t stirring, and passed
through a tared filter paper. The residue retained by the filter paper
is washed with petroleum ether until free from fat, dried in the
water-oven at 100 deg. C. and weighed.

If the amount of residue is large, it may be ignited, and the proportion
and nature of the ash determined.

The amount of impurities may also be estimated by Tate's method, which
is performed by weighing 5 grammes of fat into a separating funnel,
dissolving in ether, and allowing the whole to stand to enable the water
to deposit. After six hours' rest the water is withdrawn, the tube of
the separator carefully dried, and the ethereal solution filtered
through a dried tared filter paper into a tared flask. Well wash the
filter with ether, and carefully dry at 100 deg. C. The ether in the flask
is recovered, and the flask dried until all ether is expelled, and its
weight is constant. The amount of fat in the flask gives the quantity of
actual fat in the sample taken; the loss represents the water and other
impurities, and these latter may be obtained from the increase of weight
of the filter paper.

_Starch_ may be detected by the blue coloration it gives with iodine
solution, and confirmed by microscopical examination, or it may be
converted into glucose by inversion, and the glucose estimated by means
of Fehling's solution.

_Iodine Absorption._--This determination shows the amount of iodine
absorbed by a fat or oil, and was devised by Huebl, the reagents required
being as follows:--

(1) Solution of 25 grammes iodine in 500 c.c. absolute alcohol; (2)
solution of 30 grammes mercuric chloride in 500 c.c. absolute alcohol,
these two solutions being mixed together and allowed to stand at least
twelve hours before use; (3) a freshly prepared 10 per cent. aqueous
solution of potassium iodide; and (4) a N/10 solution of sodium
thiosulphate, standardised just prior to use by titrating a weighed
quantity of resublimed iodine dissolved in potassium iodide solution.

In the actual determination, 0.2 to 0.5 gramme of fat or fatty acids is
carefully weighed into a well-fitting stoppered 250 c.c. bottle,
dissolved in 10 c.c. chloroform, and 25 c.c. of the Huebl reagent added,
the stopper being then moistened with potassium iodide solution and
placed firmly in the bottle, which is allowed to stand at rest in a dark
place for four hours. A blank experiment is also performed, using the
same quantities of chloroform and Huebl reagent,