Cooley's Cyclopaedia of Practical Receipts Volume I Part 266

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 quant.i.ty 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. 1335), 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 sh.e.l.l-lac, 20 parts; continue the heat and stirring until perfect liquefaction has taken place, and pour the fused ma.s.s, 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 s.h.i.+p-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 a 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 quant.i.ty of gliadin. It is prepared by was.h.i.+ng 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 was.h.i.+ng.

_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 guaiac.u.m resin.

=Gluten Bread.= _Prep._ 1. From wheat flour which has been deprived of about 2-3rds of its starch by was.h.i.+ng 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 quant.i.ties in the manufacture of lead plaster, the operative chemist has only to purify it. This may be done as follows:--

The water and was.h.i.+ngs from lead plaster are mixed together, filtered, and submitted to the action of a stream of sulphuretted hydrogen to throw down the lead; the supernatant liquor is decanted from the precipitate, filtered, and evaporated to the consistence of a syrup in a water bath. To render it quite pure it is diluted with water, decoloured with a little animal charcoal, filtered, and again evaporated to the consistence of a thin syrup, after which it is further evaporated in vacuo, or over sulphuric acid, until it acquires the sp. gr. 1265.

2. (M. Bruere-Perrin.) From the sweet liquor of the stearine works (a product of the process of lime-saponification). The quant.i.ty of lime present in the sample is first determined by means of oxalic acid, and the proportion of sulphuric acid necessary for its saturation at once calculated and added; the crude liquor is then concentrated in a tinned-copper vessel, evaporation being promoted by brisk agitation, until the sp. gr. sinks to 10 Baume; it is next cooled and filtered, and accurately neutralised (if it is required) with carbonate of pota.s.sa, after which it is evaporated to the sp. gr. 24 Baume; on cooling, it deposits gelatinous sulphate of pota.s.sa; the whole is now filtered, the deposit on the filter washed with a little very weak spirit and water, the filtrate and was.h.i.+ngs mixed together and evaporated, as before, with agitation, until the sp. gr. 28 Baume, whilst hot (36 cold), is attained, when the whole is allowed to cool; the clear liquid is, lastly, decanted and filtered. In this state it has an amber colour, but may be rendered colourless and odourless by rediluting it with water, treating it with animal charcoal, filtering, and again evaporating to a proper consistence.

3. By saponifying olive oil with caustic alkali, decomposing the resulting soap with dilute sulphuric or tartaric acid, evaporating the aqueous portion to dryness (nearly), dissolving out the glycerin with cold rectified spirit, and filtering and evaporating the solution as before.

4. The residuary liquor of a soap manufactory is evaporated, and treated with alcohol to dissolve out the glycerin. The spirit is then evaporated off, the glycerin diluted with water, and finally boiled repeatedly with animal charcoal until all colour and odour are removed.

_Obs._ The products of the above processes are nearly pure, but that of Price's patent process, described below, is to be preferred to any of them.

5. (Commercial.) From sweet stearin-liquor, by precipitating the lime by a stream of carbonic acid gas, or by a solution of carbonate of soda, carefully avoiding adding the latter in excess; the liquor is then boiled a little, filtered, evaporated to a syrupy consistence, and again filtered. This is the common glycerin of the shops. It may be further purified as above.

6. (PRICE'S GLYCERIN--Patent dated 1854.) Superheated steam of from 550 to 600 Fahr.) is introduced into a distillatory apparatus containing palm oil or other fatty body. The action of the steam effects the decomposition of the fat, and glycerin and the fatty acids distil over together but no longer in combination. In the receiver the condensed glycerin, from its higher specific gravity, sinks below the fatty acids. Sufficient steam must be supplied, and the temperature nicely regulated. The glycerin is concentrated by evaporation, and if discoloured, it is redistilled. It is usually prepared with sp. gr. 124, and then contains 94% of anhydrous glycerin. It can, however, be concentrated to sp. gr. 126 when it contains 98%.

_Prop._ Pure glycerin is a colourless, odourless, uncrystallisable liquid, sweet to the taste, and of a syrupy consistence; it mixes with water in all proportions; it is unctuous and emollient, and softens bodies, like oil, but without greasing them; it does not evaporate or change in the air at ordinary temperatures, and is not susceptible of rancidity or spontaneous fermentation; mixed with yeast and kept in a warm place, it is gradually converted into propionic acid; a strong heat decomposes it, with the production of acrolein; it is neutral to test-paper, and possesses neither basic nor acid properties; it is easily charged with the aroma of the essential oils, and may be combined with soap, and many other substances, without undergoing change. Sp. gr., 127 (see _above_).

MM. Champion and Pellet recommend the following methods for testing the purity of glycerin, as being convenient in application, and giving accurate results.

_Qualitative Test._ The glycerin diluted with twice its weight of water is treated in the cold.

(1.) With tribasic acetate of lead. If an abundant precipitate be formed, and rapidly deposited, the presence of a proportion of foreign matters may be a.s.sumed which would make it unsuitable for use in various applications, such as the manufacture of nitro-glycerin, &c. The crude glycerin obtained in treating fats with sulphuric acid is frequently thus contaminated.

These foreign matters result from the action of sulphuric acid at a high temperature (about 110 C.) upon the fatty matter itself or on the impurities it may contain.

(2.) Glycerin obtained by calcareous saponification, also may contain oleate of lime. This may be detected with oxalate of ammonia, which throws down the lime as a clearly perceptible precipitate.

The colour of glycerin is in no way an index of the purity of the product.

In all cases it is useful to be a.s.sured of the neutrality of the glycerin.

The preceding tests are suited for glycerins more or less impure, but not adulterated. According to the authors' experiments the tribasic acetate of lead separates all the foreign substances due to normal impurity of the product or alteration in the glycerin during its manufacture. Any addition of glucose may be detected by Fehlings' solution.

_Quant.i.tative Test._ This test should comprehend the determination of the water, the foreign organic matter, the lime, and the glycerin.

In the following table the authors have given the density of various mixtures of water and glycerin, comparatively with the degrees Baume, and also the proportions of water corresponding to the densities. They state, that these determinations have been verified by means of pure anhydrous glycerin, prepared by keeping glycerin for several hours at a temperature of 160 C, and terminating the operation _in vacuo_. The density found was in accord with that given by Berthelot, namely, 1264.

_Estimation of Organic Matter._ Fifty grams of glycerin diluted with water are treated with an excess of tribasic acetate of lead, and the precipitate collected on two tared filters, and the lead compound weighed.

The whole is then calcined, the residue treated with nitric acid, and then with sulphuric acid, and from the sulphate of lead is calculated the quant.i.ty of oxide of lead, that was in combination with organic matters, and consequently the proportion of the latter, which rarely exceeds 1 to 15 per cent.

Lime may be estimated in the usual manner by oxalate of ammonia.

------------------------------------------------------------------------ Hydrometer Areometer Water, Hydrometer Areometer Water, Weight of Degrees, per Cent. Weight of Degrees, per Cent.

Litre. Baume. Litre. Baume. ----------------------------------- ------------------------------------ 12640 312 00 12350 286 110 12625 310 05 12335 284 115 12612 309 10 12322 283 120 12600 308 15 12307 282 125 12585 307 20 12295 280 130 12572 306 25 12280 278 135 12560 304 30 12270 277 140 12545 303 35 12255 276 145 12532 302 40 12242 274 150 12520 301 45 12230 273 155 12505 300 50 12217 272 160 12490 299 55 12202 270 165 12480 298 60 12190 269 170 12465 297 65 12177 268 175 12455 296 70 12165 267 180 12440 295 75 12150 265 185 12427 293 80 12137 264 190 12412 292 85 12125 263 195 12400 290 90 12112 262 200 12390 289 95 12100 260 205 12375 288 100 12085 259 219 12362 287 105 ------------------------------------------------------------------------

The authors consider that industrially the tribasic acetate of lead might be used for the removal of organic matter from crude glycerin.

After separation of the precipitate, excess of the lead salt could be removed by a current of sulphuretted hydrogen, and during the concentration of the glycerin, the acetic acid set free would be volatilized with injury to the product. The lead salt might be regenerated by calcination, and again converted into acetate.[337]

[Footnote 337: 'Moniteur Scientifique,' Quesneville [3], vol. iii, p.

1033.]

The following quant.i.tative test which it is said will detect upon concentration of the fluids, one-tenth per cent. of glycerin in beer; one per cent. in sherry, one per cent. in milk, and five per cent. in treacle, is based upon a fact observed by Iles, viz. that borax when treated with glycerin, gives to a Bunsen flame the green colour characteristic of boracic acid. The method of its application as given by Messrs Senier and Lowe is as follows:--The suspected solution is rendered alkaline by dilute soda, and a borax bead placed in it for a short time. The bead is then held in a Bunsen flame, and if the solution contains one per cent. of glycerin a distinct reaction is observed. Erythrite and glycol give the same colour.

If a small quant.i.ty of glycerin from which the fatty acids have not been removed, be poured into the palm, and rubbed between the hands, a peculiar fetid, mouse-like odour will be perceived.

_Uses, &c._ Glycerin is extensively employed as an excipient for medicines (see GLYCEROLES), also, either alone, or in lotions, baths, &c., as a soothing emollient, and is added to poultices and dressings instead of oil, to prevent their hardening. Diluted with water, it often succeeds in allaying itching and irritation of the skin when all other means fail. As a cosmetic, either made into a lotion or added to soap (glycerin soap), or used in small quant.i.ties (along with the water employed in was.h.i.+ng), it imparts a healthy clearness and a sensation of softness and coolness to the skin, which is very agreeable and refres.h.i.+ng. It is the best remedy known for chapped nipples, hands, lips, &c.; all of which may be prevented by its use as an article of the toilet. Glycerin is sometimes used as a sweetening agent, as a subst.i.tute for syrup.

Glycerin is employed for a great variety of purposes other than medicinal; such, for example, as for:--Keeping clay moist for the modeller, for preventing mustard from drying up, for keeping snuff damp, for the preservation of fruit, for sweetening liqueurs, wine, beer, and malt extracts. It is also used as a lubricant for some kinds of machinery, more especially for watch and chronometer works, because it is unaffected by contact with the air, does not thicken at a low temperature, and is without action on such metals as copper, bra.s.s, &c. Glycerin is also an ingredient in copying inks. It renders printing ink soluble in water; indeed it is an excellent solvent for many substances, including the Tar-colours (aniline blue, cyanine, aniline violet, and alizarine), and a.r.s.enious acid. It is also added to the pulp of paper in order to render it soft and pliable. It is said that leather driving-belts made as they usually are of weakly tanned leather, when kept in glycerin for twenty-four hours are not so liable to fray. A solution of glycerin in water is now largely used instead of water alone for the purpose of filling gas metres, as such a solution does not freeze in winter nor evaporate in summer. It has also been used for the compa.s.ses on board screw-steamers, in order to protect the inner compa.s.s-box, against the vibrations caused by the motion of the propeller. It is also employed for the preservation of anatomical preparations, and for mounting microscopic specimens; as well as for rendering wooden casks impervious to petroleum or other oils; as well as for the preparation of artificial oil of mustard, or sulpho-cyan-allyl, which is made by treating glycerin with iodide of phosphorus, whereby iodide of allyl is formed, which on being dissolved in alcohol, and next distilled with sulpho-cyanide of pota.s.sium, yields sulpho-cyan-allyl. When treated with concentrated nitric acid, glycerin yields nitro-glycerin.[338]

[Footnote 338: Wagner's 'Chemical Technology.']

Even the above long list does not exhaust the many useful purposes to which glycerin is now applied.

=Glycerin Cream for Chilblains.= Equal parts of glycerin, soft soap, and cherry-laurel water, mixed together.