ME. ABEL’S EESEAECHES ON GUN-COTTON. 
191 
were then exposed to light, and occasionally to radiated heat, in the locality selected for 
these experiments. For the first few months the depression of the mercury-column was 
only very slight; in seven months 'it amounted to 15 millims. ; after that period (during 
bright spring weather) it became more considerable, being 155 millims. after ten months’ 
exposure. During the following year the depression of the mercury continued steadily ; 
in one year and nine months it amounted to 497 millims. ; and at the expiration of the 
three following months (about two years from the commencement) the mercury was 
expelled from the tube, a result corresponding to that obtained with the gun-cotton 
confined with aqueous vapour. After exposure for 24 years the condition of the gun- 
cotton was as follows : it had a somewhat pungent odour, its explosiveness and strength 
of fibre were slightly reduced ; water extracted 0 -6 per cent, of soluble matter ; the 
solution had a slight acid reaction, contained a small quantity of nitric acid, no oxalic 
acid, and reduced cupric salt to a slight extent. The proportion of soluble matter 
amounted to 27 per cent. 
Experiment 6. — A sample (19- 8 grms.) of gun-cotton which had been submitted to 
long-continued purification in flowing water, but had not been digested in an alkaline 
bath, was exposed to light in a dry globe, like the other specimens, and by the side of it 
was placed another globe containing an equal quantity of the same gun-cotton, but 
covered with black calico, so as to have light excluded from it but to be subject to the 
effects of considerable heat during summer weather. After the first six (autumn and 
winter) months’ exposure, the depression of the mercury-column in the perfectly exposed 
tube amounted to 51 millims. (being therefore considerably greater than in the case of 
the specimen washed with alkali). During this period the gun-cotton in the dark globe 
exhibited no signs of evolving gas. After nine months’ exposure the depression of mer- 
cury in the uncovered tube amounted to 320 millims. (against 155 millims. in ten months 
produced by the sample which had been washed in an alkaline bath). The covered 
bulb-tube which had been frequently exposed to the heat of the sun during the spring- 
months, exhibited at this time a depression of 38 millims. After the expiration of twelve 
months the depression of the mercury-column in the perfectly exposed tube amounted 
to 585 millims., and the mercury was completely expelled from this tube after the lapse 
of sixteen months. 
Although, however, gas had been more rapidly disengaged from this tube than from 
the one referred to in the previous experiments, the change which the gun-cotton had 
sustained at the expiration of about 24 years was not as great as that observed in the 
specimen which had been treated with the alkaline bath but washed for a short time 
only. The specimen had only a -very faint odour, its explosiveness and strength had not 
undergone any appreciable change ; water extracted only 0 - 3 per cent, of soluble matter ; 
a trace of nitric acid was detected in the extract, but no oxalic acid and no reaction upon 
cupric salts could be obtained. The proportion dissolved by ether and alcohol amounted 
to 16 per cent. 
Neither of these specimens, in the preparation of which the complete system of puri- 
2 d 2 
