temperature of about 160 deg. C. in a platinum basin, and finish in an air
bath. Weigh until constant weight is obtained. Afterwards incinerate over
a bunsen burner, and weigh the ash.

[Footnote A: Organic matter up to .6 per cent. is not always prejudicial
to the nitrating quantities of a glycerine.]

~Silver Test.~ A portion of the sample of glycerine to be tested should be
put in a small weighing bottle, and a quarter of its bulk of N/10 silver
nitrate solution added to it, then shake it, and place in a dark cupboard
for fifteen minutes. It must be pronounced bad if it becomes black or dark
brown within that time (acrolein, formic, and butyric acids).

The German official test for glycerine for pharmaceutical purposes is much
more stringent, 1 c.c. of glycerine heated to boiling with 1 c.c. of
ammonia solution and three drops of silver nitrate solution must give
neither colour or precipitate within five minutes.

~Nitration.~ Fifty grms. of the glycerine are poured from a beaker into a
mixture of concentrated nitric acid (specific gravity 1.53) and sulphuric
acid (1.84), mixed in the proportions of 3 HNO_{3} to 5 H_{2}SO_{4} (about
400 c.c. of mixed acids). The mixed acids should be put into a rather
large beaker, and held in the right hand in a basin of water, and the
glycerine slowly poured into them from a smaller one held in the left. A
constant rotatory motion should be given to the beaker in which the
nitration is performed. When all the glycerine has been added, and the
mixture has been shaken for a few minutes longer, it is poured into a
separator, and allowed to stand for some time. It should, if the glycerine
is a good one, have separated from the mixed acids in ten minutes, and the
line of demarcation between the nitro-glycerine and the acid should be
clear and sharp, neither should there be any white flocculent matter
suspended in the liquid. The excess of acids is now drawn off, and the
nitro-glycerine shaken once or twice with a warm solution of carbonate of
soda, and afterwards with water alone. The nitro-glycerine is then drawn
off into a weighed beaker, the surface dried with a piece of filter paper,
and weighed; 100 parts of a good glycerine should yield about 230 of
nitro-glycerine. A quicker method is to take only 10 c.c. of the
glycerine, of which the specific gravity is already known, nitrate as
before, and pour into a burette, read off the volume of nitro-glycerine in
c.c. and multiply them