ulphates. It should contain no sugars and leave
no residue on burning.

_Animal Charcoal for Decolorisation._--The application of animal
charcoal for decolorising purposes dates back a century, and various are
the views that have been propounded to explain its action. Some
observers base it upon the physical condition of the so-called carbon
present, and no doubt this is an important factor, coupled with the
porosity. Others consider that the nitrogen, which is present in all
animal charcoal and extremely difficult to remove, is essential to the
action. Animal charcoal should be freed from gypsum (sulphate of lime),
lest in the burning, sulphur compounds be formed which would pass into
the glycerine and contaminate it.

The "char" should be well boiled with water, then carbonate of soda or
caustic soda added in sufficient quantity to give an alkaline reaction,
and again well boiled. The liquor is withdrawn and the charcoal washed
until the washings are no longer alkaline. The charcoal is then
separated from the liquor and treated with hydrochloric acid; opinions
differ as to the amount of acid to be used. Some contend that phosphate
of lime plays such an important part in decolorising that it should not
be removed, but it has, however, been demonstrated that this substance
after exposure to heat has very little decolorising power.

Animal charcoal boiled with four times its weight of a mixture
consisting of equal parts of commercial hydrochloric acid (free from
arsenic) and water for twelve hours, then washed free from acid, dried,
and burned in closed vessels gives a product possessed of great
decolorising power for use with glycerines.

A good animal charcoal will have a dull appearance, and be of a deep
colour; it should be used in fine grains and not in the form of a
powder.

The charcoal from the filter presses is washed free from glycerine
(which is returned to the treated lyes), cleansed from foreign
substances by the above treatment and revivified by carefully heating in
closed vessels for twelve hours.

_Glycerine obtained by other Methods of Saponification._--French
saponification or "candle crude" glycerine is the result of
concentration of "sweet water" produced in the manufacture of stearine
and by the autoclave process. It contains 85-90 per cent. glycerol,
possesses a specific gravity of 1.240-1.242, and may be readily
distinguished from the soap-crude glycerine by the absence of salt
(sodium chlo