THE HISTORY OF EXPLOSIVE AGENTS. 
389 
A small piece of compressed gun-cotton, similarly inserted in a tube, and ignited, while 
at the ordinary temperature, by platinum wire which was heated by an electric current, 
burned slowly, almost with the appearance of smouldering ; but when another fragment 
was ignited in the same way, after having been raised for some time to 100° C., and 
while still heated to that temperature, it exploded with considerable violence and 
shattered the tube. The cause of this great difference in behaviour is evidently due in 
part to the circumstance that comparatively little heat had to be expended at the in- 
stant of ignition in raising the entire mass to the exploding point, and in part to the 
state of chemical tension, or predisposition to chemical change, into which the particles 
of the gun-cotton had passed by their continued submission to heat. Similar effects 
have been readily obtained by exposing gunpowder and other explosive agents to suffi- 
cient heat previous to their ignition. 
In the case of a substance like gunpowder or mercuric fulminate, the mechanical 
condition (granulated or crystallized form) of which favours the rapid penetration of heat 
or flame throughout a mass, an explosion, of violence proportionate to the quantity 
which is ignited, must inevitably result from the inflammation of any portion. The 
circumstance that masses of compressed gun-cotton simply burn rapidly from the exte- 
rior to the centre, if ignited, imparts to this material at first sight an appearance of 
comparative safety (or of non-liability to violent explosiveness under ordinary conditions 
of exposure to flame or to an igniting temperature), which experience has shown to be 
in great measure delusive, inasmuch as it is true only so far as regards comparatively 
small quantities (a few hundred pounds) of the material, and is even then, to a consi- 
derable extent, dependent upon the circumstances under which the material is exposed 
to heat. This has been conclusively demonstrated by some experiments upon a consi- 
derable scale which have been carried out by the Government Committees on Explosive 
Agents and on Gun-cotton, of which the following is a brief account. 
Single boxes of stout wood (0-75 inch in thickness) strongly made, filled with disks of 
compressed gun-cotton (28 lb. in each) and firmly closed with screws, have been 
surrounded by inflammable material, the burning of which exposed the case and its 
contents to considerable heat, eventually igniting it, and causing the box to burn 
fiercely. In every instance the gun-cotton in the box became inflamed after a few 
minutes and burned fiercely, .the entire quantity being consumed in two or three 
seconds ; but no explosion -was brought about in any instance, and the box in which the 
gun-cotton was confined was only partially forced open by the pressure developed from 
within. Eight boxes of the same kind, each containing 28 lb. of gun-cotton, were 
afterwards placed in the centre of a pile of similar boxes, filled with earth to the same 
weight, and the contents of the innermost box in the heap were ignited by an electric 
fuse. They burned fiercely, and the flame penetrated to the gun-cotton in one other 
box ; but in neither instance was an explosion produced, and the pile of boxes was 
scarcely disturbed; the remaining six which contained gun-cotton were charred but not 
otherwise injured. Another more severe experiment, in which one of the inner boxes 
