212 
ME. ABEL’S EESEAECHES ON GUN-COTTON. 
lure of 100° C., excepting that the phenomena of decomposition, instead of appearing 
after a few minutes, only became manifest after several hours. This statement has been 
confirmed, by the results of comparative experiments which I have instituted at 90° and 
100°, to this extent, that in all instances the first signs of change become manifest in 
the specimens heated to 100°, and that sometimes the interval of time between the first 
exposure to heat and the first indications of decomposition is much greater at the lower 
than the higher temperature. The following results furnished by exposure of equal 
quantities- of the same gun-cotton, in the same condition, to 90° and 100°C., may be 
quoted in illustration of the comparative effects of the two temperatures. 
Table V. 
No. of 
experi- 
ment. 
Total period of exposure to 
First indications of change 
observed after commence- 
ment of exposure to 
Observations. 
90° C. 
100 ° c. 
90° C. 
100 ° c. 
96 
48 hours 
6 hours 
4 hours, very 
faint. 
2 hours 
At 90° only faint indications of nitrous acid 
were obtained up to the close of experiment ; 
at 100° the vapours were abundantly evolved 
after 5£ hours’ exposure. 
97 
26 hours 
26 hours 
6 horn’s 
5 hours 
In both instances the coloration of the atmo- 
sphere was very faint throughout the experi- 
ment. 
98 
40 hours ...... 
30 hours ....... 
10 hours 
45 minutes ... 
The coloration by nitrous acid was only faint 
throughout in both instances, but the speci- 
men exposed to 100° sustained a more consi- 
derable change than the other. 
99 
56 horn’s 
20 hours 
22 hours, very 
faint. 
14 hours 
The disengagement of nitrous acid was only very 
slight throughout the experiment at 90° ; in 
the other experiment it was more copious, 
though not abundant at any period. 
100 
42 hours 
10 hours ...... 
None observed 
50 minutes ... 
The specimen heated to 100° was decomposing 
rapidly after the lapse of 9 J hours ; the other 
specimen exhibited no sign of change beyond 
a slight acidity. 
101 
46 hours 
6 hours 
None observed 
2 hours, very 
faint. 
The specimen heated to 100° commenced to 
evolve nitrous acid abundantly at the expira- 
tion of 6 hours, the. other specimen showing 
no sign of change beyond a slight acidity. 
It will be observed from these experiments, which are quoted as representing nume- 
rous others of a similar description, that in most instances the decomposition of the gun- 
cotton was not only slower but also much less serious at 90° than at 100°. Exceptional 
specimens, exhibiting either a very unusual want of stability (e. g. some of the speci- 
mens from Hirtenberg and Stowmarket which have already been referred to), or a 
remarkable power of resisting decomposition at 100°, generally showed but little differ- 
ence in behaviour when subject to the influences of the two temperatures. 
EXPOSUEE OE GUN-COTTON TO TEMPEEATUEES BANGING EEOM 50° TO 60° C. 
Several experiments, corresponding in their nature to those described in the first part 
of the account of the action of light upon gun-cotton, have been instituted for the pur- 
pose of obtaining data regarding the influence , upon the material of very long-continued 
exposure to the above-named temperatures. The air-dry gun-cotton was introduced into 
large bulbs blown at the extremities of barometer-tubes, the latter being placed with 
