Though many improvements were made in the manufacture of gunpowder, such as in the preparation and purification of the raw materials from which it was produced; the methods of in corporation ; and its granulation to adapt it to special uses, this substance remained unrivaled until the end of the 18th century, when the French chemist Berthollet proposed the substi tution of potassium chlorate for the potassium nitrate and produced by this means a much stronger and quicker powder, but one which was also much more dangerous than gunpowder. Beginning with the discovery of mercuric ful minate by Howard, an English chemist, 1800, there was added to the achievements of the 19th century the discovery of nitrogen chloride by the French chemist Dulong, 1812; nitrostarch by Braconnot, 1832; guncotton by Schoenbein of Basel, Switzerland, 1845; nitroglycerin by Sobrero at Turin, Italy, 1846; the invention of blasting powder by L. DuPont of Wilmington, Del., 1856; the discovery of diazo compounds by the German chemist, Griess, 1860; the in vention of dynamite by A. Nobel of Sweden, 1866; smokeless sporting powder by Schultze of Potsdam, Germany, 1867; blasting gelatine Nobel, 1878; military smokeless powder by Vieille of France, 1886; hard-grained smokeless sporting powder by Richard von Freeden of Walsrode, Germany, 1889; homogeneous smoke less powder composed of a single chemical sub stance in a state of chemical purity by Charles E. Munroe of Newport, R. I., 1890; and the discovery of triazoic acid by Curtius of Kiel, Germany, 1890, while in the meantime picric acid, which was discovered by Woulf e 1771, was shown to possess explosive properties and adapted for use in shell, it having been pointed out by Sprengel, 1873, that it contains a suffi cient amount of available oxygen to render it, without the help of foreign oxidizers, a power ful explosive when fired with a detonator.
This growth has been coincident with the development of the chemical and physical sci ences and has been the more rapid, the more completely experimental methods of research have been perfected and applied. In addition to those enumerated above this advance in the sci ence and art of explosives has been chiefly due to the labors and intelligence of Hess, Lauer, Trauzl and von Lenk in Austria; Abel, Cundill, Debus, Dewar, Dixon, Dupre, Majendie and Noble in England; Berthelot, Chalon, Daniel, Desortiaux, Gay-Lussac, Lavoisier, Le Chatelier, Mallard, Maurouard, Roux, Sarrau, Turpin and Violette in France; Bunsen, Dittmar, Gutt mann, Liebig, Meyer, Schischkoff, Upmann, Will, von Forster and von Romocki in Ger many ; Abbot, Barnard, Craig, Emmens, Judson, Hill, Maxim, Mixter, Mowbray, Guinan, Rodman, Count Rumford and Woodbridge in the United States; Mendelieff in Russia; Cron quist in Sweden and Hebler and Lunge in Switzerland. See the biographical sketches of Abel and Berthelot who were especially prom inent in this science.
Theory of Explosives.— When wood or other combustible substances containing hydro gen and carbon are ignited in contact with air they burn, giving forth heat and light and are converted into water and carbon dioxide, which pass off as invisible and highly expanded gases.
As the wood is subdivided so as to expose a continually increased surface to the air the rapidity of the combustion is increased until, when the wood is reduced' to dust like saw dust and suspended in the air so as to be inti mately mixed with it, the velocity of the com bustion is so great and the evolution of the gases so rapid that the reaction becomes an explosive one and such a mixture of sawdust and air is an explosive. All inexplosive com bustible substances can, when finely divided and intimately mixed with air, form explosives and volatile liquids and gases are especially likely to do so. Many accidents have arisen from the ignition of mixtures of air with the dust of char coal, coal, flour, malt, soap, starch, sugar, zinc, wood and other solids; with the vapors of alco hol, ether, gasoline and other naphthas, spirits of turpentine and other liquids, or gases like ethy lene, coal gas, hydrogen and marsh gas since each of these substances, though in themselves non-explosive, form explosive mixtures with air if they be mixed with it in the right pro portions. The best proportions are those in which the volume of oxygen in the air present is just sufficient to convert all of the hydrogen in the combustible into water and all of the carbon into carbon dioxide, or, in other words, to produce complete combustion. Less violent explosions may occur when the proportion of air is greater or less than the proportion ,D the limit being fixed in each case by the char acter of the combustible substance, the quantity of the mixture, the temperature and pressure to which it is subjected and the manner in which it is ignited. Mixtures of these substances whose proportions are outside of these limits may be ignited and may burn, but do not ex plode.
If pure oxygen in the proper proportions be substituted for air in the above mixture the velocity of the reactions will be still greater, and the energy set free in unit of time and con sequently the violence of the explosion will be greatly increased. Besides the proportions that determine the limits between explosion and combustion will be extended. Such mixtures if confined and out of contact with the air will still take fire and explode. Oxygen may be supplied either in the free state or in solid bodies which contain it and which give it up when heated to comparatively low temperatures. Among such solids are the nitrates of metallic radicles, like ammonium nitrate, potassium nitrate (India saltpetre), and sodium nitrate (Chile saltpetre) ; chlorates such as potassium chlorate; peroxides like sodium peroxide, and many others. If these solids be dried, finely divided, and inti mately mixed with a combustible, in the right proportions, a solid explosive is produced. Often, as in the case of mixtures of charcoal and saltpetre the temperature to which they must be heated in order that combustion shall begin, called the point of ignition, is so high that they are difficult to ignite and in such cases a small portion of a substance like sulphur, which has a low point of ignition, is incor porated in the mixture.