Page:Popular Science Monthly Volume 21.djvu/798

780 mixture is called dynamite, or giant-powder; it is made by mixing nitro-glycerine with a siliceous earth, in the proportion of three to one by weight. This earth is a fine white powder, composed of the skeletons of microscopic animals; it is found in Hanover and also in New Hampshire—that coming from the latter locality being the finer, and therefore most used in this country. The dynamite formed by this mixture is not unlike moist brown sugar in appearance; care must be taken not to put too much nitro-glycerine in it, as there must not be such a quantity as would cause exudation. Its properties as an explosive, are, of course, those of the nitro-glycerine alone; but it can be much more readily handled, and there is less danger from either percussion or friction. It has been dropped from a height upon rocks, heavy weights have been allowed to fall upon it, and other experiments of a like nature have been made to show how readily it can bear transportation and hard knocks. This safety, however, presupposes a pure nitro-glycerine; and whenever an accident occurs it may safely be laid to the impurity of the explosive, and not to anything necessarily consequent upon the use of dynamite. Under the action of cold, dynamite freezes at 40° Fahr. in a hard, compact mass, in which condition it is very difficult to explode. Sometimes, however, it freezes in a loose and powdery state, and there is then no difficulty in causing its explosion with the ordinary fulminate-fuse. Generally speaking, however, it is best with this, as with nitro-glycerine, to thaw it out before attempting to use it. Instances have been known of careless men attempting to do this with a red-hot poker, with consequences, naturally, of a disastrous character. It will admit of being slightly moistened without injury, and hence can be used when gunpowder could not be. As a military explosive for mines and torpedoes, as also for the breaking up and destruction of guns, it has proved itself useful; and it has been used as a bursting-charge for shells, though this is considered dangerous.

Besides dynamite, there are several other mixtures of nitro-glycerine, in which the inactive siliceous earth is replaced by some active substance, such as charcoal, saw-dust, wood-fiber treated with acid, chlorate of potash, or even gunpowder. It is extremely doubtful whether anything is added to the explosive effect of the nitro-glycerine by their presence, as its own explosion is so rapid as to gain nothing from the slower combustion of these substances. Experiments with the pressure-gauge tend to show the correctness of this theory. Of all these combinations, that called cellulose dynamite is the best; it is a combination of the wood-pulp, so much used for the manufacture of paper, treated with nitric acid and nitro-glycerine; it possesses the excellent quality of being able to absorb a considerable quantity of water without injury; for this reason it may prove itself a commercial rival to dynamite pure and simple.

Large quantities of dynamite are manufactured in this country for