192 
MR. ABEL’S RESEARCHES ON GUN-COTTON. 
fication had not been pursued, were found to be as injuriously affected by the very severe 
exposure as was anticipated. The specimen which had been exposed in the blackened 
bulb has up to the present time exhibited hut slight indications of change (by develop- 
ment of gas), and only when the heat radiated upon it from the wall behind, and absorbed 
from the sun’s rays, has been very considerable. It has not been disturbed for examina- 
tion, as there is no reason whatever to believe that it would differ in any respect from 
other portions of this imperfectly purified sample which have been preserved in the dark 
in well-closed boxes, and which only exhibit a slight acidity after 2-1 years’ preservation. 
Experiment 7. — A sample (19-8 grms.) taken from a large quantity of gun-cotton 
which, for purposes to be hereafter described, had been impregnated with 05 per cent, 
of sodic carbonate, was exposed to strong light in the same way as the preceding speci- 
mens. During six months (between August and March) only a very slight indication 
of alteration was obtained; the depression of the mercury amounted to 15 millims. at the 
end of that period. Soon afterwards gas was more abundantly evolved, the depression 
amounting to 133 millims. after ten months’ exposure. After eighteen months’ exposure' 
the amount of depression was 324 millims., which had increased to 432 millims. when 
the sample had been exposed for two years. After the lapse of 2|- years the mercury 
had not been entirely expelled front the tube. The gun-cotton was not altered in 
appearance or toughness of fibre, nor did it exhibit any appreciable diminution of 
explosiveness. It had a slight odour and faint acid reaction; the aqueous extract 
amounted to T5 per cent, (a portion of which was due to soda) ; it contained no oxalic 
acid, a small quantity of nitric acid, and reduced cupric salt slightly ; ether and alcohol 
extracted 10 per cent, of soluble matter. This sample had therefore suffered less 
change than any of the others. The disengagement of gas was manifestly due in part 
to the decomposition of the sodic carbonate, by small quantities of acid developed after 
a time by the exposure of the gun-cotton as described. This sample, after having been 
washed in water, exhibits no difference whatever in character from specimens of freshly 
prepared gun-cotton, in which the proportion of soluble cellulose-products is above the 
ordinary average. 
The observations made in experiments 1-4, that the preservation of gun-cotton in an 
atmosphere saturated with moisture rendered it somewhat more prone to alteration by 
long-continued exposure to light, have been confirmed by other experiments still in pro- 
gress, in which known quantities of moist and wet gun-cotton are exposed to light in 
confined spaces, in comparison with dry gun-cotton. Thus, in one of these experiments 
43*71 grms. of perfectly dry gun-cotton and 40*045 grms. of gun-cotton in a damp con- 
dition have been enclosed in large stoppered bottles and exposed side by side to strong 
daylight and sunlight. After the lapse of two (summer) months they were carefully 
dried and their weights determined. The sample which had been exposed to light 
saturated with water had lost 0*33 per cent., the weight of the dry sample indicated a 
loss of only 0 02 per cent. They were then again exposed in the wet and dry condition 
for four months; the total loss in weight of the sample exposed in a wet condition was 
