by the tube C, the lower end dipping under a layer of
standard sulphuric acid, Z* is a funnel, with stopcock, for
conveying a solution of caustic soda to the flask, F a water
jet, and G the safety funnel, filled with fragments of broken
glass. The standard solutions required are sulphuric acid
and carbonate of soda, and are of decinormal strength —
1 c.c, acid != I c.c, alkali. They are prepared in the usual



132 BONE PRODUOTS AND MANURES

way. Through the safety funnel of the receiver is run
oO c.c. of the standard acid, the different parts of the
apparatus connected and made tight, and an excess of
caustic soda solution allowed to flow into the flask. Heat
is now applied cautiously, care being taken that no portion
of the caustic soda is mechanically carried over. On boiling
for an hour, the whole of the ammonia is driven over to the
receiver, and there absorbed by the sulphuric acid. The
receiver is now disconnected, the safety funnel washed with
water, and the washings added, and the whole contents
titrated with standard soda solution, according to the well-
known volumetric method.
Example —

Weight of sample taken

Decinormal acid used .....
Retitration with decinormal carbonate of soda

Leaving ....
Then 13 x '014 = "182, the amount of nitrogen contained in the

4 grams of the sample, the percentage being = 4'55.
4

For practical purposes, 1 part of nitrogen represents 5 '4
parts of glue, then 5-4: x 4-55 = 24-57, the percentage of
glue corresponding to the above amount of nitrogen.
The manufacturer, naturally, calculates his yield of glue
on the bones as " paid " over a weighing machine, and not on
a dry sample.
(2) Degreased Bones.
