o 15 c.c. concentrated hydrochloric acid are
poured, which are sucked up into the developing flask _f_ by opening clip
E, air being carefully kept from entering. The clip E is now closed, and
tube _i_ is put underneath the burette, and the development of NO gas is
commenced by heating the contents of the flask _f_. When the pressure of
the gas in the flask has become greater than the pressure of the
atmosphere, the connecting tube begins to swell at _i_, whereupon clip D
is opened, and the boiling continued with frequent shaking of the bulb,
until no more nitrous gas bubbles rise up into the soda lye, the
distilling over of the HCl causes a crackling noise, the clip D is closed,
and E opened. The burette is again put hermetically on the indiarubber
stopper in basin W, and the apparatus is left to cool until the water
discharged through P shows the same temperature as the water flowing
through (into the cooling jacket) Z. If the level of the soda solution in
the tube X is now put on exactly the same level as that in the burette by
lowering or elevating the tube X as required, the volume of NO obtained in
c.c. can be read off within 1/10 c.c., and the percentage of nitrogen
calculated by the usual formula.

[Illustration: FIG. 45.--Decomposition Flask for Schultze-Tieman Method.]

The solution of protochloride of iron is obtained by dissolving iron
nails, &c., in concentrated HCl, the iron being in excess. When the
development of hydrogen ceases, it is necessary to filter warm through a
paper filter, and acidify filtrate with a few drops of HCl. The soda
solution used has a sp. gr. of 1.210 to 1.260; equals 25 deg. to 30 deg. B. The
nitro-cellulose is dried in quantities of 2 grms. at 70 deg. C. during eight
to ten hours, and then three hours in an exiccator over H_{2}SO_{4}. The
results obtained with this apparatus are very accurate. The reaction is
founded upon that of MM. Champion and Pellet's method.

~The Kjeldahl Method of Determining Nitrogen.~--This method, which has
been so largely used by analysts for the determination of nitrogen in
organic bodies, more especially perhaps in manures, was proposed by J.
Kjeldahl,[A] of the Carlsberg Laboratory of Copenhagen. It was afterwards
modified by Jodlbauer, of Munich,[B] and applied to the analysis of nitro-
explosives by M. Chenel, of the Laboratoire Centrale des Poudres, whose
method of procedure is as follows:--0.5 grm. of the finely powdered
substance is digested in