Chapter II.).
A white-hot tube or rod of this material can be plunged into cold water with impunity, and no special care need be exercised in heating or cooling articles made of this substance, unless articles of great size and thickness are involved, and even with these only little caution is needed. The only disadvantages which must be balanced against the great advantages just named lie in the relatively high cost of the articles and in their somewhat sensitive behaviour to certain chemical influences. As regards cost, vitreous silica is at present available in two different forms; in the first form it resembles ordinary glass very closely in appearance, the shape and finish of the tubes and vessels of this kind having undergone very great improvements quite recently. This silica glass has, in fact, been worked from molten silica in a way more or less analogous to that in which ordinary glass is worked, the great extra cost of the silica ware being due, in part, at all events, to the extremely high temperature required for melting and working this material; ordinarily, in the production of the class of silica ware now referred to, this heat is generated by the liberal--and therefore expensive--use of oxygen gas. In great contrast to this glass-like, transparent silica ware is the other form in which this material is available. This is a series of products obtained from the fusion of silica in special forms of electric furnace; in this ware the minute bubbles so readily formed in the fusion of all forms of quartz are not even partially eliminated, and by their presence--often in the form of long-drawn-out, capillary hollows--they impart to this ware its very characteristic milky appearance. The price of this product, which is mostly used in the form of tubes, although such articles as basins, crucibles, and even muffles of considerable size are available, is much lower than that of the transparent variety, being in fact decidedly lower than that of the best porcelain; on the other hand, even this price is considerably above that of the best glass tubing.
Apart from the question of cost, the use of silica ware is further limited by its sensitiveness to all forms of basic materials. Thus alkaline solutions cannot be allowed to come into contact with this substance, since they attack it vigorously, especially when warm. At high temperatures all basic materials produce a rapid attack on silica ware, the silica, in fact, behaving as a strongly acid body at and above a red heat. The attack which occurs when such a substance as iron or copper oxide is allowed to come into contact with heated vitrified silica is, in fact, so rapid that a tube is completely destroyed in a few minutes, the formation of silicates resulting in the cracking and disintegration of the whole piece. While, therefore, silica ware, especially in its cheaper forms, undoubtedly possesses great advantages and possibilities, its use must be carried on with careful reference to its chemical nature.
Vitreous silica, in addition to the uses and advantages just named, has also an interest from the optical point of view; this arises from the fact that it is transparent to short (ultra-violet) light waves to which all ordinary varieties of glass are completely opaque. Quite recently, the Jena works have produced special glasses which are more transparent to these ultra-violet rays than ordinary glass, but even these fall far short of silica in this respect. This property of transparence to ultra-violet light is utilised in two widely different directions. One of these is in the production of ultra-violet light when required for medical or other special purposes; a most energetic source of such rays is available by the use of tubes of vitrified silica within which the mercury-vapour arc is produced. In another direction the employment of quartz lenses makes it possible to take advantage of the optical properties of ultra-violet light in connection with microscopy; for the purpose of constructing a perfect optical system, crystalline quartz would be useless, since its property of double refraction would interfere hopelessly with the performance of the lenses. This is now overcome by the use of vitreous silica lenses, in the case of the “ultra-violet microscope,” as made by Carl Zeiss, of Jena. So far, however, it has only been possible to produce quite small pieces of vitreous silica sufficiently free from bubbles to be used for optical purposes. The great difficulty lies not so much in merely melting the quartz down as in freeing it from the air-bubbles enclosed within it; the course usually adopted with glass, of raising the temperature and allowing the bubbles to rise to the surface, becomes impossible in this case, because the silica itself begins to vapourise and even to boil vigorously at temperatures not very far above its melting point. Quite recently, however, two American workers have claimed to be able to overcome this difficulty by the use of both vacuum and high pressure applied at the earlier and later stages of the fusion process respectively, so that it may shortly be possible to produce vitreous silica in large and perfectly clear blocks.
We have already indicated that glass tubing and rod form the basis upon which the glass-worker, with the aid of the blow-pipe or “lamp,” fashions his productions, which, of course, include a great number of scientific instruments and appliances used more especially in the field of chemistry. In another direction also glass tubing serves as a basis for a branch of the glass industry; this is the manufacture of certain classes of glass beads, which are formed by cutting up a heated glass tube of suitable diameter and colour into short, more or less spherical sections. In some cases the colour of the beads is secured by using glass of the desired tint, but in other cases the beads are made of colourless glass, and a colouring substance is placed in the interior of the bead.
Solid glass rods are also employed for a variety of purposes; their mode of manufacture is exactly analogous to that of tubing, except that the gathering is drawn out without having first had a hollow space produced at its centre by the blower. In its most attenuated form glass rod becomes glass thread or fibre; this is produced by drawing hot glass very rapidly, the resulting thread being wound on a large wheel. At one time this material found considerable use, since it was found possible to spin and weave the thinnest glass fibres into fabrics which could be used for dress purposes. It is not, however, to be regretted that this fashion has neither extended nor survived, since it was certainly liable to produce serious injury to health. It is a well-known fact that there are few more injurious or even dangerous substances to be inhaled into the human throat and lungs than finely-divided glass; glass fibre, moreover, when subjected to constant bending and wear, is bound to undergo frequent fracture, and the atmosphere of a ball-room, for example, in which several such dresses were worn would soon be contaminated with innumerable fine, sharp particles of glass which would produce an injurious effect on those inhaling them. At the present time glass fibre is used for little else than the “glass wool” required for certain special purposes in chemical laboratories.
Fused quartz or silica fibres, of extreme tenuity, but of relatively very great strength, are employed in many scientific instruments, where their extreme lightness and perfect elasticity and freedom from what is known as “elastic fatigue” renders them of very great value. These fibres are not drawn from a mass of molten silica, as is done with glass, but are produced by attaching a nail or bolt to a small bead of fused silica produced by the aid of an oxygen-fed blowpipe; the nail or bolt is then suddenly shot away down a long passage or similar space by means of a cross-bow, drawing a very fine fibre of silica with it; the most difficult part of this operation, however, consists in finding and handling the fibres thus produced.
_Artificial Gems._--The fact that pieces of suitably-coloured glass can be made to show a superficial, but sometimes more or less deceptive, resemblance to precious stones, has led to the manufacture of imitation jewels of all descriptions. The glass used for this purpose is usually a very dense flint-glass whose high refractive index facilitates the imitation which is aimed at. The external shapes of gems are, of course, readily imitated by cutting and grinding the glass, while the requisite colours are attainable by means of the colouring materials described in Chapter XI. To a casual observer the difference in sparkle and brilliance which arises from the difference between the refractive index of the heavy flint-glass (about 1·8) and that of minerals (which ranges from 1·7 to 2·2) is not readily apparent, but closer examination will at once reveal the difference. The determination of the optical constants by means of a refractometer would at once reveal the true character of the imitation, but an even readier test is that of hardness. The dense flint-glass is naturally soft, and is readily scratched by most of the harder minerals, while the precious stones, more particularly garnets, rubies and diamonds, are very hard. If an attempt is made to scratch an ordinary sheet of window-glass, it will be found that most real precious stones will do so readily, while flint-glass imitations will fail to make more than a slight mark, which is more smear than scratch. The test by determining the specific gravity is also obviously applicable, since the flint-glass will readily betray its presence by its high density (over 4).
In quite a different class from the imitation gems made of cut flint-glass are the artificial gems, which in nature and composition are exact reproductions of natural gems, but which have been produced by artificial processes. As far as the writer is aware these are only found in any large numbers in the case of the ruby, but in that case, at all events, it is said that the production of the artificial crystals is at least as costly as the purchase of the natural stones. There can, however, be very little doubt that as the processes of fusion and crystallisation become better known and understood, and the chemistry of silicate minerals is developed, the artificial production of mineral crystals in, at all events, moderate sizes will become increasingly possible; it is even to be hoped that their production will be so far perfected as to place their really valuable properties at the service of man.
_Chilled Glass._--In all the processes of glass manufacture described in the present book, annealing has always played an important part. The glass, after it has undergone its last treatment under the influence of heat, is subjected to a gradual cooling process with the object of freeing it from the internal strains which it would otherwise retain, and which would, ordinarily, endanger its existence and interfere with its use. It is, however, well known that surfaces of glass subjected to such internal strains as result in a compressive stress on the glass near the surface, are less liable to injury, and are apparently stronger than when the glass is annealed and the stresses are removed. On the other hand, glass surfaces under tension are extremely delicate and fragile. In some respects, therefore, glass which has not been annealed may appear to be stronger than the annealed product. The well-known case of the Rupert’s drop is an example of this kind. Rupert’s drops are produced by dropping molten glass into water; they generally take the form of a more or less spherical body having a long tail, tapering off into a thread, attached to it. Such a Rupert’s drop may be struck with a heavy hammer, and will safely resist a blow that would splinter a similar body made of annealed glass. If, however, the surface be scratched, or the tip of the tail be broken off, the entire “drop” breaks up, sometimes with a violent explosion, into minute fragments. Numerous inventors, among whom De la Bastie and Siemens figure most conspicuously, have endeavoured to utilise these properties of chilled glass, not exactly by endeavouring to produce that extreme degree of internal strain which is characteristic of the Rupert’s drop, but by producing what they describe as “tempered” glass, in which the internal strains have been reduced by less violent cooling to such an extent as to retain some of the advantages of the hardened, internally strained condition while approximating more or less to the safer state of annealed glass. At one time articles of this kind were frequently seen as curiosities, such as tumblers that could be dropped on the floor without breaking, etc., but these articles generally ended by receiving a slight scratch or chip and promptly falling into fragments. As a matter of fact, however, some tempered glass is actually manufactured by the firm of Siemens at the present time for special purposes. De la Bastie’s process was tried in England, and some success was claimed for it; but it is not in commercial operation at the present time, and never appears to have attained any great importance.
_Massive Glass._--Enthusiasts for the extension of the use of glass have endeavoured to apply it to a great variety of purposes, including the construction of buildings and the paving of streets. In the former case, which was exemplified at the Paris Exhibition of 1900, advantage was taken of the light-transmitting power of the material, but although the buildings erected with large blocks of cast glass were not displeasing in effect, this use has not found any considerable extension. For paving purposes, the hardness and durability of glass are the only useful qualities, and here also--although several trials have been made in France--no signs of any considerable application of the new products are as yet visible. What has been said above with reference to the injurious character of glass dust applies, further, to glass pavements, since their natural wear would result in the formation of considerable quantities of this dust. The advocates of glass paving, however, suggest that the hardness of glass would greatly reduce the actual amount of wear, and that consequently the dust would be reduced considerably. This is a matter which prolonged experience alone can decide, but it does not seem obvious that glass blocks should wear more slowly than stone setts made of good granite, for example. On the other hand, the glass blocks could probably be produced more cheaply, since the labour of cutting to size would be obviated by casting the blocks to the desired dimensions.
Water-glass, or silicate of soda or potash is perhaps scarcely to be classed under the heading of “Glass Manufacture” at all, but it bears a certain relationship to glass in several ways. Thus one of the modes of manufacturing water-glass is by the fusion of sand and alkali in tank furnaces somewhat resembling those used for glass production; the fused silicate, moreover, solidifies as a vitreous mass, in which respect it also resembles such substances as borax, etc. The uses of silicate of soda and potash are, however, so far removed from the field of glass-manufacture that we cannot enter into them here.
In concluding this chapter, we wish to describe one more product of the glassworks, and this includes some of the most impressive and splendid examples of the glass-maker’s art. These are the great mirrors and lenses by whose aid our lighthouses and searchlights send forth their powerful beams of light. Although these objects are called “mirrors” and “lenses,” since they fulfil the functions of such optical organs, yet in their nature and mode of manufacture they are so far removed from the glass used for the production of other kinds of lenses that they could not be included under the heading of “optical glass.”
The characteristic feature in the manufacture of optical glass is the manner in which each separate pot or melting is allowed to cool down and to break up into irregular fragments which are subsequently moulded to the desired shape. Were it attempted to manufacture the large glass bodies required for lighthouse purposes in this manner, the cost would approximate to that of the large discs used for telescope objectives, and this would of course be entirely prohibitive. The requirements as regards colour, homogeneity and freedom from other defects, which must be met in lighthouse lenses, are further not nearly so stringent as those which are essential in ordinary optical work of good quality. The reason for this difference arises from the fact that lighthouse lenses and searchlight mirrors are used merely to impart a desired direction to a beam of light, and not for the purpose of producing sharply-defined images; slight irregularities in the glass are therefore not of such serious importance.
Lighthouse glass can therefore be produced by rather less elaborate means; although every care is taken to make the glass as perfect as possible, it is brought into approximately the desired form by casting the molten glass in iron moulds of the proper shape. When removed from these moulds and annealed, the glass is fixed on large revolving tables and ground and polished to the final shape of lenses and annular lens-segments as required for the various types of Fresnel lighthouse lenses. In this way complete rings, forming annular lenses, are produced up to 48 inches diameter. Rings of larger size are usually built up of a number of segments, and these built-up rings sometimes have a radius as large as 7 feet. For the majority of lighthouse lenses, it should be added, a hard soda-lime glass having a refractive index of 1·50 to 1·52 is used, but for special purposes a dense flint-glass having a refractive index of 1·63 is employed.
Mirrors for searchlight purposes are of very varied forms and sizes, the shape depending largely upon the particular form of beam which they are designed to project. For many purposes a parabolic form is required, while in others, where a flat, fan-shaped beam is to be produced, a form having an elliptical section in a horizontal plane and a parabolic section in the vertical plane is required. In most cases these mirrors are produced by bending plates of glass, previously raised to the necessary degree of heat, over suitably shaped moulds, the surface being subsequently re-polished to remove any roughness resulting from the bending process. Another type of mirrors is that known as “Mangin,” which has two spherical surfaces placed eccentrically in such a way that the centre of the mirror is considerably thinner than the periphery; in this type of mirror the reflecting action of the back surface is modified by the refracting action of the front surface, but both are spherical, and can therefore be accurately ground and polished by the usual mechanical means. Such mirrors are manufactured of single pieces of glass up to 6 feet in diameter.
APPENDIX
BIBLIOGRAPHY.
The existing literature of glass manufacture is so limited that a complete bibliography could almost be given on a single page; in the English language, in particular, there are exceedingly few books and papers on the subject. The French and German literature of the subject is a little more extensive. In giving a list of the works, and more particularly in referring to those which he has consulted in the preparation of the present volume, the author thinks it will be an advantage to indicate their scope, and, to some extent, what he believes to be their value, in order to save the student the trouble of seeking out comparatively inaccessible works only to find that they contain little that is of value for his purpose.
_English Books and Papers on Glass Manufacture._
The Principles of Glass Making (George Bell & Sons). By Powell & Chance. An elementary book giving a clear and concise account of the older processes, more especially in connection with flint and plate-glass.
Glass. Articles in 9th Edition of Encyclopædia Britannica. A detailed account of processes, more or less covering the entire subject, but the processes described are mostly obsolete at the present time.
Glass. Article in Supplement to 9th Edition of Encyclopædia Britannica. By Harry J. Powell. A brief summary of more recent developments. Particularly valuable in reference to artistic English flint-glass.
Jena Glass. By Hovestadt, translated by J. D. and A. Everett. Contains a full account of the scientific work on glass and its practical application, done in connection with the Jena Works of Schott. Particularly interesting in connection with the subjects of Chapters I., II., XII., and XIII. As the title indicates, the book is written from the Jena point of view, and scarcely does justice to work done elsewhere. The book has gained considerably at the hands of the translators.
Some Properties of Glass. By W. Rosenhain. (Transactions of the Optical Society of London, 1903.) Gives a brief account of the properties of glass as affecting its optical uses.
Possible Directions of Progress in Optical Glass. By W. Rosenhain. (Proceedings of the Optical Convention, London, 1905.) Has been referred to in the text of this book (Chapter XII.).
Catalogue of the Optical Convention Exhibition, London, 1905. Contains historical and general notices of optical and lighthouse glass, glass-working machinery, etc.
Glass for Optical Instruments. By R. T. Glazebrook. (Cantor Lectures to the Society of Arts.) Gives an account of modern optical glass manufacture.
Old English Glasses. By Albert Hartshorne. Gives an account of the history of glass-making in England.
The Methods of Glass Blowing. By W. Shenstone. Describes the manipulation of glass-blowing for experimental purposes, _i.e._, lamp work.
_French Books on Glass Manufacture._
Guide du Verrier. By G. Bontemps. A classical work by one of the greatest experts of his day. Much of the contents of the book is, however, entirely out of date at the present time. The book is interesting as being the work of the man who introduced optical glass manufacture into England.
Verres et Emaux. By L. Coffignal. Chiefly of interest in connection with the subjects of Chapter VIII.
Le Verre et le Crystal. By J. Henrivaux. (P. Vicq Dunod et Cie., Paris.) A lengthy book profusely illustrated and giving a great wealth of detailed information. The writer was for some time the general manager of one of the largest plate-glass manufactories in Europe; his account of plate-glass manufacture is, therefore, especially valuable. Much space in this book is devoted to historical and æsthetical matter.
La Verrerie au XX^{ieme} Siècle. By J. Henrivaux. (Paris, R. Bernard et Cie., 1903.) Practically a supplement to the preceding; some of the processes and products described are, however, not of a practical nature. Chiefly valuable for recent developments in plate-glass and bottle-glass manufacture.
_German Books on Glass Manufacture._
Die Glasfabrikation. By R. Gerner. (A. Hartleben’s Verlag, Vienna and Leipzig, 1897.) A concise and clear account of most of the more important processes of glass manufacture. Very practical in character. The information given appears to be reliable, although far from complete.
Die Herstellung Grosser Glaskoerper and Die Bearbeitung Grosser Glaskoerper. By C. Wetzel. (Hartleben’s Verlag, Vienna and Leipzig, 1900 and 1901 respectively.) Describes numerous special processes and appliances devised for use in connection with large glass objects. Some of these descriptions, however, appear to be little more than transcripts from patent specifications.
Glasfabriken und Hohlglasfabrikation. By R. Dralle. (Leipzig, Baumgaertner, 1886.) Looked upon as a classic in Germany. Gives detailed plans and drawings of entire bottle-works, including furnaces and all accessories. Deals principally with bottle manufacture.
Die Glasfabrikation. By Dr. E. Tscheuschner. (Weimar, B. H. Voigt, 1888.) A full detailed account of all processes known at the time. The rapid progress of modern practice has, however, already rendered this book to some extent obsolete.
Jenaer Glas. By Hovestadt. Already referred to in respect of the English translation.
Der Sprechsaal. (Schmidt, Weimar.) A trade journal devoted to the discussion of technical matters relating to the glass and ceramic industries. Occasionally contains articles and abstracts of technical or scientific interest in connection with glass manufacture.
* * * * *
In addition to the books and papers named in the above list, a great number of scientific papers, notes, etc., are to be found scattered throughout the technical and scientific publications of the world; those that have proved of real interest and importance have, however, left their mark on the industry, and will be found described or referred to in connection with the various branches of manufacture described in the present volume or in the books named above.
INDEX
A.
Abbé, 8, 10, 210, 218
Absorption of light in glass, 32, 179
Acid, action of, on glass, 11 boric, action of, on glass, 11, 186 carbonic, action of, on glass, 12 hydrofluoric, action of, on glass, 12 phosphoric, action of, on glass, 11
Air, compressed, 91, 105, 117
Alkali chlorides, use of, in glass manufacture, 41 content of hygroscopic glass, 6 metals, 184 nitrates, 44, 78 sources of, 40
Alkaline liquids, action of, on glass, 11
Aluminium, 51, 186
Ammonia soda, 41
Anastigmatic photographic lenses, 213
Ancient windows, colours of, 16, 202
Annealing bottles, 103 kiln, 103 for optical glass, 235 for plate glass, 135 for rolled plate glass, 127
Anthracite coal, 42, 53, 79
Antimony, 188
Apochromatic objectives, 213
Arsenic, 52, 78, 105, 117, 188
Artificial gems, 246
Auerbach, 22
Aventurine, 185
B.
Bacteria, action of, on glass, 13
Barium compounds, 47, 186 crown glass, 212 glass, 7
Barytes, 48
Bases other than alkalies, sources of, 45
Beads, 244
Behaviour, chemical, of glass, 6
Bending plate glass, 144
Bevelling, 145
Black ash, 41
Blisters in sheet glass, 160, 168
Blocks, fire-clay, 58 tank, 59
Blower, sheet glass, 158
Blower’s chair, 111
Blowing glass, 89 holes, 91, 161, 189 sheet glass, 161
Blown glass, decoration of, 114 plate glass, 171
Bohemian glass, 109, 240
Boiling up, 81
Bottles, annealing of, 103 blowing, improvements in, 99 machines, 100 colour of, 96 manufacture, furnace for, 97 moulds for blowing, 98 production of, by hand, 98 raw materials for, 95 strength of, 18
Boric acid, 11
Boron, 186
Boro-silicate crown, 212
Boucher’s bottle-blowing machine, 101
Bricks, fire-clay, 58 silica, 60
Bubbles in optical glass, 230 removal of, 81
Burning, pots, 58
C.
Cadmium, 186
Calcium carbonate, 46 oxide, 45, 186 sulphate, 47
Carbon, 53, 79, 186
Carbonate of soda, 41
Carbonic acid, action of, on glass, 12
Carboys, blowing of, 104
Casting plate glass, 132
Chair, glass-blower’s, 111
Chalk, 46
Chamotte, 57
Chance, 211
Charcoal, 42, 58, 79
Charging furnaces, 75
Chemical behaviour of glass, 6 composition of glass, 5 of optical glass, 217 reactions during fusion, 76
Chilled glass, 247
Chimneys, gaslight, 23 lamp, 238
Chromium, colouring effect of, 190
Cleaning of lenses, 220
Coal, anthracite, 42, 53, 79
Cobalt, colouring effect of, 197
Coke, 42, 53, 79
Colour of ancient windows, 16 glass, 32 theory of, 181 optical glass, 208 sheet glass, 167
Coloured blown glass, 113 glass, 178 technical uses of, 203
Combustion tubing, 7, 241
Compressed air for glass blowing, 91, 105, 117
Conductivity, electrical, of glass, 30 thermal, of glass, 24, 29
Copper, colouring effect of, 184 ruby, 184, 188, 198
Corrosion of glass, 11
Covered pots, 56, 109
Crown, boro-silicate, 219 glass, 175, 211 hard, 212, 219 soft, 212 telescope, 215
Crowns, furnace, 60
Crucibles, manufacture of, 56 for glass melting, 54
Crushing strength of glass, 19
Cryolite, 52
Crystallisation of glass, 3
Crystals, mineral, 218
Cullet, 74 for optical glass, 224
Cutting rolled plate glass, 128
Cylinders, sheet glass, 161, 171
D.
Decolourisation of glass, 52, 188, 190, 193, 197
Decoration of blown glass, 114
Defects in rolled plate glass, 129 sheet glass, 166
Definition of glass, 1
De la Bastie, 248
Devitrification, 3, 11
Diamond, refractive index of, 216
Dimming of glass surfaces, 12
Dinas bricks, 61
Dipping of sheet glass, 166
Dispersion of optical glass, 209 partial, 214
Double refraction in optical glass, 221 rolling machine, 130
Drawing tubes, 239
Ductility of glass, 20
Durability of glass, tests for, 14
Dust, action of, on lenses, 220 glass, 245
E.
Elasticity of glass, 20, 24
Electrical properties of glass, 29
Epinal, 39
Etching of glass, 12
Expansion, coefficient of thermal, 24, 25
F.
Felspar, 40, 44
Fibres, glass, 245 silica, 245
Figured rolled plate glass, 87, 130 cutting of, 131
Finger-marks on lenses, 219
Fining of glass, 81 optical glass, 229
Fire-clay, action of, on glass, 6 for pots, 55 wetting up, 57
Fire-polish, 117
Flashed glass, 25, 199
Flint, 40 boro-silicate, 212 dense, 212, 246 densest, 212 extra dense, 212 glass, 7, 49, 78, 108, 211 light, 212 soda, 212 telescope, 215
Fluorite, refractive index of, 216
Fontainebleau, 38
Founding of optical glass, 227
Fourcault process, 174
Fresnel, 251
Furnace crowns, 60 gas, 63
Furnaces for bottle manufacture, 97 glass melting, 54, 62 optical glass, 225 plate glass, 133 rolled plate glass, 122 sheet glass, 151, 170 ports, 67 recuperative, 66, 156 regenerative, 66, 155 tank, 59, 69 economy of, 72
Fusion, process of, 73 temperature of glass, 5
Freezing of glass, 2
G.
Gaslight, chimneys for, 23
Gas producers, 62, 64
Gatherer, 158
Gathering of glass, 85, 88, 158
Gauge tubes, 10, 18, 23, 26
Gems, artificial, 246
Ghosts, photographic, 16
Glauber’s salt, 43
Gold, colouring effect of, 185
Grinding plate glass, 137
Gypsum, 47
H.
Hardened glass, 20
Hardness of glass, 21 tests for, 22
Heavy spar, 48
Henrivaux, 19
Hertz, 22
Hock-bottle colour, 195
Hohenbocka, 38
Hollow glass-ware, 108
Horse-shoe flame, 69
Hydrofluoric acid, action of, on glass, 12
Hygroscopic glass, alkali content of, 6
I.
Indentation modulus, 22
Index, refractive, 216
Insulating properties of glass, 29
Iron, 96 colouring effect of, 196 oxidation of, in glass, 195
Irregularities caused by rolling, 86
J.
Jena, 7, 10, 14, 26, 29, 203, 210, 213, 241
K.
Kelp, 40
Kowalski, 19
L.
Laboratory ware, 10, 23
Ladling glass, 85 rolled plate glass, 124
Lagre, 166
Lamp-chimneys, 110, 238
Lamp-work, 240, 244
Large vessels, production of, 105
Lead, 49, 183, 188
Lear for rolled plate glass, 127 sheet glass, 165
Leighton, 39
Lenses, cleaning of, 220 finger-marks on, 220 pressing small, 94
Light, action of, on glass, 15
Lighthouse glass, 178, 250
Lime, slaked, 45
Lime-stone, 46
Limited range of vitreous bodies, 4
Lippe, 38
Lynn, 39
M.
Machines, bevelling, 145 double rolling, 130 grinding, 139 polishing, 141
Magnesia, 48, 186
Manganese, 15, 52, 80
Mangin mirrors, 252
Marver, 111
Massive glass, 249
Mechanical properties of glass, 18
Metal, attachment of, to glass, 26
Minerals, crystalline, 217
Mirrors, 145 searchlight, 251
Mixing of materials, 73
Moulds for glass-blowing, 90, 110, 116 pressed glass, 119
Muffled glass, 172
Muranese glass, 123
N.
Nickel, 96 colouring effect of, 197 steel, 27, 148
Nitrates, alkali, 44, 78
O.
Objectives, apochromatic, 213 telescope, 218
Opal glass, 45, 52, 186
Opaque plate glass, 146
Open pots, 56
Optical glass, annealing, 235 chemical composition of, 217 cooling of, 233 cost of, 237 fining, 229 founding, 227 furnaces for, 225 hardness of, 220 moulding, 235 pressing, 93 range of, 216 raw materials for, 223 sorting, 235 stability of, 219 strain in, 221 stirring, 231 yield of, 236 properties of glass, 205
P.
Painting on glass, 201
Parason, 102
Patent plate glass, 171
Paving stones, glass, 249
Pearl ash, 43
Phosphoric acid, 11
Phosphorus, 188
Photographic ghosts, 16 lenses, anastigmatic, 213 colour of, 209
Pipe, glass-maker’s, 89 sheet-blower’s, 158 warmer, 158
Plate glass, annealing kiln for, 135 bending of, 144 blown, 171 casting, 132 colour of, 33 figured rolled, 87 flatness of, 134 furnaces for, 133 grinding machines, 139 of, 137 mirrors, 145 opaque, 146 polishing machines, 141 polishing of, 137 raw materials for, 132 rolled, 86, 123 silvering, 146 sizes of, 143 strength of, 15 striæ in, 143 wired, 27, 147
Platinum, 27
Polishing, theory of, 141
Pontil, 98, 176, 239
Potash, 43
Potato, use of, in glass melting, 81
Ports, furnace, 67
Pots, burning of, 58 covered, 56 drying of, 58 for flint glass, 109 optical glass, 226 manufacture of, 56 open, 56
Pouring of glass, 85, 87
Pressed glass, 92, 118 composition of, 120
Presses for glass, 119
Proofs, 82, 231
Purity of materials, 36
Q.
Quartz, 40
R.
Range, limited, of vitreous bodies, 4
Recuperative furnaces, 66, 156
Red lead, 49
Refraction, double, in optical glass, 221 of light in optical glass, 209
Refractive index, 216
Regenerative furnace, 66, 155
Reichsanstalt, 10
Resistance to crystallisation of glass, 4
Rings for lighthouse lenses, 251
Rod, glass, 245
Rolled plate glass, 86, 123 annealing, 127 cutting, 128 defects of, 129 figured, 130 furnaces, 123 ladling, 124 raw materials for, 124 rolling, 126 sorting, 129 surface of, 122
Rolling of glass, 86
Rubies, artificial, 247
Ruby, copper, 184, 188, 198 flashed, 184 gold, 185
Rupert’s drops, 248
S.
Salt-cake, 37, 42, 79, 189
Sand, 38
Sandstone, 39
Schott, 8, 19, 203, 213, 241
Scratches on sheet glass, 169
Searchlights, 250
Seed in sheet glass, 167
Selenium, colouring effect of, 190
Sheet glass, 70 blisters in, 160, 168 blowing, 161 colour of, 33, 167 compared with plate, 149 cylinders, 161, 171 defects of, 166 dipping, 166 flattening, 165 furnaces, 151, 170 lear, 165 mechanical production of, 173 raw materials for, 150 sorting, 166 splitting, 164 strength of, 18
Siedentopf, 182
Siege blocks, 59
Siemens, 248
Sievert, 92, 105, 117, 172 processes, 105, 117
Signal glasses, 203
Silica bricks, 61 glass, 5, 26, 241 sources of, 37
Silicon, colouring effect of, 187
Silver, colouring effect of, 185
Silvering plate glass, 146
Sizes of plate glass, 142
Soda ash, 41 carbonate, 41 sulphate, 37, 42, 79 sulphide, 80 sulphite, 79
Solidification of glass, 1
Solutions, analogy of, with glass, 206
Sorting rolled plate glass, 129
Specific heat of glass, 25, 29 inductive capacity of glass, 29
Stains, coloured, 200
Stassfurth, 44
Stones in rolled plate glass, 129 sheet glass, 167
Storage of materials, 37
Strain in optical glass, 221
Strength of glass, 19
Striæ in coloured glass, 203 optical glass, 206, 227 plate glass, 143 testing apparatus, 207
String in sheet glass, 168
Strontium, 86
Structure of glass, 1
Sulphur, colouring effect of, 189
Surfaces, chemical behaviour of glass, 8, 10
Szigmondi, 182
T.
Table, rolling, 126
Tank blocks, 59 furnaces, 59, 69 economy of, 72 for sheet glass, 152
Telescope objectives, 213
Temperature of fusion of glass, 5
Tempered glass, 20, 248
Tensile strength of glass, 19
Thallium, 183, 188
Theory of colours in glass, 181 polishing, 141
Thermal endurance of glass, 23 properties of glass, 23
Thermometer glass, 7, 8, 28
Tin, colouring effect of, 187
Tonnelot, 7
Transparency of glass, 31 optical glass, 208
Trautwine, 19
Tubing, 238 combustion, 7 drawing of, 239
Tumblers, 111
U.
Ultra-violet microscope, 243
V.
Vanadium, colouring effect of, 189
Veins in optical glass, 206, 227
W.
Water, action of, on glass, 10 glass, 250
Wetting up clay, 57
Winkelmann, 19
Wired plate glass, 27, 147
Witherite, 48
Wool, glass, 245
Y.
Young’s modulus, 20
Z.
Zaffre, 197
Zeiss, 213, 244
Zinc, colouring effect of, 49, 186
Zschimmer, 14
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=INDIA-RUBBER AND ITS MANUFACTURE=, with Chapters on Gutta-Percha and Balata. By H. L. Terry, F.I.C., Assoc. Inst. M.M.
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Transcriber’s Notes
Punctuation, hyphenation, and spelling were made consistent when a predominant preference was found in this book; otherwise they were not changed.
Simple typographical errors were corrected; occasional unbalanced quotation marks retained.
Ambiguous hyphens at the ends of lines were retained.
The appearance of the Table of Contents has been altered slightly.
Index not checked for proper alphabetization or correct page references.
In the Index, it was unclear to the Transcriber whether some of the indentations indicated sub-entries or implied ditto marks, so the indentations have been treated here as multiple levels of sub-entries.