MR. ABEL’S RESEARCHES OH GUN-COTTON. 
209 
were observed throughout the experiment, and the material was unaltered in character, 
excepting that it had become decidedly acid. It should be observed that this ethereal 
extract was not quite free from the matters soluble in alcohol which the gun-cotton con- 
tained, as it is apparently impossible to extract these perfectly by digestion and frequent 
washing with alcohol. 
Experiment 90. — A specimen of Waltham Abbey gun-cotton was in the first instance 
digested with dilute acetic acid and thoroughly washed, the object of this treatment 
being to remove any mineral matters from the sample which might exert a neutralizing 
action and thereby influence the effects of exposure to heat. One half of this gun-cotton 
was then digested for two days with warm alcohol, and was afterwards repeatedly washed. 
On evaporation of the alcoholic extract the usual small yellowish resinous residue was 
obtained. 
A small portion of the dry gun-cotton thus purified was heated to 100° C. in a glass tube 
side by side with some of the same specimen which had only been extracted with acetic 
acid. Early on the second day of the experiment, the latter specimen began to evolve 
nitrous acid ; and about thirty minutes afterwards the sample extracted with alcohol 
exhibited faint signs of decomposition. 
Eight grammes of each of these samples, and a similar quantity of the gun-cotton in its 
original condition, were afterwards introduced into very long-necked flasks, the openings 
of which were loosely closed with corks and exposed for six days, seven hours daily, to 
65° C. ; as none of the specimens exhibited any sign of change at the expiration of that 
period, the temperature of the water-bath was maintained at between 88° and 90°. 
After about nine hours’ exposure to this temperature, the original gun-cotton began to 
decompose, and two hours later an extremely faint indication of nitrous acid was 
observed in the sample extracted with acetic acid. After two days’ (twelve hours) 
further exposure to heat, the first signs of decomposition became apparent in the flask 
containing the sample which had been extracted with alcohol. The coloration of the 
atmosphere continued, however, to be only faint in the flasks containing both extracted 
specimens during ten days’ exposure to about 90°. 
The observation made in this experiment, that the treatment of the gun-cotton with 
acetic acid decidedly increased its power of resisting the destructive effects of heat, was 
quite at variance with the anticipated result ; for, undoubted evidence having already 
been obtained of the retarding effect upon the decomposition, exerted by the existence 
of earthy carbonates when deposited upon the gun-cotton during the washing operations, 
it was considered that the treatment of ordinary gun-cotton with the acid, if it in any 
way influenced the subsequent action of heat upon the material, would have an accele- 
rating effect. Several additional experiments confirmed, however, the correctness of the 
above observations ; the following results, furnished by different samples of gun-cotton, 
of which portions were extracted with acetic acid, may be quoted in illustration of this. 
