nt.
sulphuric acid on a spot plate, when a characteristic blood red to
violet coloration is produced. It has been proposed to differentiate
between cholesterol and phytosterol by their melting points, but it is
more reliable to compare the crystalline forms, the former crystallising
in laminae, while the latter forms groups of needle-shaped tufts. Another
method is to convert the substance into acetate, and take its melting
point, cholesterol acetate melting at 114.3-114.8 deg. C., and phytosterol
acetate at 125.6 deg.-137 deg. C.

Additional tests for cholesterol have been recently proposed by
Lifschuetz (_Ber. Deut. Chem. Ges._, 1908, 252-255), and Golodetz (_Chem.
Zeit._, 1908, 160). In that due to the former, which depends on the
oxidation of cholesterol to oxycholesterol ester and oxycholesterol, a
few milligrammes of the substance are dissolved in 2-3 c.c. glacial
acetic acid, a little benzoyl peroxide added, and the solution boiled,
after which four drops of strong sulphuric acid are added, when a
violet-blue or green colour is produced, if cholesterol is present, the
violet colour being due to oxycholesterol ester, the green to
oxycholesterol. Two tests are suggested by Golodetz (1) the addition of
one or two drops of a reagent consisting of five parts of concentrated
sulphuric acid and three parts of formaldehyde solution, which colours
cholesterol a blackish-brown, and (2) the addition of one drop of 30 per
cent. formaldehyde solution to a solution of the substance in
trichloracetic acid, when with cholesterol an intense blue coloration is
produced.

_Water._--From 5 to 20 grammes of the fat or oil are weighed into a
tared porcelain or platinum dish, and stirred with a thermometer, whilst
being heated over a gas flame at 100 deg. C. until bubbling or cracking has
ceased, and reweighed, the loss in weight representing the water. In
cases of spurting a little added alcohol will carry the water off
quietly.

To prevent loss by spurting, Davis (_J. Amer. Chem. Soc._, 23, 487) has
suggested that the fat or oil should be added to a previously dried and
tared coil of filter paper contained in a stoppered weighing bottle,
which is then placed in the oven and dried at 100 deg. C. until constant in
weight. Of course, this method is not applicable to oils or fats liable
to oxidation on heating.

_Dregs, Dirt, Adipose Tissue, Fibre, etc._--From 10 to 15 grammes of the
fat are dissolved in petroleum ether with frequen