[Illustration: Fig. 53.--Service Guncotton for Cordite made at a Private
Factory.]

Readings are taken thirty minutes from the time the nitro-cellulose is
heated, and are taken at intervals of fifteen minutes for about four
hours; fresh caustic potash is added every thirty minutes or so. It is
convenient to plot the results in curves. The curves given in Fig. 53 are
from gun-cotton manufacturers in England at a private factory. The rate of
evolution of nitrogen is as follows:--

In 1 hour. In 2 hours. In 3 hours. In 4 hours.
N. N. N. N. in milligrammes.
1.25 2.55 4.5 5.75
1.5 3.25 5.25 6.75
These results are very satisfactory, the gun-cotton was of a very good
quality. Several hours are necessary to remove all the air from the
apparatus. Dr Will stated fifteen minutes in his original paper, but this
has not been found sufficient. It has not been satisfactorily proved that
Will's test can be applied to gelatinised nitro-cellulose powders. It is
convenient to plot the results in curves; the nitrogen is generally given
in cubic centimetres or in milligrammes, and readings taken every fifteen
minutes. The steepness of the curve is a measure of the stability of the
nitro-cellulose which is being examined. The steeper the curve the more
nitrogen is evolved per unit of time, and the less stable the nitro-
cellulose. In the case of unstable nitro-celluloses heated under the
conditions described, the separation of nitrogen is much greater at first
than at a later period. If the nitro-cellulose be very unstable,
explosions are produced. If the separation of nitrogen is uniform during
the prolonged heating, then the nitro-cellulose may be regarded as