THE HISTOEY OF EXPLOSIVE AGENTS. 
505 
nitrogen through the porous plaster shell has been accomplished. These shells were 
then allowed to fall from heights of 4 feet and 20 feet u$on masses of compressed gun- 
cotton ; their explosion simply shattered the latter. 
Short tubes of stout sheet copper open at one end only, were charged with O' 75 grm. 
of the moist iodide, and they were then closed with thick plugs of plaster or of tightly 
compressed bibulous paper. When the moisture had been entirely abstracted from the 
enclosed iodide through the porous plugs, the shells were carefully transferred to the 
surfaces of pellets of compressed gun-cotton, placed under the lower opening of a vertical 
iron pipe 20 feet in height, and a weight was allowed to fall down the pipe upon them. 
The shells exploded violently and were broken up and dispersed ; but no detonation of the 
gun-cotton was effected. The same negative result was obtained with a similar shell 
charged with 1 grm. of the iodide. 
6-5 grms. (100 grains) of this substance were pressed firmly together while moist, and 
heaped upon the upper surface of a pellet of compressed gun-cotton 1-25 inch in dia- 
meter, which rested upon a flat copper plate 0 - 05 inch thick. This plate was placed 
upon a thick layer of pumice-stone fragments, saturated with concentrated sulphuric 
acid. This arrangement was situated in open air, and was enclosed under a box which 
could be readily and quietly withdrawn from a distance by means of a cord ; immediately 
over it was fixed a small vessel containing sand, which could be discharged so as to fall 
upon the iodide of nitrogen by the pull of a string. After the lapse of five days (during 
dry weather), when it was judged that the iodide of nitrogen had dried, the box was 
withdrawn and the sand allowed to fall ; a very sharp explosion was the result, but it 
was evident from the character of the sound that this was due to the explosion of the 
iodide only. The gun-cotton pellet was found to have retained sufficient moisture 
(absorbed from the iodide) to interfere with its explosibility ; the result of the experi- 
ment was therefore not decisive, but it afforded an excellent illustration of the force 
exerted by the explosion of that quantity of iodide of nitrogen. The stout copper plate 
upon which the pellet rested was bent into the shape of a watch-glass ; the gun-cotton 
pellet (which had been produced from the pulp by a pressure of about four tons on the 
square inch) was driven into the plate so as to indent the latter considerably, and a 
sharp impression of some small indentations existing upon the copper surface was found 
upon the lower surface of the pellet. 
The foregoing experiment was repeated with this difference, that the charge of iodide 
of nitrogen was placed in a flat-bottomed capsule of very thin platinum-foil, the lower 
surface of which was in close contact with the pellet of compressed gun-cotton. The 
latter was placed upon a flat copper plate (precisely similar to that used in the preceding 
experiment), which rested upon a thick layer of fused chloride-of-calcium fragments. 
After a lapse of five days the box which covered this arrangement was withdrawn and 
the iodide was exploded as before, without accomplishing the detonation of the gun- 
cotton. As in the former instance, the compressed pellet was driven into the copper 
plate and moulded to the cup-shaped indentation produced. The gun-cotton proved in 
mdccclxix. 3 Y 
