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:— The water and washings 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. 1·265. 2. (M. Bruère-Perrin.) From the sweet liquor of the stearine works (a product of the proce of lime-saponification). The quantity of lime present in the sample is first determined by means of oxalic acid, and the proportion of sulphuric acid nece ary for its saturation at once calculated and added; the crude liquor is then concentrated in a tinned-copper ve el, evaporation being promoted by brisk agitation, until the sp. gr. sinks to 10° Baumé; it is next cooled and filtered, and accurately neutralised (if it is required) with carbonate of pota a, after which it is evaporated to the sp. gr. 24° Baumé; on cooling, it deposits gelatinous sulphate of pota a; the whole is now filtered, the deposit on the filter washed with a little very weak spirit and water, the filtrate and washings mixed together and evaporated, as before, with agitation, until the sp. gr. 28° Baumé, 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 colourle and odourle by red i luting 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 dryne (nearly), di olving 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 di olve 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 proce es are nearly pure, but that of Price’s patent proce , 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 exce ; 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. 1·24, and then contains 94% of anhydrous glycerin. It can, however, be concentrated to sp. gr. 1·26 when it contains 98%. Prop. Pure glycerin is a colourle , odourle , 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 po e es neither basic nor acid properties; it is easily charged with the aroma of the e ential oils, and may be combined with soap, and many other substances, without undergoing change. Sp. gr., 1·27 (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 umed which would make it unsuitable for use in various applications, such as the manufacture of nitro-glycerin, . 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 ured of the neutrality of the glycerin. The preceding tests are suited for glycerins more or le 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. Quantitative 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 Baumé, 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 vacuô . The density found was in accord with that given by Berthe lot, namely, 1·264. Estimation of Organic Matter. Fifty grams of glycerin diluted with water are treated with an exce 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 quantity of oxide of lead, that was in combination with organic matters, and consequently the proportion of the latter, which rarely exceeds 1 to 1·5 per cent. Lime may be estimated in the usual manner by oxalate of ammonia. | Hydrometer Weight of Litre. | Areometer Degrees, Baumé. | Water, per Cent. | | 1264·0 | 31·2 | 0·0 | | 1262·5 | 31·0 | 0·5 | | 1261·2 | 30·9 | 1·0 | | 1260·0 | 30·8 | 1·5 | | 1258·5 | 30·7 | 2·0 | | 1257·2 | 30·6 | 2·5 | | 1256·0 | 30·4 | 3·0 | | 1254·5 | 30·3 | 3·5 | | 1253·2 | 30·2 | 4·0 | | 1252·0 | 30·1 | 4·5 | | 1250·5 | 30·0 | 5·0 | | 1249·0 | 29·9 | 5·5 | | 1248·0 | 29·8 | 6·0 | | 1246·5 | 29·7 | 6·5 | | 1245·5 | 29·6 | 7·0 | | 1244·0 | 29·5 | 7·5 | | 1242·7 | 29·3 | 8·0 | | 1241·2 | 29·2 | 8·5 | | 1240·0 | 29·0 | 9·0 | | 1239·0 | 28·9 | 9·5 | | 1237·5 | 28·8 | 10·0 | | 1236·2 | 28·7 | 10·5 | | 1235·0 | 28·6 | 11·0 | | 1233·5 | 28·4 | 11·5 | | 1232·2 | 28·3 | 12·0 | | 1230·7 | 28·2 | 12·5 | | 1229·5 | 28·0 | 13·0 | | 1228·0 | 27·8 | 13·5 | | 1227·0 | 27·7 | 14·0 | | 1225·5 | 27·6 | 14·5 | | 1224·2 | 27·4 | 15·0 | | 1223·0 | 27·3 | 15·5 | | 1221·7 | 27·2 | 16·0 | | 1220·2 | 27·0 | 16·5 | | 1219·0 | 26·9 | 17·0 | | 1217·7 | 26·8 | 17·5 | | 1216·5 | 26·7 | 18·0 | | 1215·0 | 26·5 | 18·5 | | 1213·7 | 26·4 | 19·0 | | 1212·5 | 26·3 | 19·5 | | 1211·2 | 26·2 | 20·0 | | 1210·0 | 26·0 | 20·5 | | 1208·5 | 25·9 | 21·9 | 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, exce 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] [337] ‘Moniteur Scient i fique,’ Quesneville [3], vol. iii, p. 1033. The following quantitative 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 Me rs 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 quantity 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, . Glycerin is extensively employed as an excipient for medicines (see Glyceroles ), also, either alone, or in lotions, baths, ., as a soothing emollient, and is added to poultices and dre ings 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 quantities (along with the water employed in washing), it imparts a healthy clearne and a sensation of softne and coolne to the skin, which is very agreeable and refreshing. It is the best remedy known for chapped nipples, hands, lips, .; 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 substitute 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 , . 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 arsenious 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 es on board screw-steamers, in order to protect the inner compa -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 di olved in alcohol, and next distilled with sulpho-cyanide of pota ium, yields sulpho-cyan-allyl. When treated with concentrated nitric acid, glycerin yields nitro-glycerin. [338] [338] Wagner’s ‘Chemical Technology.’ Even the above long list does not exhaust the many useful purposes to which glycerin is now applied.