The Romance of Modern Chemistry

EXPLOSIONS AND EXPLOSIVES be employed. During the time the cotton is in contact with the nitric acid the temperature must be kept down, and subsequently every trace of acid must be washed away with water. It was owing to want of attention to this last simple precaution that many of the explosions which attended the early manufacture of gun-cotton were due. Any trace of acid left in the finished article acts like an irritant, and leads sooner or later to the decom- position of the explosive. Gun-cotton is a most curious substance. It takes fire much more easily than gunpowder, and the rate at which it burns altogether depends on the way in which it has been ignited, and the conditions to which it is subject. A piece of loose gun-cotton may actually be burned on the hand without scorching the skin, merely by touching it with a hot glass rod; it can be fired on the top of a heap of gunpowder without igniting the latter. Under such conditions the combustion of the gun-cotton is rapid, but not explosive. When, however, it is fired in a confined space, and the flame from the portion first ignited is driven into the remaining mass, the tem- perature is forced up and the combustion becomes an explosion. It was therefore very naturally thought for a long time that in order to utilise the explosive force of gun- cotton it must be enclosed in some strong casing. Some forty years ago, however, the very interesting discovery was made that this was unnecessary, and that gun- cotton which was merely compressed, not confined in an enclosed space, could be exploded by a detonator, such as mercury fulminate. It is indeed a curious fact that if a little of this latter substance is exploded in the im- mediate neighbourhood of a mass of unconfined, compressed 175