Part 187

=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]

[Footnote 334: See 'The Journal of the Society of Arts' for January 11th, 1878.]

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]

[Footnote 335: Supplement to 'Ure's Dictionary of Arts, Manufactures, &c., 1878.]

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, 4-3/4%; 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.

_b._ For PORCELAIN:--

_Prep._ (Rose.) Felspar, 27 parts; borax, 18 parts; finest siliceous sand, 4 parts; nitre, soda, and purest china clay (Cornish), 3 parts; mix, heat to a 'frit,'[336] powder, and add of calcined borax, 3 parts.

[Footnote 336: A technical term for the half-fused mass formed by heating together the materials of which glass is composed.]

_c._ For STONEWARE:--

1. (Ure.) White felspar, 26 parts; soda, 6 parts; nitre, 2 parts; borax, 1 part; 'frit' together as last. Of the product take 13 parts; red lead, 50 parts; white lead, 40 parts; flints, 12 parts; reduce the whole to powder as before. For painted stoneware.

2. From common salt, which is thrown into the heated furnace containing the ware. It is volatilised and decomposed by the joint agency of the silica of the ware and of the vapour of water always present; hydrochloric acid and soda are produced, the latter forming a silicate, which fuses over the surface of the ware, and gives a thin but excellent glaze. 'SALT-GLAZED STONEWARE' is now generally used for large chemical vessels, drain-pipes, &c.

_Obs._ Glazes must be reduced to very fine powder. For use, they are ground with water to a very thin paste or smooth cream, into which the articles, previously baked to the state called 'biscuit,' are then dipped; they are afterwards exposed to a sufficient heat in the kiln to fuse the glaze. Another method of applying them is to immerse the biscuit in water for a minute or so, and then to sprinkle the dry powder over the moistened surface.

=GLI'ADIN.= _Syn._ GLUTIN, VEGETABLE GELATIN. One of the proximate principles of wheat gluten, soluble in alcohol.

=GLIADINPFLASTER= (A. L. Klose, Berlin). For rheumatism. A thin paper on which is spread a solution of gelatin containing spirit and some acrid substance, such as cantharides or euphorbium.--_Hager._

=GLOB'ULIN.= _Syn._ CRYSTALLIN. An albumenoid body existing in the crystalline lens of the eye.

=GLOVE POW'DER.= _Prep._ 1. From Castile soap, dried by exposure to a warm dry atmosphere for a few days, and then reduced to fine powder in a mortar. Used to clean gloves.

2. Pipe-clay, coloured with yellow ochre, umber, or Irish slate q. s., and afterwards scented with a little powdered orris root or cloves. Used to colour gloves made of doe-skin and similar leather.

=GLOVES.= _Syn._ GANTS, Fr. Although gloves constitute a less costly article of dress at the present day than they did during the Middle Ages, the following information may nevertheless be sometimes found of value to their wearers:--

GLOVE CLEANING. 1. (KID GLOVES.)--_a._ Damp them slightly, stretch them gently over a wooden hand of appropriate size, and clean them with a sponge dipped in benzol, recently rectified oil of turpentine, or camphine; as soon as they are dry, withdraw them gently from the stretcher, and suspend them in a current of air for a few days, or until they cease to smell of the cleaning liquid used. The smell of benzol passes off very quickly. Heat must be avoided. The cleaning liquid should be used liberally, and the first dirty portion should be sponged off with clean liquid.

_b._ By employing a saponaceous compound. See GANTEINE.

2. (DOE-SKIN and WASH-LEATHER GLOVES.)--_a._ Stretch them on a hand, or lay them flat on a table, and rub into them a mixture of finely powdered fuller's earth and alum; sweep it off with a brush, sprinkle them with a mixture of dry bran and whiting, and, lastly, dust them well off. This will not do if they are very dirty.

_b._ Wash them in lukewarm soft water, with a little Castile or curd soap, ox-gall, or bran tea; then stretch them on wooden hands, or pull them into shape without wringing them; next rub them with pipe-clay and yellow ochre, or umber, or a mixture of them in any required shade made into a paste with ale or beer; let them dry gradually, and, when about half dry, rub them well, so as to smooth them and put them into shape; when they are dry, brush out the superfluous colour, cover them with paper, and smooth them with a warm (not hot) iron.

GLOVE DYEING. LEATHER GLOVES, if not greasy, may be dyed with any of the ordinary dyes by brushing the latter over the gloves stretched out smooth. The surface alone should be wetted, and a second or third coat may be given after the former one has become dry. When the last coat has become thoroughly dry, the superfluous colour should be well rubbed out, a smooth surface given them by rubbing them with a polished stick or piece of ivory, and the whole gone over with a sponge dipped in white of egg.

=Gloves, Cosmetic.= _Syn._ GANTS COSMETIQUES. These are mock kid or lambskin gloves rubbed over, on the inside, with the following composition:--Spermaceti cerate, 3 oz.; melt, add of balsam of Peru, 1/2 dr., stir for 5 minutes, and, after a few minutes' repose, pour off the clear portion; to this add of oil of nutmeg, 15 drops; oil of cassia and essence of ambergris, of each 6 drops; and stir until cold. Used by ladies to soften the hands and to prevent or cure chilblains and chaps. They are commonly worn all night in bed.

=GLUCI'NUM.= Gl. _Syn._ BERYL'LIUM. The metallic base of glucina. It was first obtained by Wöhler, in 1828, by a similar process to that adopted for aluminum, a metal which it greatly resembles. See ALUMINUM.

=Gluci'num, Oxide of.= _Syn._ GLUCINA, BERYLLIA. A pulverent white substance, found as silicate in the beryl, emerald, &c.

_Prep._ The beryl, in fine powder, 1 part; carbonate of potassium, 3 parts; expose the mixture to a strong red heat for half an hour, dissolve the calcined mass in hydrochloric acid, and evaporate the solution to dryness; redissolve the residuum in very dilute hydrochloric acid, and precipitate with pure ammonia; wash the precipitate well, digest it with a large quantity of carbonate of ammonium, filter, and boil the solution as long as carbonate of glucinum subsides. By exposure to a red heat the carbonic acid may be expelled, and the earth rendered anhydrous.

_Prop., &c._ Glucina closely resembles alumina, from which, however, it is distinguished by its solubility when freshly precipitated in a cold solution of carbonate of ammonia, from which it is again thrown by boiling. Glucina is classed with the earths. The beryl contains 14% of this substance.

=GLU'COSE.= See SUGAR (Grape).

=GLUE.= _Syn._ GLUTEN, GLUTINUM, L.; COLLE, COLLE FORTE, Fr. Inspissated animal jelly, or gelatin, used as a cement.

_Prep._ Glue is principally prepared from the parings and waste-pieces of hides and skins, the refuse of tanneries, and the tendons and other offal of slaughter-houses. These substances, when intended for the glue-maker, are steeped for 14 or 15 days in milk of lime, then drained, and dried by exposure to the air. This constitutes what is termed the 'cleansing' or 'preparation,' and in this state the 'glue pieces,' as they are called, may be kept for a long time, and transported to any distance without suffering decomposition. Before conversion into glue, they are usually again steeped in weak milk of lime, and next well washed and exposed to the air for 24 to 30 hours. They are then placed in a copper boiler two thirds filled with water, and furnished with a perforated false bottom, to prevent them from burning, and as much is piled on as will fill the vessel and rest on the top of it. Heat is next applied, and the whole gently boiled or simmered together, until the liquor on cooling forms a firm gelatinous mass. The clear portion is then run off into another vessel, and a very small quantity of alum (dissolved) added; here it is kept hot by a water bath, and allowed to repose for some hours to deposit its impurities, after which it is run into the 'congealing boxes,' and placed in a cool situation. The next morning the cold gelatinous masses are turned out upon boards wetted with water, and are cut horizontally into thin cakes with a stretched piece of brass wire, and then into smaller cakes with a moistened flat knife. The latter are placed on nettings to dry. The dry cakes of glue are next dipped one by one into hot water, and slightly rubbed with a brush wetted with boiling water, to give them a gloss; they are, lastly, stove-dried for sale. This furnishes the palest and best glue.

As soon as the liquor of the first boiling has drained off, the undissolved portion of skins, &c., left in the copper is treated with fresh water, and the whole operation is repeated again and again, as long as any gelatinous matter is extracted. In this way a second and other inferior qualities of glue are obtained. The product from dried glue-pieces is about 50%.

_Var._ These chiefly depend on the care with which the process is conducted. HATMAKERS' GLUE is prepared from the tendons of the legs of neat cattle and horses. It is brown, opaque, and soft; and grows moist in damp weather, but it does not render felt brittle like the other varieties. FISH GLUE is made in like manner from various membranous and solid parts of fishes. PARCHMENT GLUE is prepared from shreds or shavings of parchment, vellum, white leather, &c., dissolved by boiling them in water. It is scentless, and nearly colourless.

_Qual._ The best glue is transparent, nearly colourless, and tasteless, has very little smell, even when melted, and is extremely adhesive. The presence of more than a trace of alum is objectionable; an undue quantity may be easily detected by the usual tests. The strongest glue is that obtained from skins, more especially from the hides of oxen and cows. That obtained from the bones, cartilages, and tendons, is weaker.

=Glue, Liq'uid.= _Prep._ (Dumoulins.) Soft water, 1 quart; best pale glue, 2 lbs.; dissolve in a covered vessel by the heat of a water bath, cool, and add, gradually, of nitric acid (sp. gr. 1·335), 7 oz.; when cold put it into bottles. Very strong, and does not gelatinise. For the 'LIQUID GLUE' sold in the shops, see CHINESE CEMENT.

=Glue, Marine.= _Prep._ 1. India rubber (cut small), 1 part; coal tar or mineral naphtha, 12 parts; digest in a covered vessel with heat and agitation, and when the solution is complete, add of powdered shell-lac, 20 parts; continue the heat and stirring until perfect liquefaction has taken place, and pour the fused mass, whilst still hot, on slabs of polished metal or stone, so as to form thin sheets. For use, it is heated to its melting-point (248° to 250° Fahr.) in an iron vessel, and applied in the liquid state with a brush. Employed in ship-building, &c.

2. Caoutchouc, 15 to 20 gr.; chloroform, 2 fl. oz.; dissolve, and add of powdered mastic, 1/2 oz. It must be kept well corked and in a cool place, to prevent loss by evaporation. Used for small, fine work.

=Glue, a New.= Ordinary glue is dissolved in nitric ether, and a little bit of caoutchouc added. This solution forms a very strong glue, and does not get thick or pasty. ('Dengler's Journal.')

=Glue, Port'able.= _Syn._ BANK-NOTE GLUE. MOUTH G., INDIAN G.; COLLE À BOUCHE, Fr. _Prep._ From the best pale glue, 1 lb.; water, q. s.; dissolve in a double glue-pot or water bath, and of pale-brown sugar, 1/2 lb., continue the heat until the mixture is complete, and pour it into moulds; or pour it on a marble slab, and when cold cut it into small pieces and dry them in the air. This glue is very useful to draughtsmen, architects, &c., as it dissolves almost immediately in warm water, fastens paper, &c., without the process of damping, and may be softened for many purposes with the tongue. When great strength not required, 4 oz. more of sugar may be used.

=GLU'TEN.= _Syn._ GLUTIN. A peculiar substance found in the grain of wheat. It is composed of true vegetable fibrin and a small quantity of gliadin. It is prepared by washing paste made of the flour of wheat or rye in successive waters until all starchy matter is removed. The paste may be conveniently enclosed in a bag of fine linen during the washing.

_Prop., Uses._ Gluten is believed to be eminently nutritious. It is the presence of gluten in wheaten flour that imparts to it its viscidity or tenacity, and confers upon it its peculiar excellence for the manufacture of MACARONI, VERMICELLI, and similar pastes. The superiority of wheaten over other bread depends upon the greater tenacity of its dough, which during the fermentation is puffed up by the evolved carbonic acid, and retained in its vesicular texture so as to form a light loaf.

Gluten is greyish coloured, and extensible whilst fresh and moist, like caoutchouc. It turns blue when mixed with guaiacum resin.

=Gluten Bread.= _Prep._ 1. From wheat flour which has been deprived of about 2-3rds of its starch by washing it with water.

2. From gluten flour. Recommended in diabetes.

=Gluten Choc'olate.= (Gentile's.) A mixture of cocoa and gluten flour. As a nutritious and appropriate food in diabetes.

=Gluten Flour.= _Prep._ 1. From the waste gluten of the starch works, washed, dried, and ground.

2. (Gentile's.) From the last, mixed with about an equal weight of wheat flour.

=GLYC'ERIN.= C_{3}H_{3}O_{3}. _Syn._ GLYCERIN, HYDRATED OXIDE OF GLYCERYL; GLYCERINUM, L. A sweet syrupy liquid formed during the saponification of oils and fats.

_Prep._ 1. Olive oil (or other suitable oil), protoxide of lead, and water are heated together until an insoluble soap of lead (lead plaster) is formed. The glycerin remains in the aqueous liquid. As this crude solution of glycerin is produced in great quantities in the manufacture of lead plaster, the operative chemist has only to purify it. This may be done as follows:--