ME. ABEL’S EESEAECHES ON GUN-COTTON. 
187 
Exposure to strong daylight and to sunlight, either in the open air or in confined 
spaces for a few days (two to four), developes in the gun-cotton a very faint aromatic 
odour ; and if litmus-paper be allowed to remain in close contact with the confined ma- 
terial, it acquires a rose-coloured tinge similar to that produced by carbonic acid, and 
recovers its original colour after brief exposure to air. If, after exposure to light in 
open air for some days, the gun-cotton he placed in the dark, in cases which are not air- 
tight, the odour becomes gradually fainter, and the effect upon litmus-paper slighter ; 
if the packages containing the gun-cotton are air-tight, the odour and action upon 
litmus do not increase during storage for several years (the actual experience gained at 
Woolwich extends over nearly four years). 
If the gun-cotton be exposed for protracted periods to daylight with free access of 
air, it speedily loses all odour and power of affecting litmus. If exposure to diffused 
daylight in confined spaces be continued, the first results of the action of light are, of 
course, retained ; but up to the present time no single indication of their increase has 
been observed ; indeed, the very faint acid reaction described, which was developed at 
first, has frequently disappeared, probably in consequence of the neutralizing action of 
small quantities of earthy carbonates contained in the gun-cotton. 
But if the material be exposed continuously in a perfectly confined space to the action 
of sunlight or strong daylight, it furnishes, after a time, much greater evidence of change 
than that already described. The acidity gradually becomes more manifest ; the odour 
increases, and becomes in time somewhat pungent and indicative of the presence 
of very small quantities of nitrous acid; and litmus-paper, if confined in the vessel 
with gun-cotton thus exposed, becomes entirely bleached after two or three months. 
Although specimens of gun-cotton always undergo some spontaneous change under 
these very special circumstances, the decomposition proceeds with extreme slowness; 
and the results of the observations instituted by me are, therefore, in this respect quite 
at variance with those recently published by De Luca, who states that the specimens 
operated upon by him decomposed upon exposure to sunlight, some on the first day of 
the experiment, others after several days’ exposure. 
The following account of special experiments instituted with gun-cotton manufactured 
at Waltham Abbey, will serve to illustrate the rate and nature of the decomposition 
suffered by this material when exposed to the action of sunlight in confined spaces. 
Experiments 1 and 2. — 16*37 grins, of air-dry gun-cotton were introduced into a 
large bulb blown at the extremity of a barometer tube of 10 millims. internal diameter, 
the length of which below the bulb was 812 millims. The bulb-tube was supported 
with the open extremity dipping into mercury. 
1 9T2 grms. of the same gun-cotton were placed in a bulb-tube with a stem of the same 
length. The extremity of this tube was also dipped into mercury ; but a small quantity 
of water was afterwards passed up into the end of the tube, so that the gun-cotton 
in the bulb might receive the maximum proportion of moisture which it was capable 
of absorbing. On the 20th of October, 1863, these two samples of gun-cotton were 
