Glycerin is also a product of certain kinds of fermentation, especially of the alcoholic fermentation of sugar; consequently it is a constituent of many wines and other fermented liquors.
Prominent among these are glycerin and succinic acid.
7 succinic acid, 3.2 glycerin and 1.
A-propylene glycol, CH 3 CH(OH) CH 2 OH, a liquid boiling at 188° to 189°, and obtained by heating glycerin with sodium hydroxide and distilling the mixture; and trimethylene glycol, CH 2 OH CH 2 CH 2 OH, a liquid boiling at 214° C. and prepared by boiling trimethylene bromide with potash solution (A.
It is obtainable from most natural fatty bodies by the action of alkalis and similar reagents, whereby the fats are decomposed, water being taken up, and glycerin being formed together with the alkaline salt of some particular acid (varying with the nature of the fat).
Owing to their possession of this common property, these natural fatty bodies and various artificial derivatives of glycerin, which behave in the same way when treated with alkalis, are known as glycerides.
In the ordinary process of soap-making the glycerin remains dissolved in the aqueous liquors from which the soap is separated.
Glycerin was discovered in 1779 by K.
Chevreul, who named it glycerin, M.
Berthelot, and many other chemists, from whose researches it results that glycerin is a trihydric alcohol indicated by the formula C 3 H 5 (OH) 3j the natural fats and oils, and the glycerides generally, being substances of the nature of compound esters formed from glycerin by the replacement of the hydrogen of the OH groups by the radicals of certain acids, called for that reason "fatty acids."
The relationship of these glycerides to glycerin is shown by the series of bodies formed from glycerin by replacement of hydrogen by "stearyl" (C18H350), the radical of stearic acid (C18H350.
OH): The process of saponification may be viewed as the gradual progressive transformation of tristearin, or some analogously constituted substance, into distearin, monostearin and glycerin, or as the similar transformation of a substance analogous to distearin or to monostearin into glycerin.
By means of water alone or by an acid), the acid set free and the glycerin are obtained together in a form which usually admits of their ready separation.
Some other glycerides isolated from natural sources are analogous in composition to tristearin, but with this difference, that the three radicals which replace hydrogen in glycerin are not all identical; thus kephalin, myelin and lecithin are glycerides in which two hydrogens are replaced by fatty acid radicals, and the third by a complex phosphoric acid derivative.
Palm oil, it exists in the free state, so that it can be separated by washing with boiling water, which dissolves the glycerin but not the fatty glycerides.
Glycerin is a viscid, colourless liquid of sp. gr.
The simplest modes of preparing pure glycerin are based on the saponification of fats, either by alkalis or by superheated steam, and on the circumstance that, although glycerin cannot be distilled by itself under the ordinary pressure without decomposition, it can be readily volatilized in a current of superheated steam.
Commercial glycerin is mostly obtained from the "spent lyes" of the soap-maker.
Of mercury, and, when of specific gravity 1.295 (corresponding to about 80% of glycerin), it is distilled under a vacuum of 28 to 29 in.
The impure glycerin obtained as above is purified by redistillation in steam and evaporation in vacuum pans.
- Besides its use as a starting-point in the production of "nitroglycerin" (q.v.) and other chemical products, glycerin is largely employed for a number of purposes in the arts, its application thereto being due to its peculiar physical properties.
Glycerin acts as a preservative against decomposition, owing to its antiseptic qualities, which also led to its being employed to preserve untanned leather (especially during transit when exported, the hides being, moreover, kept soft and supple); to make solutions of gelatin, albumen, gum, paste, cements, &c. which will keep without decomposition; to preserve meat and other edibles; to mount anatomical preparations; to preserve vaccine lymph unchanged; and for many similar purposes.
Its solvent power is also utilized in the production of various colouring fluids, where the colouring matter would not dissolve in water alone; thus aniline violet, the tinctorial constituents of madder, and various allied colouring matters dissolve in glycerin, forming liquids which remain coloured even when diluted with water, the colouring matters being either retained in suspension or dissolved by the glycerin present in the diluted fluid.
Glycerin is also employed in the manufacture of formic acid.
Certain kinds of copying inks are greatly improved by the substitution of glycerin, in part or entirely, for the sugar or honey usually added.
In its medicinal use glycerin is an excellent solvent for such substances as iodine, alkaloids, alkalis, &c., and is therefore used for applying them to diseased surfaces, especially as it aids in their absorption.
Given by the mouth glycerin produces purging if large doses are administered, and has the same action if only a small quantity be introduced into the rectum.
Glycerin is useless as a food and is not in any sense a substitute for cod-liver oil.
Glycerin when treated with hydrochloric acid gives propenyl dichlorhydrin, which may be oxidized to s-dichloracetone.
These discoveries of Geoffroy and Scheele formed the basis of Chevreul's researches by which he established the constitution of oils and the true nature of soap. In the article Oils it is pointed out that all fatty oils and fats are mixtures of glycerides, that is, of bodies related to the alcohol glycerin C 3H5(OH)3 i and some fatty acid such as palmitic acid (C 16 H 31 0 2)H.
The corresponding decomposition of a glyceride into an acid and glycerin takes place when the glyceride is distilled in superheated steam, or by boiling in water mixed with a suitable proportion of caustic potash or soda.
A lotion containing ten minims of the dilute acid to an ounce of water and glycerin will relieve itching due to any cause; and is useful in some forms of neuralgia.
They are also formed when grape sugar is heated with ammonia or when glycerin is heated with ammonium chloride and ammonium phosphate (C. Stoehr, Journ.
-Dimethylpyrazine, or ketine, C4H2(CH3)2N2, is obtained by reducing isonitrosoacetone, or by heating glycerin with ammonium chloride and ammonium phosphate.
When heated with glycerin to ioo C. it yields formic acid and carbon dioxide; above this temperature, allyl alcohol is formed.
Instances of its application are found in the separation of orthoand para-nitrophenol, the o-compound distilling and the p- remaining behind; in the separation of aniline from the mixture obtained by reducing nitrobenzene; of the naphthols from the melts produced by fusing the naphthalene monosulphonic acids with potash; and of quinoline from the reaction between aniline, nitrobenzene, glycerin, and sulphuric acid (the product being first steam distilled to remove any aniline, nitrobenzene, or glycerin, then treated with alkali, and again steam distilled when quinoline comes over).
Distillation in a vacuum is practised in two forms: - if the pump draws off steam as well as air it is termed a "wet" air-pump; if it only draws off air, it is a "dry" air-pump. In the glycerin industry the lyes obtained by saponifying the fats are first evaporated with "wet vacuum" and finally distilled with closed and live steam and a "dry vacuum."
Fischer showed that methose was identical with the a-acrose obtained by himself and Tafel in 1887 by decomposing acrolein dibromide with baryta, and subsequently prepared by oxidizing glycerin with bromine in alkaline solution, and treating the product with dilute alkali at o°.
Glycerin appears to yield, on mild oxidation, an aldehyde, CH20H CH(OH) CHO, and a ketone, CH 2 OH CO CH 2 OH, and these condense as shown in the equation: CH 2 OH CH (OH) CHO + CH 2 OH [[Coch 2 Oh = Ch20h Ch(Oh) Ch(Oh) Ch(Oh) Co.Ch20h+H20]].
1837) he synthesized glycerin, starting from propylene.
Some glycerin may be re-formed, but with very strong alkaline solutions little of the glycerin molecule escapes destruction, oxalic acid and several other products resulting.
Calcium or potassium sulphides and potassium hydrosulphides completely reduce nitroglycerin to glycerin, some of the sulphur being oxidized and some precipitated.