There is something about fire which fascinates every one, yet the action of explosives arouses even a livelier interest, since the accompanying fiery phenomena are more intense and are attended with a shocking report and a violent destruction of the surrounding material, while this train of events, with all its marked effects, is set in operation by what appears to be a very slight initial cause. It is evident on brief consideration that these bodies, like a coiled spring, a bent bow, or a head of water, are enormous reservoirs of energy which can be released at a touch, and which, if the explosive be properly placed in well-proportioned amounts and discharged at the right time, can be made to do useful and important work that can not be as conveniently and quickly accomplished in most cases, and in some cases can not be accomplished at all by any other means. [Illustration: GUN-COTTON FACTORY. Digestion troughs.] The marked characteristic of all explosive substances, and especially of the so-called high explosives, is that the energy, as developed, is at high potential, and the uses to which energy in this condition can be economically put are so manifold that the production of explosives has become one of the most important of our chemical industries, this country alone producing, in 1890, 108,735,980 pounds, having a value of nearly $11,000,000. The number of possible substances possessing explosive properties is exceedingly large; the number actually known is so great that it has taxed the ingenuity of inventors to provide them with suitable names; but these various explosive substances vary to so great an extent in the energy they will develop in practice and in their safety in storage, transportation, and use that but a comparatively small number have met with wide acceptance. All may be classified under the heads of physical mixtures like gunpowder, or chemical compounds like nitroglycerin, and they owe their development of energy to the fact that, like gunpowder, they are mixtures in which combustible substances such as charcoal are mixed with supporters of combustion such as niter; or that, like chloride of nitrogen, they are chemical compounds, the formation of whose molecules is attended with the absorption of heat; or that, like gun cotton, they are chemical compounds whose molecules contain both the combustible and the supporter of combustion, and whose formation from their elements is attended with the absorption of heat; while occupying a middle place between the gunpowder and the gun cotton class, and possessing also to some degree the properties of the nitrogen-chloride class, are the nitro-substitution explosives, of which melinite, emmensite, lyddite, and joveite furnish conspicuous examples. [Illustration: GUN-COTTON FACTORY. Final press.]