758 GUN-COTTON 



even to comparatively high temperatures, is subject to very considerable modifications, 

 which may be in great measure determined by the conditions of treatment. Illustra- 

 tions of this were obtained at an early period of these investigations, in experiments 

 instituted with the view to ascertain the average temperature at -which gun-cotton 

 explodes. 



The following is a summary of the observations made on this head by Mr. Abel. 



Exploding -point of gun-cotton. The apparatus employed in the experiments on this 

 subject consisted of a small air-bath, fitted with a thermometer, and closed with a 

 mica-plate, having a circular opening in the centre, through which the gun-cotton 

 might be introduced, and which was kept closed, when not in use. The mode of opera- 

 ting was modified in various ways. In the first instance, the gun-cotton was combed out 

 into a very loose condition, and allowed to rest upon metal in the air-bath. The tem- 

 perature of the latter was then raised very gradually from 15 C. to 204 or 20f> C. 

 When the time occupied in the passage to the maximum temperature was two hours 

 and upwards, the gun-cotton did not explode at all (in six experiments), but gradually 

 became dark brown, quite friable, and deprived of all explosive properties. When a 

 considerably shorter time (about one hour) was occupied in the attainment of the maxi- 

 mum temperature, the gun-cotton exploded on one or two occasions, but not until its 

 temperature had reached 205 C. 



In the next experiments, the gun-cotton was employed in very small compact 

 masses, and resting upon a wooden support, was exposed to a continuously-increasing 

 temperature. The passage from 15 C. to the exploding-point ranged in these experi- 

 ments from 45 minutes to 2 hours. 



Temperature at commencement of experiment = 26 C. 



No. of Experiment Time occupied Explodiug-Point 



8 45 minutes. . 137'5 C. 



1 hour 25 minutes 

 1 hour 



1 hour . 



2 hours 



136. 

 137'5 C. 

 138'5C. 

 138. 



Another series of experiments was instituted for ascertaining in what particular 

 mechanical condition the gun-cotton exploded most readily, and at most uniform tem- 

 peratures ; and ultimately the material was employed in the form of pieces of loosely- 

 twisted strand about 20 millimeters long, and its exploding-point was determined by 

 first raising the atmosphere of the air-bath to 105 C., then allowing the specimen to 

 fall upon a diaphragm of wire gauze in the air-bath, at once increasing the temperature 

 as rapidly as possible ; and carefully reading the thermometer until the explosion 

 occurred. The results of eight observations thus conducted were as follow : 



No. of Experiments Exploding- Point 



13 151'5C. 



14 . 151 



15 151 



16 150'5 C. 



17 150-5 C. 



18 148'5C. 



19 . ' 151 



19a 147 



These last experiments, which appear the most trustworthy, indicate that the aver- 

 age temperature at which the gun-cotton explodes, when in a condition most favour- 

 able to its rapid heating, is about 150 C. For two observations, in which the gun- 

 cotton was in a very open condition, the temperature being raised more rapidly 

 than usual, the explosions occurred when the thermometer indicated 14;Y J and 

 143 0- 5 C. ; and in the experiments preceding these, which were differently conduct i-d, 

 compact gun-cotton being exposed to heat fora considerable time, the point of ignition 

 ranged between 136 and 138'5 C. Schrotter, Redtenbachor, and Schneider, in 

 their report upon Von Lenk's gun-cotton, mention that 136 C. is the lowest tempera- 

 ture fixed by Von Ebner, at which this material explodes. 



Action of light on gun-cotton. The following arc the results obtained up to tho 

 present time by exposure to light, under various circumstances, of gun-cotton pr 

 and purified, according to Von Lenk's directions. 



Exposure to strong daylight and to sunlight, cither in tho open air, or in confined 

 spaces for a few days (two or four), dovelopos in the gun-cotton a very faint 

 aromatic odour ; and if litmus-paper bo allowed to remain in close contact with tho 

 confined material, it acquires a rose-coloured tinge similar to that produced by carbonic 



