EXPLOSIVES. There is a question as to the influence, direct or indirect, Upon modern civilization of the introduction of explosive agents for the purpose of war. Some eminent authors have gone so far as to consider the invention of gunpowder as next in importance, in its ultimate effects, to those of printing and the application of steam power. However this may be, it is well to remember that explosive substances are now of immense utility in the arts of peace; indeed, it is not too much to say that without their aid many of the great engineering enterprises of the present day would either be impossible, or else have to be carried out at a vast additional expenditure of time and labor. The germ of all the knowledge which we possess of explosive reaction undoubtedly lay in the probably accidental discovery, many ages ago, of the deflagrat iug properties of the natural substance niter or saltpeter when in contact with incandescent charcoal. By distilling niter with oil of vitriol, the alchemists obtained a corrosive fluid which they called aquafortis, now known as nitric acid which parts with its oxygen even more rapidly than saltpeter; so that if the strongest nitric acid be poured upon finely powdered charcoal, the latter takes fire at the ordinary tem perature. Somewhat less than half a century hack, it was discovered by some French chemists that upon treating various organic substances, such as starch, the sugars, cot ton fabrics, and even paper, with concentrated nitric acid under proper precautions, the chemical constitution of the substances underwent a great change, and they became endowed with violently explosive properties, while remaining for the most part unal tered in external characteristics. To this discovery we owe a distinct class of explo sive compounds, the most powerful for practical purposes as yet known.
Examining into those principles of constitution and action which are more or less common to all explosive substances, we may define, for our purpose, the term " explo sive " as the sudden or extremely rapid conversion of a solid or liquid body of small bulk into gas or vapor, occupying very many times the volume of the original substance, and, in addition, highly expanded by the heat generated during the transformation.
This sudden or very rapid expansion of volume is attended by an exhibition of force, more or less violent according to the constitution of the original substance and the circum stances of explosion. Any substance capable of undergoing such a change upon the application of heat, or other disturbing cause, is called " explosive." The most explo sive substances that are practically the most important essentially contain carbon, oxygen, and nitrogen, the last always existing in a state of feeble combination with the whole or part of the oxygen, and thtis creating that condition of unstable chemical equilibrium which is necessary. When explosion takes place, the nitrogen parts with its oxygen to the carbon, for which it has a greater affinity, forming carbonic acid and carbonic oxide (CO) gases, the combination being accompanied with great genera tion of heat, and the nitrogen is set free. In most explosives there is also hydrogen accompanying the carbon, and by its combustion producing an extremely high tempera ture: it combines with part of the oxygen to form water in the form of greatly expanded vapor. Other subordinate elements are often present; in gunpowder, for instance, the potassium binds the nitrogen and oxygen loosely together in the state of saltpeter, and there is sulphur, a second combustible, whose oxidation evolves greater heat than that of carbon. When chlorate of potash is present, the chlorine plays the part of nitrogen, and is set free in the gaseous state. Two very unstable and practically useless explo sive substances, the so-called chloride and iodide of nitrogen, contain neither carbon nor oxygen; but their great violence is equally caused by the feeble affinities of nitrogen for other elements, large volumes of gaseous matter being suddenly disengaged from a very small quantity of a liquid and solid body respectively.