228 
ME. ABEL’S EESEAECHES ON GUN-COTTON. 
cotton which had been silicated, varied greatly in their powers of resisting change at 
high temperatures, but they were invariably rendered decidedly more prone to change 
if thoroughly washed in distilled water previous to their exposure to heat. 
It is remarkable how very small a proportion of a carbonate deposited upon the fibre 
of gun-cotton, exerts a notable influence upon its power of resisting the effects of heat. 
Thus, a portion of a sample of gun-cotton which had been carefully freed from carbo- 
nates, was saturated with perfectly clear lime-water, wrung out and dried. Upon ex- 
posure to 100° in comparison with an equal weight of the sample purified from carbo- 
nates, the very small quantity of calcic carbonate which had been deposited upon the 
gun-cotton proved sufficient to delay to a notable extent the period of first decomposi- 
tion, and to modify somewhat the results of change produced by exposure for a definite 
period at 100°C. 
In experiment 138, conducted at 90° C., the alkalized gun-cotton was heated in a flask 
to which a delivery-tube was attached, and the gas which escaped was examined. It 
was then observed that, upon the second day’s exposure, a very small quantity of carbonic 
acid was continuously evolved ; that the quantity increased somewhat upon the third 
day ; and that no nitrous vapours escaped until the sixth day, when the temperature 
was accidentally raised to 95°. Carbonic acid was then still evolved in small quantity. 
Similar evidence of the slow decomposition of the carbonate, which always preceded 
any disengagement of nitrous acid, was obtained in other experiments. 
Some experiments were instituted in sealed tubes with the gun-cotton impregnated 
with 04 percent, of sodic carbonate. 
Experiment 144. — A specimen was enclosed in a tube with air at the atmospheric 
pressure, and exposed to 100° C. for 3f hours, on the first day, during which period no 
trace of nitrous vapour was visible. It was afterwards heated to 100° six hours daily for 
thirteen days, and no coloration of the air in the tube was observed at any time during 
this treatment. After four days’ exposure, the tube was opened and gas escaped under 
somewhat considerable pressure. The tube was sealed up again, and at the close of the 
experiment it was opened once more, when gas escaped only under slight pressure. The 
specimen became discoloured in a few T places after some time (which is invariably the 
case when gun-cotton containing alkaline matter is exposed to a high temperature), but 
exhibited no other signs of change. In similar experiments conducted with ordinary 
gun-cotton, deep nitrous vapours were observed in the tubes within three hours from the 
commencement of the experiment, and the material was always converted into a gum- 
like mass ; in some instances the tube exploded violently after a time. 
Experiment 145. — An experiment similar to the preceding was instituted with alka- 
lized gun-cotton in a more closely packed condition, the tube being exhausted, filled 
with nitrogen, and re-exhausted before sealing. This tube was heated to 100° for ten 
hours (in two days), and afterwards left exposed to light for twenty-four hours, without 
the slightest coloration by nitrous vapours being observed. On being again heated, 
