ay not be
locally in excess.

~The Lead Oxide Method.~--Two grms. of sample are mixed with about 40
grms. of pure litharge, and heated in an air bath to 130 deg. C. until the
weight becomes constant, care being taken that the litharge is free from
such lead compounds and other substances as might injuriously affect the
results, and that the heating of the mixture takes place in an air bath
free from carbonic acid. The increase in weight in the litharge, minus the
weight of substance not volatilisable from 2 grms. of glycerine at 160 deg.
C., multiplied by the factor 1.243, is taken as the weight of glycerine in
the 2 grms. of sample. The glycerine must be fairly pure, and free from
resinous substances and SO_{3}, to give good results by this process.

~Analysis of the "Waste Acids" from the Manufacture of Nitro-Glycerine or
Gun-Cotton.~ Determine the specific gravity by the specific gravity bottle
or hydrometer, and the oxides of nitrogen by the permanganate method
described under nitro-glycerine. Now determine the total acidity of the
mixture by means of a tenth normal solution of sodium hydrate, and
calculate it as nitric acid (HNO_{3}), then determine the nitric acid by
means of Lunge nitrometer, and subtract percentage found from total
acidity, and calculate the difference into sulphuric acid, thus:--

Total acidity equals 97.46 per cent.--11.07 per cent. HNO_{3} = 86.39 per
cent., then (86.39 x 49)/63 = 67.20 per cent. H_{2}SO_{4}.

Then analysis of sample will be:--

_
Sulphuric acid = 67.20 per cent. |
Nitric acid = 11.07 " |- Specific gravity = 1.7075.
Water = 12.73 " _|

This method is accurate enough for general use in the nitric acid factory.
The acid mixture may be taken by volume for determining nitric oxide in
nitrometer. Two c.c. is a convenient quantity in the above case, then 2 x
1.7075 (specific gravity) = 3.414 grms. taken, gave 145 c.c. NO (barometer
= 748 mm, and temperature = 15 deg.C.) equals 134.9 c.c. (corr.) and as 1 c.c.
NO = .0282 grm. HNO_{3} 135 x .0282 = .378 grm. = 11.07 per cent. nitric
acid.

~Sodium Nitrate.~ Determine moisture and chlorine by the usual methods,
and the total, NaNO_{3}, by means of nitrometer--0.45 grm. is a very
convenient quantity to work on (gives about 123 c.c. gas); grind very
fine, and dissolve in a very little hot water in the cup of the
nitrometer; use about 15 c.c. concentrated H_{2}SO_