A CYCLOPÆDIA OF PRACTICAL RECEIPTS, PROCESSES, AND COLLATERAL INFORMATION (continued 43)

Tests. The only tests applicable to gems and precious stones are the determination of their relative hardness and their specific gravity. By the first test, pastes or factitious gems are readily detected; but beyond this, owing to the difficulty of applying it, it ceases to be useful to persons unconnected with the trade. The determination of the specific gravity is, however, of more general application, as gems are generally dismounted when offered for sale, or are so set that they may be removed from their ‘mountings’ without injury or inconvenience. See Specific Gravity, and below.

Obs. The relative hardness of the different substances is measured by the power they possess of cutting or scratching the other substances having a smaller number attached to them in the table. Thus, no gem but the DIAMOND (20) will scratch either the RUBY (17) or the SAPPHIRE (16); and, for the same reason, a blue stone that will cut the EMERALD or the TOPAZ can be no other than the SAPPHIRE. The sp. gr. is ascertained in the usual manner, and will be found sufficiently indicative of the true nature of the stone when considered in connection with its other characteristics. The index of refraction is a certain key to the quality of the stone, in the hands of those who are capable of determining it, and may be applied to either mounted or unmounted gems. The most convenient instrument for the purpose is Wollaston’s ‘REFLECTING-GONIOMETER,’

Gems, Facti′′tious. These, with few exceptions, are made of very pure, fusible, highly transparent, and dense glass, usually termed ‘PASTE’ or ‘STRASS,’ which is generally formed of oxide of lead, potassa, and silica, with small quantities of other ingredients to increase the brilliancy and clearness. The characteristic tints are imparted by the addition of metallic oxides. The beauty of artificial stones and gems depends, chiefly, upon the tint of the real stones being exactly imitated, and upon proper care and skill being exercised in the cutting, polishing, and mounting them. All the coloured glasses, and enamels, may be worked up into artificial gems.

Table of the Hardness, Specific Gravity, and Refractive Power of the principal Gems and Precious Stones, and some other Minerals; compiled expressly for this work.

Name.Relative Hardness.Specific Gravity.Index of Reflection.

Agate122·6

Amethyst (occidental)112·7

Calcareous spar62·7

Chalk32·7

Chrysolite103·7

Cornelian112·7

Crystal112·6

Diamond (bluish)193·32·439

Diamond (cubic)183·2

Diamond (from Ormus)203·7

Diamond (pink)193·4

Diamond (yellowish)193·3

Diamond (average colourless)19 to 203·3 to 3·55

Emerald122·8

Fluor spar73·51·434

Garnet124·41·815

Glassvarious2·3 to 3·621·525 to 2·028

Glass (crystal or flint)3·0 to 3·61·830 to 2·028

Glass (plate)2·5 to 2·61·514 to 1·542

Gypsum52·3

Jasper (green)112·7

Jasper (reddish yellow)92·6

Onyx122·6

Opal102·6

Quartz102·71·548

Ruby174·21·779

Ruby (pale, from Brazil)173·5

Ruby (spinelle)133·41·764

Sapphire (deep blue)163·81·794

Sapphire (paler)173·8

Sardonyx122·6

Schoerl103·6

Topaz154·2

Topaz (Bohemian)112·8

Topaz (whitish)143·5

Tourmaline103·0

Zeolite82·1

Zircon——1·961

MM. Fremy and Feil have lately succeeded in manufacturing artificial corundum, ruby and topaz, having a composition the same as the natural stones. The process by which they have effected this consists in fusing together at a red heat, in the furnace of a glass works for a considerable time, a fusible aluminate (such as aluminate of lead), and some silicious body.

The silica is found to unite with the lead, and to liberate the alumina in the crystalline form. When equal weights of alumina and red lead are heated together in a crucible made of some refractory silicious substance, the above conditions if the temperature has been maintained sufficiently long and high ensue, and there is found in the crucible at the end of the operation a layer of silicate of lead, and very frequently another of pure crystallised alumina or corundum.

The ruby colour is given by adding to the mixture in the crucible two or three per-cent. of bichromate of potash, the blue being produced by the addition of a small quantity of oxide of cobalt, with a trace only of bichromate of potash. A film of silicate of lead very frequently adheres to the ruby crystals, and this has to be removed.

In some instances, however, the crystals occur nearly pure, and are precisely similar to the natural gems in crystalline form, composition, hardness, and lustre.

Upon being heated, the artificial ruby, like the natural one, loses its rose colour, and recovers it again on cooling. It is said that the factitious gems hitherto obtained are not, as a rule, equal in lustre to the natural ones, and are consequently not so well suited for jewellers’ work; also that they do not present to the lapidary conditions favorable to cleavage or cutting. They are, however, very well adapted for the works of watches. See Enamels, Pastes, &c.

GENE′VA. See Gin and Hollands.

GEN′TIAN ROOT. Syn. Gentinæ Radix, L. The dried root of Gentiana lutea, or ‘yellow gentian.’ Dose, 10 to 30 gr.; as a simple bitter tonic, and stomachic, in dyspepsia, loss of appetite, gout, &c. It was formerly a favourite remedy in agues. “Joined with galls or tormentil, and given in sufficient quantity, it has not failed in any intermittents in which I have tried it.” (Dr Cullen.) In excessive doses it is apt to relax the bowels and disturb the system. When taken for some time, it imparts its bitter flavour to the perspiration and urine. See Decoction, Extract, &c.

GEN′TIANIN. Syn. Gentianine; Gentianina, L. A substance obtained by MM. Henry and Caventou from the root of common gentian.

Prep. 1. Gentian root (in powder) is digested for 2 or 3 days in cold ether, with agitation, and the filtered tincture evaporated to dryness; the residuum is dissolved in rectified spirit, and the solution is again evaporated; the semi-crystalline mass is, lastly, redissolved in either alcohol or ether, and crystallised by careful evaporation.

2. (Magendie.) The ethereal extract is exhausted with cold alcohol (rectified spirit), as before, and the resulting tincture is evaporated to dryness; the residuum is dissolved in water, calcined magnesia added in excess, and the whole boiled and filtered; the sediment is digested in ether, and the ethereal tincture allowed to crystallise by slow evaporation.

Prop., &c. Gentianin forms golden-yellow needles, scarcely soluble in cold water, but very soluble in alcohol and ether. It is a powerful bitter and stomachic.—Dose, ¹⁄₂ gr. to 2 gr.

GER′MAN PASTE. Prep. From pea-meal, 2 lbs.; sweet almonds (blanched), 1 lb.; fresh butter or lard, ¹⁄₄ lb.; moist sugar, 5 oz.; hay saffron, ¹⁄₂ dr.; beat to a smooth paste, adding cold water q. s., granulate the mass by passing it through a colander, and expose the product to the air in a warm place, until quite hard and dry. The addition of 2 or 3 eggs improves it. Used to feed larks, nightingales, and other insectivorous birds. It will keep good for 12 months in a dry place.

GER′MAN SILVER. Syn. Albata, Argentan, Electrum, Nickel Silver, Tutenag, Virginian Plate, White Copper. A well-known alloy, the finer varieties of which nearly equal silver in whiteness and susceptibility of receiving a high polish, whilst they surpass it in hardness and durability. The following formulæ are from the highest authorities, or are the results of actual analysis of the finest commercial samples:—

Prep. 1. Copper, 50 parts; nickel, 20 parts; zinc, 30 parts. Very malleable, and takes a high polish.

2. Copper, 50 parts; nickel, 26 parts; zinc, 24 parts. Closely resembles silver; an excellent sample.

3. Copper and zinc, of each 41 parts; nickel, 18 parts. Rather brittle.

4. (M. Gersdorff.) Copper, 50 parts; nickel and zinc, of each 25 parts. Very white and malleable, and takes a high polish. Recommended as a general substitute for silver.

5. (Gersdorff.) Copper, 60 parts; nickel and zinc, of each 20 parts. For castings, as bells, candlesticks, &c.

6. (Gersdorff.) Copper, 60 parts; nickel, 25 parts; zinc, 20 parts. For rolling and wire. Very tough and malleable.

7. (Sample made from the ore of Hilburghausen.) Copper, 40¹⁄₂ parts; nickel, 31¹⁄₂ parts; iron, 2¹⁄₂ parts; zinc, 25¹⁄₂ parts. Equal to the best Chinese sample.

8. (Pelouze.) Copper and nickel, equal parts. Recommended by M. Pelouze as superior to any of the alloys containing zinc.

9. (Pelouze.) Copper, 2 parts; nickel, 1 part. Not so white as the last, but more malleable.

10. (White Copper from China.)—a. Copper, 30 parts; nickel, 36 parts; zinc, 34 parts.

b. (Said to be prepared from native ore.) Copper, 41 parts; nickel, 32 parts; iron, 2¹⁄₂ parts; zinc, 24¹⁄₂ parts. Silvery white, takes a high polish, very sonorous, malleable both cold and at a dull-red heat, and may be rolled into leaves or formed into wire.

11. (White metal spoon, sold as ‘German Plate.’) Copper, 55 parts; nickel, 24 parts; zinc, 16 parts; tin, 3 parts; iron, 2 parts.

Anal. This may be briefly described as follows:—a. 100 gr. of the alloy is digested in nitric acid q. s., diluted with a little water. If the sample is unequally attacked by the acid, and a white external shell is observed which dissolves more slowly than the internal portion, it is ‘plated’ on those parts with silver. If this silver shell or casing has a polished surface on both sides, the article has been ‘electro-plated,’ if the contrary is the case, it has most probably been plated in the usual way.

b. The solution being completed, heat is applied to expel the excess of acid, and the remainder is largely diluted with distilled water; dilute hydrochloric acid is now dropped in as long as it occasions a precipitate, and the whole, after being moderately heated for a short time, and cooled, is thrown upon a small paper filter; the precipitate on the filter is next washed with distilled water, carefully dried, and ignited in a small porcelain crucible, the filter itself being separately burnt on the cover of the crucible, and the ashes added to its contents prior to ignition. Every 143¹⁄₂ gr. of the resulting fused chloride is equal to 108 gr. of metallic silver.

c. The filtered liquid (see b) is next treated with a stream of sulphuretted hydrogen, and the black precipitate is collected, washed, and digested in strong nitric acid; when the solution is complete sulphuric acid is dropped in to precipitate the lead (if any is present); if a precipitate is formed, the whole is evaporated to dryness, and the excess of sulphuric acid expelled by a rather strong heat applied towards the end; the dry mass is now collected on a filter, washed with a mixture of water and alcohol, dried, and exposed to slight ignition in a porcelain crucible. Every 152 gr. of the resulting dry sulphate is equal to 104 gr. of lead.

d. The liquor filtered from the sulphate of lead, or (in its absence) the nitric solution of the precipitate produced by the sulphuretted hydrogen (see c), is next treated with potassa, &c., as described under the analysis of brass. Every 40 gr. of the dry protoxide thus obtained represents 32 gr. of pure copper.

e. The liquor which was filtered from the precipitate produced by the sulphuretted hydrogen (see c) is boiled until it loses its offensive odour, and is then precipitated with carbonate of soda, in slight excess, and again boiled for a few minutes; the precipitate (mixed oxides of nickel and zinc) is collected, washed, and redissolved in dilute acetic or nitric acid, in excess; a current of sulphuretted hydrogen is next passed through the solution, the precipitate collected on a filter, washed, redissolved in hydrochloric acid, and the solution again treated with carbonate of soda; the last precipitate (oxide of zinc) is washed, dried, and gently ignited. Every 40 gr. of this oxide is equivalent to 32 gr. of metallic zinc.

f. The washings of the precipitated oxides and the liquid filtered from the precipitate occasioned by the sulphuretted hydrogen (see e) are mixed together, pure solution of ammonia added in considerable excess, and the mixture agitated for some time; the undissolved portion of the precipitate is then collected on a filter, washed with distilled water, redissolved in dilute nitric acid, again precipitated with solution of potassa, and this last precipitate (ferric oxide) washed, dried, ignited, and weighed. Every 80 gr. represents 50 gr. of metallic iron.

g. The ammoniacal solution filtered from the precipitate of sesquioxide of iron (see f) is precipitated with pure solution of potassa, boiled for a few minutes, and, when cold, thrown on a filter; the precipitate is, lastly, washed with hot water, dried, ignited, and weighed. Every 37¹⁄₂ gr. of the oxide thus obtained is equal to 29¹⁄₂ gr. of metallic nickel.

Obs. The manufacture of nickel or German silver has of late acquired an importance which is second only to that of silver plate itself. The superior quality of this alloy, and the graceful patterns which it is often made to assume in the hands of the accomplished artist cannot fail to have attracted the admiration of the majority of our readers. The value of correct information regarding the preparation of this alloy, and of a ready method of determining the composition of the most improved commercial samples will, therefore, be fully appreciated by every metallurgist who wishes to throw his wares into the arena of public competition. Much that is vended under the name of German silver is little better than the Britannia metal or PLATE PEWTER formerly so plentiful in every establishment in this country. German silver has quite superseded copper as the basis of ‘electro-plated goods.’

The union of the metals in the above formulæ is effected by heat with the usual precautions. When iron is ordered, it is generally added under the form of ‘tin plate.’ See Alloy, Brass, Britannia Metal, Bronze, &c.

GER′MAN TIN′DER. See Amadou.

GERMINA′TION. The growth or vegetation of a seed by which a young plant is produced. The conditions essential to germination are the presence of warmth, air, and moisture. The most favorable temperature is between 60° and 85° Fahr., according to the habitat of the respective plants. Below 40° Fahr. most of the more perfect seeds either refuse to vegetate, or vegetate slowly and feebly; and at or near the freezing-point none of them undergo this change. At a temperature above 100° Fahr. the young germ is usually injured, and at about 125°, if it forms, it soon withers and dies. See Malting, Seed, &c.

GERMS. The ‘germ theory of disease’ may be briefly stated to be that which supposes the cause of epidemic and contagious maladies to be due to the agency of specific, inconceivably small germs,—different germs giving rise to different diseases.

These disease germs gaining an entrance by means of air, water, or food into the healthy body, and being possessed of extraordinary powers of increase and subdivision, are supposed to set up the particular disease, and at the same time to multiply to an incredible extent by feeding upon the tissues best suited for their support. Further, they are conceived to be thrown off into the atmosphere from the body of the patient, whence they are conveyed as before described into other healthy animal organism, in which, comporting themselves as in the previous case, they set up a similar disease. See Bacteria as originators of disease.

GHEE. A sort of butter used by the natives of India. Prep. Milk is boiled in large earthen pots for an hour or two, then allowed to cool, a little curdled milk called ‘dhye’ being added, in order to make the whole coagulate. After a lapse of some hours the contents of each to the depth of 5 or 6 inches are removed and placed in a larger earthenware utensil, in which they are churned by means of a piece of split bamboo for about half an hour; then hot water is poured in, and the churning continued for half an hour longer, after which time the butter is found to be formed. When this becomes rancid, it is melted in an earthen vessel, and boiled until all the water has evaporated; after which a little salt or betel-leaf is put into it, and finally it is poured off into suitable vessels in which it can be preserved from the air. Bottles are commonly used for this purpose. See Butter.

GHER′KINS. Syn. Gir′kins. Small cucumbers adapted for pickling. See Pickles.

GILD′ING. Syn. Dorure, Fr. The art or process of covering the surfaces of bodies with a thin film of gold, for the purpose of increasing their durability or improving their appearance. For the sake of brevity we shall briefly notice the leading varieties of gilding, and their applications, in alphabetical order.

Gilding, Burnished. This is distemper gilding to which a ‘face’ has been given with the ‘burnisher.’ It is chiefly employed for the polished portions of the frames of pictures and mirrors, the more prominent parts of statuettes, &c.

Gilding, Chemical. Those varieties in which the film of gold is formed on the surface through the agency of chemical affinity, in opposition to mechanical gilding, in which the gold is made to adhere by the intervention of some glutinous substance.

Gilding, Cold. The articles (copper or brass) to be gilded, after being softened, annealed, and polished in the usual manner, are rubbed with a little gilding powder by means of a piece of cork moistened with a solution of salt in water; after which the work is burnished with a piece of hematite or polished steel. (See below.)

Gilding, Distemper. This is applied to wood, plaster, marble, &c. It is commonly performed in this country by giving the wood, first, a coating of good size, and next, several successive coats of size thickened with finely powdered whiting, Spanish white, or plaster of Paris until a good face is produced; observing to let each coat become quite dry, and to rub it perfectly smooth with fine glass paper, before the application of the following one. When the proper ‘face’ is obtained, the surface is thinly and evenly gone over with gold size, and when this is nearly dry, the gold leaf is applied, and afterwards burnished with an agate or dog’s tooth. The process, as adopted by the Parisian artists, who greatly excel in this species of gilding, is very complicated, and is divided into at least 17 distinct operations, each of which they declare to be essential to its excellence.

Gilding, Electro-. See Electrotype.

Gilding, Grecian. In this variety sal-ammoniac and corrosive sublimate, equal parts, are dissolved in nitric acid, and a solution of gold made with this menstruum; after slight concentration the liquid is applied to the surface of silver, which immediately becomes black, but on being heated exhibits a rich gilded surface.

Gilding, Japanner’s. The surface is covered with oil size thinned with spirits of turpentine, and gold, in powder, is gently dabbed on with a puff of wash leather. This gives the appearance of ‘frosted gold.’ A coating of varnish is next given, followed by exposure to a gentle heat in the ‘stove.’

Gilding, Leaf. This term is commonly applied to the gilding of paper, vellum, &c., by applying leaf gold to the surface, previously prepared with a coating of gum water, size, or white of egg. It is usually burnished with an agate or dog’s tooth.

Gilding, Mechanical. See Chemical gilding (above).

Gilding, Mercurial. See Wash gilding (below).

Gilding, Oil. This species of gilding may be divided into several operations. The following are the abridged instructions of a Parisian artist on the subject:—1. The surface is prepared by a coating of white lead in drying oil.—2. Another coat is given, made with calcined white lead or massicot, ground in linseed oil and turpentine. 3 or 4 coats of this mixture are often given, at intervals of at least 23 hours, observing to carefully smooth off each coat with pumice stone or shave grass before the application of the following ones.—3. The ‘Gold Colour,’ or paint, is next applied. It is usually very adhesive gold size, or the bottom of the pot or dish in which painters wash their brushes. For this purpose it is thoroughly ground and strained.—4. When the gold colour becomes partially dry and sufficiently tenacious, the gold leaf is applied, and pressed on with a wad of cotton-wool or a soft brush. It is now left for several days to harden.—5. A coat of spirit varnish is next given, and the object is cautiously passed over a chafing-dish of charcoal, observing to avoid stopping the motion of the piece whilst doing so, as the work would then become discoloured and blistered.—6. The work is ‘finished off’ with pale oil varnish. For out-door gilding and common work the varnishing process is generally omitted. This species of gilding is applied to woodwork, plaster, metal, &c.

Gilding, Varnish. This is a mere variety of oil gilding, applied to equipages, furniture, mirror and picture frames, &c., the surface being highly varnished and polished before it receives the size or gold colour; and after the gilding has become quite dry, a coat of spirit varnish, fumed with the chafing dish as above, is applied, followed by 2, 3, or more coats of the best copal varnish, at intervals of 3 or 4 days each. The whole is, lastly, carefully polished with tripoli and water.

Gilding, Wash, Amalgam g., Mercurial g., Water g. This consists in the application of a thin coating of amalgam of gold to the metallic surface (brass, bronze, or copper) to be gilded, and the subsequent volatilisation of the mercury by heat. It is the usual method of gilding articles of copper and its alloys, and possesses great beauty and durability when skilfully executed. The occupation is, however, an unhealthy one, owing to the continual exposure of the workman to the fumes of mercury. The furnace invented by M. D’Arcet obviates this evil, as the whole of the volatilised mercury is carried off, and again condensed for further use. It should, therefore, be adopted by every water-gilder who studies economy and the health of those in his employ.

The process of water gilding consists in several distinct operations, and can only be successfully performed by those who have been schooled in the art by an apprenticeship to the trade. It would, therefore, be waste of space to enter into details here. Formulæ for several of the articles employed for the purpose will be found in the alphabetical places in this work.

Gilding, Water. See above.

Among the applications of the process of gilding that deserve a separate notice are the following:—

The gold letters and figures on the covers of BOOKS are thus formed:—Gum mastic, in fine powder, is dusted over the surface to be gilded; an iron or brass tool bearing the design upon its face is then heated to a proper temperature, and gently pressed upon a piece of leaf gold, which slightly adheres to it; the two are then transferred to the cover, and the tool is gently pressed on it, by which means the mastic softens and retains the gold. The loose gold and powdered mastic are then dusted off with a brush. Gold leaf will adhere to leather without the use of mastic, but not so firmly as when it is employed.

The edges of the leaves of books and paper are first cut perfectly smooth, and then washed over with a solution of isinglass in weak spirit, or with a varnish made of Armenian bole, 4 parts, and powdered sugar-candy, 1 part, mixed up to a proper consistence with strained white of egg. The coating is allowed to dry, and is then smoothed with a wet rag, after which the gold leaf is applied and polished with the burnisher.

Brass buttons, formerly so much in demand, are covered by a rough species of wash gilding. The buttons are polished in the lathe and thrown into a pan with a little amalgam of gold, and as much aquafortis diluted with water as will wet them all over. Here they are well stirred up, until they assume a silvery appearance, when they are washed with clean water. They are then submitted to a sufficient heat in a suitable apparatus, until the mercury is volatilised. The buttons are next cooled, and well tossed and rubbed about with a painter’s brush; and are, lastly, burnished by washing them well with beer or ale grounds.

Twelve dozen (1 gross) of buttons, of 1 inch in diameter, may be perfectly gilded on both sides with only 5 gr. of gold. By an Act of Parliament, which is still unrepealed, this is the smallest quantity of gold permitted to be used for a gross of buttons of the above size.

Glass, PORCELAIN, and EARTHENWARE, are gilded by blending powdered gold with gum-water and a little borax, and applying the mixture by means of a camel-hair pencil; the article is then heated in an oven or furnace, by which means the gum is burnt, and the borax, vitrifying, cements the gold to the surface. It is afterwards polished with a burnisher. Names, dates, or any fancy device, may thus be permanently and easily fixed on glass, china, earthenware, &c.

Japanned work is gilded by the method explained as ‘Japanner’s gilding’ (above).

Leather is gilded in the same way as the covers of books. (See above.) For common work, silver leaf, or even tin foil, is applied to the surface, previously covered with size or white of egg, and after being burnished down and dried, is washed over with gold-coloured lacquer.

The LETTERS of sign-boards and the ornamental gilding for out-door work are done by first covering the design with yellow paint, then with oil gold-size, and when this is nearly dry applying the leaf gold, observing to shield it properly from the wind, lest it be blown away or become crumpled before being properly attached. The work is, lastly, varnished.

Polished metals may be gilded by one or other of the methods already noticed. Articles in silver, copper, brass, and bronze, are usually coated by the process of wash or water gilding; or, directly, by the application of gold leaf, as follows:—The piece or article is heated to a bluish tint, and gold leaf pressed gently and carefully on it with the burnisher; heat is again applied, and the process repeated with fresh leaves of gold until the gilding has acquired the proper thickness and tone. The surface is lastly polished with the burnisher, or is coloured in the usual manner at the stove. This succeeds with iron, steel, silver, copper and its alloys, &c. Another method for polished articles in iron and steel, which, however, is less durable than the preceding, is to apply an ethereal solution of gold to the surface with a camel-hair pencil. The ether flies off and leaves the surface coated with gold, which is then polished as before. In this way, any fancy device or writing may be executed on steel or iron with extreme facility.

Silks, SATINS, WOOLLENS, IVORY, BONE, &c., may be readily gilded by immersing them in a solution of neutral terchloride of gold (1 of the salt, and 3 to 6 of water), and then exposing them to the action of hydrogen gas. The latter part of the process may readily be performed by pouring some dilute sulphuric acid on zinc or iron filings, in a wide-mouthed bottle, and placing it under a jar or similar vessel, inverted, at the top of which the articles to be gilded are suspended. Flowers or other ornamental designs may be produced by painting them on the surface with a camel-hair pencil dipped in the solution. The design, after a few minutes’ exposure to the hydrogen, shines with all the splendour of the purest gold, and will not tarnish on exposure to the air, or in washing.

Gilded thread or GOLD THREAD is merely a thread of yellow silk covered with a very thin flatted wire of gold, by means of a revolving wheel.

Wire (copper, silver, or brass) is occasionally gilded, in coils, by a similar process to that adopted for BUTTONS; but more frequently as follows:—Rods (usually of silver) are covered with gold foil of a thickness proportionate to the quality of the intended wire, and the compound bar is then drawn into wire, in the usual way. 100 gr. of gold was formerly the lowest legal quantity that could be employed for 1 lb. of silver.

Patents. Among the varieties of chemical gilding may be mentioned

1. (Elkington’s patent—German gilding, Bonnet’s GILDING PROCESS.) The articles to be gilded, after being perfectly cleaned from scale or grease, and receiving a proper ‘face,’ are suspended, by means of wires, in the gilding liquid (boiling hot), and moved about therein for a period varying from a few seconds to a minute, or longer; the precise time required depending on the newness and strength of the liquid. When sufficiently gilded, the articles are withdrawn from the ‘solution of gold,’ washed in clean water, and dried; after which they undergo the usual operation of ‘colouring,’ &c. A dead gold appearance is produced by the application to the articles of a weak solution of nitrate of mercury previously to the immersion in the gilding liquor; or the deadening may be given by applying a solution of the nitrate to the newly gilded surface, and then expelling the mercury by heat.

The gilding liquor.—Take of fine gold, 5 oz. (troy); nitro-muriatic acid, 52 oz. (avoirdupois); dissolve by heat, and continue the heat until red or yellow vapours cease to be evolved; decant the clear liquid into a suitable vessel; add of distilled water, 4 galls.; pure bicarbonate of potassa, 20 lbs.; and boil for 2 hours. The nitro-muriatic acid is made with pure nitric acid (sp. gr. 1·45), 21 oz.; pure muriatic acid (sp. gr. 1·15), 17 oz.; and distilled water, 14 oz.

This process, though patented by Mr Elkington in England, was in reality discovered and first practised by M. Bonnet, a foreigner. Articles thus gilded do not bear friction and the operations of being put in colour (mise en couleur) so well as those gilded by the mercurial process, or by the methods of cold or leaf gilding as applied to polished metals.

2. (Talbot’s patent.) By this process polished metallic articles are gilded by simple immersion in a solution of gallic acid in water, ether, or alcohol, to which a solution of gold has been previously added. Silvering and PLATINISING may be effected in the same manner, by using a solution of either of these metals instead of one of gold.

⁂ These and other chemical processes have been almost completely superseded by the certain and economical process of ELECTRO-GILDING. See Electrotype.

Gilding Amalgam. See Amalgam.

Gilding Liquor. This name has been given to various solutions of gold, and to other liquids employed in gilding. The former are noticed elsewhere. Among the latter are the following:

Deading aquafortis. From mercury, 1 part; aquafortis (sp. gr. 1·33), 3 parts; dissolve, and add of soft water, 7 parts. Used to produce a dead-gold effect. It is applied (diluted) to the articles, before spreading the amalgam over them, in water gilding; or before placing them in the ‘gilding liquor,’ in the chemical processes.

Mercurial solution. From mercury, 10 parts, dissolved in aquafortis (sp. gr. 1·33), 11 parts, and the solution diluted with 25 times its weight of water. Used to moisten the scratch brush before drawing it over the amalgam, in mercurial gilding; also to deaden the gilded surface, by moistening the latter with it, and then exposing the piece to a heat sufficiently high to drive off the mercury.

Gilder’s pickle. From alum and common salt, of each 1 oz.; nitre, 2 oz.; dissolved in water, ¹⁄₂ pint. Used to impart a rich colour to gold surfaces, especially of trinkets. Its application should not be too long continued, as it dissolves a small portion of the gold. For common purposes it is best used largely diluted with water.

Vermeil, Vermeil coating, Or-molu c. From annotta and salt of tartar, of each 1 oz.; dragon’s blood, ¹⁄₂ oz.; water, 1 quart; simmer down to about one fourth, add saffron, 20 gr., and when merely tepid, strain through fine muslin into a bottle. Used to give lustre and fire to distemper gilding. A little is floated over the surface with a very soft, flat, camel-hair brush.

Gilding Metal. The metal employed as a base for gilding is usually brass, or a mixture of brass and copper. The following proportions have been recommended:—

1. Copper, 6 parts; brass, 1 part.

2. Copper, 4 parts; Bristol brass, 1 part.

3. Copper, 13 parts; old Bristol brass, 3 parts; tin, 14 parts.

Gilding Powder. Prep. 1. Pure gold, 5 dr.; pure copper, 1 dr.; aqua regia, 10 oz.; dissolve, moisten clean linen rags with the solution, dry them, and burn them to ashes. The latter contain the gold in a state of minute division, and must be carefully collected.

2. Grain gold, 1 dr.; rose copper, 15 gr.; aqua regia, 2 fl. oz.; proceed as last. Used in ‘Gold Gilding.’

3. See Gold (in powder).

Gilding Shells. See Gold Shells.

Gilding Size. See Gold Size.

Gilding Wax. Syn. Gilding varnish, Gilder’s wax. Prep. 1. From beeswax, 4 oz.; verdigris and sulphate of copper, of each 1 oz.; melted together.

2. Beeswax, 4 oz.; verdigris, red ochre, and alum, of each 1 oz. Used to give a red gold colour to water gilding.

GIN. Syn. Gene′va. Corn spirit flavoured with either oil of juniper or oil of turpentine.

Gin was originally and, for some time, wholly imported from Holland, and was a rich, soft spirit, flavoured, chiefly, with juniper berries; on which account it had obtained the name of ‘GENEVA,’ from ‘GENIÈVRE,’ the French for juniper. After a time the distillation of an imitation geneva sprung up in this country, when the foreign spirit came to be called ‘Hollands,’ or ‘Hollands geneva,’ to distinguish it from the spirit of home manufacture. The English monosyllable ‘GIN’ is a corruption of geneva, the primary syllable of which, as in numerous other instances, was seized on by the vulgar, and adopted as a short and convenient substitute for the whole word.

The liquor at present known by the name of ‘gin’ in this country is a very different article to that imported from Holland, and consists of plain corn-spirit, flavoured with oil of turpentine and small quantities of certain aromatics. The thousand and one receipts for this article, which have from time to time been printed in books, produce a flavoured spirit bearing no resemblance to the more esteemed samples of English gin; and, if possible, the products are even more unlike genuine Hollands. Any persons may easily satisfy himself of the truth of this assertion by actual experiment on the small scale. The cause of this incongruity has arisen chiefly from the writers not being practically acquainted with the subject, and from the disinclination of well-informed practical men to divulge, gratuitously, what they conceive to be valuable secrets. Hence the utter failure of any attempts to produce either gin or Hollands from the receipts usually published. The authors appear to have all imbibed a juniper-berry mania—probably from the imbibition of their favourite beverage. Oil of juniper, in the hands of these gentlemen, appears to be a perfect aqua mirabilis, that readily converts whisky into gin, and imparts the rich creamy flavour of ‘Schiedam Hollands’ to crude corn or molasses spirit. But theory and experiment sometimes disagree. In practice, it is found that the true flavour of foreign geneva cannot be imparted to spirit by juniper alone, and that the English gin of the present day depends for its flavour on no such a substance. The following formulæ are merely given as specimens; and it is proper to remark, that every distiller has his own receipt for this notorious beverage. Hence it is that the gins of no two distillers are of precisely the same flavour; and this difference is still more marked when the distillers reside in parts of the country remote from each other. Booth’s, Smith’s, and Nicholson’s gins have each a characteristic flavour, readily perceived by their respective votaries; whilst the difference between ‘Plymouth’ or ‘Bristol gin,’ and the ‘gin of the metropolis,’ is as remarkable as that between ‘Barclay’s XXX’ and ‘Guinness’s bottled stout.’ These variations in flavour generally depend on the use of more or less flavouring matter, or of a spirit more or less clean or free from taint; and, less frequently, on the addition of a small quantity of some peculiar aromatic, which exercises a modifying influence on the chief flavouring ingredient. In many cases the flavour has originated from accident, but the consumers having become accustomed to, and hence relishing, that particular ‘palate,’ it is found to be unwise or commercially impossible to alter it. Any change in these matters is therefore looked upon in every distillery as a dangerous innovation, which would prove more prejudicial to the prosperity of its exchequer than the repeal of the duty on French wines and brandy, or even a frightful conflagration. The distillers, like the brewers, are thorough conservatives in all matters connected with the flavour of their liquors.

In the preparation of gin, both sweetened and unsweetened, and indeed of liquors generally, the greatest possible care must be taken to avoid an excess of flavouring. The most esteemed samples are those that consist of very pure spirit, slightly flavoured.

Prep. 1. Clean corn spirit, at proof, 80 galls.; newly rectified oil of turpentine, 1¹⁄₄ pint; mix well by violent agitation, add culinary salt, 14 lbs., dissolved in water, 40 galls.; again well agitate, and distil over 100 galls., or until the faints begin to rise. Product. 100 galls. of gin 22 u. p., besides 2 galls. contained in the faints. If 100 galls. at 17 u. p. are required, 85 galls. of proof spirit, or its equivalent at any other strength, must be employed.

2. Proof spirit (as above), 8 galls.; oil of turpentine, 1 fl. oz.; salt, 1¹⁄₂ lb., dissolved in water, 4 galls.; draw over 10 galls., as before. 22 u. p.

3. Clean corn spirit, 80 galls.; oil of turpentine, 1 pint; pure oil of juniper, 3 fl. oz.; salt, 21 lbs.; water, 35 galls.; draw over 100 galls., as before. 22 u. p.

4. To the last, before distillation, add, of oil of caraway, ¹⁄₂ fl. oz.; oil of sweet fennel, ¹⁄₄ fl. oz.; cardamoms (ground), 8 oz.

5. To No. 3 add, of essential oil of almonds, 1 dr.; essence of lemon, 4 dr.

6. To No. 1, before distillation, add of creasote, 3 fl. dr.

7. To No. 3 add of creasote, 2 dr.

8. Proof spirit, 80 galls.; oil of turpentine, ³⁄₄ pint; oil of juniper, ¹⁄₄ pint; creasote, 2 dr.; oranges and lemons, sliced, of each 9 in no.; macerate for a week, and distil 100 galls. 22 u. p.

9. To No. 1 add of rectified fusel oil, ¹⁄₂ pint.

10. To No. 1 add of oil of juniper, ¹⁄₂ pint.

Concluding Remarks. The oil of turpentine for this purpose should be of the best quality, and not that usually vended for painting, which always contains resin and often fixed oil. Juniper berries, bitter almonds, and the aromatic seeds, may be used instead of the essential oils; but the latter are the most convenient. Turpentine conveys a plain-gin flavour,—juniper berries or oil gives a Hollands flavour,—creasote imparts a certain degree of smokiness, or whiskey flavour,—lemon and the other aromatics, a creaminess, fulness, and richness. The flavour imparted by cardamoms, when used judiciously, is peculiarly agreeable and appropriate. That from caraways is also in general esteem. Cassia in extremely small proportions also tells well. Fusel oil gives a whiskey-gin flavour; and in conjunction with creasote or crude pyroligneous acid, a full whiskey flavour. The only danger in the employment of all these articles is using too much of them. When this misfortune happens, the remedy is to add sufficient plain spirit to reduce the flavour to the proper standard. The creaminess and smoothness so much admired in ‘foreign geneva’ results chiefly from age. The English rectifier endeavours to imitate this by the addition of a little sugar. A rich mellowness, that combines well with gins turning on the ‘Hollands flavour,’ is given by a very small quantity of garlic, and with Canadian balsam or Strasburg turpentine. The peculiar piquancy, or the property of ‘biting the palate,’ regarded as a proof of strength and quality by the ignorant gin-drinker, is imparted to the liquor by the addition of a little caustic potassa. Sliced horseradish gives piquancy as well as mellowness. Grains of paradise, cayenne pepper, and sulphate of zinc, are also commonly added by fraudulent dealers.

Although gin is always prepared on the large scale by distillation, it may also be made by the simple solution or digestion of the flavouring ingredients in the spirit; but it is, of course, better for distillation. If made in the former way, no salt must be employed. The gin produced by the above formulæ is that denominated in the trade ‘UNSWEETENED GIN,’ ‘GROG GIN,’ &c.; but the gin usually sold in the metropolis is a sweetened spirit, and hence is technically distinguished by the terms ‘SWEETENED,’ or ‘MADE UP,’ The generality of London gin-drinkers prefer the latter article, even when weaker and inferior, which it usually is, as the addition of sugar permits adulteration and watering to an enormous extent with absolute impunity. Sweetened spirit cannot be easily tested for its strength, and is taken by the Excise at the strength which it is declared to possess by the dealer. To ascertain whether gin is sweetened or not, a little may be evaporated in a spoon, over a hot coal or a candle, when, if it is pure, it will leave the spoon scarcely soiled; but if, on the contrary, it has been sweetened, a small quantity of syrupy liquid, or sugar, will be obtained, the sweetness of which may be easily recognised by tasting it.

The whole of the casks and utensils employed for gin should be perfectly clean, and properly prepared, so as not to give colour; as, if this spirit acquires the palest coloured tint, its value is lessened, and if much coloured it is rendered unsaleable. When gin has once become much stained, the only remedy is to re-distil it; when it is only slightly stained, the addition of a few lbs. of acetic acid (B. P.) to a pipe or butt, a spoonful or two to a gallon, or a few drops to a decanterful, will usually decolour it, either at once or as soon as it is mixed with water to make grog. See Alcoholometry, Casks, Distillation, Hollands, Spirits, &c., and below.

Gin, Cor′dial. This is gin sweetened with sugar, and slightly aromatised.

Prep. Good gin (22 u. p.), 90 galls.; oil of almonds, 1 dr.; oils of cassia, nutmeg, and lemon, of each 2 dr.; oils of juniper, caraway, and coriander, of each 3 dr.; essences of orris root and cardamoms, of each 5 fl. oz.; orange-flower water, 3 pints; lump sugar, 56 to 60 lbs.; dissolved in water, 4 galls. The essences are dissolved in 2 quarts spirit of wine, and added gradually to the gin until the requisite flavour is produced, when the sugar (dissolved) is mixed in, along with a sufficient quantity of soft water, holding 4 oz. of alum in solution, to make up 100 galls. When the whole is perfectly mixed, 2 oz. of salt of tartar, dissolved in 2 or 3 quarts of hot water, are added, and the liquor is again well rummaged up; after which the cask is bunged up, and allowed to repose. In a week, or less, it will have become brilliant, and may be either ‘racked,’ or drawn from the same cask. Product. 100 galls., about 30 u. p.

Gin, Sweetened. Prep. From unsweetened gin (22 u. p.), 95 galls.; lump sugar, 40 to 45 lbs., dissolved in clear water, 3 galls.; mix well, and fine it down as above. Product. 100 galls., at 26 u. p. This, as well as the last, is usually ‘permitted’ at 22 or 24 u. p., which is also done when the gin has been further lowered with water so as to be even 30 or 35 u. p. See Spirits, and above.

GIN′GER. Syn. Ginger root; Zingiberis radix, Zingiber (B. P.), L. “The scraped and dried rhizome” (rootstock or underground stem) of “Zingiber officinale”—(B. P.). Ginger is an aromatic stimulant and stomachic, very useful in flatulence and spasms of the stomach and bowels, and in loss of appetite and dyspepsia, arising from debility, or occurring in old or gouty subjects. A piece chewed an hour before dinner tends to provoke the appetite; as a masticatory, it often relieves toothache, relaxation of the uvula, tender gums, and paralytic affections of the tongue. Made into a paste with warm water, and spread on paper, it forms a useful and simple ‘headache-plaster,’ which frequently gives relief when applied to the forehead or temples. As a condiment and flavouring ingredient, it is perhaps one of the most wholesome of the aromatic kinds, and is less acrid than the peppers.—Dose, 10 gr. to ¹⁄₂ teaspoonful, stirred up in any simple liquid.

Pur., &c. The best is that known in commerce as ‘unbleached Jamaica ginger,’ which is an uncoated pale variety, occurring in large, bold, fleshy pieces (‘RACES’), which cut soft, bright, and pale-coloured. The inferior varieties occur in smaller pieces, and are darker-coloured, flinty, and shrivelled. The dealers frequently ‘dress up’ the common dark-coloured gingers by washing them in water, drying them, and then ‘rouncing’ them in a bag with a little calcined whiting or magnesia (WASHED GINGER); or they bleach them by dipping them into a solution of chloride of lime, or by exposing them to the fumes of burning sulphur (BLEACHED GINGER); or they dip them into a milk formed of quicklime or whiting and water (WHITE-WASHED GINGER). The last has a chalk-white surface, which cannot be mistaken for the natural one. Powdered ginger is with difficulty obtained pure and good. The common adulterants are wheat-flour, or East Indian arrow-root, and plantain-meal. The first may be detected by the microscope, the others by the flavour and action of hot water. See Lozenges, &c.

GINGERIN. Syn. Oleoresina Zingiberis. Prep. (Pharm., U. S.) Put 1 lb. (Troy) of ginger in fine powder into a percolator, and pour on it 12 ounces (old measure) of pure ether. When this has been absorbed, add rectified spirit until 12 ounces (old measure) have been obtained. Recover the greater part of the ether by distillation over a water bath, and expose the residue in a porcelain dish until the volatile part has evaporated. Keep it in a stoppered bottle.

GINSENG. The root of the Panax Schinseng (Ginseng) is greatly esteemed in China, where it is regarded as a panacea for nearly all diseases, and where it realises a high price in consequence. This opinion of its therapeutic value is not shared by British and American practitioners, who look upon it as a comparatively inert substance. An allied species, the Panax quinquefolium, is sold in America, less for the sake of its very feeble demulcent properties, than to supply the demand of those who have acquired a taste for it. “The root has a somewhat bitter taste, and is somewhat mucilaginous. It occurs in pieces usually about three or four inches long, often partially divided, being joined together at the base; when clean it has a semi-transparent appearance.”[333]

Preserved Ginger. Syn. Conditum zingiberis, L. An excellent stomachic sweetmeat or preserve. It is chiefly imported from the West Indies and China. See Candying, &c.

A Factitious Preserved Ginger is sometimes met with, prepared from the stalks of lettuces just going to seed, using a concentrated syrup, strongly flavoured with Jamaica ginger. See Candy, &c.

GIN′GER BEER. See Beer.

GIN′GERBREAD. Prep. 1. (Dr Colquhoun.) Flour, 1 lb.; carbonate of magnesia, ¹⁄₄ oz.; mix; add, of treacle, ¹⁄₂ lb.; moist sugar, ¹⁄₄ lb.; melted butter, 2 oz.; tartaric acid (dissolved in a little water), 1 dr.; make a stiff dough, then add of powdered ginger and cinnamon (cassia), of each 1 dr.; grated nutmeg, 1 oz.; set it aside for half an hour or an hour before putting it into the oven. Obs. It should not be kept longer than two or three hours at the utmost, before being baked.

2. Flour and treacle, of each 1 lb.; butter, 1¹⁄₂ oz.; carbonate of magnesia, 1 oz.; add spices (ginger, cinnamon, nutmeg, allspice, cayenne, corianders, &c.) to taste; mix as last. Obs. Fit for baking in from four to six hours.

3. Flour, 2 lbs.; carbonate of magnesia, ¹⁄₂ oz.; mix; add, treacle, 1¹⁄₂ lb.; butter, 2 oz.; spice, q. s.; tartaric acid, ¹⁄₄ oz.; mix quickly, and make it into forms. Obs. Ripe for the oven in half an hour to one hour.

4. Instead of tartaric acid in the last formula, use cream of tartar (dissolved in water), 2 oz. Obs. Ripens in 40 or 50 minutes.

5. Flour or fine pollard, 1 lb.; treacle, ³⁄₄ lb.; salt of tartar, ¹⁄₂ oz., dissolved in water, q. s., butter, 1 oz.; spices, to palate. Obs. Takes several days to ripen; sometimes a fortnight.

6. (Extemporaneous.)—a. From flour, 1¹⁄₄ lb.; moist sugar and treacle, of each ¹⁄₂ lb.; butter, 2¹⁄₂ oz.; baker’s salt (carbonate of ammonia), ¹⁄₄ oz., dissolved in cold water, q. s.; ginger, 3 dr.; nutmeg, 2 dr.; cassia, 1 dr.; cayenne pepper (best), ¹⁄₂ dr.

b. From flour, 6 lb.; powdered ginger, 2¹⁄₂ oz.; caraway seeds, 1 oz. (and other spices to palate); candied lemon and orange peels, of each 2 oz.; moist sugar and melted butter, of each ¹⁄₂ lb.; treacle, 4 lb.; volatile salt, 2 oz.; water, q. s.; mix as above. May be baked at once.

c. From Jones’s patent flour, 2 lbs.; treacle, 1 lb.; moist sugar, ³⁄₄ lb.; butter, 2¹⁄₂ oz.; spice, q. s.; mix as quickly as possible, and bake it instantly. If the dough is expertly mixed up, the quality of the product is fully equal, if not superior, to that of any of the preceding formulæ.

Obs. Gingerbread is either rolled out into thin sheets and cut into cakes or nuts (GINGERBREAD NUTS) with the top of a wine-glass or canister, or is formed into thick cakes, which are baked in ‘batches’ (ordinary GINGERBREAD). Both varieties require a pretty brisk oven; the thinner kinds (nuts, &c.), especially, must be baked as crisp as possible, without being burnt. The varieties called LEMON GINGERBREAD, CARAWAY G., &c., have a perceptible predominance of these flavouring ingredients. The addition of a little alum, dissolved in water, makes the bread both lighter and crisper, and causes it to ripen quicker, but at the same time lessens its wholesomeness.

GIN′GER CAN′DY. See Candying.

GIN′GER DROPS. See Drops (Confectionery).

GLAIRE. White of egg. See Albumen and Egg.

GLAN′DERS. Syn. Farcinoma, L. A contagious disease, generally confined to the horse, ass, and mule, but communicable to man, in whom it assumes a highly malignant and often fatal character. This disease appears under two forms—1. Simple acute glanders, marked by copious discharge of foul mucous matter from the nostrils and adjacent parts; and—2. Farcy, Farcin, or Farcy glanders, when it attacks the lymphatics of the skin, either generally, producing a distended appearance of the vessels, like moles or buttons (LEAD or BUTTON FARCY), or locally, when it takes the form of dropsical accumulations in the legs (WATER FARCY).

Treat. Mr Youatt considers it useless to attempt the cure of glandered horses; but that farcy in its earlier stages and milder forms may be often successfully treated. “All the mercurials have been used with benefit in farcy; but they must be discontinued as soon as the mouth is sufficiently affected, or sickness, loss of appetite, and like symptoms, are produced.” (Blaine.) Feeding the animal entirely on green food appears to be the best mode of treatment in both varieties. The buttons are generally removed with caustic or a red-hot iron.

“Glanders is quite incurable, but by generous diet, good stabling, and mineral tonics, life, except in extremely acute cases, may be prolonged for many weeks. This, however, is not desirable; for it involves great risk, not only to other horses, but also to the attendants.” (Finlay Dun.)

GLASS. Syn. Vitrum, L. This well-known substance is essentially a mixture of silicates with an excess of silica or silicic acid. It generally contains the silicates of potassa, soda, lime, baryta, magnesia, alumina, and lead, coloured by small portions of iron, manganese, cobalt, uranium, copper, or gold. In its usual form it is brittle, transparent, noncrystalline, insoluble, and fusible; but it sometimes exhibits other properties.

The manufacture of glass is one of the highest beauty, and, considering the comparative worthlessness of the materials of which it is made, and the various purposes of a useful, ornamental, and scientific nature which it subserves, it may be regarded as, perhaps, the most important in the history of inventions. The principle of its production is very simple, although great skill and experience are necessary to ensure its excellence. Silica (commonly under the form of sand) is heated with carbonate of potassa or of soda, and slaked lime or oxide of lead, until the mixture fuses, and combination takes place. After a time the melted mass becomes perfectly limpid and free from air-bubbles, when it is allowed to cool until it assumes the peculiar tenacious condition proper for working. The operation of fusion is conducted in large crucibles of refractory fire-clay, which, in the case of ‘lead-glass,’ are covered with a dome at the top, and have an opening at the side by which the materials are introduced, and the melted glass withdrawn.

The manufacture of glass is only conducted on the large scale, and the precise character and proportions of the ingredients used by the glass-maker must necessarily greatly depend upon the nature of the raw materials furnished by his locality, or otherwise at his command. The attention of the manufacturer should be directed to the use of his materials in such proportions as will furnish, in the melting-pot, the proper quantities of the essential ingredients, as determined from the known composition of the best commercial samples. The purity of the raw materials and the accuracy of his proportions and quantities are proved or disproved by the excellence of the product; and the cause of error (if any) may be at once determined by carefully ascertaining the quality of the ingredients employed, and the composition of the defective glass.

A writer (in ‘Chem. Centr.,’ 1872, 528) points out that very generally the soda used in glass making, contains sulphate, and that when this is so a poor glass is produced. The addition of ·75-1 part of wood charcoal for every 100 parts of true soda—improves the quality of the glass.

Prep. The following formulæ exhibit the composition of the leading commercial glasses, as shown by chemical analysis, together with the proportions of the raw materials used in their production.

Bottle glass. Sp. gr. 2·700 to 2·735.—

a. Composition by analysis:—

1. Silica, 53·55%; lime, 29·22%; mixed alkali, 5·48%; alumina, 6·01%; oxide of iron, 5·74%. Dark green.

2. Silica, 52%; baryta, 21·6%; soda, 26·1%; oxides of iron and manganese, ·3%. Pale green; very superior.

b. Raw materials used:—

1. Yellow sand, 20%; kelp, 8%; lixiviated wood-ashes, 30%; fresh wood-ashes, 8%; pale clay, 16%; ‘cullet’ (broken glass), 18%. This is the common mixture for coarse bottles, in Belgium, France, and Germany.

2. To the last add of black oxide of manganese, 2¹⁄₂ to 3%. Has a rich yellowish colour; used for Rhenish-wine bottles.

3. Pale sand, 51%; lixiviated wood-ashes, 33%; pearl-ashes (dried), 8%; common salt, 7¹⁄₂%; white arsenic, ¹⁄₂%; charcoal, q. s. Very pale green.

4. Siliceous sand (pale), 68¹⁄₂%; potash (or its equiv.), 4%; lime, 23¹⁄₂%; heavy spar, 2¹⁄₂%; peroxide of manganese, 1¹⁄₂%. This forms the celebrated ‘flask-glass’ of St. Etienne.

Glass, Broad, Spread window glass. Sp. gr. 2·642.—

a. By analysis:—

Silica, 69·70%; lime, 13·30%; soda, 15·25%; oxide of iron (and loss), 1·75%.

b. Materials used:—

1. White sand, 50%; dried sulphate of soda, 22%; charcoal (in powder), 9%; ‘cullet,’ 41%; peroxide of manganese, a little. Pale.

2. White sand, 60%; potashes (good), 24%; common salt, 10%; nitre, 5%; white arsenic, 1%; peroxide of manganese, a little (¹⁄₁₂ to ¹⁄₁₀%); pale ‘cullet,’ at will (10 to 30%). Very pale. This is the ‘spread’ or ‘sheet window-glass’ in common use.

Glass, Chemical. Sp. gr. 2·390 to 2·396.—

a. By analysis:—

1. Silica, 72·80%; potassa, 16·80%; lime (with a trace of alumina), 9·68%; magnesia, 40%; traces of oxide of manganese and iron (and loss) ·32%. This is the difficultly fusible ‘Bohemian tube-glass,’ so valuable in chemical manipulations.

2. Silica, 69·3%; potassa, 15·8%; soda, 3%; lime, 7·6%; alumina, 1·2%; magnesia, 2%; oxide of iron, ·5%; oxide of manganese (and loss), ·6%. English chemical glass (without lead). More fusible than the last.

b. Materials used:—

1. Quartz (hyalin, in powder), 60%; calcined purified pearlash, 30%; fresh-burnt lime (very pure), 9%; nitre (dried), ³⁄₄%; arsenious acid or peroxide of manganese, ¹⁄₄%. Said to be the proportions used in the production of a, 1 (above).

2. (M. Peligot.) Quartz, 71¹⁄₂%; carbonate of potassa (or its equiv., dry), 20%; quicklime, 8¹⁄₂%; (manganese, a little). Said to be the formula for the hardest and least fusible ‘Bohemian tube-glass.’ It is very intractable and infusible, except at a very high temperature; but the addition of an exceedingly small quantity of boracic acid, borax, or arsenious acid, causes it to flow into a glass possessing great brilliancy and hardness, and capable of being wrought at the highest heat of the ordinary furnace.

Glass, Crown, White window-glass. Sp. gr. 2·486 to 2·488.—

a. By analysis:—

1. Silica, 62·8%; potassa, 22·1%; lime, 15·5%; alumina (with traces of oxide of iron and manganese), 2·6%. Crown-glass of Bohemia, according to Dumas. Very beautiful.

2. Silica, 72·5%; soda, 17·75%; lime, 9·75%. English crown-glass; excellent quality, but not so white as the last.

b. Materials used:—

1. Finest white siliceous sand, 64%; purified potashes (dry), 23%; lime, 12%; white arsenic, ³⁄₄%; oxide of manganese, ¹⁄₄%. Said to be used in Bohemia.

2. (Schweigger.) Pure sand, 57%; dry sulphate of soda, 28¹⁄₂%; quicklime, 11¹⁄₂%; powdered charcoal, 3 or 4%. Corresponds to a, 2, above (nearly).

3. Pure sand, 40%; soda ash, 24%; lime, 5%; white ‘cullet,’ 31%, Rather superior to the last.

Crystal, Crystal glass. The ‘crystal glass’ of England is flint glass’ of superior quality; that of Bohemia is noticed under Table glass.

Glass, Flint, Crystal. Sp. gr. 3·000 to 3·620.—

a. By analysis:—

1. (Berthier.) Silica, 59·19%; oxide of lead, 28·68%; potassa, 12·13%; oxides of iron and manganese, traces. Finest colourless English crystal.

2. (Brande; Faraday.) Silica, 52%; oxide of lead, 34%; potassa, 34%. Crystal.

3. (Faraday.) Silica, 44·30%; oxide of lead, 43·05%; potassa, 11·75%; alumina, ·50%; oxides of iron and manganese, ·12%; (loss 28%). Heaviest of three samples of flint glass examined.

b. Materials used:—

1. Finest Lynn-sand (calcined, sifted, and washed), 51%; litharge (purest), 28% (or red lead, 29%), refined pearlashes (calcined before being weighed), 16%; nitre (purified), 4³⁄₄% arsenious acid and peroxide of manganese, of each, ¹⁄₈%. Very fine crystal.

2. (M. Payen.) Fine sand, 46%; red lead, 31%; purified carbonate of potash, 23%. French crystal.

3. (Geddes.) White Lynn-sand, 51%; red lead or litharge, 33%; refined pearlashes, 13%; nitre, 3%; a very little arsenious acid and peroxide of manganese. Ordinary English flint-glass. Crystal ‘cullet’ may be added at will to the above. This glass was originally prepared from powdered flints, a fact to which it owes its common name.

Glass, Optical. 1. (Crown glass.) Purest siliceous sand, 55%; carbonate of soda (dry), 12%; chalk (dry), 11%; carbonate of baryta, 22%.

2. (Flint glass.)—

a. By analysis:—

Silica, 44·30%; oxide of lead, 43·05%; potassa, 11·75%. This is Guinand’s ‘dense optical glass.’

b. Materials used:—

1. Purest quartz, 42%; red lead (finest), 42%; purified potash, 14³⁄₄%; purified nitre, 1¹⁄₄%. These are the proportions used for the last.

2. (Korner.) Finest quartz (reduced to powder, treated with hydrochloric acid, washed, and dried), 47¹⁄₂%; red lead, 38¹⁄₄%; cream of tartar, 14¹⁄₂%. The above are used by opticians in the construction of achromatic object-glasses.

Glass, Plate. Sp. gr. 2·488 to 2·600.—

a. By analysis:—

1. (Dumas.) Silica, 75·9%; soda, 17·5%; lime, 3·8%; alumina, 2·8%. French mirror-glass.

2. (Mitscherlich.) Silica, 60%; potassa, 25%; lime, 12·5%; loss, 2·5%(?). Finest Bohemian plate.

b. Materials used:—

1. Finest siliceous sand, 45%; dried carbonate of soda, 25%; lime, 5%; nitre (purified), 2%; plate-glass cullet, 23%; peroxide of manganese and cobalt azure, a very little. Ordinary English plate.

2. Whitish quartz sand, 60%; purified carbonate of soda (dried), 20%; lime (slaked by exposure to the air), 9%; plate-glass cullet, 11% (or more). Sometimes as much cullet as sand is used; but in all cases 1% to 1¹⁄₂% of its weight in carbonate of soda is added with it, besides that ordered in the formula, to compensate for loss of alkali by remelting. Used at the celebrated plate-glass works at Saint-Gobain, France. The product possesses an amount of excellence which British manufacturers have yet failed to equal.

Glass, Table Bohemian crystal. Sp. gr. 2·6 to 2·8.—

a. By analysis:—

1. (M. Berthier.) Silica, 71·7%; potassa, 12·7%; soda, 2·3%; lime, 10·3%; alumina, ·4%; oxides of iron and manganese (and loss), 2·6%. Very white, hard, and beautiful table glass.

2. (Dumas.) Silica, 70%; potassa, 20%; lime, 4%; alumina, 5%; oxide of iron, ·6%; peroxide of manganese, ·4%. A beautiful white wineglass.

b. Materials used:—

1. Finest sand, 50%; purified potashes, 25%; chalk, 10%; nitre, 2%; crystal cullet, 27%; manganese, a little (say ¹⁄₁₆%). Used in England recently for table glass.

2. Quartz (hyalin, in powder), 63%; purified potashes, 26%; slaked lime (carefully sifted), 11%; manganese, a little; crystal cullet, at will. Used in Bohemia.

3. (M. Perdonnet.) Powdered quartz, 44%; carbonate of potassa, 33%; quicklime (in fine powder), 22%; nitre, 1%; and a very small quantity of arsenious acid and peroxide of manganese. Said to be the formula used at Neuwelt for the glass a, 1 (above).

Qual., &c. These are denoted by its hardness, transparency, homogeneity, strength, and power of resisting the action of water, air, light, and the stronger acids and alkalies. The power of glass to resist the action of menstrua is readily tried by exposing it to boiling oil of vitriol, and hot but dilute solution of caustic potassa. Neither of these tests should cause the glass to lose its transparency or to become dim.

Swallowed glass. Glass and enamel, both in fragments and in powder, have occasionally been swallowed, with different results. These bodies are insoluble in the fluids of the body, and, consequently, any injurious action they may exert upon the system whilst they are retained in it must entirely depend upon mechanical attrition or irritation. As treatment, we must administer an emetic, and assist its action by thick mucilaginous liquids, and afterwards have recourse to antiphlogistics, if necessary.

Anal.—a. A portion of the sample for examination is heated to dull redness, and then suddenly thrown, whilst still hot, into a vessel of cold water. It is next dried, and reduced to fine powder in an agate or hardened-steel mortar.

b. 100 gr. of the prepared powder is thoroughly mixed with 200 gr. of pure potassic hydrate, and the whole is exposed to heat in a silver or platinum crucible or capsule until perfect fusion takes place; when cold, the crucible and its contents are boiled in about half a pint of distilled water; nitric acid is added to the resulting solution, in excess, and the mixture, together with any sediment, is evaporated to dryness, after which the heat is gradually increased to 400° or 500° Fahr.; the dry residuum is next reduced to powder, and digested in water acidulated with nitric acid, until exhausted of soluble matter; the insoluble portion is then carefully dried, gently ignited and weighed. The weight in grains represents the per-centage of silica in the sample examined.

c. The mixed liquid and washings of b is next acidulated with nitric acid, and treated to a stream of sulphuretted hydrogen, which, if it produces a precipitate, is continued for some time; the precipitate is collected on a very small filter, washed, and dried; the filter with the precipitate next placed in a beaker glass, and strong fuming nitric acid is cautiously added, drop by drop, until complete solution takes place; after boiling the solution for a few minutes, diluting with distilled water, and allowing it to cool, it is precipitated with sulphuric acid, in excess; this precipitate (sulphate of lead) is washed, dried, slightly ignited in a porcelain crucible, and weighed. The weight in grains, multiplied by ·7369, gives the per-centage of oxide of lead or litharge.

d. The filtered liquid from c is evaporated to dryness, and redissolved in water acidulated with hydrochloric acid, and treated with a solution of ammonium chloride, and afterwards with ammonia, in excess; the precipitate (alumina and oxide of iron) is collected, washed, and boiled in a solution of potassium hydrate; the undissolved portion is collected on a filter, washed with boiling water, ignited, and weighed. This gives the per-centage of peroxide of iron.

e. The liquid filtered from the oxide of iron holds the alumina (if any) in solution; a solution of carbonate of ammonium is dropped in; the resulting precipitate is washed, dried, ignited, and weighed. This gives the per-centage of alumina.

f. The filtrate from the alumina and oxide of iron (see d), after being evaporated to dryness, is redissolved in a large quantity of distilled water, and is treated with a solution of oxalic acid (a solution of oxalate of ammonium is preferable when no baryta is present); the precipitate is washed, dried, gently ignited, and weighed. The weight of the resulting carbonate of calcium, in grains, multiplied by ·56292, gives the per-centage of lime required.

g. The filtrate from f is now mixed with carbonate of potassium, in considerable excess, and boiled for a long time; the resulting precipitate (if any) is then collected on a filter, slightly washed with hot water, dried, and exposed to a full red heat for some time (say 2 hours); the residuum of the calcination is then weighed. This furnishes the per-centage value of the sample in magnesia.

h. The filtrate from f is treated with dilute sulphuric acid or the solution of a sulphate, as long as a precipitate falls; the precipitate (sulphate of barytum,) is washed, dried, gently ignited, and weighed. The weight, in grains, multiplied by ·6589, gives the per-centage of baryta in the sample.

The above may be varied by gently concentrating the liquid filtered from the precipitate of alumina and oxide of iron (see d), and precipitating it with dilute sulphuric acid; the mixed precipitate is exhausted by digestion in water holding chloride of ammonium in solution; the undissolved residuum (sulphate of barytum,) is washed, dried, and otherwise treated as before; whilst the solution with the washings is treated with a solution of carbonate of ammonium; the precipitate is carbonate of calcium, which is to be washed, &c., as directed under f. The liquor, &c., filtered from the lime, is lastly tested for magnesia. (See g.)

i. A second 100 gr. of the powdered glass (see a) is mixed with 200 gr. of fluor spar, also in powder; the compound is placed in a platinum or leaden capsule, 500 gr. of strong sulphuric acid are added, and the whole cautiously stirred together with a silver stirrer or spoon, care being taken to avoid inhaling the fumes; the heat of a spirit lamp is next applied, and at first is kept at about 212° Fahr., but towards the conclusion of the process is raised to 300° Fahr., or even higher, and is continued for at least 2 hours, or until fumes entirely cease to be evolved; 5 or 6 fl. oz. of distilled water are next poured on the residuary mass, and, after thorough agitation, the whole is thrown on a filter, more water being at last poured on to wash out any remains of soluble matter; to the filtrate, carbonate of ammonium is added in excess, and after a time the earthy salts are removed by filtration; the filtered liquor is now evaporated to dryness, and ignited to dull redness for 2 or 3 minutes; the residuum (sulphate of potassium or sodium, or of both), after being weighed (the weight being carefully noted down), is redissolved in distilled water; a solution of chloride of barium is then added as long as it disturbs the liquor, and after a time the whole is again filtered; the filtrate is concentrated by evaporation, and solution of bichloride of platinum added in excess; the whole is now gently evaporated to dryness, mixed with alcohol, collected on a filter, carefully washed with weak alcohol, dried at a temperature under 212° Fahr., and weighed. The weight, in grains, multiplied by ·1940, gives the per-centage of potassa sought.

k. The weight of sulphate of potassium in the ignited residuum in i is calculated from that of the potassium last found (47 parts of the one being equal to 87 parts of the other), and this weight is deducted from the gross weight of the ignited sulphates; the remainder represents the quantity of sulphate of sodium present. The weight of the latter, in grains, multiplied by ·4367, gives the per-centage of pure soda required.

Concluding Remarks. One of the chief points to which the skilful glass manufacturer directs his attention, is the quality of the materials. Great care is exercised in the selection of the sand for all the finer varieties of glass. The usual practice is to test it before using it, by exposing it to a very high temperature. The purest sand is that which is the whitest and freest from iron, and which, consequently, suffers the least alteration by this treatment. The alkalies (potash, soda) employed are purified by solution and crystallisation. The red lead and litharge must be pure and absolutely free from oxide of copper (a common contamination), which gives a green tint to the glass. The former, which is the most costly, is preferable to the finest crystal. Care must also be taken that the lime, clay, &c., are respectively of proper purity; and that the ‘cullet,’ or broken glass, which is almost always remelted with the other materials, is of proper quality, and of the same kind as that to which it is added. Potassa produces a better glass than soda, although the latter is now very generally employed, from its lower price. It is, however, quite inadmissible as an ingredient in the manufacture of the better class of crystal and plate glass, as, however pure it may be, it imparts to the product a slight greenish tinge more or less destructive of its beauty. When sulphate of soda (Glauber salt) is used as a source of soda, it is gently calcined to dissipate its water of crystallisation, and requires the addition of about 8% of charcoal to effect its reduction in the melting-pot. Common salt is also employed as a source of soda in the same manner. Sometimes native sulphide of lead (galena) is used to decompose the sulphate of soda, and in lieu of part of the oxide of lead; in which case about 5 parts of the sulphuret are taken for every 9 parts of the calcined sulphate.

To anticipate the results of his processes, and to carry out with certainty his various intentions, the glass manufacturer, perhaps more than any other person, requires the aid of science and experience. All his most essential operations depend on chemical principles. The products of his furnaces are not formed by the mere mechanical admixture of their several ingredients whilst in the state of fusion, but result from the play of delicate affinities which only act under certain conditions, and when the materials are presented to each other in uniform and definite proportions. Chemically speaking, the glasses are mixed super-silicates of the respective bases which enter into their composition (potassium, calcium, lead, &c.), and, like all other compounds which are formed by elective attraction, obey the common laws of combination, as developed by Dalton, and now so successfully applied in almost every department of industrial art. It has been shown by the most careful analysis, that in all the more valuable and beautiful commercial glasses the relative proportions of the materials are conformable to these laws, and that several of them are true atomic compounds, as perfect in this respect as the crystalline bodies commonly denominated salts. In some of the harder glasses of Bohemia the number of atoms or equivalents of silica are to each of the bases with which it is united, nearly as 5 to 1; whilst in a softer glass of German manufacture the proportions of the two are found to be as 4 to 1. The celebrated plate glass of St. Gobain is an atomic compound formed of 1 equivalent of trisilicate of soda united to 1 equivalent of trisilicate of lime, with a small per-centage of alumina in combination with silicic acid, also in atomic proportion. Glasses in which the ingredients bear no atomic ratio to each other are never homogeneous, but always more or less striated and of unequal colour and refractive power. The absence of atomic proportion between the substances entering into its composition appears to be the only reason why the best English plate and mirror glass is so greatly inferior to that of France and Germany, that comparison of the two becomes absurd. The only variety of glass in the production of which the English manufacturer excels is flint glass or crystal, and here he certainly surpasses all his numerous competitors. The subject is doubtless involved in difficulty, owing to the precise temperature necessary to effect the perfect combination of the bases with the silicic acid, varying with the character of the compound, and not being satisfactorily settled by observation or experience. The modifying influence of temperature is shown by the fact that the lower the heat employed in the process, the smaller the quantity of silica which enters into the composition of the resulting glass; whilst at higher temperatures a part of the base is dissipated in fumes, until such proportions of base and acid result as are required to produce a permanent atomic compound corresponding to the temperature employed. If the heat is excessive or improperly continued, the loss of base produces an opposite effect, and an opaque, semi-vitrified mass is formed, resembling ‘Reaumur’s porcelain.’ The quality of the resulting glass depends on this change being more or less complete. If the furnace yields the right temperature, and the duration of the exposure to its action is neither too short nor too prolonged, nature makes up for the unskilful conduct of the operative, and removes the stumbling blocks which his ignorance had placed in the way of his own attempts at excellence. The proceedings and their results are accidental; but being once obtained, the first are repeated without further trouble or inquiry. This accounts for the same mixture of materials yielding products of different qualities at different times, and in different works, which the operative contents himself with referring to the ‘going of the furnace.’ The common plan in this country is to regulate the proportions and firing by experience only, rather than by theory and practice combined. Now, although the chemist has much yet to learn on the precise constitution of the glasses, and although theory may not be able to ensure unvarying success, it is nevertheless certain that, in all cases, it can afford much valuable assistance in that direction. Indeed, it has been asserted by one of the leading Continental chemists, that ingredients that will yield the proper equivalent proportions in the melting pot cannot produce a bad glass, if exposed to such a temperature as to permit of perfect combination taking place.

It is found that those glasses which contain a predominance of alkali are acted on by water, and when this is in great excess they are perfectly soluble in that fluid. Ordinary flint glass is affected by long coction in water, whilst crown glass, which contains less alkali, is unaltered by that trial. Glass which contains any considerable quantity of lead is acted on by sulphuretted hydrogen. This is the cause of the surface of flint glass, under certain circumstances, becoming opaque and iridescent. Glasses made of silica and alkali alone are incapable of permanently resisting the action of water. The addition of lime or oxide of lead appears to be necessary to give them this quality. Glasses that have a slight greenish or bluish tint may be often whitened, or rendered colourless, by exposure to light and air. This arises from the peroxidation of the iron, to whose protoxide they owe their tint. Other glasses become purpled by exposure, owing to the peroxidation of the manganese.

Different colours are communicated to glass by the addition of metallic oxides. Thus, oxide of manganese gives an amethyst; oxide of cobalt, a blue; oxide of iron, a brown; black oxide of copper, a green; oxide of gold, a purple; suboxide of copper, a ruby-red; oxide of tin, a white; oxide of silver, a yellow, &c. These substances are either added to the melted contents of the glass-pot, as in preparing artificial gems, &c., or they are applied in a thin layer to the surface of the object, which is then heated until fusion of the coloured compound occurs, as in enamelling and painting on glass.

Glass is FORMED or FASHIONED into articles by the processes of blowing, casting, drawing, rolling, or spreading. In the process of BLOWING GLASS the workman begins by collecting a proper quantity of glass in a soft, pasty state, at the end of his blow-pipe (an iron tube, five or six feet in length, terminated by a mouth-piece of wood), which he then commences blowing through, by which the lump is expanded into a kind of flask, susceptible of having its form modified by the position in which it is held, and the velocity of rotation continually given to the iron tube. If an open-mouthed vessel is to be made, an iron rod, called a ‘pontil’ or ‘puntil,’ is dipped into the glass-pot and applied to the bottom of the flask, to which it thus serves as a handle, the blow-pipe being removed by the application of a cold iron to the neck. The vessel is now re-heated, and the aperture enlarged, and the vessel otherwise altered in figure by the aid of a few simple tools until completed. It is then detached, and carried to the ‘annealing oven,’ where it undergoes slow and gradual cooling during many hours. In this way bottles, flasks, carboys, and an almost infinite variety of other articles, are formed. The large circular tables of CROWN-GLASS are made by a joint process of BLOWING and SPREADING. The globular flask at first produced, transferred from the blow-pipe to the ‘pontil,’ is suddenly made to assume the form of a flat disc by the centrifugal force of the rapid rotatory movement given to the rod. Spread or BROAD GLASS is formed into sheets in a nearly similar manner. Plate-glass is cast upon a flat metal table, and, after very careful annealing, is ground and polished by suitable machinery. Tubes are made by rapidly drawing out a hollow cylinder; and from these a great variety of useful small apparatus are constructed with the help of a lamp and blowpipe, or, still better, the bellows-table of the barometer-maker. Glass beads are made from small tubes chopped into pieces of suitable lengths, which are stirred first in a mixture of sand and wood-ashes, in the cold, and afterwards in an iron pan over the fire until they assume a rounded form. Small tubes are bent in the flame of a spirit lamp or gas-jet, and cut by a file, a scratch being made, and the two portions pulled or broken asunder in a way easily learned by a few trials. Large tubes require the heat of a powerful blowpipe and lamp, or that of a furnace.

The following hints respecting the MANAGEMENT OF GLASS may prove useful to the inexperienced:—

Annealing. The process of annealing glass has been briefly referred to before. The extreme brittleness of imperfectly annealed wrought glass may generally be remedied on the small scale by immersing the articles in a bath of oil, or a concentrated solution of chloride of calcium, or common salt, and heating the whole gradually and cautiously to the boiling-point, and letting it again cool—the slower the better. By this treatment the glass will be enabled to bear any alterations of temperature between the two extremes to which it has been exposed.

Blowing. By the ingenious art of GLASS-BLOWING and GLASS-DRAWING, as practised on the small scale, with a blowpipe lamp furnace, a variety of articles of ornament and utility may be made, their number being limited only by the ingenuity of the artist. The details of the various operations are, however, too lengthy to describe here.

Cleaning. 1. Windows, looking-glasses, &c., may be quickly cleaned as follows:—Dip a slightly moistened rag or flannel into whiting, fuller’s earth, wood-ashes, or rotten-stone, in impalpable powder, with which smear the glass, and wipe it off with a dry, soft cloth. This does well when the surface is very dirty. In other cases, a little thumb blue, whiting, or chalk, in fine powder, tied up in muslin, may be dusted on the glass, which should then be cleaned off with chamois leather. This gives a fine polish.

2. The vessel to be cleansed, is filled, or, if large, rinsed, with a moderately dilute solution of permanganate of potash, contact being prolonged till a film of hydrated manganic oxide has been deposited; the solution is then poured away, and the glass vessel rinsed with some strong hydrochloric acid.

Cutting. Glass may be easily cut with a common well-hardened steel file, provided it be moistened with oil of turpentine, or plunged under water. It may be also perforated with a common steel brad-awl in the same way. Glass vessels, as bottles and tubes, may be readily cut or shortened by placing a heated iron ring over the spot, or a piece of loose string or cotton dipped in oil of turpentine and set on fire, and immediately on the withdrawal of either applying cold water to the part. Glass vessels or tubes thus treated will generally crack round, and may be readily divided into two parts. In this manner a common Florence oil-flask may be converted into an evaporating dish and a funnel. By a little practice a crack may be led in almost any direction, or a new one made, by the point of a red-hot poker or a spring coal (an ignited crayon of prepared charcoal). The parts may then be separated by a little force or a smart rap, and the divided edges smoothed by the flame of a blowpipe, or by grinding them with powdered emery and water on a flat stone. In this way many broken articles in glass may be converted into others scarcely less useful.

Etching on glass has been already noticed under the head of Etching.

Gilding of glass. Gold chloride is dissolved in boiling water; the solution is filtered, and the filtrate so far diluted, that 200 cubic centimètres contain 0·0648 gram of the metal, and it is then made alkaline with soda. The reducing agent is alcohol saturated with marsh gas; this is diluted with its own volume of water. 25 cubic centimetres of this solution are mixed with the alkaline gold chloride solution, and this mixture is poured between the perfectly well-cleaned plate to be gilded, and another sheet of glass placed at a distance of 3 mm. under the first. After two to three hours’ rest the gilding is effected. The plate is removed and washed. (‘Dingler’s Journal.’)

Grinding. This, on the large scale, like glass-cutting, forms a distinct occupation. On the small scale, glass may be roughed or ground by friction with powdered emery and water and a flat rubber of wood; care being taken that the article, if a plate, is laid on a perfectly flat surface, or, if hollow, is supported by a core of cement or plaster. The frosted appearance of ground glass is given to the panes of windows by gently dabbing the glass over with a piece of glazier’s putty, stuck on the ends of the fingers. When applied with a light and even touch, the resemblance is considerable. Another method is to dab the glass over with thin white paint, or flour paste, by means of a brush, but the effect is much inferior to the above.

Glass, packing. This subject will be considered under the general head of Packing.

Writing on glass may be performed by a piece of French chalk or crayons prepared for the purpose; or even with a common pen held nearly perpendicular. Indian ink, or, when the article will be exposed to damp, shell-lac ink or varnish, thickened with a little Vermillion, or lampblack, is best adapted to this purpose. Common ink is not sufficiently opaque.

Glass, to prevent the cracking of, by boiling water. When new, all glass and earthenware should be placed in cold water in a saucepan, and after some hours the saucepan containing the vessel or vessels, should be placed over the fire, until the water reaches the boiling point.

Glass. This term was applied by the older chemists to various substances to which a vitreous appearance has been given by heat. Thus we have ‘GLASS OF ANTIMONY,’ ‘GLASS OF BORAX,’ &c. It is now obsolete.

Glass, Iridescent. The inventor of the process by which this beautiful variety of glass is made is M Clémandot.

The ‘Chemical News’ states that the principle observed in its manufacture consists in submitting the glass articles to the action of dilute hydrochloric, sulphuric, or other acid, under a pressure of from two to six atmospheres. M Clémandot claims to be able to imitate the nacreous films which are seen on ancient glass which has been exposed to combined atmospheric influences for thousands of years.

Glass, Pow′dered. Syn. Vitrum pulverisatum, L. Prep. Heat the glass red hot, throw it into cold water, dry, and powder it. Used to filter acids, and glued upon paper as a polishing powder; also to wear down corns upon the feet, after the feet have been well soaked, and dried.

Glass, Sol′uble. Syn. Water glass; Vitrum solubile, L. An impure alkaline silicate. Prep. Silica, 1 part; carbonate of potassium or of sodium, 2 parts; fused together.

Carbonate of sodium (dry), 54 parts; carbonate of potassium (dry), 70 parts; silica, 192 parts; as last. Soluble in boiling water, yielding a fine, transparent, semi-elastic varnish.

Carbonate of potassium (dry), 10 parts; powdered quartz (or sand free from iron and alumina), 15 parts; charcoal 1 part; fused together. Soluble in 5 or 6 times its weight of boiling water; and the filtered solution, evaporated to dryness, yields a transparent glass, permanent in the air.

M. F. Capitaine, who, acting upon a suggestion made by Liebig, some twenty years since, has recently taken up the subject of the manufacture of soluble glass, and silicate of potash, from farine fossile (an infusorial earth), has published an account of his researches in ‘Dingler’s Polytechnic Journal.’[334]

Although M. Capitaine does not think that the farine will be able to compete in cheapness with flint (where this latter is abundant) for the preparation of the alkaline silicates, he states that it possesses the advantage over flint of being much more soluble, and of yielding a far more neutral glass; added to which the production of the silicate is said to be effected with much less trouble than when flint is employed. An important condition is, that the farine must be first well calcined, since if the least trace of organic matter be left in it, the resulting solution will have a yellowish or brownish tint, which will make it unsaleable.

“The lyes being prepared partly with caustic soda, and partly with carbonate of soda, had densities ranging from 1·22 to 1·24 which were found to be most advantageous. A reservoir furnished with mechanical agitators, was about two thirds filled with lye, and the necessary quantity of calcined farine added, the stirring being kept up continually. The proportion of farine is easily calculated on the datum, that one part of hydrate of soda dissolves about 2·8 parts of chemically pure farine, the quality of which varies but little. Lye of the density indicated produces a rather light solution, which presents little resistance to the agitators. If steam is afterwards introduced the solution becomes very rapid, when the pressure reaches about three atmospheres, and at the end of about three hours the silica is completely dissolved.

“For the preparation of silicate of potash for surgical purposes the farine fossile is said to be peculiarly adapted. In this case the boiling must be continued for one or two hours longer than in the case of soluble glass, with an addition of 10 to 15 per cent. of farine.”

Uses. &c. Soluble glass, in solution, has been used to render textile fabrics less combustible, as a varnish to protect stone, and as a vehicle in fresco-painting, The soda compound (silicate of sodium) is largely used as a dung-substitute in calico-printing, and by soap manufacturers in place of the resinates formerly in use. 10 or 12 tons are produced weekly in the district of South Lancashire. The potassa compound (silicate of potassium) has been recommended as a remedy for gouty concretions by Mr Ure.—Dose, 10 to 15 gr., in 6 or 8 fl. oz. of water twice a day. See Dunging, Varnish, &c.

Glass, Toughened. Syn. Verre Trempé. M. de la Bastie’s process for converting ordinary, into toughened, tempered, or hardened glass, may in general terms be said to consist in heating the glass to a certain temperature, and then plunging it into an oleaginous bath. For the process, however, to be successful, the observance of a number of minute details is essential; if these be neglected failure is certain to ensue. Thus it is found, that if the glass be insufficiently heated it will, when immersed in the bath, fail to be affected by it, and will consequently experience no alteration in properties. Again, if overheated, it will then get out of shape; or, further it may be heated to the right temperature, and yet be spoilt as it is being transferred to the bath. Moreover, the exact composition of the bath itself, and its temperature constitute very important conditions, the most trifling departure from which may give rise to unsatisfactory results. All these obstacles appear to have been overcome by M. de la Bastie, who has designed plant in the shape of furnaces and baths, by means of which the tempering process can be carried out, without chance of failure. When the glass is brought to the required temperature, all that is necessary is that they should be plunged into the bath, and instantly withdrawn. The cost of the operation is stated to be very small.

“The process as carried out at New York is thus described:—The glass after being run from the furnaces and moulded as usual, instead of being put into annealing pans, is immersed in a hot bath consisting of three parts of flaxseed oil, and one part of tallow. The bath stands at about 320°; and after remaining in this the ware is removed to a second, and similar bath, by which it is cooled down to about 200°. Finally the pieces are immersed in a water bath, and then dipped into a quantity of ordinary refined burning oil. They are then cleaned, ready for packing, with plaster of Paris powder. The work is but in its infancy, and but one small furnace is used in the experiments. Improvements will doubtless be made, by which the cleaning can be done more rapidly than by the powdered plaster, probably some chemical being used for the purpose. It is supposed that the oil works into the pores of the hot glass, and thus toughens it. Great care has to be exercised in the final cooling by water, as too long a contact with the air in changing from one bath to another, makes the ware crack. Articles cooled entirely in oil retain the oil on the surface, but are thus rendered stronger than otherwise.

This new process is very much employed in the manufacture of lamp chimneys, though they have the disadvantage of flying into small pieces, and with violence when they do break, which sometimes does occur.”[335]

The results so far obtained when glass is subjected to M. de la Bastie’s process are variable. In some cases the articles subjected to it possess great toughness, and the glass bears a blow without experiencing any fracture. In other instances, however, a slight fall or blow shivers it to atoms. When the toughened glass under any circumstances breaks, it possesses a disadvantage over ordinary broken glass, in distributing itself into a great number of small, sharply angular fragments.

Another process for toughening glass, which has been patented by Herr F. Siemens, consists in heating, and then pressing, and suddenly cooling the glass to be hardened; but when the articles are such as are usually moulded, the hardening and tempering are accomplished at the same time as the pressing; thus the molten glass is run into suitable moulds, and while still highly heated, is squeezed, the moulds effecting the necessary cooling, a proceeding which renders the employment of the oleaginous bath unnecessary. Mr Bauer’s method for toughening glass consists in heating ordinary glass plates so strongly that they begin to bend from softening, and then plunging them into a liquid paraffin bath having a temperature of 200°.

Toughened glass is liable to rupture under circumstances that have not yet been accounted for.

M. de la Bastie conceives that the fragile nature of glass is due to the weakness of the cohesion of its particles, and that if this cohesive power can be increased, the strength of the material will be improved in proportion. M. de la Bastie first tried to obtain this end by forcibly compressing the glass while in a plastic or fluid condition, but without success; and it was only after various experiments that he was enabled to harden the glass, by dipping it into oil or any other liquid that permitted of being heated to a temperature considerably above that of water.

GLAZE. Syn. Glazing. Any coating or varnish applied to a surface to render it smooth and glassy; any factitious, shining exterior. The following applications of this term are the following:—

Glaze. In cookery, is commonly understood to be gravy or clarified soups boiled until it gelatinises on cooling. It is used as a species of varnish to cover various dishes for the table, and may be spiced and flavoured according to the fancy of the cook. White of egg is generally used as a glaze for pastry.

Glaze. In the porcelain and earthenware manufacture, the vitreous coating which is so essential to the beauty and utility of potter’s ware. Glazes are either white or coloured. The former, by the addition of the colouring ingredients used for enamels, are converted into the latter.

a. For Earthenware:—

Prep. 1. (With lead.) White lead (pure), 53 parts; quartz or ground flints, 36 parts; Cornish stone, or felspar, 16 parts; white flint glass, 5 parts; reduce the whole to an impalpable powder. For common earthenware.

2. (Without lead.) Fine washed sand, 10 parts; purified potash, 8 parts; nitre, 1 part; slaked lime, 2 parts; nitre, 4³⁄₄%; powder, mix, heat the mixture in a blacklead crucible in a reverberatory furnace, till the mass flows into a clear glass; let this cool, then reduce it to fine powder. For glazing pharmaceutical and chemical vessels.