ME. ABEL’S EESEABCHES ON GUN-COTTON. 
193 
then found to amount to 0-6 per cent., that of the dry sample only to 0-14 per cent, 
(after six months’ exposure). 
A trifling oxidation at the expense of oxygen in the water, established by the agency 
of sunlight, is doubtless the cause of the slight but decided influence which, under these 
circumstances, water has been observed to exert upon the permanence of gun-cotton ; 
an influence which is quite opposed to that exerted by the presence of water in gun- 
cotton stored in the dark, or exposed to high temperatures, as will be presently demon- 
strated. 
The statement made by De Luca*, that when once decomposition has been established 
in gun-cotton, resulting in the development of nitrous acid, the progress of the change 
cannot be arrested, is not borne out by the results of numerous observations - made by 
me. Many specimens of gun-cotton which, by exposure to high temperatures (100° and 
90° C.) or by very long-continued exposure to lower temperatures (50° to 65°), have 
suffered considerable change, resulting in the development of nitric peroxide and of 
other products, have been afterwards preserved in glass bottles, both tightly closed 
and partially open, and freely exposed to light for periods ranging from one to three 
years, without undergoing additional change. In a few exceptional instances, further 
decomposition has after a time been established by the influence of light ; but in those 
the gun-cotton was impregnated to a considerable extent Avith free (nitric) acid. Such 
specimens, in case they Avere then thoroughly washed, a slightly alkaline solution being- 
employed in their first purification, have afterwards not been found, up to the present 
time, to exhibit any greater tendency to decomposition by exposure to light, than the 
original gun-cotton. 
Part II.— EFFECTS OF HEAT UPON GUN-COTTON. 
The behaviour of gun-cotton under exposure even to comparatively high temperatures 
is subject to very considerable modifications, Avhich maybe in great measure determined 
by the conditions of treatment. Illustrations of this were obtained at an early period 
of these investigations, in experiments instituted Avith the view to ascertain the average 
temperature at which gun-cotton explodes. 
The following is a summary of the observations made on this head. 
JExploding-point of gun-cotton . — The apparatus employed in the experiments on this 
subject consisted of a small air-bath fitted Avith a thermometer and closed Avith a mica- 
plate, having a little circular opening in the centre, through which the gun-cotton 
might be introduced, and Avhich Avas kept closed when not in use. The mode of 
operating was modified in various ways. In the first instance the gun-cotton was combed 
out into a very loose condition, and alloAved to rest upon metal in the air-bath. The 
temperature of the latter was then raised very gradually from 15° C. to 204°, or 205 C°. 
When the time occupied in the passage to the maximum temperature Avas tAvo hours 
and upwards, the gun-cotton did not explode at all (in six experiments), but gradually 
* Comptes Bendus, vol. lix. p. 487. 
