged 
 by the Committee of Chemical Arts of the 
 Society of Encouragement (of Paris) to make 
 a report on this instrument, was astonished at 
 the facility with which the author, in his pre- 
 sence, reduced the oxide of cobalt to the metallic 
 state, and fused the metal to a globule ; an 
 experiment which even M. Berzelius could not 
 perform with the simple blowpipe, since he 
 expressly says, in his work on that instrument, 
 that oxide of cobalt suffers no change when 
 heated before the blowpipe. The results ob- 
 tained with cast iron, oxide of tin, &c. — expe- 
 riments which are exhibited every day at the 
 public lectures given by the author — evidently 
 prove the superiority of this apparatus over all 
 the blowpipes that have hitherto been contrived. 
 
 A detailed account of the glass tubes belonging 
 to this improved blowpipe will be found in the 
 fourth part of this work, at the article Blowpipe^ 
 
 THE LAMP. 
 
 While occupied in rendering popular, if we 
 may so speak, the use of the blowpipe — an in- 
 strument which is so advantageous in a great 
 number of circumstances — we have also en- 
 deavoured to improve the lamp, which has,^ 
 until the present time, been used by all those 
 who employ the glass-blower’s table. The 
 lamp which we recommend (pi. 1, fig. 23) is of 
 a very simple construction. It possesses the 
 advantages of giving much less smoke than 
 the old lamp, and of being cleaned with the 
 greatest facility. It also gives sensibly more 
 
THE ART OF CLASS-BLOWING. 
 
 9 
 
 heat ; because the portion of flame which, in 
 the common lamps, rises perpendicularly, and 
 is not used, is, in this case, beaten down by a 
 cap or hood, and made to contribute to the 
 force of the jet. This cap also keeps the flame 
 from injuring the eyes of the operator, and 
 destroys the smoke to such an extent, that the 
 large hoods with which glass-blowers commonly 
 garnish their work table, to carry off the smoke, 
 become unnecessary. This is a peculiar ad- 
 vantage in the chamber of a student, where a 
 large hood or chimney can seldom be conve- 
 niently prepared. 
 
 THE CANDLESTICK. 
 
 For mineralogical researches, chemical assays, 
 and the soldering of small objects, as in jewel- 
 lery, we recommend the use of a little candle- 
 stick, which, by means of a spring fixed to the 
 bottom, maintains the candle always at the 
 same height. A reservoir, or shallow cup, 
 formed at the top of the candlestick, to hinder 
 the running away of the tallow or wax, allows 
 the opeiator to consume the fragments of tallow 
 or grease which are ordinarily lost in domestic 
 economy. There is a little hole in the centre 
 of the cup or upper part of the candlestick, 
 through which the wick of the candle passes, 
 o, pi. 1, fig. 22, is a representation of this 
 candlestick. 
 
 COMBUSTIBLES. 
 
 Oil Tallow, <^c . — Among the substances 
 which have been employed to feed the fire of 
 
10 
 
 THE ART OF GLASS-BLOWING. 
 
 the glass-blower’s lamp, those to which the 
 preference is to be given are wax, olive oil, 
 rape oil, poppy oil, and talloM'. Animal oils, 
 such as bone oil and hsh oil, are much esteemed 
 by some glass-blowers, who pretend that with 
 these substances they obtain better results than 
 with other combustibles. Nevertheless, animal 
 oils, generally speaking, do not give so much 
 heat as purified rape oil, while they exhale an 
 odour which is extremely disagreeable. 
 
 As to alcohol, which is sometimes used with 
 the eolipyle, its combustion furnishes so feeble 
 a degree of heat that its employment cannot be 
 recommended. 
 
 Purified rape oil is that of which the use is 
 the most general. Next to olive oil and wax, 
 it affords the greatest heat, and the least smoke. 
 Put, in a word, as in the working of glass, the 
 operator has more need of a bright flame with- 
 out smoke, than of a high temperature, any 
 combustible may be employed which is capable 
 of furnishing a flame possessing these two 
 qualities. The vegetable oils thicken, and 
 suffer alterations more or less sensible, when 
 they are long exposed to the action of the air. 
 They should be chosen very limpid, and they 
 may be preserved in that state by being enclosed 
 in bottles, which should be kept quite full and 
 well corked. 
 
 The Wicks . — There has never been any 
 substance so generally used for wicks as 
 cotton ; some glass-blowers, indeed, have em- 
 ployed wicks of asbestus, but without deriving 
 from them the advantages which might have 
 
THE ART OF GLASS-BLOWING. 
 
 11 
 
 been expected ; the greater number, therefore, 
 keep to cotton. 
 
 But it has been observed that cotton which 
 has been for some time exposed to the air no 
 longer possesses the good properties for which 
 glass-blowers esteem it. The alteration of the 
 cotton is probably brought about by the dust 
 and water which the air always holds in sus- 
 pension. Such cotton burns badly, forms a 
 bulky coal, and permits with much difficulty 
 the capillary ascension of the liquid which 
 serves to support the flame ; so that it is impos- 
 sible to obtain a good fire, and necessary to be 
 incessantly occupied in snuffing the wick. 
 Cotton is equally subject to alteration when 
 lying in the lamp, even though impregnated 
 with oil. You should avoid making use of 
 wicks that are too old. When you foresee 
 that you will remain a long time without having 
 occasion to employ the lamp, pour the oil into 
 a bottle, which can be corked up, and let the 
 wick be destroyed, previously squeezing from 
 it the oil which it contains. 
 
 It is indispensable to make use of none but 
 new and good cotton ; it should be clean, soft, 
 fine, and not twisted. It is best to preserve it 
 in boxes^ after having folded it in many double 
 papers, to exclude dust and moisture. W^hen 
 you wish to make wicks, take a skein of cotton 
 and cut it into four or six pieces, dispose them 
 side by side in such a manner as to make a 
 bundle, more or less thick, and eight or ten 
 inches in length ; pass a large comb lightly 
 through the bundle, to lay the threads even, and 
 
12 THE ART OF GLASS-BLOWING. 
 
 tie it gently at each end, to keep the threads 
 from getting entangled. 
 
 Relation between the diameters of the 
 beaks of the blowpipe, and the wicks of the 
 lamp. — We believe that we cannot place 
 better than here a few observations respecting 
 the size of the opening in the beak of the blow- 
 pipe, considered in relation to the size of the 
 wick of the lamp. These observations will 
 probably be superfluous to those who are 
 already conversant with the use of the blowpipe ; 
 but as every thing is interesting to beginners, 
 who are frequently stopped in their progress by 
 very slight difficulties, and as this Treatise is 
 particularly designed for beginners, we do not 
 hesitate to enter into the minutest details on 
 subjects which we deem interesting. 
 
 The point of your blowpipe should be formed 
 in such a manner, that you can fix upon it 
 various little beaks or caps, the orifices in 
 which, always perfectly round, ought to vary in 
 size according to the bulk of the flame upon 
 which you desire to act. You cannot, without 
 this precaution, obtain the maximum of heat 
 which the combustion of the oil is capable of 
 aflbrding. This employment of little moveable 
 caps offers the facility of establishing a current 
 of air, greater or smaller, according to the ob- 
 ject you wish to effect ; above all, it allows you 
 to clean with ease the cavity or orifice of the 
 beak, as often as it may be necessary. 
 
 These caps can be made of different materials. 
 It is most advisable to have them made of 
 copper or brass ; those which are formed of 
 
THE ART OF GLASS-BLOWING. 
 
 13 
 
 tin plate (white iron), and which are commonly 
 used in chemical laboratories, are the worst 
 kind of all. They soon become covered with 
 grease or soot, which either completely closes 
 np the orifices, or, at least, very soon alters the 
 circular form which is necessary to the produc- 
 tion of a good fire. Glass caps are less liable 
 to get dirty, and are much cheaper than the 
 above ; but, on the other hand, they have the 
 disadvantag;e of being easily melted. This 
 can to a certain extent be remedied by making 
 the points of very thick glass, and by always 
 keeping them at some distance from the flame. 
 Moreover, as you can make them yourself when 
 you are at leisure, their use is very commodious. 
 If they are to be used with the blowpipe de- 
 scribed in this work, they must be fixed in the 
 cork that closes the passage through which the 
 current of air arrives. C c and C c (pi. 1, 
 fig. 19) are two glass beaks, c c are the 
 corks, which can indifierently be adapted to c, 
 in the wooden vice, by which the various parts 
 of the blowpipe are connected when it is in 
 action. 
 
 Of whatever material the beak may be made, 
 its orifice must be perfectly round, and the 
 size of the orifice, as we have before observed, 
 must have a relation to the size of the wick 
 which is to be used with it. You can as- 
 certain the diameters of the orifices by inserting 
 into them a little plate of brass, having the 
 form of a long isoceles triangle, such as is re- 
 presented by pi. 1, fig. 2. It should be an inch 
 long, the twelfth of an inch wide at one end, 
 c 
 
14 
 
 THE ART OF GLASS-BLOWING. 
 
 and diminish to nothing at the other. When 
 divided into eight equal parts, it will give, at the 
 divisions, the respective proportions of 1, 2, 3, 
 4, 5, 6, 7 eighths of the diameter at the wide 
 end, as is exemplified by the figure above 
 referred to. We have stated in the following 
 table the relative diametei’s which long expe- 
 rience has recommended to us, as being adapted, 
 to produce the greatest effect ; yet it is not to 
 be imagined that these proportions are mathe- 
 matically correct and indispensable for the ob- 
 taining of good results. A sensible difference 
 of effect would be perceived, however, were 
 these proportions departed from in a notable 
 manner. 
 
 Diameter of the 
 wick, 
 in inches. 
 
 Diameter of the 
 orifice of the 
 beak, 
 
 in parts of an inch. 
 
 Height of the wick 
 above the surface 
 of the oil, 
 in inches. 
 
 k 
 
 9eth 
 
 i 
 
 i 
 
 48th 
 
 h 
 
 1 
 
 24th 
 
 % 
 
 
 16th 
 
 1 
 
 2 
 
 12th 
 
 H 
 
 It must be mentioned, that this table has been 
 formed from experiments made with a glass- 
 blower’s lamp of the ordinary construction ; so 
 that, with the new lamp with the hood, de- 
 scribed in this work, it will not be necessary to 
 employ wicks of so great a bulk, nor yet to 
 elevate them so much above the level of the oil. 
 
THE ART OF GLASS-BLOWING. 
 
 15 
 
 in order to produce the same effect. Hence 
 there will be a very considerable saving in oil. 
 
 The wicks of a quarter of an inch in diameter 
 are only adapted for mineralogieal examinations, 
 for soldering very fine metallic substances, and 
 for working very small tubes. When the ob- 
 jects are of considerable bulk, it is in general 
 necessary to have a flame sufficiently large to 
 cover the whole instrument, or at least all the 
 portion of the instrument which is operated upon 
 at once. For working tubes, of which the sides 
 are not more than the twelfth of an inch in 
 thickness, you should have a wick at least as 
 wide as the tube that is worked upon. The 
 diameter of the lamp-wick usually employed is 
 one inch ; a wick of this size is sufficient for 
 all the glass instruments which are in common 
 
 use. 
 
THE 
 
 ART OF GLASS-BLOWING. 
 
 II . — Preliminary Notions of the Art. 
 
 THE FLAME. 
 
 It is only by long habitude, and a species of 
 routine, that workmen come to know, not only 
 the kind of flame which is most proper for each 
 object they wish to make, but the exact point of 
 the jet where they ought to expose their glass. 
 By analysing the flame, upon the knowledge of 
 which depends the success of the work, we can 
 immediately obtain results, which, without that, 
 could only be the fruit of long experience. 
 
 Flame is a gaseous matter, of which a por- 
 tion is heated to the point of becoming lumi- 
 nous ; its form depends upon the mode of its 
 disengagement, and upon the force and direc- 
 tion of the current of air which either sup- 
 ports its combustion or acts upon it mechani- 
 cally. (PI. 1. fig, 1.) 
 
 I’he flame of a candle, burning freely in still 
 air, presents in general the form of a pyramid, 
 of which the base is supported on a hemisphere. 
 It consists of four distinct parts : the imrae- 
 
THE ART OF GliASS-BLOWING. 
 
 17 
 
 dlate products of the decomposition of the com- 
 bustible by the heat which is produced^ occupy 
 the centre, o, where they exist in the state of 
 an obscure gaseous matter, circumscribed by a 
 brilliant and very luminous envelope, s; the 
 latter i§ nothing but the obscure matter itself, 
 in the circumstances where, on coming into 
 contact with the atmosphere, it combines with 
 the oxygen which exists therein, and forms 
 what is properly called jlatne. 
 
 The blueish light which characterises the in- 
 ferior part of the flame, s, is produced by a 
 current of cold air, which, passing from below 
 upwards, hinders the combustion from taking 
 place at the bottom of the flame, at the same 
 temperature that exists in the parts of the flame 
 not immediately subject to this influence. 
 
 Finally, on observing attentively, we per- 
 ceive a fourth part, which is but slightly lu- 
 minous, and exists as an envelope of all the 
 other parts of the flame. The greatest thick- 
 ness of this envelope corresponds with the 
 summit of the flame. From this point it gra- 
 dually becomes thinner, till it arrives at the 
 lowest part of the blueish light, where it alto- 
 gether disappears. It is in this last-described 
 portion of the flame that the combustion of the 
 gas is finished, and there it is that we find the 
 seat of the most intense heat which the flame 
 of the candle aflbrds. If we compare the tem- 
 perature of the different parts of the flame, we 
 find that the maximum of heat forms a ring 
 corresponding to the zone of insertion, A A i 
 
18 
 
 THE ART OF GLASS-BLOWING. 
 
 a point which is the limit of the superior ex- 
 tremity of the blueish light. 
 
 When the flame is acted upon by the blow- 
 pipe, it is subject to two principal modifica- 
 tions : — 
 
 1. If, by means of a blowpipe with a very 
 fine orifice, you direct a current of air through 
 the middle of the flame, you project a portion 
 of the flame in the direction of the blast. The 
 jet thus formed appears like a tongue of fire, 
 blueish, cylindrical, straight, and very long; 
 the current of air occupies its interior. This 
 flame is enveloped on all sides by an almost in- 
 visible light, which, extending beyond the blue 
 flame, forms a jet. A' B, very little luminous, 
 but possessing an extremely high temperature. 
 It is at the point A', which corresponds with 
 the extremity of the blue flame, that the maxi- 
 mum of heat is found. The extreme point of 
 the jet B possesses a less degree of heat. This 
 flame is adapted for mineralogical assays, for 
 soldering, for working enamels, and in general 
 for all small objects. 
 
 2. When the orifice of the blowpipe is 
 somewhat large, or when (the orifice being ca- 
 pillary) the current of air is very strong, or the 
 beak is somewhat removed from ihe flame, the 
 jet of fire, instead of being prolonged into a 
 pointed tongue, is blown into a brush. It 
 makes then a roaring noise, and spreads into 
 an irregular figure, wherein the diflerent parts 
 of the flame are confounded beyond the possi- 
 bility of discrimination. This flame is very 
 
THE ART OF GLASS BLOWING. 
 
 19 
 
 proper for the working of glass, and particu- 
 larly of glass tubes ; it ought to be clear and 
 very brilliant, and above all should not depo- 
 sit soot upon cold bodies suddenly plunged into 
 it. The maximum of temperature in this flame 
 is not well marked ; we can say, however, that 
 in general it will be found at about two-thirds 
 of the whole length of the jet. As this roar- 
 ing flame contains a great quantity of carbu- 
 retted hydrogen, and even of vapour of oil, es- 
 caped from combustion, it possesses a disoxidiz- 
 ing or reducing property in a very high degree. 
 
 PLACES FIT TO WORK IN. 
 
 Every place is adapted for a workshop, pro- 
 vided it is not too light and the air is tranquil. 
 The light of the lamp enables one to w'ork with 
 more safety than day-light, which does not per- 
 mit the dull-red colour of hot glass to be seen. 
 Currents of cold air are to be avoided, because 
 they occasion the fracture of glass exposed to 
 them on coming out of the flame. 
 
 MEANS OF OBTAINING A GOOD FIRE. 
 
 The lamp should be firmly seated upon a 
 steady and perfectly horizontal table, and 
 should be kept continually full of oil. The oil 
 which escapes during the operation, from the 
 lamp into the tin-stand placed below it, should 
 be taken up with a glass tube having a large 
 bulb, and returned to the lamp. 
 
 When you set to work, the first thing you 
 have to do is to examine the orifice of the beak. 
 
20 
 
 THE ART OF GLASS-BLOWING. 
 
 If it is closed^ or altered in form^ by adhering 
 soob you must carefully clean it, and open the 
 canal by means of a needle or fine wire. In 
 the next place, you freshen the wick by cutting 
 it squarely, and carrying oflF with the scissars 
 the parts which are carbonised. You then 
 divide it into two principal bundles, such as 
 C, K (pi. 1. fig. 21), which you separate 
 sufficiently to permit a current of air, directed 
 between the two, to touch their surfaces lightly, 
 without being interrupted in its progress. By 
 pushing the bundles more or less close to one 
 another, and by snuffing them, you arrive at 
 length at obtaining a convenient jet. It is a 
 good plan to allow, between the two principal 
 bundles and at their inferior part, a little por- 
 tion of the wick to remain : you bend this 
 down in the direction of the jet, and make it lie 
 immediately beneath the current of air. 
 
 The wick must be prevented from touching 
 the rim of the lamp, in order to avoid the run- 
 ning of the oil into the stand of the lamp. This 
 is easily managed by means of a bent iron-wire, 
 disposed as it is in the lamp described in this 
 work ; see pi. 1, fig. 23, where the wire is seen 
 in an elevated position. When the wick is in 
 the lamp, the wire is brought down round the 
 wick and level with the surface of the lamp. 
 A few drops of oil of turpentine, spread on the 
 wick, makes it take fire immediately, over its 
 whole extent, on the approach of an inflamed 
 substance. 
 
 To obtain a good fire, it is necessary to 
 
THE ART OF GLASS-BLOWING. 
 
 21 
 
 place the lamp in such a position that the orifice 
 of the blowpipe shall just touch the exterior 
 part of the flame. The beak must not enter 
 the flame, as it can then throw into the jet only 
 an inconsiderable portion of the ignited matter. 
 See pi. 1, fig. 20. On the other hand, if the 
 lamp be too far away from the blowpipe, the 
 flame becomes trembling, appears blueish, and 
 possesses a very low degree of heat. 
 
 For mineralogical experiments, and for ope- 
 rations connected with watch-making and 
 jewellery, the current of air should project the 
 flame horizontally. For glass-blowing, the 
 flame should be projected in the direction inti- 
 mated by the arrow in pi. 1, fig. 20 — that is to 
 say, under an angle of twenty or twenty-five 
 degrees. 
 
 The current of air ought to be constant, 
 uniform, and sufficiently powerful to carry the 
 flame in its direction. When it is not strong 
 enough to produce this effect, it is necessary 
 to add weights to the bellows or the bladder, 
 according as the glass-blowers’ table or our 
 lamp is employed. The point to which you 
 should apply, in the use of these instruments, 
 is to enable yourself to produce a current of 
 air so uniform in its course that the projected 
 flame be without the least variation. 
 
 Finally, when you leave off working you 
 should extinguish the flame, by cutting ofl the 
 inflamed portion of the wick with the scissars. 
 This has the double advantage of avoiding the 
 production of a mass of smoke and of leaving 
 the lamp in a fit state for another operation- 
 
22 
 
 THE ART OP GLASS-BLOWING. 
 
 CHOICE AND PRESERVATION OF GLASS. 
 
 The only materials employed in the fabrica- 
 tion of the objects described in this Treatise, are 
 tubes of common glass or of flint-glass. They 
 can be had of all diameters, and of every va- 
 riety of substance. They are commonly about 
 three feet long, but some are found in commerce 
 which are six feet in length. You should choose 
 tubes thatare very uniform — thatis tosay,straight 
 and perfectly cylindrical, both inside and out- 
 side. A good tube should have the same dia- 
 meter from one end to the other, and the sides 
 or substance of the glass should be of equal 
 thickness in every part. This is indispensable 
 when the tubes are to have spherical bulbs 
 blown upon them. \Ye shall describe, in the 
 article GirctducttioH, the method of ascertaining 
 whether or not a tube is uniform in the bore. 
 
 The substance of the glass should be per- 
 fectly clear, without bulbs, or specks, or 
 stripes. The tubes are so much the more easy 
 of use, as the glass of which they are made is 
 the more homogeneous. Under this point of 
 view, the white glass, known in commerce by 
 the name of crystal or flint-glass, is preferable 
 to common glass : it is more fusible, less fra- 
 gile, and less liable to break under the alterna- 
 tions of heat and cold ; but it is dearer and 
 heavier, and has the serious disadvantage of 
 beconiing permanently black when exposed to 
 a certain part of the flame. This is an eflect, 
 the causes and consequences of which will be 
 explained in a subsequent chapter. 
 
THE ART OF GLASS-BLOWING. 
 
 23 
 
 You must take" care never to employ flint- 
 glass for instruments vi'hicli are to be submitted to 
 the action of certain fluids — such as sulphuretted 
 and phosphuretted hydrogen, and the hydro- 
 sulphurets ; for these compounds are capable 
 of decomposing flint-glass, in consequence of 
 its containing oxide of lead. In general, hard 
 common glass is preferable to flint-glass for all 
 instruments which are to be employed in che- 
 mistry. Flint-glass should only be used for 
 ornamental objects, and for the barometers, 
 thermometers, and other instruments employed 
 in philosophical researches. 
 
 It sometimes happens that glass tubes lose 
 their transparence and ductility, and suddenly 
 become almost infusible, in the fire of the lamp: 
 this effect takes place when they have been 
 kept for some time in a melted state. It is 
 then almost impossible to bring them back to 
 their original condition ; it can only be done 
 by exposing them for a long time to an exceed- 
 ingly high temperature. You can prevent this 
 accident by working such kind of glass with 
 considerable rapidity, and in a pretty brisk 
 fire. There are tubes, however, which vitrify 
 so promptly that it is only a person well versed 
 in the art who can make good use of them. 
 It is best not to employ such glass. But how 
 can it be discriminated before-hand ? It is ex- 
 perience, sooner than any characters capable 
 of description, that will teach you how to 
 make choice of good glass ; nevertheless we 
 have observed, that, among the glass tubes 
 which occur in commerce, those possessing a 
 
24 THE ART OF GLASS-BLOWING. 
 
 very white colour manifest this bad quality 
 most particularly. It may be observed, that, 
 for tubes which are to have thin sides, this 
 vitrifiable sort of glass is better than any other. 
 
 For certain philosophical instruments it is 
 necessary to employ flat tubes. These are 
 formed of flint-glass, are very small, and have 
 a canal or bore, which, instead of being round, 
 as in common tubes, has the form of a long and 
 very flat oval. This disposition has the ad- 
 vantage of rendering more perceptible the co- 
 lumn of liquid that may be introduced, and 
 which in a round canal would scarcely be visi- 
 ble. In choosing this sort of tubes, carefully 
 avoid those of w^hich the canal is twisted, and 
 not found to be in the same plane, in the whole 
 length of the tube. 
 
 The tubes should be sorted, according to 
 their sizes and qualities, and should be depo- 
 sited in large drawers or on long shelves, in 
 such a manner as to be equally supported 
 through their whole extent. They should also 
 be sheltered from dust and from moisture. If 
 you cannot conveniently warehouse them in 
 this manner, you should tie them up in parcels, 
 and support them in a perpendicular position. 
 It is a very bad plan to place them in an in- 
 clined direction, or to support them by their 
 extremities on wooden brackets, as it is the 
 fashion to do in chemical laboratories ; because, 
 as the tubes are then supported only at certain 
 points, they bend, in course of time, under 
 the influence of their own weight, and contract 
 a curvature which is extremely prejudicial in 
 
THE ART OF GLASS-BLOWING. 
 
 25 
 
 certain instruments, and which it is almost im- 
 possible to correct. 
 
 PREPARATION OF TUBES BEFORE HEATING 
 THEM. 
 
 Before presenting a tube to the flame, you 
 should clean it well both within and without, 
 in order to remove all dust and humidity. If 
 you neglect to take this precaution, you run 
 the risk of cracking or staining the glass. 
 When the diameter of the tube is too small to 
 permit of your passing a plug of cloth or paper 
 to clean its interior, you can accomplish the ob- 
 ject by the introduction of water, which must, 
 many times alternately, be sucked in and 
 blown out, until the tube is deemed clean. 
 One end of it must then be closed at the lamp, 
 and it must be gradually exposed to a charcoal 
 fire, where, by raising successively all parts of 
 the tube to a sufficiently high temperature, you 
 endeavour to volatilize and expel all the water 
 it contains. In all cases you considerably faci- 
 litate the disengagement of moisture by renew- 
 ing the air in the tube by means of a bottle of 
 Indian-rubber fastened to the end of a long nar- 
 row tube, which you keep in the interior of 
 the tube to be dried during the time that it is 
 being heated. Yoti can here advantageously 
 substitute alcohol for water, as being much 
 more volatile, and as dissolving greasy matters ; 
 but these methods of cleansing should only be 
 employed for valuable objects, because it is 
 extremely difficult fully to expel moisture from 
 a tube wherein you have introduced water, 
 
 D 
 
26 
 
 THE AKT OF GLASS-BLOWING. 
 
 and because alcohol is too expensive to be em- 
 ployed where there is no particular necessity. 
 
 When the tubes no longer contain dust, or 
 moisture, you measure them, and mark the 
 divisions according to the sort of work which 
 you propose to execute. 
 
 METHOD OF PRESENTING TUBES TO THE FIRE, 
 AND OF WORKING THEM THEREIN. 
 
 The two arms are supported on the front 
 edge of the table, and the tube is held with the 
 hands either above or below, according as it 
 may be necessary to emploj'^ more or less force, 
 more or less lightness. You ought, in general, 
 to hold the tube horizontally , and in such a 
 manner that its direction may be perpendicular 
 to that of the flame. Yet, when you wish to 
 heat at once a large portion of the tube, or to 
 soften it so that it shall sink together in a par- 
 ticular manner, as in the operation of sealing, 
 you will find it convenient to incline the tube, 
 the direction of which, however, must always 
 be such as to turn the heated part continually 
 towards you. 
 
 We are about to give a general rule, upon 
 the observance of which we cannot too strongly 
 insist, as the success of almost every operation 
 entirely depends upon it. The rule is, never to 
 present atuheto the flame without 
 TURNING it ; and turning it, too, with such a 
 degree of rapidity that every part of its cir- 
 cumference may be heated and softened to the 
 same degree. As melted glass necessarily 
 tends to descend, there is no method of pre- 
 
THE ART OF GLASS-BLOWING. 27 
 
 venting a heated tube from becoming deformed 
 but that of continually turning it, so as to bring 
 the softened part very frequently uppermost. 
 When vou heat a tube near the middle, the 
 movement of the two hands must be unifoTm 
 and simultaneous, or the tube will be twisted 
 and spoiled. 
 
 When the tubes have thick sides, they must 
 not be plunged into the flame until they have 
 previously been strongly heated. You expose 
 them at first to the current of hot air, at some 
 inches from the extremity of the jet ; you keep 
 them there some time, taking care to turn them 
 continually, and then you gradually bring them 
 towards, and finally into, the flame. The 
 thicker the sides of the tubes are, the greater 
 precaution must be taken to elevate the tem- 
 perature gradually : this is the only means of 
 avoiding the fractures which occur when the 
 glass is too rapidly heated. Though it is 
 necessary to take so much care with large and 
 thick tubes, there are, on the contrary, some 
 tubes so small and so thin that the most sudden 
 application of the fire is insufiicient to break 
 them. Practice soon teaches the rule which 
 is to be followed with regard to tubes that come 
 between these extremes. 
 
 Common glass ought to be fused at the 
 maximum point of heat ; but glass that con- 
 tains oxides capable of being reduced at that 
 temperature (such as flint-glass) require to be 
 worked in that part of the flame which 
 possesses the highest oxidating power. If you 
 operate without taking this precaution, you run 
 
28 
 
 THE ART OF GLASS-BLOWING. 
 
 the risk of decomposing the glass. Thus, for 
 example, in the case of flint-glass, you may reduce 
 the oxide of lead, which is one of its constituents, 
 to the state of metallic lead. The consequence 
 of such a reduction is the production of a black 
 and opaque stain upon the work, which can only 
 be removed by exposing the glass, during a 
 very long time, to the extremity of the jet. 
 
 You must invariably take the greatest care 
 to keep the flame from passing into the interior 
 of the tube ; for when it gets there it deposits a 
 greasy vapour, which is the ordinary cause of 
 the dirt which accumulates in instruments that 
 have been constructed without suflScient pre- 
 caution as to this matter. 
 
 In order that you may not blacken your 
 work, you should take care to snuff" the 
 wick of the lamp whenever you perceive the 
 flame to deposit soot. 
 
 You can judge of the consistence of the 
 tubes under operation as much by the/ee/as by 
 the look of the glass. The degree of heat 
 necessary to be applied to particular tubes, de- 
 pends entirely upon the objects for which they 
 are destined. As soon as the glass begins to 
 feel soft, at a brownish-red heat, for example, 
 you are at the temperature most favourable to 
 good bending. But is it intended to blow a 
 bulb? The glass must, in this case, be com- 
 pletely melted, and subjected to a full reddishr- 
 white heat. \Ye shall take care, when speak- 
 ing hereafter of the different operations to be 
 performed, to mention the temperature at which 
 each can be performed with most success. 
 
the art of glass-blowing. 29 
 
 When an instrument upon which you have 
 been occupied is finished, you should remove it 
 from the flame gradually, taking care to turn 
 it continually, until the glass has acquired sut- 
 ficient consistence to support its own weight 
 without becoming deformed. Every instru- 
 ment formed thus of glass requires to undergo a 
 species of annealing, to enable it to be pre- 
 served and employed. To give the instrument 
 this annealing, it is only necessary to remove it 
 from the flame very gradually, allowing it to 
 repose some time in each cooler place to which 
 you successively remove it. The thicker or the 
 more equal the sides of the glass, the more 
 carefully it requires to be annealed. No in- 
 strument should be permitted to touch cold or 
 wet bodies while it is warm. 
 
THE 
 
 ART OP GLASS-BLOWING. 
 
 III . — Fundamental Operations in Glass- 
 Blowing. 
 
 All the modifications of shape and size which 
 can be given to tubes in the construction of va- 
 rious instruments, are produced by a very 
 small number of dissimilar operations. We 
 have thought it best to unite the description of 
 these operations in one article, both to avoid 
 repetitions and to place those who are desirous 
 to exercise this art in a state to proceed, 
 without embarrassment, to the construction of 
 any instrument of which they may be provided 
 with a model or a drawing ; for those who at- 
 tend properly to the instructions given here, 
 with respect to the fundamental operations of 
 glass-blowing, will need no other instructions 
 to enable them to succeed in the construction 
 of all kinds of instruments capable of being 
 made of tubes. These fundamental operations 
 can be reduced to ten, which may be named as 
 follows : — 
 
THE ART OF OLASS-BLOWING. 
 
 31 
 
 1. Cutting. 
 
 2. Bordering. 
 
 3. Widening, 
 
 4. Drawing out. 
 
 5. Choking. 
 
 6. Sealing. 
 
 7. Blowing. 
 
 8. Piercing. 
 
 9. Bending. 
 10. Soldering, 
 
 proceed to give & detailed account of 
 these different operations. 
 
 1. — CUTTING. 
 
 The different methods of cutting of glass 
 tubes which have been contrived, are all found- 
 ed on two principles ; one of these is the 
 division of the surface of glass by cutting 
 instruments, the other the effecting of the same 
 object by a sudden change of temperature ; and 
 sometimes these two principles are combined in 
 one process. 
 
 The first method consists in notching the 
 tube, at the point where it is to be divided, with 
 the edge of a file, or of a thin plate of hard 
 steel, or with a diamond ; after which, you 
 press upon the two ends of the tube, as if to 
 enlarge the notch, or, what is better, you give 
 the tube a slight smart blow. This method is 
 sufficient for the breaking of small tubes. 
 Many glass-blowers habitually employ an agate, 
 or a common flint, which they hold in one hand, 
 while with the other they rub the tube over the 
 sharp edge of the stone, taking the precaution 
 of securing the tube by the help of the thumb. 
 For tubes of a greater diameter, you can em- 
 ploy a fine iron wire stretched in a bow, or, 
 stili better, the glass-cutters’ wheel ; with ei- 
 ther of these, assisted by a mixture of emery 
 
32 
 
 THE ART OF GLASS-BLOWING. 
 
 and water^ you can cut a circular trace round 
 a large tube, and then divide it with ease. 
 
 When the portion which is to be removed 
 from a tube is so small that you cannot easily 
 lay hold of it, you cut a notch with a file, and 
 expose the notch to the point of the blowpipe 
 flame : the cut then flies round the tube. 
 
 This brings us to the second method of cut- 
 ting tubes — a method which has been modified 
 in a great variety of ways. It is founded on 
 the property possessed by vitrified matters, of 
 breaking when exposed to a sudden change of 
 temperature. Acting upon this principle, some 
 artists apply to the tube, at the point where 
 they desire to cut it, a band of tused glass. 
 If the tube does not immediately separate into 
 two pieces, they give it a slight smart blow on 
 the extremity, or they drop a little water on 
 the heated ring. Other glass-blowers make 
 use of a piece ot iron heated to redness, an 
 angle or a corner of which they apply to the 
 tube at the point where it is to be cut, and 
 then, if the fracture is not at once effected by 
 the action of the hot iron, they plunge the tube 
 suddenly into cold water. 
 
 The two methods here described can be 
 combined. After having made a notch with a 
 file, or the edge of a flint, you introduce into 
 it a little water, and bring close upon it the 
 point of a very little tube previously heated to 
 the melting point. This double application of 
 heat and moisture obliges the notch to fly rio-ht 
 round the tube. ^ 
 
 When the object to be cut has a large dia- 
 
THE ART OF GLASS-BLOWING. 
 
 33 
 
 meter, and very thin sides — when it is such a 
 vessel as a drinking-glass, a cup, or a gas 
 tube — you may divide it with much neatness by 
 proceeding as follows. After having well 
 cleaned the vessel, both within and without, 
 pour oil into it till it rises to the point, or very 
 nearly to the point, where you desire to mit it. 
 Place the vessel, so prepared, in an airy situa- 
 tion; then take a rod of iron, of about an inch 
 in diameter, make the extremity brightly red- 
 hot, and plunge it into the vessel untd the ex- 
 tremity of the iron is half an inch below the 
 surface of the oil: there is immediately formed 
 a great quantity of very hot oil, which as- 
 sembles in a thin stratum at the surface of the 
 cold oil, and forms a circular crack where it 
 touches the sides of the glass. If you take 
 care to place the object in a horizontal position, 
 and to plunge the hot iron without communi- 
 cating much agitation to the oil, the parts so 
 separated will be as neat and as uniform as you 
 could desire them to be. By means of this 
 method we have always perfectly succeeded in 
 cutting very regular zones from ordinary glass. 
 
 The method which is described in some 
 works, of cutting a tube by twisting round it 
 a thread saturated with oil of turpentine, and 
 then inflaming the thread, we have found to be 
 unfit for objects which have thick sides. 
 
 Some persons employ cotton wicks dipped in 
 sulphur. By the burning of these, the glass is 
 strongly heated in a given line, or very narrow 
 space, which is instantly cooled by a wet fea- 
 ther or a wet stick. So soon as a crack is pro- 
 
34 
 
 THE ART OF GLASS-BLOWING. 
 
 duced, it can be led in any required direction 
 by a red-hot iron, or an inflamed piece of char- 
 coal. 
 
 Finally, you may cut small portions from 
 glass tubes in a state of fusion, by means of 
 common scissars. 
 
 2. BORDERING. 
 
 To whatever use you may destine the tubes 
 which you cut, they ought, almost always, to 
 be bordered. If you merely desire that the 
 edges shall not be sharp, you can smoothen 
 them with the file, or, what is better, you can 
 expose them to the flame of the lamp until they 
 are rounded. If you fear the sinking in of the 
 edges when they are in a softened state, you 
 can hinder this by working in the interior of 
 the tube a round rod of iron, such as pi. I, 
 fig. 5. The rod of iron should be one-sixth of 
 an inch thick ; one end of it should be filed 
 to a conical point, and the other end be insert- 
 ed into a thin, round, wooden handle. You 
 will find it convenient to have a similar rod 
 with a slight bend in the middle. 
 
 When you desire to make the edges of the 
 tube project, bring the end to a soft state, then 
 insert in it a metallic rod, and move it about in 
 such a manner as to widen a little the opening. 
 While the end of the tube is still soft, place it 
 suddenly upon a horizontal surface, or press it 
 by means of a very flat metallic plate. The ob- 
 ject of this operation is to make the end of the 
 tube flat and uniform. The metallic rod which 
 you employ may be the same as we haye de- 
 
THE ART OF GLASS-BLOWING. 35 
 
 scribed in the preceding paragraph. Instead 
 of agitating the rod in the tube, you may hold 
 it in a fixed oblique position^ and turn the tube 
 round with the other hand, taking cax'e to 
 press it continually and regularly against the 
 rod. See pi. 1. fig. 6. Very small tubes can 
 be bordered by approaching their extremities 
 to a flame not acted upon by the blowpipe ; 
 particularly the flame of a spirit-lamp. 
 
 When the edges of a tube are to be rendered 
 capable of suffering considerable pressure, you 
 can very considerably augment their strength 
 by soldering a rib or string of glass all round 
 the end of the tube‘— see pi. fig. 12. Hold- 
 ing tlie tube in the left hand^ and the. string of 
 glass in the right, you expose them both at once 
 to the flame. When their extremities are suflSi- 
 ciently softened, you attach the end of the-rib 
 of glass to the tube at a very short distance 
 from its extremity ; you then continue gradually 
 to turn the tube, so as to cause the rib of glass 
 to adhere to it, in proportion as it becomes 
 softened. When the rib has made the entire 
 circumference of the tube, yon separate the 
 surplus by suddenly darting a strong jet of fire 
 upon the point where it should be divided ; 
 and you continue to expose the tube to the 
 flame, always turning it round, until the ring 
 of glass is fully incorporated with the glass it 
 was applied to. You then remove the instru- 
 ment from the flame, taking care to anneal it in 
 so doing. During this operation you must 
 take care to prevent the sinking together of 
 the sidc§ of the tube, by now and then turning 
 
36 THE ART OF GLASS-BLOWING. 
 
 the iron rod in its interior. It is a Ted heat, 
 or a brownish red heat, that is best adapted to 
 this operation. 
 
 3 . WIDENING. 
 
 When yon desire to enlarge the diameter of 
 the end of a tube, it is necessary, after having 
 brought it to a soft state, to remove it from the 
 flame, and to press the sides of the glass out- 
 wards by means of a large rod of iron with a 
 conical point. The tube must be again heated, 
 and again pressed with the conical iron rod, 
 until the proper enlargement is effected. This 
 operation is much the same as that of bordering 
 a tube with projecting edges. 
 
 4 . DRAWING OUT. 
 
 You can draw out or contract a tube either 
 in the middle or at the end. Let us in the 
 first place consider that a tube is to be drawn 
 out in the middle. If the tube is long, you 
 support it with the right hand heloiv, and the 
 left hand above, by which means you secure 
 the force that is necessary, as well as the posi- 
 tion which is commodious, for turning it conti- 
 nually and uniformly in the flame. It must be 
 kept in the jet till it has acquired a cherry red 
 heat. You then remove it from the flame, and 
 always continuing gently to turn it, you gra- 
 dually separate the hands from each other, and 
 draw the tube in a straight line. In this man- 
 ner you produce a long thin tube in the centre 
 of the original tube, which ought to exhibit two 
 uniform cones where it joins the thin tube, and 
 
THE ART OF GLASS-BLOWING. 
 
 37 
 
 to have the points of these cones in the prolon- 
 gation of the axis of the tube. See pi. 1, tig. 3. 
 
 To draw out a tube at its extremity, you heat 
 the extremity till it is in fusion, and then re- 
 move it from the flame ; you immediately seize 
 this extremity with the pliers, and at the same 
 time separate the two hands. The more rapidly 
 this operation is performed, the glass being sup- 
 posed to be well softened, the more capillary 
 will the drawn-out point of the tube be ren- 
 dered. Instead of pinching the fused end with 
 the pliers, it is simpler to bring to it the end of 
 a little auxiliary tube, which should be pre- 
 viously heated, to fuse the two together, and 
 then to draw out the end of the original tube 
 by means of the auxiliary tube— see pi. 1, 
 fig. 4 and 11. In all cases, the smaller the 
 portion of tube softened, the more abrupt is 
 the part drawn out. 
 
 When you desire to draw out a point from 
 the side of a tube, you must heat that portion 
 alone, by holding it fixedly at the extremity of 
 the jet of flame. ^Vhen it is sufficiently 
 softened, solder to it the end of an auxiliary 
 tube, and then draw it out. PI. 1, fig. 18, ex- 
 hibits an example of a tube drawn out laterally. 
 A red heat, or a cherry red heat, is best adapted 
 to this operation. 
 
 5. CHOKING. 
 
 We do not mean by choking, the closing or 
 stopping of the tube, but simply a diminution 
 of the interior passage, or bore. It is a sort of 
 contraction. For examples, see pi. 2, fig. 15, 
 
 E 
 
38 
 
 THE ART OF GLASS-BLOWING. 
 
 120, 29. You perform the operation by pre- 
 senting to the flame a zone of the tube at the 
 point where the contraction is to be effected. 
 When the glass is softened, you draw out the 
 tube, or push it together, according as you 
 desire to produce a hollow in the surface of 
 the tube, or to have the surface even, or to 
 cause a ridge to rise above it. A cherry red 
 heat is the proper temperature to employ. 
 
 6. SEALING. 
 
 If the sides of the tube to be sealed are thin, 
 and its diameter is small, it is sufficient to ex- 
 pose the end that you wish to close to the 
 flame of the lamp. When the glass is softened 
 it sinks of itself, in consequence of the rotatory 
 motion given to it, towards the axis of the 
 tube, and becomes rounded. The application 
 of no instrument is necessary. 
 
 If the tube is of considerable diameter, or 
 if the sides are thick, you must soften the end, 
 and then, with a metallic rod or a flat pair of 
 pliers, mould the sides to a hemisphere, by 
 bringing the circumference towards the centre, 
 and continuing to turn the tube in the flame, 
 until the extremity is well sealed, and perfectly 
 round. Examples of the figure are to be seen 
 in pi. 2, fig. 3 and 5. Instead of this method, 
 it is good, when the extremity is sufficiently 
 softened, to employ an auxiliary tube, with 
 the help of which you can abruptly draw 
 out the point of the original tube, which be- 
 comes by that means cut and closed by the 
 flame. In order that this part may be well 
 
THE ART OF GLASS-BLOWING. 
 
 39 
 
 rounded, you may, as soon as the tube is sealed, 
 close the other extremity with a little wax, and 
 continue to expose the sealed part to the flame, 
 until it has assumed the form of a drop of tallow. 
 See pi. 2, fig. 15. You can also seal in this 
 fashion, ^y blowing, with precaution, in the 
 open end^f the tube, while the sealed end is 
 in a softened state. 
 
 If you desire the sealed part to be flat, like 
 pi. 3, fig. 30, you must press it, while it is 
 soft, against a flat substance. If you wish it to 
 be concave, like the bottom of a bottle, or pi. 3, 
 fig. 2, you must suck air from the tube with the 
 mouth ; or, instead of that, force the softened 
 end inwards with a metallic rod. You may 
 also draw out the end till it be conical, as 
 pi. 2, fig. 4, or terminate it with a little button, 
 as pi. 2, fig. 6. In some cases the sealed end 
 is bent laterally ; in others it is twirled into a 
 ring, having previously been drawn out and 
 stopped in the bore. In short, the form given 
 to the sealed end of a tube can be modified in 
 an infinity of ways, according to the object for 
 which the tube may be destined. 
 
 You should take care not to accumulate too 
 much glass at the place of sealing. If you 
 allow it to be too thick there, you run the risk 
 of seeing it crack during the cooling. Some 
 farther observations on sealing will be found at 
 the article Water Hammer, in a subsequent 
 section. The operation of sealing succeeds 
 best at a cherry-red heat. 
 
 7. BLOWING. 
 
 The construction of a great number of philo- 
 
40 THE ART OF GLASS-BLOWING. 
 
 sophical instruments requires that he who would 
 make them should exercise himself in the art 
 of blowing bulbs possessing a figure exactly 
 spherical. This is one of the most difficult 
 operations. 
 
 To blow a bulb at the extremity of a tube, 
 you commence by sealing it ; after which, 
 you collect at the sealed extremity more or less 
 glass, according to the size and the solidity 
 which you desire to give to the bulb. When 
 the end of the tube is made thick, completely 
 sealed, and well rounded, you elevate the tem- 
 perature to a reddish vjJiite heat, taking care 
 to turn the tube continually and rapidly between 
 your fingers. When the end is perfectly soft 
 you remove it from the flame, and, holding the 
 tube horizontally, you blow quickly with the 
 mouth into the open end, without discontinuing 
 for a single moment the movement of rotation. 
 If the bulb does not by this operation acquire 
 the necessary size, you soften it again in the 
 flame, while under the action of which you turn 
 it very rapidly, lest it should sink together at 
 the sides, and become deformed. When it is 
 sufficiently softened you introduce, in the same 
 manner as before, a fresh quantity of air. It is 
 of importance to observe that, if the tube be of 
 a large diameter, it is necessary to contract the 
 end by which you are to blow, in order that 
 it may be turned round with facility while in the 
 mouth. 
 
 When the bulb which you desire to make is 
 to be somewhat large, it is necessary, after 
 having sealed the tube, to soften it for the space 
 of about half an inch from its extremity, and 
 
THE ART OF GLASS-BLOWING. 
 
 41 
 
 then, with the aid of a flat piece of metal, to 
 press moderately and repeatedly on the softened 
 portion, until the sides of the tube which are 
 thus pressed upon, sink together, and acquire a 
 certain degree of thickness. During this ope- 
 ration, however, you must take care to blow, 
 now and then, into the tube, in order to retain 
 a hollow space in the midst of the little mass 
 of glass, and to hinder the bore of the tube from 
 being closed up. When you have thus, at the 
 expense of the length of the tube, accumulated 
 at its extremity a quantity of glass sufficient 
 to produce a bulb, you have nothing more to 
 do than to heat the matter till it is raised to a 
 temperature marked by a re.ddish-white colour, 
 and then to expand it by blowing. 
 
 Instead of accumulating the glass thus, it is 
 more expedient to blow on the tube a series of 
 little bulbs close to one another (see pi. 1, fig. 8), 
 and then, by heating the intervals, and blowing, 
 to unite these little bulbs into a large one of 
 convenient dimensions. 
 
 We have already observed, and we repeat 
 here, that it is indispensably necessary to hold 
 the glass out of the flame during the act of 
 blowing. This is the only means of maintain- 
 ing uniformity of temperature in the whole 
 softened parts of the tube, without which it is 
 impossible to produce bulbs with sides of equal 
 thickness in all their extent. 
 
 When you desire to form a bulb at the ex- 
 tremity of a capillary tube, that is to say, of a 
 tube which has a bore of very small diameter, 
 such as the tubes which are commonly employed 
 E 2 
 
42 
 
 THE ART OF GLASS-BLOWING. 
 
 to form thermometers, it would be improper to 
 blow it with the mouth ; were you to do so, the 
 vapour which would be introduced, having a 
 great affinity for the glass, would soon obstruct 
 the little canal, and present to the passage of 
 the air a resistance, which, with the tubes of 
 smallest interior diameter, would often be in- 
 surmountable. But, even when the tubes you 
 employ have not so very small an internal 
 diameter, you should still take care to avoid 
 blowing with the mouth ; because the introduc- 
 tion of moisture always injures fine instruments, 
 and it is impossible to dry the interior of a 
 capillary tube when once it has become wet. 
 It is better to make use of a bottle of Indian 
 rubber, which can be fixed on the open end 
 of the tube by means of a cork with a hole 
 bored through it. You press the bottle in the 
 hand, taking care to hold the tube vertically, 
 with the hot part upwards ; if you were not to 
 take this precaution, the bulb would be turned 
 on one side, or would exhibit the form of a 
 pear, because it is impossible, in this case, to 
 give to the mass in fusion that rotatory motion 
 which is necessary, when the tube is held hori- 
 zontally, to the production of a globe perfectly 
 spherical in its form, and with sides of equal 
 thickness. 
 
 Whenever you blow into a tube you should 
 keep the eye fixed on the dilating bulb, in 
 order to be able to arrest the passage of air 
 at the proper moment. If you were not to 
 attend to this, you would run the risk of giving 
 to the bulb too great an extension, by which 
 
THE ART OF GLASS-BLOWING. 
 
 43 
 
 the sides would be rendered so thin that it 
 would be liable to be broken by the touch of 
 the lightest bodies. This is the reason that, 
 when you desire to obtain a large bulb, it is 
 necessary to thicken the extremity of the tube, 
 or to combine many small bulbs in one, that it 
 may possess more solidity. 
 
 In general, when you blow a bulb with the 
 mouth, it is better to introduce the air a little at 
 a time, forcing in the small portions very 
 rapidly one after the other ; rather than to at- 
 tempt to produce the whole expansion of the 
 bulb at once : you are then more certain of being 
 able to arrest the blowing at the proper time. 
 
 When you desire to produce a moderate ex- 
 pansion, either at the extremity or in any other 
 part of a tube, you are enabled easily to effect 
 it by the following process, which is founded on 
 the property possessed by all bodies, and 
 especially by fluids, of expanding when heat- 
 ed ; a property which characterises air in a 
 very high degree. After having sealed one end 
 of the tube and drawn out the other, allow it 
 to become cold, in order that it may be quite 
 filled with air ; close the end which has been 
 drawn out, and pr-event the air within the tube 
 from communicating with that at its exterior ; 
 then gradually heat the part which you desire 
 to have expanded, by turning it gently in the 
 flame of a lamp. In a short time the softened 
 matter is acted on by the tension of the air 
 which is enclosed and heated in the interior of 
 the tube ; the glass expands, and produces a 
 bulb or swelling more or less extensive, ac- 
 
44 
 
 THE AllT OF GLASS-BLOWING. 
 
 cording as you expose the glass to a greater or 
 lesser degree of heat. 
 
 To blow a bulb in the middle of a tube, it is 
 sufficient to seal it at one of its extremities, to 
 heat the part that you wish to inflate, and, 
 when it is at a cherry-red heat, to blow in the 
 tube, which must be held horizontally and 
 turned with both hands, of which, for the 
 sake of greater facility, the left may be held 
 above and the right below. 
 
 If the bulb is to be large, the matter must 
 previously be thickened or accumulated, or, 
 instead of that, a series of small bulbs first 
 produced, and these subsequently blown into a 
 single larger b ulb, as we have already mentioned. 
 See pi. 1, fig. 8. 
 
 For some instruments, the tubes of which 
 must be capillary, it is necessary to blow the 
 bulbs separately, and then to solder them to 
 the requisite adjuncts. The reason of this is, 
 that it would be too difficult to produce, from 
 a very fine tube, a bulb of sufficient size and 
 solidity to answer the intended purpose. 
 
 You make choice of a tube which is not 
 capillary, but of a sufficient diameter, very 
 cylindrical, with equal sides, and tolerably 
 substantial : it may generally be from the 
 
 twentieth to the twelfth of an inch thick in the 
 glass. You soften two zones in this tube, 
 more or less near to each other, according to 
 the bulk you desire to give to the bulb, and 
 you draw out the melted part in points. The 
 talent consists in well-centering — that is to 
 say, in drawing out the melted tube in such a 
 
THE ART OF GLASS-BLOWING. 
 
 45 
 
 manner that the thin parts or points shall be 
 situated exactly in the prolongation of tlie axis 
 of the little portion of the original tube re- 
 maining between them. This operation is 
 technically termed drawing a cylinder between 
 two points. The tube so drawn out is exhi- 
 bited by pi. 1, fig. 4. You cut these points at 
 some distance from the central or thick parb 
 and seal one end ; you next completely soften 
 the little thick tube and expand it into a bulb, 
 by blowing with the precautions which have 
 already been described. You must keep the 
 glass in continual motion, if you desire to be 
 successful in this experiment. Much rapidity 
 of movement, and at the same time lightness 
 of touch, are requisite in the operation here 
 described. It is termed blowing a bulb be- 
 tween two points. PI. 1, fig. 10, exhibits a 
 bulb blown between two points. 
 
 To obtain a round bulb, you should hold 
 the tube horizontally ; to obtain a flattened 
 bulb, you should hold it perpendicularly, with 
 the fused extremity turned above ; to obtain a 
 pear-shaped bulb, you should hold the fused 
 extremity downwards. 
 
 When you are working upon a bulb between 
 two points, or in the middle of a tube, you 
 should hold the tube horizontally, in the ordi- 
 nary manner ; but you are to push the softened 
 portion together, or to draw it out, according as 
 you desire to produce a ridge or a prolonga- 
 tion. 
 
 When you are at liberty to choose the point 
 from which you are to blow, you should prefer. 
 
46 
 
 THE ART OF GLASS-BLOWING. 
 
 1st, that where the moisture of the breath can 
 be the least prejudicial to the instrument which 
 is to be made ; 2dly_, that which brings the 
 part which is to be expanded nearest to your 
 eye ; 3dly, that which presents the fewest dif- 
 ficulties in the execution. When bulbs are 
 to be formed in complicated apparatus, it is 
 good, to reflect a little on the best means of 
 effecting the object. It is easy to understand 
 that contrivances which may appear very 
 simple on paper, present difficulties in the 
 practical execution which often call for con- 
 siderable management. 
 
 8. — PIERCING. 
 
 You first seal the tube at one extremity, and 
 then direct the point of the flame on the part 
 which you desire to pierce. When the tube 
 has acquired a reddish-ivhite heat, you sud- 
 denly remove it from the flame, and forcibly 
 blow into it. The softened portion of the tube 
 gives way before the pressure of the air, and 
 bursts into a hole. You expose the tube again 
 to the flame, and border the edges of the hole. 
 
 It is scarcely necessary to observe, that, if 
 it be a sealed extremity which you desire to 
 pierce, it is necessary to turn the tube between 
 the fingers while in the fire ; but if, on the con- 
 trary, you desire to pierce a hole in the side of 
 a tube, you should keep the glass in a fixed 
 position, and direct the jet upon a single point. 
 
 If the side of the tube is thin, you may dis- 
 pense with blowing. The tube is sealed and 
 allow'ed to cool ; then, accurately closing the 
 
THE ART OF GLASS-BLOWING. 
 
 47 
 
 open extremity with the finger, or a little wax, 
 you expose to the jet the part which you desire 
 to have pierced. When the glass is sufficiently 
 softened, the air enclosed in the tube being ex- 
 panded by the heat, and not finding at the 
 softened part a sufficient resistance, bursts 
 through the tube, and thus pierces a hole. 
 
 You may generally dispense with the sealing 
 of the tube, by closing the ends with wax, or 
 with the fingers. 
 
 There is still another method of performing 
 this operation, which is very expeditious, and 
 constantly succeeds with objects which have 
 thin sides. Y ou raise to a reddish white heat 
 a little cylinder of glass, of the diameter of the 
 hole that you desire to make, and you instantly 
 apply it to the tube or globe, to which it will 
 strongly adhere. You allow the whole to cool, 
 and then give the auxiliary cylinder a sharp 
 slight knock ; the little cylinder drops off, and 
 carries with it the portion of the tube to which 
 it had adhered. On presenting the hole to a 
 slight degree of heat, you remove the sharp- 
 ness of its edges. 
 
 When you purpose to pierce a tube late- 
 rally, for the purpose of joining to it another 
 tube, it is always best to pierce it by blowing 
 many times, and only a little at a time, and 
 with that view, to soften the glass but mode- 
 rately. By this means the tube preserves 
 more thickness, and is in a better state to sup- 
 port the subsequent operation of soldering. 
 
 There are circumstances in which you can 
 pierce tubes by forcibly sucking the air out 
 
48 
 
 THE ART OF GLASS-BLOWING. 
 
 of them ; and this method sometimes presents 
 advantages that can be turned to good account. 
 Finally, the orifices which are produced by 
 cutting otF the lateral point of a tube drawn 
 out at the side, may also be reckoned as an 
 operation belonging to this article. 
 
 9. — BENDING. 
 
 If the tube is narrow, and the sides are 
 pretty thick, this operation presents no difficulty. 
 You heat the tube, but not too much, lest it be- 
 come deformed ; a reddish brown heat is suffi- 
 cient, for at that temperature it gives way to 
 The slightest effort you make to bend it. You 
 should, as much as possible, avoid making the 
 bend too abrupt. For this purpose, you heat 
 a zone of one or two inches in extent at once, 
 by moving the tube backwards and forwards in 
 the flame, and you take care to bend it very 
 gradually. 
 
 But if the tube is large, or its sides are thin, 
 and you bend it without proper precautions, 
 the force you employ entirely destroys its cylin- 
 drical form, and the bent part exhibits nothing 
 but a double flattening, — a canal, more or less 
 compressed. To avoid this deformity it is 
 necessary, first, to seal the tube at one ex- 
 tremity, and then, while giving it a certain 
 curvature, to blow cautiously by the other ex- 
 tremity, which for convenience sake should pre- 
 viously be drawn out. When tubes have been 
 deformed by bad bending, as above described, 
 you may, by following this method, correct the 
 fault ; that is to say, upon sealing one ex- 
 
THE ART OF GLASS-BLOWING. 
 
 49 
 
 tremity of the deformed tube, heating the flat- 
 tenedpart, and blowing into the other extremity, 
 yon can with care reproduce the round form. 
 
 In general, that a curvature may be well- 
 made, it is necessary that the side of the tube 
 which is to form the concave part be sufficiently 
 softened by heat to sink of itself equally in 
 every parfduring the operation, while the other 
 side be only softened to such a degree as to 
 enable it to give way under the force applied to 
 bend it. On this account, after having softened 
 in a cherry-red heat one side of the tube, you 
 should turn the other side, which is to form the 
 exterior of the curvature, towards you, and^ 
 then, exposing it to the point of the jet, you 
 should bend the tube immediately upon its be- 
 ginning to sink under the heat. 
 
 When you desire to bend the extremity of a 
 tube into a ring you must employ a metallic 
 rod, with which, by pressing on the tube, you 
 separate with a curve, C, (see pi. 1, fig. 14) all 
 the portion A C which is necessary to produce , 
 the desired curl. You then successively soften 
 all parts of this curve, and gradually twist it in 
 the direction indicated by the arrow, pressing 
 the iron rod constantly upon the extremity of 
 the curve. When the end A comes into con- 
 tact with the bend C you solder them together 
 at this point, and thus complete the ring. 
 PI. 2, fig. 27, and pi. 3, fig. 27, exhibit exam- 
 ples of rings formed by this process. 
 
 10. SOLDERING. 
 
 ^ If the tubes which you propose to solder 
 F 
 
50 
 
 THE ART OF GLASS-BLOWING. 
 
 are of a small diameter, pretty equal in size, 
 and have thick sides, it is sufficient, before 
 joining them together, to widen them equally at 
 their extremities, by agitating a metallic rod 
 within them. (PL 1, fig. 17.) 
 
 But if they have thin sides, or are of a large 
 diameter, the bringing of their sides into juxta- 
 position is very difficult, and the method of 
 soldering just indicated becomes insufficient. 
 In this case you are obliged to seal, and sub- 
 sequently to pierce, the two ends which you 
 desire to join. Tlie disposition which this ope- 
 ration gives to their sides very much facilitates 
 the soldering. 
 
 Finally, when the tubes are of a very dif- 
 ferent diameter, you must draw out the ex- 
 tremity of the larger and cut it where the part 
 drawn out corresponds in diameter to the tube 
 which it is to be joined to. PI. %• 9 and 
 15, exhibit examples of this mode of adapting 
 tubes to one another. 
 
 For lateral solderings you must dispose the 
 tubes in such a manner that the sides of the 
 orifices which you desire to join together coin- 
 cide with each other completely. See pi. 1, 
 
 fig. 7. 
 
 When the holes are well prepared, you heat 
 at the same time the two parts that are to be 
 soldered together, and join them at the mo- 
 ment when they enter into fusion. You must 
 push them slightly together, and continue to 
 heat successively all their points of contact ; 
 whereupon the two tubes soon unite perfectly. 
 As it is almost always necessary, when you de- 
 
THE ART OF GLASS-BLOWING. 51 
 
 sire the soldering to be neatly done, or the joint 
 to be imperceptible, to terminate the operation 
 by blowing, it is proper to prepare the ex- 
 treme ends of the tubes before-hand. That 
 end of the tube by which you intend to blow 
 should be carefully drawn out, provided it be 
 so large as to render drawing out necessary ; 
 and the other end of the tube, if large, should 
 be closed with wax, as in pi. 1, fig. 9, or if 
 small, should be sealed at the lamp (pi. 1, 
 fig. 15). When the points of junction are per- 
 fectly softened, and completely incorporated 
 with each other, you introduce a little air into 
 the tube, which produces a swelling at the 
 joint. As soon as this has taken place, you 
 must gently pull the two ends of the joined 
 tube in different directions, by which means 
 the swelled portion at the joint is brought down 
 to the size of the other parts of the tube, so that 
 the whole surface becomes continuous. The 
 soldering is then finished. 
 
 To solder a bulb or a cylinder between two 
 points, to the extremity of a capillary tube, you 
 cut and seal one of the points at a short dis- 
 tance from the bulb (pi. 1, fig. 16), and at the 
 nioment when this extremity is in fusion you 
 pierce it by blowing strongly at the other ex- 
 tremity. By this means the opening of the 
 reservoir is terminated by edges very much 
 widened, which facilitates considerably its be- 
 ing brought into juxta-position with the little 
 tube. In order that the ends of the two tubes 
 may be well incorporated the one with the 
 
52 
 
 THE ART OF GLASS-BLOWING. 
 
 other, you should keep the soldered joint for 
 some time in the flame, and ought to blow in 
 the tube, push the ends together and draw them 
 asunder, until the protuberance is no longer 
 perceptible. 
 
 If, after having joined two tubes, it should 
 be found that there still exists an open- 
 ing too considerable to be closed by simply 
 pushing the two tubes upon one another, you 
 can close such an opening by means of a 
 morsel of glass, applied by presenting the fused 
 end of an auxiliary tube. 
 
 You should avoid soldering together two 
 different species of glass — for example, a tube 
 of ordinary glass with a tube of flint-glass ; 
 because these two species of glass experience 
 a different degree of contraction upon cooling, 
 and, if joined together while in a fused state, 
 are so violently pulled from one another as they 
 become cool, that the cohesion of the point ot 
 soldering is infallibly overcome, and the tube 
 breaks. You ought also, for a similar reason, 
 to take care not to accumulate a greater mass 
 of glass in one place than in another. 
 
 If the first operation has not been sufficient 
 to complete the soldering, the tube must be 
 again presented to the flame, and again pushed 
 together at the joint, or drawn asunder, or blown 
 into, according as it may appear to be neces- 
 sary. In all cases the soldering is not truly 
 solid, but inasmuch as the two masses of 
 glass are well incorporated together, and pre- 
 sent a surface continuous in all points. 
 
THE ART OF GLASS-BLOWING. 
 
 53 
 
 The mineralogical flame (pi. 1 , fig. 1, A' B) 
 is that which is to be employed in preference to 
 the larger flame, when yon desire to effect a 
 good joining : it is sufficient to proportion the 
 size of the flame to the object you wish to 
 execute. 
 
THE 
 
 ART OF GLASS-BLOWING. 
 
 IV . — Construction of Chemical and Philo- 
 sophical Instruments. 
 
 When a person is well acquainted with the 
 fundamental operations which we have just 
 described, the preparation of the instruments 
 ot which we are about to speak can present 
 scarcely any difficulty. Indeed, some of them 
 are so extremely simple, and are so easy of 
 execution, that it is sufficient to cast a glance 
 upon the figures which represent them, to seize 
 at once the method which must be followed in 
 their construction. Of such instruments we 
 shall not stop to give a detailed description, 
 but shall content ourselves with piesenting the 
 design. 
 
 On the other hand, it is of importance to ob- 
 serve that a certain number of instruments are 
 graduated or furnished with pieces, or mount- 
 ings, of which it is not the object of our art to 
 teach the construction, and which demand a 
 more or less extensive knowledge of the sci- 
 
THE ART OP GLASS-BLOWING. 55 
 
 ences. We shall treat of these mountings but 
 summarily, referring the student, for more de- 
 tailed instructions, to the works on natural phi- 
 losophy and chemistry, in which these instru- 
 ments are especially treated of. Our reason 
 for this is, that we do not wish to abandon the 
 plan we had adopted of describing simply the 
 art of glass-blowing. To describe the use and 
 application of philosophical instruments, or to 
 explain the principles on which they act, would 
 be passing quite out of our province. 
 
 Adapters. — These are tubes of glass of va- 
 rious forms, employed in chemistry to connect 
 together the ditferent pieces constituting an 
 apparatus — as, for example, to join a retort to 
 a receiver during the operation of distillation. 
 You should take care to border the extremities 
 of an adapter ; or you may widen them into 
 the form of the month of a bottle, when they 
 are to be closed air-tight by corks. Besides this, 
 there is nothing particular to be observed in 
 the preparation of adapters. 
 
 Apparatus for Boiling in Vacuo. — Re- 
 presented by pi. 3, tig. 19. Employ a tube about 
 a quarter of an inch in diameter. Blow two 
 bulbs ; give the tube the necessary curvature ; 
 till one of the bulbs with nitric ether ; boil the 
 ether to expel the atmospheric air from the ap 
 paratus, then seal the opening in the other bulb. 
 
 Apparatus for Freezing in Vacuo. The 
 Cryophortis . — Take a tube one-third of an inch 
 or rather more in diameter, and pretty thick in 
 
66 
 
 THE ART OF GLASS-BLOWING. 
 
 the sides. Blow a bulb at each end ; the first 
 at the sealed part of the tube, the other at the 
 open point ; then give to the tube the curvature 
 represented by pi. 3, fig. 32. Introduce as 
 much water as will half fill one of the bulbs ; 
 make the water boil, and draw off the point 
 and seal the apparatus during the ebullition. 
 
 Apparatus for conducting Water in bent 
 Tubes. — Solder a funnel (see Funnels) to the 
 end of a tube ; pierce two holes in this tube in 
 the same line, and solder to each a little addition 
 proper to receive a cork. Finish the instru- 
 ment by bending it in the manner indicated by 
 
 pi. 4, fig. 18. 
 
 Apparatus for Experiments on Running 
 Liquids. — A tube bent once at a right angle, 
 mounted with a funnel, pierced laterally, and 
 soldered at the same point to a smaller tube. 
 See pi. 3, fig. 17. 
 
 Apparatus for Exhibiting the Phenomena 
 OF Capillary Tubes. — This apparatus consists 
 of a capillary tube soldered to another tube of 
 a more considerable diameter. Sometimes it is 
 bent like the letter U. PI. 3, fig. 15. 
 
 Apparatus for the Preparation of Phos- 
 phuret of Lime. — An apparatus that can be 
 employed for the preparation of phosphuret of 
 lime, as well as in a variety of other chemical 
 experiments, consists of a tube sealed at one 
 extremity, slightly bent and choked at two 
 
THE ART OF GLASS-BLOWING. 57 
 
 inches and a half from the sealed part, and 
 drawn out (after the introduction of the sub- 
 stances to be operated upon) at the other ex- 
 tremity. This little distillatory apparatus is 
 represented by pi. 3, fig. 29. 
 
 Archimedes’s Screw. — There is no parti- 
 cular process for the making of this instrument. 
 It is, however, necessary for one who would 
 succeed in making it, to exercise himself in 
 the art of well bending a tube. After a few 
 attempts, you may finish by producing a pretty- 
 regular spiral. The tube chosen for this in- 
 strument should be six or seven feet long, and 
 about one-third of an inch in diameter. You 
 commence by making a bend, nearly at a right 
 angle, about four inches from one of its extre- 
 mities. This bent portion serves afterwards 
 as a handle, and very much facilitates the 
 operation ; it represents the prolongation of 
 the rational axis which may be conceived to 
 pass through the centre of the spiral. See 
 
 pi. 4, fig. 10. 
 
 Barker’s Mill, — Apparatus for exhibiting 
 the rotatory motion produced by the running 
 of Contract a tube at its two extre- 
 
 mities, pierce it laterally about the middle of 
 its length, and solder to the hole an additional 
 tube, terminated by a funnel. Soften the prin- 
 cipal tube at the side opposite to the part that 
 waS pierced, and form there a conical cavity 
 by pressing the softened glass inward with the 
 
58 
 
 THE ART OF GLASS-BLOWING. 
 
 aid of a metallic rod. This cavity must be so 
 carefully made that the whole apparatus can be 
 supported on a pivot. Bend the contracted 
 ends of the tube horizontally^ and in different 
 directions, cut off their extremities at a proper 
 length, and slightly border the edges of the 
 orifices. See pi. 3, fig. 33. 
 
 You may produce this apparatus under a 
 different form, as may be seen at pi. 3, fig. 5. 
 
 Barometers. — Barometers serve to measure 
 the pressure of the atmosphere. The following 
 are the varieties most in use. 
 
 Cistern Barometer. — Take a tube about 
 thirty-two inches long, and at least one-third of 
 an inch in diameter, internally ; seal one of its 
 extiemities, free it with most particular care 
 from moisture, fill it with mercury, and make 
 the mercury boil in the tube, by heat, in order 
 to drive out every particle of air which might 
 be present. When the tube is full of mercury, 
 and the boiling has taken place, turn it upside 
 down, and plunge the open end into a cistern 
 also filled with mercury which has been boiled. 
 See pi. 2, fig. 4. 
 
 Dial (or Wheel) Barometer. — The tube 
 intended for this barometer should be very re- 
 gular in the bore. It should be thirty-nine 
 inches long. Close it at one end, and bend it 
 like the letter U at about thirty-two inches from 
 the sealed extremity. See pi. 2, fig. 5, and 
 Graduation of tlte Dial Barometer. 
 
THE ART OF GLASS-BLOWING. 
 
 59 
 
 Syphon Barometer. — Make use of such a 
 tube as might be employed for a Cistern Ba- 
 rometer ; solder to its open end a cylindrical 
 or spherical reservoir, and bend the tube close 
 to the point of junction in such a manner as to 
 bring the cylinder parallel with the tube. If 
 the reservoir is to be closed with a cover of 
 leather, cut off the remaining point of the cy- 
 linder, slightly widen the orifice, and then 
 border it. If no leather is to be applied, but 
 the point of the cylinder left open, it is neces- 
 sary, after the introduction of the mercury, to 
 draw otF the point abruptly, and to leave an 
 opening so small that mercury cannot pass by 
 it. PI. 2, fig. 6. 
 
 Stop-Cock Barometer. — This differs from 
 the preceding barometer only by having a stoo- 
 cock mounted in iron between the reservoir 
 and the tube. 
 
 Compound Barometers. — Blow a bulb at 
 each end of a barometer tube of about thirty- 
 three inches in length. Solder a small and 
 almost capillary tube to the point which termi- 
 nates one of the bulbs, and bend the great 
 tube very near this bulb. This must be done 
 in such a manner that the centre of one bulb 
 shall be thirty inches from the centre of the 
 other bulb. Introduce a quantity of mercury- 
 sufficient to fill the great tube and half the two 
 bulbs ; fill the remaining space in the last bulb 
 with alcohol. 
 
 You may give a different disposition to this 
 
60 
 
 THE ART OF GLASS-BL, OWING. 
 
 instrument. Divide a barometer tube into 
 two, three, or four pieces, and reunite the 
 pieces by intermediate capillary tubes, so as to 
 form a series of large and small tubes, soldered 
 alternately the one at the end of the other. 
 Then communicate to this compound tube the 
 form exhibited by pi. 3, fig. 25, and join, at 
 each superior bend, a little tube, for the con- 
 venience of easily filling the instrument with 
 mercury : seal these tubes as soon as the mer- 
 cury is introduced. The graduation of com- 
 pound barometers is made by bringing them 
 into comparison with a good standard baro- 
 meter. After taking two or three fixed points, 
 it is easy to continue the scale. 
 
 Gay Lussac’s Barometer. — Take a tube 
 which is very regular in the bore, four-tenths 
 of an incli in diameter, and thirty-five inches 
 and a half in length. Seal one of its extremi- 
 ties and draw out the other ; then cut the tube 
 at about two-thirds of its whole length from the 
 sealed end, and reunite the two pieces by 
 means of a capillary tube soldered between 
 them, the whole being kept in a line. See 
 pi. 2, fig. 1. Pierce laterally the part of the 
 tube which is drawn out, at some inches from 
 the base of the point, and force the margin of 
 the hole into the interior of the tube, by means 
 of a conical point of metal, in such a manner as 
 to form a little sunk funnel, of which the ori- 
 fice must be very small. After having intro- 
 duced the proper quantity of mercury into the 
 instrument, boil it, and assist the disengage- 
 
THE ART OF GLASS-BLOWING. 
 
 61 
 
 ment of the bubbles of air by agitating a line 
 iron wire within the tube. Then remove the 
 part of the tube which was drawn out, by 
 sealing the end of the wide part. Give to the 
 whole iiistrument the curvature indicated by 
 pi. 2, fig. 3. 
 
 Bunten’s Baro 31 Eter. — This instrument dif- 
 fers from the preceding but in one point, 
 namely, that the capillary tube is formed of 
 two soldered pieces, of which the one, passing 
 into the other, is terminated by a capillary 
 point. This arrangement is exhibited by pi. 2, 
 tig. 2. 
 
 Barometer pierced laterally for De- 
 monstrations. — Take a tube thirtj'-nine inches 
 long, with thick sides, and two-tenths of an 
 inch internal diameter. Seal it at one end, 
 and choke it at the distance of eight inches 
 therefrom. Pierce a hole in the tube about 
 twelve or sixteen inches from the choked part, 
 and solder to the hole an additional piece, 
 which can be closed by a cork or covered by 
 a piece of bladder. The instrument is repre- 
 sented by pi. 2, fig. 15. 
 
 Bell-Glasses for Experiments. — These 
 are pieces of tube sealed at one end, and 
 widened or bordered at the other. They are 
 extremely useful, and much employed in che- 
 mical experiments. They also supply the 
 place of bottles for preserving small quantities 
 ol substances. Sometimes they are required 
 
 G 
 
62 
 
 THE ART OF GLASS-BLOWING. 
 
 to be straight, as pi. 3, fig. 12, Sometimes 
 they need to be curved, as pi. 3, fig 29. This 
 is particularly the case when they are to be 
 employed as retorts, for which purpose the 
 sealed part should be made thin. PI. 3, fig. 6, 
 exhibits a retort with a tubulure. 
 
 Blowpipe. — We shall give in this article an 
 account of the various pieces of glass Avhich 
 form part of the blowpipe described in the 
 early part of this work. See pi. 1, fig. 19. 
 
 The beak C, which is employed with the 
 candlestick, is merely a bent tube, at the extre- 
 mity of which a bulb is blown. The bulb is 
 terminated by a point, the thickness of the 
 sides of which is augmented by turning it for a 
 long time in the flame. 
 
 As for the beak used with the lamp, it is 
 simply a bent tube C', of which the orifice has 
 been diminished by turning it round in the flame. 
 The point of this beak is not drawn out like 
 that of the beak described in the preceding pa- 
 ragraph, but is allowed to be thick, that it may 
 not melt in the flame of the lamp. 
 
 The tube D F has four tenths of an inch in- 
 ternal diameter, and is pretty thick in the sides. 
 You must commence by bordering and slightly 
 widening one of its extremities, and then pro- 
 ceed to choke it at about two inches from its 
 other extremity, taking care to give to the 
 choked part a figure as perfectly conical as 
 possible, in order that the valve may act well. 
 We have described the valve at length at p. 6. 
 
 The tube d is as much narrower than the 
 
THE ART OF GLASS-BLOWING. 
 
 63 
 
 tube D F as is necessary to permit it to pass up 
 and down within the latter. Its use is to 
 lengthen or shorten the tube for the convenience 
 of the blower. The lower end is wound 
 round with waxed thread, to make it fit air- 
 tight. The mouth-piece is executed by widen- 
 ing the end of the tube^ and then, while the 
 widened part is still soft, by pressing the two 
 sides obliquely, one against the other. By this 
 means you give to the mouth-piece a flattened 
 form, which adapts it better to the lips. The 
 tube is finished by slightly bending this extre- 
 mity. 
 
 In order that the bladder, or air reservoir, 
 may be conveniently and securely attached to 
 the tube E, you must take care to widen the 
 end of this tube, and to turn up the edges 
 strongly, by pressing the soft end against a 
 flat metallic surface. 
 
 Capsules. — These are very small mercury 
 funnels, of which the opening or neck has been 
 closed. To transform these funnels into cap- 
 sules, you must cut the neck as close as possi- 
 ble, and then soften, close, and flatten the 
 opening. In performing this operation, hold 
 the capsule by the edge with your pincers, and 
 employ a piece of metal to press the glass to- 
 gether and make it close the hole and form 
 the flat bottom of the capsule. See pi. 2, 
 fig. 23. 
 
 Another Method . — After having blown a 
 bulb at the end of a point, soften a narrow 
 
64 
 
 THE ART OF GLASS-BLOWING. 
 
 zone of the bulb, and then blow suddenly and 
 strongly into it ; by which means you separate 
 the bulb into two capsules, which only need to 
 be bordered. If you find any difficulty in pre- 
 senting to the flame the capsule which forms 
 the part of the bulb opposed to the point, you 
 can attach to it a little rod of glass, which you 
 can afterwards easily separate by a slight 
 smart blow. 
 
 Occasionally you will have to make capsules 
 ivith double sides, which will be described at 
 the article Nicholson’s Hydrometer. 
 
 Cartesian Devils. — Blow a bulb at the 
 extremity of a very small tube, and heat a por- 
 tion of the bulb, for the purpose of prolonging 
 it into a beak. This can be effected with the 
 aid of an auxiliary tube, which, on being join- 
 ed to the heated part of the bulb, carries away 
 with it the portion of glass w'hich adheres. 
 This portion of the bulb becomes thus pro- 
 longed into a little point, which must be cut at 
 its extremity, so as to leave a small opening. 
 The principal tube must be cut at the distance 
 of half an inch from the bulb, and the ends of 
 it must be drawn out and twisted into a ring. 
 Instead of forming laterally a little beak to the 
 bulb, you may pierce the tail, after twisting it 
 into the form of a ring, or you may manage in 
 such a manner as not to obliterate the canal of 
 the twisted part. In general, little enamel 
 figures are suspended to the ring of these 
 globes, as is represented by pi. 2, fig. 22. A 
 
THE ART OF GLASS-BLOWING, 
 
 G5 
 
 simple bulb, blown at the extremity of a small 
 portion of tube, can supply the place of the 
 Ludion or Cartesian devil. See pi. 2, fig, 8. 
 
 Communicating Vases. — Employ a tube of 
 a large diameter ; terminate one of its extre- 
 mities with a funnel, fashion the other like 
 the neck of a bottle ; and bend the tube into 
 the shape shewn by pi. 4, fig. 11. Then twist 
 some other tubes into various forms, according 
 to the end you propose to attain, and adjust 
 these tubes to the neck of the large tube by 
 means of corks, which have holes bored 
 through them. In this manner an exchange of 
 tubes is provided for various experiments. 
 
 Drofping Tubes. — The name dropping tube 
 is given to an instrument of glass which is very 
 much employed in chemistry, for the purpose 
 of transferring small quantities of liquor from 
 one vessel into another, without disturbing either 
 of the vessels. Dropping tubes are made of 
 a great variety of forms and sizes, according to 
 the purposes to which they are intended to 
 be applied. 
 
 Blow a bulb between two points, and then, 
 before the glass has regained its consistence, 
 lengthen the bulb into an oval form. Cut and 
 border the two points. 
 
 If the bulb, or reservoir, is to be so large 
 that it cannot be formed at the expense of the 
 thickness of the tube, and yet be sufficiently 
 strong, it must be blown separately from a 
 larger tube^ and then soldered to two smaller 
 g 2 
 
G6 
 
 THE ART OF GLASS-BLOWING. 
 
 tubes, one of which should have a certain cur- 
 vature given to it. See pi. 2 , fig, 20. 
 
 Sometimes a dropping tube is employed to 
 measure small quantities of liquid. In this 
 case the point should be drawn off abruptly, 
 and the scale should be marked on the shank 
 o” tube with spots of black enamel. 
 
 PI. 2, fig. 21, represents a peculiar variety 
 of dropping tube employed in some experi- 
 ments. It is made in the same manner as the 
 common dropping tubes, excepting that, when 
 the tail is formed, it is sealed at the extremity, 
 bent there into a ring, and then pierced at A. 
 
 PI. 3, fig. 26, represents another variety of 
 dropping tube, a description of which is unne- 
 cessary. 
 
 Fountains. — It will readily be understood 
 by those acquainted with the construction of 
 hydraulic apparatus, that, by means of a judi- 
 cious arrangement of glass tubes, a great va- 
 riety of fountains may be produced. The fol- 
 lowing are given as examples. 
 
 Fountain of Circulation. — Take a tube, 
 twenty-four or thirty inches long, nearly half an 
 inch in diameter, and with pretty thick sides ; 
 blow a bulb at one of its extremities, and bend 
 the other into a U, after having drawn it out as 
 indicated by pi. 3, fig, 4. Pierce the tube at 
 B, and join there a short piece adapted to re- 
 ceive a cork. Then prepare a bulb of the 
 same size as the first bulb, and solder it to the 
 extremity of a very long and almost capillary 
 
THE ART OF GLASS-BLOWING. 67 
 
 lube^ which you must bend in zig-zag, in such 
 a manner as to make it represent a Maltese 
 cross, a star, a rose, or any other figure that 
 may be suggested. The side of the bulb op- 
 posite to that which is attached to this twisted 
 tube, ought to be formed like the neck of a 
 bottle, in order that it may receive the drawn- 
 out part of the larger tube, which should enter 
 the bulb until the point of the large tube nearly 
 touches the neck of the little tube at its junc- 
 tion with the bulb. This disposition is shewn 
 in tlie figure. Seal now the other end of the 
 little tube to the bulb of the large tube ; then, 
 with a little cement or sealing-wax, close the 
 space between the bulb of the little tube and 
 the point of the large tube. The instrument 
 being thus prepared, as much alcohol, previ- 
 ously coloured red, must be inserted by the 
 neck b as is sufficient to fill one of the bulbs. 
 The neck is then closed with a cork, and a little 
 cement or sealing-wax. Or, instead of form- 
 ing this neck to the instrument, the additional 
 piece may be drawn out to a point, which per- 
 mits it to be sealed hermetically. 
 
 Fountain of Compression. — Introduce into 
 a tube of large diameter a piece of capillary 
 tube with thick sides. This must pass a little 
 beyond the extremity of the large tube, which 
 is to be softened and soldered to the other, so 
 that it shall be fixed concentrically. The com- 
 mon point is then to be drawn out. When the 
 tube is quite cold, and the small tube properly 
 fixed in the centre of the large one, cut the 
 
68 THE ART OF GLASS-BLOWING. 
 
 latter at a proper distance, border it, and choke 
 it near the end, which must be fashioned in 
 such a manner as to be capable of being com- 
 pletely closed by a cork. See pi. 2, fig. 29. 
 
 Intermitting Fountain. — This apparatus is 
 represented by pi. 3, fig. 16. Solder a cylin- 
 drical reservoir to the extremity of a capillary 
 tube, pierced at a, and sealed at its extremity. 
 Draw out abruptly the point of the reservoir, 
 and give it a very small orifice ; then give to 
 the capillary tube the form indicated by the 
 figure. Prepare next a funnel resembling a 
 mercury-funnel, but much larger ; choke the 
 neck of this funnel, and bend the tube into the 
 form of a syphon. 
 
 Hero’s Fountain. — Solder a bulb to the ex- 
 tremity of a tube, and transform the bulb into 
 a funnel. Close the funnel M'ith a cork, and 
 solder to the other end of the tube a bulb simi- 
 lar to the first. Next, solder a third bulb be- 
 tween two tubes, of which one must be twice 
 as long the other; solder the longer of these 
 tubes to the bulb of the first tube, and draw 
 out the point of the shorter tube. You have 
 now a long tube, with a funnel at one end, a 
 contracted point at the other, and two bulbs in 
 its length. Give to the whole apparatus the 
 form indicated by pi. 3, fig. 21. 
 
 Funnels. — It will be seen, upon looking 
 over the engravings, that funnels require to be 
 made for a great variety of instruments ; you 
 
THE ART OF GLASS-BLOWING. 
 
 69 
 
 ought therefore to acquire as soon as possible 
 the art of making them well. The following 
 are those most frequently required. 
 
 Retort Funnel. — Blow a bulb at the ex- 
 tremity of a tube ; present the superior hemi- 
 sphere of the bulb to the flame, and when it is 
 sufficiently softened, blow strongly into the 
 other end of the tube. The air will force its 
 way through the bulb, making a hole which 
 will be larger or smaller according to the extent 
 of surface which may have been softened. 
 The opening of the funnel being made thus, 
 there is nothing more to do than to adjust the 
 edges, which, in the present state, are both 
 fragile and irregular. This it is very easy to 
 do. The edges are softened, the most promi- 
 nent parts are cut off with the scissars, and the 
 parts which are thin are bent back on them- 
 selves, that they may become thicker. Upon 
 turning the funnel round in the flame, the 
 smaller irregularities give way, and the edges 
 become rounded. See pi. 2, fig. 24. 
 
 When the funnel is desired to be very large 
 in proportion to the size of the tube, a bulb is 
 made from a larger tube, and afterwards sol- 
 dered to the small tube, and transformed into a 
 funnel in the manner above described. 
 
 Funnel for introducing Mercury into 
 NARROW TUBES. — The mercury-funnel is repre- 
 sented by pi. 2, fig. 25. Blow a bulb between 
 two points 5 cut olT one of the points, and 
 
70 
 
 THE ART OF GLASS-BLOWING. 
 
 open the bulb at that place, in the manner de- 
 scribed in the preceding article. 
 
 Hydrostatic Funnel. — This is represented 
 by pi. 3, fig. 31. It is an instrument of con- 
 stant use in chemical experiments. Form a 
 funnel at the extremity of a tube in the manner 
 described above, having previously blown a 
 bulb near the middle of the tube. When this 
 has been done, bend the tube into the form 
 shown by the figure. 
 
 Hour-Glasses. — Blow four bulbs on a tube 
 close to each other ; open the two end bulbs 
 like funnels, and then form them into flat sup- 
 ports or pedestals, according to the method 
 described at the article Test-glass with a foot. 
 Obstruct entirely the canal which separates 
 one of these feet ; choke to a certain extent the 
 passage between the two remaining bulbs ; 
 and close the canal between the other foot and 
 the bulbs, after introducing the quantity of sand 
 which you have found to be necessary. See 
 pi. 3. fig. 13. 
 
 Hydraulic Ram. — This instrument is repre- 
 sented by pi. 4, fig. 15. Employ a tube about 
 six feet long, with thick sides and of large 
 diameter. Seal it at one extremity, k, and 
 border it at the other ; solder at p an addi- 
 tional piece, choked so as to receive a valve. 
 Pierce the tube at I ; draw it out, and fix a 
 funnel there ; then twist the tube into a spiral. 
 
THE ABT OP GLASS-BLOWING. 
 
 71 
 
 Form, on the other hand, a fountain of com- 
 pression, o, and a funnel, m ; and tix both of 
 these pieces by means of sealing-wax, as soon 
 as the two valves p and I have been put into 
 their places. 
 
 Hydrometers. — Hydrometers are instru- 
 ments which, on being plunged into liquids, 
 indicate immediately their density or specific 
 gravity. Areometers differ from hydrometers 
 sometimes in graduation, sometimes merely in 
 name. The following are examples of hydrome- 
 ters, of which a great many varieties are in use. 
 
 Baume’s Hydrometer. — Make a cylinder 
 between two points, and solder it to the extre- 
 mity of a tube with thin sides, and which must 
 be very regular on the outside. Close the 
 open part which is to form the stalk of the 
 hydrometer with a little wax. See pi. 1, fi^. 
 9 and 15. When the soldering, which must 
 be well done, is complete, and the stalk well 
 centered, choke the reservoir at a little distance 
 from the base of the point, by drawing it out 
 in such a manner as considerably to diminish 
 the canal in this part. Remove then the ball 
 of wax which closed the tube, draw off the 
 point of the cylinder, and make the part which 
 was pulled away from the cylinder by the 
 choking, into a bulb, by blowing with precau- 
 tion into the tube. If the reservoir is required 
 to be spherical instead of cylindrical, it must 
 be softened and expanded by blowing. When 
 it is intended to ballast the instrument with 
 
72 
 
 THE ART OF GLASS-BLOWING. 
 
 mercury, the canal must be completely stopped 
 at the point where it is choked. In this case, 
 the part drawn away from the cylinder is ex- 
 panded into a bulb by blowing through the 
 extreme point, which is to be cut off after the 
 instrument is completed. 
 
 In the first case, you ballast the instrument 
 with lead shot, which you fix in the lower bulb 
 by means of a little wax, which closes the 
 canal at the choked part. In the second case, 
 after having proved the ballast by putting it 
 first into the large reservoir, it is removed into 
 the little bulb, and the latter is immediately 
 sealed. 
 
 One of the essential conditions of a good 
 hydrometer is that the stalk should keep a per- 
 fectly vertical position when the instrument is 
 plunged in water. If, therefore, on proving 
 the ballast, you perceive the stalk to rest ob- 
 liquely, you must take care, on retiring it from 
 the water, to wipe it dry, and to present the 
 choked part between the cylinder and the little 
 bulb to the flame ; when it is softened, it is 
 easy, by giving it a slight bend in the direction 
 where the stalk of the hydrometer passes from 
 the vertical, to rectify the defect. 
 
 Finally, when the instrument is ballasted, 
 you must seal the stalk, after having fixed in its 
 interior the strip of paper which bears the gra- 
 duated division. 
 
 This method of operation serves equally for 
 all the areometers known under the names of 
 areometer of Baiime, pese-sels, pese-liqueiirs, 
 pese-acides, miA hydrometers, which differ only 
 
THE ART OF GLASS-BLOWING. 
 
 73 
 
 in the scheme of their graduation. As to the 
 size and the length of the stalks, they depend 
 upon the dimensions you desire to give to the 
 degrees of the scale, and upon the use to which 
 the instruments are destined. For the areome- 
 ter of Baume, and for the pese-sels, the stalks 
 are generally thicker and shorter than for hy- 
 drometers. PI. 4, fig. 19, 20, and 21, repre- 
 sent different hydrometers. 
 
 Nicholson’s Hydrometer. — Solder a bulb 
 to the extremity of a capillary tube ; open if so 
 as to form a very wide funnel, or rather capsule ; 
 border the edges, and melt the point of junc- 
 tion with the tube so as to close the opening of 
 the latter. Solder the other extremity of the 
 tube to a cylindrical reservoir. Soften the 
 point at the lower extremity of the cylinder, 
 and obstruct the canal so as to convert the point 
 into a glass rod ; bend this rod into a hook. 
 Now blow a bulb at the end of a point, as if 
 to make a mercury funnel; but, after having 
 softened the hemisphere of the bulb opposite to 
 the point, and placed the latter in the mouth, 
 instead of blowing into the bulb so as to make 
 a funnel, strongly suck air from the bulb : by 
 this means the softened part of the glass is 
 drawn inwards, and you obtain a capsule with 
 double sides; as exhibited by pi. 2, fig. 17. 
 This capsule must have a small handle fastened 
 across it, by which it may be hung to the 
 hook formed at the bottom of the cylinder de- 
 scribed above. 
 
 This hydrometer being always brought to 
 
 H 
 
74 
 
 THE ART OF GLASS-BLOWING. 
 
 the same level, the point to which it must be 
 sunk in the liquid experimented with, is marked 
 on the stalk by applying a little spot of black 
 enamel. The instrument is represented by 
 pi. 4, fig. 23. A variation in form is shewn 
 by pi. 4, fig. 22. 
 
 Hydrometer with two Branches. — To 
 measure the relative density of two liquids 
 which have no action on each other, you employ 
 a simple tube, bent in the middle and widened 
 at its two extremities. See pi. 2, fig. 11. 
 
 Hydrometer with three Branches. — This 
 consists of a tube bent in such a manner that 
 the two branches become parallel. To this lube 
 another is soldered at the point of curvature, 
 and is bent in the direction exhibited by pi. 2, 
 fig. 12. When the two branches are put into 
 different liquids, and the operator sucks air 
 from the third branch, the two liquids rise in 
 their respective tubes to heights which are 
 in the inverse ratio of their specific gravities. 
 
 Hydrometer with four Branches. — This 
 is merely a tube bent three times, and widened 
 at its extremities. PI. 2. fig. 13. 
 
 To graduate hydrometers with two, three, 
 and four branches, you have to divide their 
 tubes into a certain number of equal parts. 
 
 Manometers.— -Make choice of a tube nearly 
 capillary, very regular in the bore, and with 
 
THE ART OF GLASS-BLOWING. 
 
 75 
 
 sides more or less thick, according to the degree 
 of pressure which it is to support. Seal this 
 tube at one end, blow a bulb with thick sides 
 near the middle, and curl it in S, just as is re- 
 presented by pi. 2, fig. 9. For manometers 
 which serve to measure the elasticity of the 
 air under the receiver of the air-pump, what 
 is generally employed is a tube closed at one 
 end and bent into a U. PI. 2. fig. 10. You 
 should take care to contract these at some dis- 
 tance from the sealed part, in order to avoid 
 the breaking of the instrument on the sudden 
 admission of air. Manometers are graduated, 
 as will be explained in the sequel. 
 
 Mariotte’s Tube. — This is represented by 
 pi. 2, fig. 7. It consists of a tube thirty-nine 
 inches long, closed at one end, bordered and 
 widened at the other, and bent into a U at the 
 distance of eight inches from its sealed end. 
 The graduation of this instrument will be de- 
 scribed hereafter. 
 
 Phosphoric Fire-Bottle. — ^This is a short 
 piece of tube closed at one end, and widened 
 and bordered at the other, in such a manner as 
 to receive a cork. PI. 3, fig. 34. It is in this 
 little vessel that the phosphorus is enclosed. 
 Glasses of this form can be employed in a great 
 variety of chemical experiments. 
 
 Pulsometer. — This instrument consists of a 
 tube, of which each extremity is terminated by 
 a bulb ; it is partly filled with nitric ether, and 
 
76 
 
 THE ART OF GLASS-BLOWING, 
 
 sealed at the moment when the ebullition of the 
 ether has chased the atmospheric air wholly from 
 the interior of the vessel. PI. 2 , fig. 16. 
 
 Pump. — Solder a cylinder, B (pi. 4, fig. 12), to 
 the extremity of a small tube, C, and form their 
 point of coincidence into a funnel, to which you 
 will adapt a valve. Pierce the wide tube or 
 body of the pump at D, and solder there a 
 piece of tube bent into an elbow and widened 
 at the other end into a funnel, which is to be 
 furnished with a second valve, as is represented 
 in the figure. Prepare then the fountain of 
 compression E, and, by means of a cork and a 
 little sealing-wax, fix it upon the branch D. To 
 prepare the piston. A, blow a bulb at the end of 
 a tube, flatten the end of the bulb, and choke it 
 across the middle, in order to form a place 
 round which tow can be twisted, to make it fit 
 tlie tube air-tight. Finish the piston by twist- 
 ing the other end of the tube into a ring, as at 
 A. The valves are formed of small cones of 
 cork, or wood, having in the centre an iron 
 wire of sufficient size and weight to enable 
 them to play well. 
 
 Retort for Chemical Experiments.' — Plate 
 3, fig. 9, represents a combination of a large 
 and a small tube, forming a retort, which can be 
 employed with much advantage in many chemi- 
 cal experiments. When a gas is to be distilled 
 by means of such a vessel, the ingredients are 
 put into the wide tube, which is previously 
 closed at one end, and then the other end of the 
 
THE ART OF GLASS-BLOWING. 77 
 
 tube is either drawn out or soldered to a nar- 
 row tube. PI. 3, fig. 8 and 29, represent such 
 vessels under different forms. Very often a sort 
 of retort can be formed by joining a wide tube 
 to a long bent narrow tube, by means of a 
 cork. 
 
 Tubulated Retort. — This is represented by 
 pi. 3, fig. 6. Prepare a retort, such as is de- 
 scribed in the preceding article, but one which 
 is bent near the closed end ; pierce it at A 
 (fig. 6), and solder there a little piece of tube 
 previously drawn out and sealed, such as is re- 
 presented by pi. 1, fig. 11. V<^hen the solder- 
 ing is finished, soften the end of the little tube, 
 pierce it, and fashion it into a bottle neck, so that 
 it can be closed by a cork. Finish the instru- 
 ment by forming the open end according to the 
 purpose to which it may be destined. In the 
 figure, the end is represented as drawn out for 
 the convenience of blowing into the retort to 
 pierce the tubulure. 
 
 Rumford’s Thermoscope. — This instrument 
 is represented by pi. 3, fig. 35. It is necessary 
 to take a tube almost capillary, to solder a bulb 
 at each extremity, to pierce it laterally at h, and 
 to solder there a piece of tube previously drawn 
 out, but of which yon open the point for the 
 purpose of finishing the sealing of the bulb A. 
 After doing this, you bend the two branches, 
 as shewn in the figure. When the liquid has 
 been introduced into the instrument, you must 
 H 2 
 
78 
 
 THE ART OF GLASS-BLOWING. 
 
 seal the little piece of tube which serves as a 
 reservoir. 
 
 This instrument can be made in another man- 
 ner. Take two pieces of tube, one of them 
 twice as long as the other ; solder a bulb at one 
 end of each of these tubes, and at about the 
 third part of the length of the long tube, parting 
 from the bulb, bend it at a right angle ; pierce 
 the little tube at a corresponding distance, and 
 solder to the hole the end of the long tube. The 
 soldering being finished, and the whole system 
 having the form indicated by pi. 3, fig. 35, in- 
 troduce, by the open end of the short tube, a 
 small quantity of coloured acid, and then seal 
 the end of the short tube, which serves as a 
 reservoir. 
 
 The interior diameter of the tubes which are 
 generally employed as thermoscopes, is one- 
 eighth or one-twelfth of an inch. The mode 
 of graduation is described in a subsequent 
 chapter. 
 
 Syphons. — The simple syphon is a glass tube 
 bent, at a little distance from the middle, into a 
 form which is intermediate between those of 
 
 and the legs being stretched apart like 
 those of the latter, but the bend being rounded 
 like that of the former. The tube is bent near 
 the middle, and not exactly at the middle, in 
 order that the legs may be of unequal lengths; 
 an arrangement which is indispensable. Sy- 
 phons are made of difibrent lengths and diame- 
 ters, ior various purposes. They can be made 
 
THE AllT OF GliASS-ULOWING. 
 
 79 
 
 of tubes so capillary that it is sufficient to put 
 them into water to make them act : the liquid 
 rises in them by capillary attraction^ and does 
 not require to be sucked through the tube, as 
 it does when large syphons are employed. 
 
 WiRTEMBERG Syphon. — This syphon is the 
 same as the simple syphon, excepting that the 
 two branches are of equal length, and are bent 
 in U at both extremities. PI. 3, fig. 22. 
 
 Syphon with three Branches. — This in- 
 strument is represented by pi. 2, fig. 19. Close 
 a tube at one end and draw it out at the other ; 
 pierce it at some inches from the contracted ex- 
 tremity, and solder to the hole a little tube of 
 which the other end has been closed with wax. 
 Give the tube the bend necessary to constitute a 
 syphon, and open the two branches. The sol- 
 dering of the two tubes is facilitated by giving 
 to the extremity of the little tube a bend which 
 adapts it to be applied parallel to the large tube. 
 When the syphon is desired to be well finished, 
 the month-piece of the little tube must be bor- 
 dered and widened, and a bulb must be blown 
 near the mouth-piece. 
 
 Syphon with Jet of Water. — This instru- 
 ment is represented by pi. 3, fig. 1. Take a 
 tube of a large diameter, close it at one end, 
 and draw it out at the other. Cut the contract- 
 ed part in such a manner as to be able to intro- 
 duce, through the orifice, the extremity, also 
 drawn out^ of another tube, which should be 
 
80 
 
 THE ART OF GLASS-BLOWING. 
 
 almost capillary. Solder these together in such 
 a manner that the point of the small tube shall 
 remain fixed about an inch within the interior of 
 the reservoir. Pierce again the latter, at B, 
 and solder there another branch of the same 
 diameter as the former ; but fix it in such a 
 manner that its side shall be contiguous to the 
 side of the reservoir. Finally, give to the 
 branches the bend represented by the figure. 
 
 Spoons. — Solder a bulb to the extremity of 
 a capillary tube ; open the bulb as for a funnel, 
 but make the opening laterally. Cut with scis- 
 sars the edges of the part blown open, and in 
 such a manner as to form a spoon or a ladle, 
 according as the bulb had the form of a sphere 
 or an olive. This instrument is useful for 
 taking small quantities of acids. PI. 3, fig. 1 1. 
 
 Spirit Level. — The spirit level is repre- 
 sented by pi. 2, fig. 28. Choose a piece of 
 tube very straight, and with sides precisely of 
 the same thickness in all parts. Seal it at one 
 end, and draw it out abruptly at the other. 
 Fill it almost entirely with alcohol, and seal the 
 point by the jet of a candle. 
 
 Test Glass with a Foot. — Take a tube 
 drawn out at one end ; choke it at an inch 
 from the base, in such a manner as to obstruct 
 the canal almost entirely. PI. 1, fig. 12. Cut 
 off the point, close the opening, and soften the 
 whole end completely ; then blow it into a 
 bulb and burst it into a funnel. Now present 
 
THE ART OF GLASS BLOWING. 
 
 81 
 
 the contracted part to the fire, so as totally to 
 close the passage. Border and soften the fun- 
 nel, and by pressing it against a flat plate of 
 metal give it the form of a foot, or pedestal. 
 Cut the tube at the length which you desire the 
 test-glass to have, and border the edges of the 
 opening. This is a very useful little chemical 
 instrument. It is represented by pi. 3, fig. 10. 
 
 Thermometers. — Thermometers are instru- 
 ments employed for appreciating changes of 
 temperature, either in the atmosphere or in sub- 
 stances which we have occasion to examine. 
 The following are the principal varieties now 
 employed. 
 
 Ordinary Thermometer. — If you desire to 
 make standard thermometers, you must have 
 capillary tubes of perfect accuracy in the bore. 
 You are assured of regularity in the diameter 
 of a tube when a drop of mercury, made to 
 pass along the canal by means of a gentle in- 
 clination, or by air blown from an Indian-rub- 
 ber bottle, gives everywhere a metallic column 
 of the same length. 
 
 For ordinary thermometers this precaution is 
 superfluous. In all cases you employ a tube 
 more or less capillary, at one of the extremities 
 of which you blow or solder a spherical or cy- 
 lindrical reservoir. See pi. 4, fig. 1 and 2. 
 You fill the instrument with well-purified mer- 
 cury, or alcohol, which you boil in the tube, in 
 order to chase the air from it. As it is neces- 
 sary to heat the instrument throughout its 
 whole length, you must place it on a railing of 
 
82 
 
 THE ART OF GLASS-BLOWING. 
 
 iron wire, inclined in the manner represented by 
 pi. 4, fig, 14, and covered with burning char- 
 coal, or red-hot wood ashes. It is better, how- 
 ever, to employ a kind of muff, formed of two 
 concentric wire grates, between which you put 
 burning charcoal, and reserve the centre for the 
 instrument. The tube is thus kept in a vertical 
 position, which allows the bubbles of air to 
 escape with more facility. An iron wire is 
 made use of to fasten the tube precisely in the 
 centre of the column of fire. The operation is 
 considerably promoted by soldering a little 
 funnel to the upper extremity of the thermoihe- 
 ter tube; and, in order to avoid the interrup- 
 tion of the column of liquid by bubbles of air, 
 it is better to give to the superior part of the 
 reservoir the form of a cone (pi. 4, fig. 3), ra- 
 ther than to preserve the completely spherical 
 form indicated by pi. 4, fig. 2. 
 
 When the ebullition has expelled all the air 
 which was contained in the mercury, or alcohol, 
 you immediately plunge the open extremity of 
 the instrument into a vessel filled with one or the 
 other of these liquids ; or, instead of this, you 
 pour the liquid into the funnel, in order that the 
 instrument may be quite filled at the common 
 temperature. You then cut off the funnel, if 
 one has been used, and, by properly elevating 
 the temperature of the reservoir, you expel so 
 much of the liquid that the summit of the co- 
 lumn rests at the point which you desire to 
 make choice of for the mean temperature : this 
 operation is termed regulating the course of 
 the thermometer. 
 
 There are two methods of closing thermome- 
 
THE ART OF GLASS-BLOWING. 
 
 83 
 
 ters : you may either produce a vacuum above 
 the column of mercury j, or you may allow air 
 to remain there. In the first case^ after having 
 drawn out the end of the tube, you heat the 
 liquid until a single drop passes out of the. 
 opening ; you then instantly bring the point 
 into the jet. and seal it. 
 
 In the second case, you seal the instrument 
 at the ordinary temperature, and having pre- 
 viously raised to a reddish-white heat the 
 button of glass which is formed by the sealing, 
 you suddenly elevate the temperature of the 
 mercury. The liquid, on rising, compres.ses 
 the enclosed air, which dilates the red-hot 
 button at the summit of the tube, and produces 
 a species of reservoir. This reservoir is indis- 
 pensably necessary when you leave air above 
 the column of liquid, in order to provide 
 against the bursting of the instrument on those 
 occasions when the temperature of the mercury 
 comes to be considerably elevated. See pi. 4, 
 fig. 13. 
 
 Dial Thermometer. — Terminate a piece of 
 tube, of six-tenths of an inch in diameter, with 
 two points, and solder to one of these points a 
 tube one-eighth of an inch in diameter and six 
 inches long ; close the end of this small tube, 
 and, heating a zone of the reservoir, near the 
 base of the other point, blow a bulb there. 
 Cut off the point by which you have blown, at 
 a little distance from the bulb ; open and bor- 
 der the end of the narrow tube, and bend it 
 into a U. See pi. 4, fig. 16. 
 
84 
 
 THE AKT OF GLASS-BLOWING. 
 
 Fill the bulb and the reservoir with alcohol, 
 and add a drop of mercury which fills a cer- 
 tain space in the narrow tube. This mercury 
 bears on its surface a little iron weight, to 
 which a thread is I'astened; the other end of 
 this thread passes over a pulley, whose axis 
 turns a needle. The expansion or contraction 
 of the alcohol causes the mercury to rise and 
 fall, and consequently produces a movement of 
 the needle or index of the dial. This thermo- 
 meter is graduated like the others, by being 
 brought into comparison with a standard ther- 
 mometer. 
 
 Chemical Thermometer. — This instrument 
 is merely a common thermometer, the divisions 
 of which, graduated on paper, are enclosed in 
 a very thin glass tube, to hinder them from 
 being altered or destroyed when the instrument 
 is plunged into liquids. PI, 4, fig. 4, 5, 6, and 
 7, represent chemical thermometers of various 
 kinds. 
 
 The case of the thermometer can be made 
 in two different ways. According to the first, 
 you take a tube of a pretty large diameter, and 
 with very thin sides ; you draw out one end and 
 obliterate the point, which you bend into a 
 ring, in a direction perpendicular to that of the 
 case ; you pass through this ring the stalk of 
 the thermometer, which is thus placed parallel 
 to the large tube. After having fixed the gra- 
 duated scale in the interior of the case, by 
 means of a small drop of sealing-wax, which 
 has been dropped on the slip of paper, and 
 
THE ART OF GLASS-BLOWING. 
 
 85 
 
 which, being supported against the side of the 
 case, needs only to be warmed to adhere there 
 and fix the scale securely to its envelope, you 
 close the upper extremity of the case by draw- 
 ing it out, obliterating the canal and soldering 
 it to the thermometer tube which has been in- 
 troduced into the ring at the lower end of the 
 case. You heat the connecting piece till it is 
 soft, and then push the thermometer up and 
 down until the zero marked on its tube cor- 
 responds with the zero marked on the scale 
 within the case. See pi. 4, fig. 6 and 7. 
 
 The second method of making the case is as 
 follows : — You take a tube with thin sides, and 
 sufficiently large to contain the entire thermo- 
 meter ; you draw out the tube at one end, and 
 choke it at some distance trom the point of the 
 contracted part. This you must do in such a 
 manner as to form a little bulb, which is to be 
 ballasted in the manner described at the article 
 Hydrometers. After having introduced into 
 the case a little ball of cotton, you place there- 
 in the thermometer, furnished with its scale, 
 and in such a manner that the reservoir rests on 
 the cotton. You terminate the upper end of 
 the case either with a ring or by a contraction 
 which permits the instrument to be suspended 
 by a cord. See pi. 4, fig. 4 and 5. 
 
 Spiral Thermometer. — Take a tube which 
 is not capillary, but which has thin sides ; close 
 one of its ends, and bend it round by pie.ssing 
 it with a metallic rod ; continue to bend it 
 round till it has made several turns, all in the 
 1 
 
86 
 
 THE ART OF GLASS-BLOWING. 
 
 same plane. See pi. 1, fig. 13. The latter 
 turns may be managed with the fingers instead 
 of the metallic rod. When the reservoir so 
 formed is sufficiently large, solder to the end of 
 it a capillary tube, which you point in a direc- 
 tion perpendicular to that of the axis of the 
 spiral. The instrument is represented by pi. 4, 
 fig. 8. 
 
 Pocket Thermometer. — The pocket ther- 
 mometer differs in nothing from the thermome- 
 ter just described, except that the capillary tube, 
 instead of passing away from the spiral in a 
 straight line, is turned round, so as to form a 
 continuation of the spiral. See pi. 4, fig. 17. 
 
 Maximum Thermometer. — This instrument 
 consists of an ordinary mercurial thermometer, 
 bent at a right angle near the origin of the re- 
 servoir, and in the horizontal column of which 
 a little steel or iron rod has been introduced: 
 this rod, by gliding in the tube, where it ex- 
 periences very little friction, serves as an index. 
 Since this index does not permit the instrument 
 to be sealed with the vacuum above the mer- 
 cury, you must terminate the sealing by a little 
 reservoir, as we have described at the article on 
 the second method of closing thermometers. 
 The instrument is represented by pi, 4, fig. 24. 
 
 Minimum Thermometer. — This instrument 
 is constructed pretty nearly in the same man- 
 ner as the preceding. The liquid, however, 
 must be alcohol, and the index a little rod of 
 
THE ART OF GLASS-BLOWING. 87 
 
 enamel, which ought not to be quite so large as 
 the bore of the thermometer tube. You seal 
 the tube by making a vacuum above the column. 
 
 Bellani’s Maximum Thermometer. — This 
 thermometer is represented by pi. 4, fig. 9. 
 Take a tube which is very regular, and about 
 one-eighth or one-twelfth of an inch diameter in 
 the bore ; solder a reservoir at each end, one 
 of them much larger than the other; make a 
 bend near the large reservoir, and then fill the 
 instrument with alcohol to A. Above that, 
 place the first index, which consists of a very 
 small piece of tube closed at one end and cut 
 otf square at the other. In the interior of this 
 tube the two ends of a hair are fixed, by means 
 of a little rod of iron, which is pushed into the 
 tube. Introduce a quantity of mercury above 
 this index, make the bend B, add again mer- 
 cury as far as C, then another index similar to 
 the first. Finally, fill the rest of the tube and 
 the half the little reservoir with alcohol, and 
 seal the point. 
 
 Differential Thermometer. — This instru- 
 ment is represented by pi. 3, fig. 14. Take a 
 tube ten or twelve inches long, and one-eighth 
 or one-twelfth of an inch internal diameter ; 
 blow a b\db at one end, and bend the tube at a 
 right angle towards the fourth part ot its length. 
 Prepare a second tube in the same manner, and 
 solder the bent ends together, so as to form a 
 single tube with a bulb at each end, having pre- 
 
88 
 
 THE ART OF GLASS-BLOWING. 
 
 viously poured into one of the bulbs a small 
 quantity of sulphuric acid tinged red. 
 
 Instead of following the above method, you 
 may take a single tube of twenty or twenty- 
 four inches in length, and of the above-men- 
 tioned diameter ; you solder a bulb at each end, 
 bend the tube tmce till it represents the figure, 
 pour in the acid, and then seal the open points. 
 The graduation of the differential thermometer, 
 as well as of all the other thermometers, is de- 
 scribed in a subsequent section. 
 
 Tube for Crystallizing Spermaceti, — 
 Take a little capillary tube ; curl one of its ends 
 into a ring, and solder the other to a cylindri- 
 cal reservoir, two-thirds of the capacity of 
 which you fill with very pure spermaceti dis- 
 solved in sulpliuric ether; you then seal the 
 point of the reservoir. See pi. 3, fig. 27. 
 
 Tube for demonstrating the non-con- 
 DUCTABiLiTY OF Heat BY LiQUiDs — This is re- 
 presented by pi. 2, fig. 26, It is a tube sealed 
 at one end, bordered at the other, and bent in 
 such a manner as conveniently to permit the 
 upper part of a column of liquid to be exposed 
 to heat. 
 
 Tube for estimating the Density op 
 Vapours, — Represented by pi. 2, fig. 14. It 
 is merely a tube sealed at one end, bordered at 
 the other, and bent as shewn by the figure. 
 
THE ART OF GLASS-BLOWING. 
 
 89 
 
 Tubes for exposing Substances to Heat 
 AND Gases. — This instrument consists of a 
 tube bent in the middle into a U. PI. 3, fig. 3. 
 It is much employed in chemistry, for con- 
 taining substances which we wish at the same 
 time to expose to an elevated temperature and 
 to the action of certain gases. This tube can 
 also be employed for cooling gases, or liquids, 
 in distillation ; the bent part being, in this case, 
 dipped into water or a freezing mixture, or en- 
 veloped in wet paper or cloth. 
 
 Tubes for the Preservation of Objects 
 OF Natura_l History, or of Chemical Pre- 
 parations. — Take a tube of which the width 
 and length corresponds with the object which is 
 to be enclosed; draw it out at one end, and, 
 after having obstructed the point, twist it into a 
 ring. Intr oduce the object by the open extre- 
 mity, which you must afterwards draw out; 
 fill the tube with the liquid necessary to pre- 
 serve the object, and then seal the point. See 
 pi. 2. fig. 27. 
 
 If you desire to have the power of taking out 
 the object at will — as, for example, when grain 
 is preserved, or when, in chemistry, the tube is 
 employed to contain salts and other compounds, 
 of which small quantities are now and then re- 
 quired for use — you do not seal the end of the 
 receiver, but border it in such a manner that it 
 can be closed by a cork. 
 
 In some cases a cork is not sufl&cient to se- 
 cure the sirbstance from the action of air : it 
 must then be assisted with a little cement. By 
 
 I 2 
 
90 
 
 THE ART OF GLASS-BLOWING. 
 
 melting together two parts of yellow wax, one 
 part of turpentine, and a small (juantity of 
 Venetian red, a very useful cement for such 
 purposes is obtained. 
 
 It is sometimes necessary to suspend the ob- 
 jects enclosed within the tube : you then intro- 
 duce a little glass hook, the tail of which you 
 solder to the upper extremity of the tube ; 
 managing this operation at the same time that 
 you make the external ring for the support of 
 the instrument. By turning the hook round 
 cautiously, which is done when the end of the 
 tube is in a soft state, and by cooling the whole 
 with care, you may succeed in fixing the hook 
 in the centre of the tube. See pi. 3, fig. 20. 
 
 Tube for emptying Eggs. — It is a simple 
 tube, drawn out to a capillary point at one end, 
 and bent there into a V. See pi. 3, fig. 23. 
 
 The application which the author has made 
 of this instrument, and of the tube represented 
 by pi. 3, fig. 26, has been shewn in a memoir 
 inserted in the Annales des Sciences Natu- 
 relles, Tom. XV. Novembre 1828, concern- 
 ing a new method of preparing and rendering 
 durable collections of eggs destined for cabi- 
 nets of Natural History. 
 
 Vial of the Four Elements. — This instru- 
 ment is represented by pi. 2, fig. 27. Take a 
 tube drawn out at one end, obstruct the canal 
 two inches from the extremity, and twist the 
 contracted part into a ring. Draw out the 
 other end of the tube, introduce the proper 
 
THE ART OF SLASS-BLOWING. 
 
 91 
 
 liquids, remove the point of the tube, and seal 
 it. The liquids generally employed for filling 
 the vial of the four elements are, 1. Mercury ; 
 2. A very concentrated solution of carbonate of 
 potash ; 3. Oil of turpentine ; 4. Alcohol. A 
 portion of air is also allowed to remain in the 
 tube. 
 
 Water Hammer. — PL 2, fig. 18, is a re 
 presentation of this instrument. Choose a tube 
 of a good diameter, and with thick sides ; seal 
 it at one end and draw it out at the other. 
 Blow a bulb at the base of the contracted part ; 
 then, having put a quantity of water in the 
 tube, let it boil therein, to expel the atmosphe- 
 rical air. When you imagine that all the air 
 has been expelled, and that nothing remains in 
 the tube but steam and water, seal the open 
 point. 
 
 When you have to seal a tube in this man- 
 ner, you should be careful to draw out the ex- 
 tremity of the tube somewhat abruptly, and 
 leave a very small opening, so that it shall be 
 sufficient to expose the point to the jet of a 
 candle blown by a mouth blowpipe, to have the 
 sealing completely and suddenly effected. You 
 can afterwards round this sealed part by turn- 
 ing it in the flame of the lamp, provided, how- 
 ever, that you have preserved a sufficient thick- 
 ness of glass at the sides of the point. If you 
 omit to take this precaution, the pressure of the 
 atmosphere, acting with great force on the 
 softened glass when it is unsupported by the 
 partial vacuum within the tube, is capable of 
 
92 
 
 THE ART OF GLASS-BLOWING. 
 
 producing such a flattenings or even sinking in 
 of the matter, as could not subsequently be rec- 
 tified ; except, indeed, by heating simultane- 
 ously the liquid contained in the tube and the 
 glass to be mended, which is an operation of a 
 very delicate description. 
 
 Welter’s Safety Tubes. — After having 
 closed a tube at one end and drawn it out at 
 the other, give it the curvature exhibited by 
 plate 3, fig. 18. Pierce it then laterally, in the 
 middle of the part a b, and solder there the ex- 
 tremity of a tube, to the other end of which a 
 funnel has been soldered : it is necessary that 
 the funnel be closed by a cork. The soldering 
 being terminated, a bulb must be blown and 
 the tube bent in S, in the manner shewn by the 
 figure. Then open the closed end, and cut off 
 the contracted point. 
 
THE 
 
 ART OF GLASS-BLOWING. 
 
 V . — Graduation of Chemical and Philoso- 
 phical Instruments^ 
 
 OF THE SUBSTANCES EMPLOYED IN THE PREPA- 
 RATION OF THESE INSTRUMENTS. 
 
 Before proceeding to the subject of gradua- 
 tion, it is necessary to say a few words respect- 
 ing the substances which are generally em- 
 ployed to fill a variety of instruments, particu- 
 larly barometers and thermometers. 
 
 Mercury. — It ought to be completely puri- 
 fied from all foreign substances. You can 
 separate it from the dust it may contain by 
 passing it through a piece of chamois leather; 
 you tie a very hard knot, and by pressure oblige 
 the mercury to pass out in a fine rain. This 
 process is sufficient for the purification of mer- 
 cury which merely contains extraneous bodies 
 in suspension ; but it is not sufficient when the 
 mercury to be purified contains tin, lead, or 
 other metals, in solution. It is then necessary 
 to distil the mercury ; upon which the fixed 
 
94 THE ART OF GLASS-BLOWING. 
 
 metals remain behind. The oxide of mercury 
 produced by the distillation is removed by agi- 
 tating the distilled metal with sulphuric acid, 
 and subsequently washing it with a large quan- 
 tity of water, till all the acid is removed ; it is 
 then dried as completely as possible with blot- 
 ting-paper, and afterwards is moderately 
 warmed. 
 
 Alcohol ought to be very pure and well rec- 
 tified. It is necessary to colour it, because, 
 being colourless of itself, it could not be seen 
 in capillary tubes. To colour alcohol, you in- 
 fuse carmine in it, and, after some time, decant 
 or filter the clear solution. The liquid should 
 be perfectly transparent, and free from all ex- 
 traneous substances. It is not proper to em- 
 ploy alcohol in the construction of standard 
 thermometers ; mercury being much preferable. 
 
 Sulphuric Acid . — It is made use of for the 
 differential thermometer, and the thermoscope 
 of Rumford. It has the advantage of being 
 lighter than mercury, and very slightly volatile : 
 these two qualities, joined to its tendency to 
 absorb the vapour of water, render it very 
 proper to be employed for various instruments. 
 It must be very concentrated, and tinged red 
 by carmine. 
 
 Ether. — Sulphuric and nitric ether, with 
 which some small instruments are filled, are 
 merely employed to shew with what facility 
 these liquids are brought to their boiling point. 
 
 Of Graduation in general. — Graduation, 
 generally speaking, consists in dividing lines. 
 
THE ART OF GLASS-BLOWING. 
 
 95 
 
 surfaces, and capacities, into a certain number 
 of equal or proportional parts. It is not our 
 intention to treat here of the methods furnished 
 by practical geometry for effecting such di- 
 visions with mathematical accuracy ; these 
 methods are known to every body. We shall 
 coniine ourselves to describing the processes of 
 graduation which are peculiar to the instruments 
 constructed by the glass-blower. 
 
 Examination op the Bore of Tubes. — 
 We have already observed, that, for standard 
 thermometers and other instruments which re- 
 quire to be made very accurate, it is necessary 
 to employ tubes which are extremely regular in 
 the bore. When a drop of mercury, passed 
 successively along all parts of the tube, forms 
 everyw'here a column of the same length, the 
 examiner is assured of the goodness of the 
 tube. 
 
 That a tube may be regular in the bore, it is 
 not necessary that the bore be cylindrical ; it 
 is sufficiently accurate when equal lengths corre- 
 spond to equal capacities. A tube with a flat 
 canal, for example, can be perfectly accurate 
 without at all approaching the cylindrical form. 
 It is only necessary that a drop of mercury oc- 
 cupy everywhere the same length. We may 
 observe, by , the way, that, in flat canals, the 
 flattening should be always in the same plane. 
 
 Division of Capillary Tubes into parts 
 OF EQUAL CAPACITY. — As it is very difficult to 
 meet with capillary tubes which are exactly re- 
 gular in the bore, it happens that the tubes 
 
96 
 
 THE ART OF GLASS-BLOWING. 
 
 which glass-blowers are obliged to employ have 
 different capacities in parts of equal length. 
 You commence the division of these tubes into 
 parts of equal capacity by a process described 
 by M. Gay-Lussac. You introduce a quantity 
 of mercury, sufficient to fill rather more than 
 half the tube, and make a mark at the extre- 
 mity of the column. You then pass the mer- 
 cury to the other end of the tube, and again 
 mark the extremity of the column. If you so 
 manage that the distance between the two 
 marks is very small, you may consider the en- 
 closed space as concentric, and a mark made 
 in the middle of the division will divide the 
 tube into two parts of evidently equal capacity. 
 You divide one of these parts, by the same 
 process, into two equal capacities, and each of 
 these into two others ; and in this manner you 
 continue to graduate the tube until you have 
 pushed the division as far as you judge proper. 
 
 But it is still more simple to introduce a drop 
 of mercury into the tube, so as to form a little 
 cylinder, and then to mark the two extremities 
 of the cylinder. If it were possible to push 
 the drop of mercury from one end of the tube 
 to the other, in such a manner as to make it 
 coincide, at every removal, with the last mark, 
 it would be very easy to divide the tube accu- 
 rately ; but as it is very difficult, not to say 
 impossible, to attain this precision of result in 
 moving the column of mercury, you must en- 
 deavour to approach exactness as nigh as may 
 be. You measure, every time you move the 
 mercury, the length of the cylinder it produces, 
 
THE ART OF GLASS-BLOWING. 
 
 97 
 
 and carry this length to the last mark, pre- 
 suming the small space which is found between 
 the mark and the commeticement of the column 
 to be fairly represented by the same space after 
 the column. You thus obtain a series of small 
 and corresponding capacities. 
 
 Graduation of Gas Jars, Test Tubes, &c. 
 — If the tube is regular in the bore, close one 
 end, either by sealing it at the lamp, or by in- 
 serting a cork, and pour into the interior two 
 or three small and equal portions of mercury, 
 in order to have an opportunity of observing 
 the irregularities produced by the sealed part. 
 Take care to mark, with a writing diamond, 
 the height of the mercury, after the addition of 
 each portion. When equal portions of mer- 
 cury are perceived to fill equal spaces, take 
 with the compass the length of the last portion, 
 and mark it successively along the side of the 
 tube, where you must previously trace a line 
 parallel to its axis. 
 
 For tubes which are irregular in the bore, 
 and where equal lengths indicate unequal ca- 
 pacities, it is necessary to continue the gradua- 
 tion in the same manner that you commenced 
 it — that is to say, to fill the tubes by adding 
 successively many small and equal portions of 
 mercury, and marking the height of the me- 
 tallic column after every addition. These di- 
 visions will of course represent parts of an 
 ounce or of a cubic inch according to the mea- 
 sure which you make use of. When you have 
 Ihus traced on the tube a certain number of 
 
98 
 
 THE ART OP GLASS-BLOWING. 
 
 equal parts, you can, by means of the com- 
 passes, divide each of them into two other 
 parts of equal length. The first divisions being 
 very close ^o one another, the small portion of 
 tube between every two may be considered 
 without much risk of error as being sensibly of 
 equal diameter in its whole extent. 
 
 When the tube Avhich you desire to graduate 
 is long and has thin sides, it would be difficult 
 to fill it with mercury without running the risk 
 of seeing it break under the weight of the 
 metal. In this case, you must use water in- 
 stead of mercury. 
 
 Bell-glasses of large dimensions are gradu- 
 ated by filling them with water, placing them in 
 an inverted position on a smooth and horizontal 
 surface, which is slightly covered with water, 
 and passing under them a series of equal mea- 
 sures of air. But it is then necessary to 
 operate constantly at the same temperature 
 and under the same atmospheric pressure, be- 
 cause air is very elastic and capable of being 
 greatly expanded. 
 
 In all cases, tubes, bell-glasses, &c. ought 
 to be held in a position perfectly vertical. The 
 most convenient measure is a dropping- tube, 
 on the stalk of which a mark has been made, 
 or a small piece of tube, sealed at one end, and 
 ground flat at the other ; the latter can be ac- 
 curately closed by a plate of glass. 
 
 The marks which are traced on tubes being 
 generally very close to one another, you facili- 
 tate the reading of the scale by giving a greater 
 length to those marks which represent every 
 
THE ART OF GLASS-BLOWING. 
 
 99 
 
 fifth division, and by writing the figures merely 
 to every tenth division. See pi. 4, fig. 8. The 
 number of divisions is somewhat arbitrary ; 
 nevertheless, 100, 120, 360, 1000, are divi- 
 sions which, in practice, offer most advantages. 
 
 Graduation of Hydrometers. — Cut a 
 band of paper on which the graduation of the 
 instrument can be traced, and let fall upon it a 
 little drop of sealing-wax ; then roll the paper 
 upon a little glass tube, and introduce it into 
 the stalk of the hydrometer. The instrument 
 is afterwards to be plunged into distilled water, 
 whicl^is carefully kept at the temperature of 
 40“ F. above zero. Give the instrument suffi- 
 cient ballast to make it sink till the point 
 («, pi. 4, fig. 20,) which you desire to make to 
 represent the density of water, touches the 
 surface of the water. Mark this point with 
 much precision ; it is the zero of the instru- 
 ment. The other degrees are taken by plung- 
 ing the hydrometer into distilled water to which 
 you have added 1, 2, 3, 4, 5, &c. tenths, or 
 1, 2, 3, 4, 5, &c. hundredths, of the substance 
 for which you wish to construct the hydrome- 
 ter, according as you desire the scale to indi- 
 cate tenths or hundredths. 
 
 When you have thus marked the degrees on 
 the stalk of the instrument, transfer them to 
 the paper with the help of the compasses. The 
 scale being completed, replace it in the tube of 
 the hydrometer, where it must be fixed j in so 
 doing, take care to make the degrees on the 
 scale coincide precisely with those marked on 
 the stalk. 
 
100 
 
 THE ART OF GLASS-BLOWING. 
 
 You can thus procure hydrometers for 
 alcohol, acids, salts, &c. which are instru- 
 ments that indicate the proportion of alcohol, 
 acid, salt, &c. contained in a given mass of 
 water. 
 
 But if it were necessary to plunge the hy- 
 drometer in a hundred different solutions in 
 order to produce the scale, it is easy to con- 
 ceive that that would be extremely troublesome, 
 especially for hydrometers which are employed 
 in commerce, and which do not need to be so 
 extremely accurate. When the density of the 
 mixtures or solutions is a mean between those 
 of the substances which enter into them, you 
 may content yourself with marking the zero 
 and one other fixed point, {a and b, pi. 4, fig. 20.) 
 Then, as the stalk of the hydrometer is evidently 
 of equal diameter in all its extent, you can di- 
 vide the space which separates the two fixed 
 points into a certain number of equal parts. 
 One of these, being taken for unity, represents 
 a particular quantity of the substance which 
 you have added to a determined weight of dis- 
 tilled water. By means of this unity you can 
 carry the scale up and down the stalk of the 
 instrument. It is thus, that, to obtain a Baume’s 
 hydrometer, after having obtained the zero by 
 immersion in distilled water, you plunge the 
 instrument into a solution containing a hundred 
 parts of water and fifteen of common salt, to 
 have the 15th degree, or containing a hundred 
 water and thirty salt, to have the .lOth degree. 
 Upon dividing the interval into fifteen or thirty 
 equal parts, accoiding as you have employed 
 one or the other solution, you obtain the value 
 
XilE ART OF GLASS-BLOWING. 
 
 101 
 
 of the degree, which you can carry upwards 
 or downwards as far as you wish. 
 
 Among the substances for which hydrometers 
 are required in commerce, are some which it is 
 impossible to obtain free from water — such are 
 alcohol, the acids, &c. In this case it is neces- 
 sary to employ the substances in their purest 
 state, and deprived of as much water as 
 possible. 
 
 The employment of hydrometers is very ex- 
 tensive : they are used to estimate the strength 
 of leys, of soap solutions, of wines, milk. See. 
 There is, in short, no branch of commerce in 
 which these instruments are not required for 
 the purpose of ascertaining the goodness of 
 the articles which are bought and sold. The 
 employment of hydrometers w’ould be still 
 more general, if they could be made to give 
 immediately the absolute specific gravity of 
 the liquids into which they might be plunged, 
 the specific gravity of water being considered 
 as unity. It is possible to graduate a thermo- 
 meter of this description by proceeding as 
 follows : — 
 
 Make choice of a hydrometer of which the 
 exterior part of the stalk is very regular. In- 
 troduce the band of paper on which the scale 
 is to be written, and then ballast the instru- 
 ment. Make a mark where the surface of the 
 distilled water touches the stalk. Remove the 
 hydrometer from the water, wipe it perfectly 
 dry, and weigh it very accurately with a sen- 
 sible balance. Then pour info it a quantify of 
 mercury equal to its own weight; plunge it 
 
102 
 
 THE ART OP GLASS-BLOWING. 
 
 again into the vvater, and again mark the point 
 where the stalk touches the surface of the 
 water. Pour the mercury out of the instru- 
 ment, transfer the two marks to the scale, and 
 divide this fixed distance into fifty equal parts. 
 Having by this operation obtained the value of 
 the degree, you carry it upwards and down- 
 wards, to augment the scale. If you take the 
 first point near the reservoir, the hydrometer 
 will be proper to indicate the density of li- 
 quids which are heavier than water; if you 
 take it towards the middle of the tube, the con- 
 trary will be the case. 
 
 If you destine the hydrometer for liquids 
 much heavier than water — such as acids, for 
 example — you might, after having determined 
 the first point, add to the original ballast as 
 much mercury as is equal to the weight of the 
 whole instrument; then the point where the 
 stalk would touch the surface of the water, and 
 which would be represented by 100, would be 
 very high, and the second point, which would 
 be found below, would be represented by 200. 
 On dividing the space into a hundred equal 
 parts, you would have the value of the degree, 
 which could be carried up and down for the 
 extension of the scale. 
 
 The specific gravities being in the inverse 
 ratio of the volumes plunged into the liquid, 
 the numbers of the scale which mark the specific 
 gravities diminish from below ; so that, on 
 marking the lowest point 100, you have, on 
 proceeding upwards, the successive degrees 
 0-99, 0-98, 0 97. 0-96. &c. 
 
THE ART OP GLASS-BLOWING. 
 
 103 
 
 The hydrometers with two, three, and four 
 branches, are graduated by having their tubes 
 divided into a hundred or a thousand equal 
 parts. The divisions on each branch must 
 correspond with those on the odier branches. 
 
 Graduation of Barometers. — The gradua>- 
 tion of this instrument consists in dividing a 
 piece of metal, wood, or ivory, into inches and 
 parts of inches. The divided rod is then em- 
 ployed to measure the height of the mercury in 
 the tube. As the rule is moveable, the opera;- 
 tion presents no sort of difficulty ; all that is 
 necessary is to make the zero of the scale coin- 
 cide with the inferior level of the mercury ; the 
 point which corresponds with the superior level 
 of the mercury, seen in the tube, indicates the 
 height of the barometric column. It is in this 
 manner that the cistern barometer is graduated. 
 
 But if the barometer is one of those in which 
 the surface of the mercury is variable, such as 
 the barometer of Gay-Lussac, it is necessary 
 to have recourse to a different process of gra- 
 duation. If the two branches of the instru- 
 ment are very regular, and of equal diameter, 
 you first measure with precision the height of 
 the column of mercury, then divide it in the 
 middle, and fix the scale, which must be gradu- 
 ated in such a manner that the mark of fitteen 
 inches corresponds exactly with the middle 
 point. This mode of graduation serves to in- 
 dicate merely the apparent height of the baro- 
 metric column. If you desire that the scale 
 should innnediately indicate the real height, you 
 
104 
 
 THE ART OF GLASS-BLOWING. 
 
 must fix the zero at the middle of the column, 
 and then double the figure which marks each 
 degree. 
 
 When you do not wish to write the real 
 height, you make two divisions, of which one 
 proceeds upwards, the other downwards. You 
 do not, in this case, double the value of each 
 division, but in observations made with such a 
 barometer scale you add the degree marked by 
 the two surfaces, in order to find the real height. 
 
 It is in an analogous manner that you gra- 
 duate the gauges or short barometers which are 
 employed to measure the density of air under 
 the recipient of the air-pump. You take the 
 height of the mercury in the gage, and fix at 
 the middle of the column the zero of a double 
 scale, of which one division proceeds upwards, 
 the other downwards ; or, instead of this, if 
 you choose to have only one scale, and that an 
 ascending scale, you double the value of every 
 degree. 
 
 The zero of the barometric scale can be 
 fixed below the inferior surface of the mercury ; 
 but then, to have the real height, it is necessary 
 to measure precisely the height of the mercury 
 in the two branches of the instrument, and to 
 deduct the smaller from the larger. 
 
 Dial (or Wheel) Harometer . — The dispo- 
 sition which should be given to this instrument 
 is precisely the same as that of the Dial Ther- 
 7nometer, described in a preceding section. 
 You make a small iron weight float on the in- 
 ferior surface of the mercury, and fix to this 
 weight a silk thread, which is stretched by a 
 
the art of glass-blowing. 105 
 
 counterpoise, and rolls over a very moveable 
 pulley. The axis of this pulley carries a needle, 
 which turns backwards or forwards according 
 as the column of mercury augments or di- 
 minishes. You arrrange the whole in such a 
 manner that the extreme variations of this co- 
 lumn cannot make the needle describe more 
 than one circumference; with this view you 
 give the pulley a diameter of nearly an inch. 
 
 The dial barometer being rather an object of 
 luxury than an instrument of precision, you gra- 
 duate it by inscribing the following words, at 
 full length, on the scale. In pi. 4, fig. 16, for 
 example, you write. 
 
 At the point a 
 
 
 b 
 
 
 ... c 
 
 
 d 
 
 
 ... e 
 
 Fine Weather. 
 
 ... f 
 
 
 ••• g 
 
 
 You write nothing at the inferior division. 
 
 Graduation of the Manometer. — The 
 graduation of this instrument consists in 
 dividing the tube where the air is to be com- 
 pressed, into a given number of parts of equal 
 capacity ; but as, in general, such tubes are 
 employed as are nearly capillary and very regu- 
 lar, the operation is reduced to a linear division, 
 where every degree occupies an equal space. 
 
 Graduation of Thermometers. Construc- 
 tion of Standard Thermometers. — Having 
 
106 
 
 THE ART OF GLASS-BLOWING. 
 
 constructed your instrument with a very regix- 
 lar tube, or one which has been divided into 
 parts of equal capacity, and having filled it with 
 the proper liquid, according to the instructions 
 given in a preceding section, the graduation is 
 to be effected as follows. Procure very pure 
 ice, break it into small pieces, and fill a vessel 
 with it. When the ice begins to melt, plunge 
 the thermometer into the middle of it, in such 
 a manner that, without touching the sides 
 of the vessel, the whole thermometer, or at 
 least that part of it which contains the liquid, 
 may be covered with ice. Allow the instru- 
 ment to remain in this state until, in spite of 
 the gradual melting of the ice, the surface of 
 the column of liquid remains at a fixed point, 
 and neither falls nor rises. Mark this point 
 very carefully on the stalk of the thermometer, 
 either with a thread or a little drop of sealing- 
 wax, or with the trace of a diamond or a flint. 
 This is freezing point, the zero of the cen- 
 tigrade scale, the thirty-second degree of 
 Fahrenheit’s scale. 
 
 As for the second fixed point, it is marked 
 during an experiment with boiling water, per- 
 formed as follows : — You employ a vessel of 
 tin plate sufficiently high to enclose the xvhole 
 thermometer ; you pour into this vessel distilled 
 water, till it is about an inch deep, and then 
 you heat it. The vessel is surmounted by a 
 cover pierced with two holes, one of which is 
 intended to receive the stalk of the thermo- 
 meter, the other to allow the steam to escape. 
 When, on continuing the ebullition, you ob- 
 
THE ART OF GLASS-BLOWING. 
 
 107 
 
 serve that the mercury ceases to rise in the tube, 
 you mark the point at which it has stopped, 
 just as you marked the first point. The last 
 mark indicates the boiling point ; the one hun- 
 dredth degree of the centigrade scale, the two 
 hundred and twelfth degree of Fahrenheit’s 
 scale. You transfer to paper the distance 
 which is found between the first point and the 
 second point determined, and you divide this 
 distance into one hundred equal parts, or de- 
 grees, for the centigrade thermometer, into 
 eighty parts for the thermometer of Reaumur, 
 and into one hundred and eighty for that of 
 Fahrenheit. If the tube of the instrument is 
 very regular in the bore, the degrees should be 
 equal in length ; if, on the contrary, you have 
 been obliged to divide it into parts of equal 
 capacity, you find how many of these parts or 
 little spaces it is necessary to take to consti- 
 tute one of the above degrees. You find this 
 by dividing their whole number by 100, or 80, 
 or 180, according to the degrees of the scale 
 which you intend to make use of. Thus, if 
 you find between the two points fixed by melt- 
 ing ice and boiling water, three hundred divi- 
 sions of equal capacity, it is necessary to in- 
 clude three of these divisions in every degree 
 of the centigrade scale. 
 
 The vessel employed to take the boiling 
 point must be of metal, and its surface should 
 be perfectly clean and well polished, and have 
 no rough points. If sand, or other matters, 
 were permitted to repose on the vessel, and to 
 
108 THE ART OF GLASS-BLOWING. 
 
 form asperities, the water would enter into 
 ebullition at an inferior temperature. 
 
 This operation should, moreover, be per- 
 formed under an atmospherical pressure, which 
 is indicated by the barometer when the mercury 
 stands at twenty-nine inches and a half. But 
 as this pressure is different according to the 
 elevation of the place of operation, and, indeed, 
 suffers continual variations even in the same 
 place, it follows that the temperature of boiling 
 water is subject to continual changes, and that, 
 in the graduation of the thermometer, it is in- 
 dispensably necessary to take notice of the 
 height of the barometer at the very moment 
 that the point denoting the degree of boiling- 
 water is fixed upon. You succeed in making 
 the necessary corrections by the help of the 
 following table, which is founded on the ex- 
 periments of Sir G. Shuckburg and of the 
 ■Gommittee of the Royal Society. 
 
 £See the Table on the opposite page.] 
 
 Common Thermometers. — Having, by the 
 method which we have just described, obtained 
 a Standard Thermometer, you may procure 
 with facility as many ordinary thermometers as 
 you desire. It is proper to employ the most 
 regular tubes which you can obtain, and when 
 the instruments are ready to be graduated, you 
 must bring them into comparison with your 
 standard thermometer. You place them toge- 
 ther into a liquid of which you gradually raise 
 the temperature, and you mark several points 
 on the scale of the new thermometer, the inter- 
 
THE ART OF GLASS-BLOWING, 
 
 109 
 
 Height of the Barometer in Inches. 
 
 
 
 
 
 Correction in 
 
 When the boiling 
 
 When the boiling 
 
 lOOOths of the 
 
 point is found 
 
 point is found 
 
 interval between 
 
 by immersing 
 
 by immersing 
 
 the freezing 
 
 the Instrument 
 
 the Instrument 
 
 and boiling points 
 
 in Steam. 
 
 in Water. 
 
 of Water. 
 
 
 30.60 
 
 10' 
 
 
 ... 
 
 30.50 
 
 9 
 
 & 
 
 30.71 
 
 30.41 
 
 8 
 
 -ti 
 
 30.50 
 
 30.29 
 
 7 
 
 1 s 
 
 30.48 
 
 30.18 
 
 6 
 
 
 30.37 
 
 30.07 
 
 5 V & 
 
 30.25 
 
 30.95 
 
 4 
 
 ^ i ^ 
 
 30.14 
 
 30.84 
 
 3 
 
 3 ^ 
 
 30.03 
 
 30.73 
 
 2 
 
 ^ bo 
 
 29.91 
 
 30.61 
 
 1 
 
 
 29.80 
 
 30.50 
 
 oj 
 
 
 
 
 t >* 
 ca fc. 
 
 29.69 
 
 29.58 
 
 29.39 
 
 29.28 
 
 n 
 
 2 
 
 s 3 
 
 ai 
 
 29.47 
 
 29.17 
 
 3 
 
 <u 
 
 29.36 
 
 29.06 
 
 4 
 
 
 29.25 
 
 28.95 
 
 5 
 
 h S'" 
 
 D 0.0 
 
 29.14 
 
 28.84 
 
 6 
 
 “ Ss 
 
 29.03 
 
 28.73 
 
 7 
 
 
 28.92 
 
 28.62 
 
 8 
 
 •S.S 
 
 28.81 
 
 28.51 
 
 9 
 
 a 
 
 28.70 
 
 
 lOj 
 
 Eh S 
 
 yals between which are subsequently divided 
 into as many degrees as are marked on the scale 
 of the standard thermometer. Thus, for exam- 
 ple, you mark the 10° and 15°, and afterwards 
 divide the interval into five equal parts. This 
 gives you the length of a degree on the stalk 
 
 L 
 
no 
 
 THE ART OF GLASS-BLOWING. 
 
 ot‘ the new instrument. The more you multi- 
 ply these fixed points, the more you insure the 
 precision of the thermometer. When you have 
 taken a certain number of points, you measure 
 the remainder with the compasses. 
 
 The zero, 0”, of the thermometer of Fahren- 
 heit, is taken by means of a mixture of snow 
 and commoti salt, and its maximum point is, 
 like that of the preceding thermometer, taken 
 by means of boiling water ; but this interval is 
 divided into 212 degrees ; so that the scale 
 marks 32° where the centigrade and Reaumur’s 
 scales mark 0”. 
 
 The thermometer of Delisle has but one 
 fixed point, which is the heat of boiling water ; 
 this is the zero of the instrument. The infe- 
 rior degrees are 0,0001 (one ten-thousandth 
 part] of the capacity of the bulb and stalk of 
 the thermometer. It marks 150° at 0° of the 
 centigrade, or 32° of Fahrenheit’s thermometer. 
 
 The dial, the maximum and the minimum 
 thermometers, are graduated according to the 
 same principles as the common thermometers. 
 
 You can, with a mercurial thermometer, make 
 the centigrade scale rise to 300 or 400 degrees 
 above zero ; but with an alcohol thermometer, 
 you must never go beyond the heat of boilipg 
 water. On the contrary, the inferior degrees 
 of the alcohol thermometer can be carried to 
 the very lowest point, while those of the mer- 
 curial thermometer should be stopped at thirty 
 or thirty-five degrees below the zero of the cen- 
 tigrade scale, as the mercury then approaclies very 
 near the point of its congelation. In all cases, 
 
THE ART OF GLASS-BLOWING. Ill 
 
 the degrees of thermometer scales are indicated 
 by the sign — when they are below zero^ and 
 by the sign + when they are above it ; the — 
 is always marked, but the -j- generally omitted. 
 See pi. 4, fig. 6. 
 
 We may obseive here that it is proper from 
 time to time to plunge the standard thermome- 
 ter into melting ice, for the purpose of veri- 
 fying its exactness. It has been found that 
 thermometers constructed with a vacuum above 
 the column of mercury gradually become inac- 
 curate, the 0° ascending, until it corresponds 
 with 4- 1° or -f 2°. This singular elfect is 
 attributable to the constant pressure of the at- 
 mosphere, which, being supported merely by 
 the resistance of the very thin sides of the 
 thermometer, finally presses them together, and 
 diminishes the capacity of the reservoir. It is 
 partly for the sake of avoiding this inconve- 
 nience that we consider it good not to make an 
 entire vacuum above the mercury, but to leave 
 a portion of air in the tube, and at the same 
 time to form a little reservoir at the summit of 
 the instrument. 
 
 Differential Thermometer. — To graduate 
 this instrument, you first maintain the two 
 bulbs at an equal temperature, by which you 
 determine the first fixed point, which is zero. 
 Then, enveloping one of the tvvo bulbs with 
 melting sno;v, and elevating the other by 
 means of a vessel with warm water, to a known 
 temperature— to 20“ Centigrade, for example — 
 you fix a cer ain space, which you afterwards 
 divide into 50 equal parts or degrees. The 
 
112 ' TifE ART OF GLASS-BLOWING. 
 
 scale is continued by carrying successively to 
 each side the known value of a degree. 
 
 Graduation of Rumford’s Thermoscope. — 
 This instrument is graduated by dividing the 
 tube which separates the two bulbs into equal 
 parts, the number of which is arbitrary, though, 
 in general, the thermoscope tube is divided into 
 nine or eleven parts. There is always an odd 
 number of degrees, and you manage so that 
 the odd degree is found in the middle of the 
 tube. It carries the mark of zero at each end, 
 and the figures 1, 2, 3, &c. proceed from each 
 end of this middle degree, and form two cor- 
 responding scales. 
 
 Graduation of Mariotte’s Tube. — You 
 divide the little branch which is sealed at die 
 end into a certain number of parts of equal 
 capacity, and the large branch into inches and 
 parts of inches. It is necessary to take care 
 that the zero of the two ascending s*ales cor- 
 respond, and are situated above the inferior 
 bend formed by the two branches of the in- 
 strument. 
 
 THE END. 
 
 U’. WILSON, PIUNXKU, 57 , SKlNNJiR-STBEKT, LONDON..