254 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
Nitrocellulose.—Nitrocellulose is obtained by the nitration of cel- 
lulose. The latter is not a clearly defined substance, but a generic 
term applied to a class of substances which have many chemical and 
physical characteristics in common. The composition of the cellu- 
lose corresponds to the empirical formula C,,H,,0,,.. In the process 
of nitration, a number of atoms of hydrogen are replaced by a num- 
ber of molecules of nitric peroxide (NO,) giving a product nitrocellu- 
lose of the general formula C,,Hy)—nO(NO,)n. It has been found 
possible to introduce more than 12 (NO,) groups into the cellulose 
molecule. This gives a nitrogen content by. weight equal to 14.16 
per cent. The highest stable nitrocellulose contains, however, only 
about 13.5 per cent of nitrogen, and the one most used in the manu- 
facture of smokeless powder contains about 12.5 per cent. The 
purest form of natural cellulose is cotton. This material is accord- 
ingly used almost exclusively in the manufacture of nitrocellulose 
for smokeless powder. The several steps in the process of manu- 
facturing nitrocellulose may be described briefly as follows: 
The cotton used is generally the short fiber which is detached from 
the cotton seed rather late in the process of removal. After being 
bleached and purified it is run through a picker, which opens up the 
fiber and breaks up any lumps. It is then thoroughly dried and is 
ready for nitration. The most generally used method of nitration 
is to put the cotton into a large vessel, nearly filled with a mixture 
of nitric and sulphuric acids. The sulphuric acid is used to absorb 
the water developed in the process of nitration, and which would other- 
wise too greatly dilute the nitric acid. After a few minutes immersion 
the pot is rapidly rotated by machinery and the acid permitted to 
escape. The nitrated cotton is washed in a preliminary way, then 
removed from the nitrator and repeatedly washed and boiled to 
remove all traces of free acid. In the process of nitration, the cotton 
has not changed its appearance, but has become a little harsh to the 
touch. As the keeping qualities are dependent upon the thoroughness 
with which it is purified, the specifications for powder for the United 
States Army and Navy require that the nitrocellulose shall be given 
at this stage of manufacture at least five boilings with a change of 
water after each boiling, the total time of boiling being 40 hours. 
Following this preliminary purification, the nitrocellulose is cut up 
into still shorter lengths by being repeatedly run between cylinders 
carrying revolving knives. This operation was found necessary as 
cotton fibers are hollow tubes making it very difficult to remove 
traces of acid from the interior unless cut into very short lengths. 
After being pulped, the nitrocellulose is given six more boilings with 
a change of water after each, followed by 10 cold-water washings. 
The completed material is known as guncotton or pyrocellulose. 
Before adding the solvent, the pyrocellulose must be completely 
