chloride. Care must be
taken that the flask used is strong enough to stand the pressure, or it
will burst.

The same chemists (_Compt. Rendus_, lxxxiii. 707) also devised the
following method for determining the NO_{2} in nitro-glycerine:--A known
quantity of a solution of ferrous sulphate of previously ascertained
reducing power is placed in a flask, acidified with hydrochloric acid, and
its surface covered with a layer of petroleum oil. About .5 grm. of the
nitro-glycerine is then introduced, and the flask heated on the water
bath. When the sample is completely decomposed, the liquid is heated to
boiling to remove nitric oxide, and the excess of ferrous sulphate
ascertained by titration with standard permanganate; 56 of iron (Fe)
oxidised by the sample correspond to 23 of NO_{2} in the sample of
nitro-glycerine.

~The Schultze-Tieman Method~ for determining nitrogen in nitro-explosives,
especially nitro-cellulose and nitro-glycerine.--The figure (No. 44) shows
the general arrangement of the apparatus. I am indebted for the following
description of the method of working it to my friend, Mr William Bate, of
Hayle. To fill the apparatus with the soda solution, the gas burette is
put on the indiarubber stopper of basin W, and firmly clamped down. Then
the taps A and C are opened, and B closed. When the burette is filled with
soda solution half-way up the funnel Y, A and C are closed, and B opened.
The arrows show the inlet and outlet for the cooling water that is kept
running through the water jacket round the nitrometer tube. To collect the
gas, raise the nitrometer off the rubber stopper, and place the gas tube
from the decomposition apparatus in the glass dish W and under the opening
of the nitrometer.

[Illustration: Fig. 44. SCHULTZE-TIEMAN APPARATUS.]

For the estimation of nitrogen in nitro-cellulose take .5 to .65 grm., and
place in the decomposition flask _f_ (Fig. 45), washing in with about 25
c.c. of water by alternately opening clips D and E. The air in the flask
is driven out by boiling, whilst the air is shut off by the tube _i_
dipping into the basin W, which is filled with the soda lye, and tube K is
placed in the test tube R, which contains a few c.c. of water. As soon as
all the air is completely driven out, clips D and E are closed, and the
gas jet is taken away. (This flask must be a strong one, or it will
burst.) Into test tube R, 25 c.c. of concentrated solution of
protochloride of iron and 10 t