7 
losing the elements of water into less volatile compounds: Diglycerid 
acrolein (CgH^Oa), acetic acid, carbonic acid, and inflam- 
mable gases. 
Glycerin should be neutral in reaction. 
The density of the anhydrous fluid is 1.269 (1.265, Lyons), but as it is 
very hygroscopic it can not be kept in this state when exposed to the 
air without absorbing moisture, and therefore commercially the 
extreme point of concentration is 1.260, which corresponds to 0.03 to 
0.01 per cent of water. The United States and British pharmaco- 
poeias require glycerin to have a specific gravity of 1.250; the German 
pharmacopoeia requires 1.225 to 1.235. 
Completel}^ deprived of water by several distillations in vacuum, 
glycerin crystallizes into orthorhombic prisms, having a density of 
1.360, fusible at 15° C. 
Glycerin is soluble in all proportions in water and alcohol; insoluble 
in ether, chloroform, benzine, flxed oils, or volatile oils. It dissolves 
almost all substances soluble in water or in alcohol. Its great affinit}?^ 
for water is one of its best-known properties. Its properties of dis- 
solving albumin and preventing putrefaction have special reference to 
its use in adding it to vaccine virus. 
The number of chemical combinations with glycerin is numerous. 
PREPARATION. 
Glycerin is obtained by decomposing fat into its proximate con- 
stituents, either by a caustic alkali, as in the manufacture of soap, or 
by lead oxide, as in the preparation of lead plaster, or by the action 
of water at an elevated temperature under pressure. It is purified by 
distillation. 
IMPURITIES. 
Glycerin is used more or less pure, depending upon the various 
purposes for which it is employed. It may contain lead, iron, lime as 
an alkali, or sulphate, carbonate, or chlorid; oxalic, formic, or butyric 
acid. It is sometimes adulterated with large quantities of water, 
sugar, glucose, or dextrine, etc. Arsenic is also found in glycerin, 
particularly that which comes from the manufacture of soap. Glyc- 
erin which is. obtained by treating stearine with lime is free from 
arsenic. 
TESTS FOR IMPURITIES. 
A. Catillon (loc. cit., p. 20) gives the following tests for impurities 
in glycerin: 
After testing color, odor, and taste; 
1. Reaction must be exactly neutral. 
2. Specific gravity, which is an evidence of the watery contents. 
3. On heating 10 grams of glycerin over an alcohol lamp it should evaporate with- 
out disagreeable odor, without carbonizing, and without leaving a residue. 
