Glycerine, per cent.
Glycerine, per cent.
Below 35° C.
Another authority gives: -
In January 1867, some glycerine sent in tin cans from Germany to England froze into pea-sized octahedral crystals; these while melting had a constant temperature of 45° F. (7°.2 C), but would not freeze again even when cooled to 0° F. (-18° C). According to Werner, commercial glycerine will freeze more readily if chlorine gas be passed into it. In purifying glycerine by cold, the whole mass is cooled to nearly 32° F. (0° C), and some crystals of solid glycerine are added; almost the whole mass solidifies on agitation, and a centrifugal is used to separate the solid from the liquid parts. Treated in this way, glycerine at 28° B. yields crystals which, when melted, are 30°.8 B.
Pure glycerine is a viscid, colourless, and transparent liquid, with an intensely sweet taste, soluble in water in all proportions, in alcohol, chloroform, and carbon bisulphide, but not in ether; its sp. gr. is 1.267; it solidifies at - 32° F. (- 40° C.) to an amorphous mass. When distilled, it decomposes, umless steam be present , hence its boiling-point cannot be accurately determined at atmospheric pressure. According to Bolas, at 12.5 mm. pressure it boils at 355° F. (179°.5 C), and at 50 mm. at 410° F. (210° C); while Heminger gives 354° F. (179° C.) as its boiling-point under 20 mm.
It burns with a clear flame like oil, if there be free access of air and a high temperature for kindling it.
Commercial glycerine is liable to contain various impurities, arising from its mode of preparation; also certain adulterants, of which cane-sugar and glucose are the chief. Glucose may be detected by the brown colour formed when the suspected glycerine is boiled with caustic soda; cane-sugar is shown by its deposition when the glycerine is agitated with chloroform, or, more certainly, by a polarising saccharimeter, since glycerine has no rotatory action on the plane of polarisation. Lead is detected by sulphuretted hydrogen; lime, by the addition of alcohol and sulphuric acid, a white precipitate of calcium sulphate being formed; butyric and formic acids, by the characteristic smell of their ethers, produced by boiling the suspected glycerine with alcohol and strong sulphuric acid; oxalic acid by the addition of calcium chloride and ammonia; sodium chloride, by the addition of silver nitrate, which should give no precipitate with pure glycerine after 24 hours' standing. A rough and ready test for impurities generally is to agitate the glycerine with an equal bulk of chloroform, when they collect in the intermediate layer.
Under the title of "Adulteration of Glycerine" F. Jean contributes an article to the Journal de Pharmacie d' Alsace-Lorraine, in which he considers not merely adulterations intentionally added, but impurities due to carelessness in its manufacture or purification. Among them are oxide of lead, lime, and butyric acid. French perfumers and manufacturers of cosmetics test their glycerine with nitrate of silver. If no turbidity or change of colour takes place in 24 hours, it is considered good. The chloroform test for glycerine consists in mixing equal volumes of chloroform and glycerine, shaking thoroughly, and then letting them stand. The upper stratum is pure glycerine, while the lower one is chloroform containing all the impurities. If there were no impurities in the glycerine, the chloroform remains unchanged, otherwise there will be a turbid layer just beneath the glycerine. On adding a few drops of dilute sulphuric acid to a mixture of equal parts of glycerine and distilled water, and then a little alcohol, the presence of lime or lead will be shown by a white precipitate. The latter is reorganised by sulphydric acid, which turns the precipitate black.
Butyric acid is detected by mixing the glycerine with absolute alcohol and sulphuric acid of 66° B. On gently heating the mixture, the butyric ether is easily recognised by its agreeable odour. Formic and oxalic acids are also found in glycerine, impurities which are of special importance to pharmacists. They are detected as follows: - Equal volumes of glycerine and sulphuric acid, sp. gr. 1.83, are mixed together. Pure glycerine does not give off any carbonic oxide gas, but if either of the acids mentioned is present, an evolution of that gas will be observed. To decide whether both acids are present, and if not which one, some alcohol of 40° B. and one drop of sulphuric acid are added, and then gently heated. Formic acid (used in making essence of peaches) will be recognised at once by its characteristic odour, and proves the presence of formic acid. To another sample of the glycerine add a little solution of chloride of calcium (free from carbonate), when it will give a precipitate of oxalate of lime, if oxalic acid is present.
Sugar, glucose, dextrine, and gum are often used as intentional adulterations of glycerine, and are tested for as follows: The glycerine is mixed with 150 or 200 drops distilled water, and 1/2 gr. molyb-date of ammonia is added, and one drop of pure nitric acid. It is boiled about 30 seconds. If sugar or dextrine is present, the mixture will be blue. Glycerine adulterated with loaf sugar or syrup acquires a brownish black colour when boiled with sulphuric acid. • Glucose is detected by boiling it with caustic soda, which turns it brown. If detected qualitatively, the quantity may be estimated by the following method: 5 grm. glycerine are weighed out and mixed with 5 cc. distilled water. It is boiled in a little flask, with Barreswil's alkaline solution of tartrate of copper. The suboxide of copper is precipitated, and the precipitate is dissolved again in hydrochloric acid. An excess of ammonia is added, and it is poured into a vessel containing an excess of nitrate of silver. A precipitate of metallic silver is formed and filtered out. It is washed with warm water and ammonia, calcined at a red heat, and weighed; 109*6 parts metallic silver represent 100 of glucose.