Page:The American Cyclopædia (1879) Volume VII.djvu/47

 EXPLOSIVES 39 be useless if once frozen. It leaves no solid residue. Fulminates. The compounds of cy- anogen comprise many highly explosive sub- stances, among which the fulminates, or salts of fulminic acid, are the most important. Fulrninic acid (Lat. fulmen, a thunderbolt) is, according to the most modern formula (Kekule's), a nitro- compound of the group C 4 ETsN (acetonitril), and hence called nitro-acetonitril. One of the hydrogen atoms is replaced with an atom of NO 4, giving for the acid C 4 (NO 4 )H 2 N. In the salts the hydrogen is replaced with a metal ; thus the fulminate of silver is C 4 (NO 4 )Ag 2 N. This hypothesis explains the fact that the ful- minates react very differently from the cya- nates (mono-,di-, and tribasic), all of which have the same proportions of 0, ' N", and metallic base, but doubtless different atomic arrange- ments. Mercury fulminate (empirical formula, C 4 N 2 4 Hg 2 ) is prepared by dissolving at a moderate heat, in 12 parts of nitric acid of the specific gravity of 1'35, 1 part of mercury, and adding 11 parts of 90 to 92 per cent, alcohol. Liebig recommends a glass flask, the capacity of which is 18 times the volume of the mixture. In this the mercury is dissolved in cold acid, the nitrous fumes being retained in the flask. The solution is poured into a second vessel, containing one half the alcohol ; and the mix- ture is then returned into the first flask, where it reabsorbs the nitrous fumes. In a few mo- ments bubbles rise from the bottom, where a heavy liquid begins to be segregated. By gentle shaking this is mixed with the supernatant liquid, and a tempestuous ebullition takes place, with evolution of white fumes, and some ni- trous acid, the mass becoming black from segre- gated metal. The remainder of the alcohol is gradually added; the black color disappears, and the fulminate is deposited in sparkling brownish gray crystals. The vapors are chiefly carbonic acid and nitrous ether. Mercury ful- minate is scarcely soluble in cold water, but dissolves in 180 parts of boiling water, which gives a means of refining it by recrystallization. It explodes at 186 C., or under friction or percussion between hard substances. When moistened with 5 per cent, of water, only the portion actually struck explodes. In contact with a tightly packed explosive mixture, its detonation explodes the mixture more rapidly and completely than any other method of firing. Hence its universal employment in the manufacture of percussion caps and detonating fusees. According to the French method, one kilo of mercury gives 1 kilo of fulminate, sufficient for 40,000 caps. It is ground with 30 per cent, of water under a wooden muller on a marble bed, and 6 parts gunpowder are added for every 10 of fulminate. The mixture dried, granulated, and sized. A drop of gum is introduced into each cap, and the fulminate powder is dropped upon it. Some caps are varnished, to make them water-proof. English fulminating powder consists of 3 parts mercury fulminate, 5 parts chlorate of potassa, 1 part sulphur, and 1 part powdered glass. Gum is sometimes added in the mixture. Nitre is also recommended. Samuel Guthrie of Sackett's Harbor, N. Y., whose extensive and perilous experiments are described in the " American Journal of Science " for January, 1832, found that 1 part oxide of tin with 3 parts mercury fulminate, ground together with a stiff solution of starch, made a very effective compound. During these experiments Mr. Guthrie dis- covered chloroform, as did French and German investigators at about the same time. Silver fulminate is more explosive and dangerous than the mercury salt. It may be made like the latter, using fine silver instead of mercury ; or by introducing finely pulverized nitrate of silver into concentrated alcohol, shaking it well, and adding an equal amount of fuming nitric acid ; or by treating freshly precipitated oxide of silver with ammonia. It is employed in the manufacture of explosive toys. Gold and platinum fulminates are similar compounds to the foregoing, but they are not employed in the arts. Fulminating aniline, or chromate of diazobenzole, obtained by the action of ni- trous acid upon aniline, and the precipitation of the product by the aid of a hydrochloric acid solution of bichromate of potassa, is, according to Caro and Griess, an efficient sub- stitute for fulminating mercury. General The- ory of Explosives. Explosive substances are said to u possess potential energy by virtue of certain unsatisfied affinities between the ele- ments of which they are compounded." In the act of explosion these affinities are satis- fied, and the potential energy becomes kinetic, taking first the form of heat, which is par- tially expended in giving elastic force to the new gaseous compounds generated. Perhaps this statement does not exactly cover cases like the chloride of nitrogen, which explodes by dissociation, leaving free chlorine and ni- trogen. The elastic force at any instant of an explosion and the total energy developed are two different things. The intensity of the force depends upon: 1, the amount of actual heat developed; 2, the volume which a unit of the mass of the products occupies at the instant ; 3, the specific heat of these products ; or, in other words, upon : 1, the volume of the products; 2, their temperature. The total energy is dependent upon: 1, the ratio be- tween final volume of products and original volume of explosive ; 2, the total actual heat of the explosion. The maximum intensity de- pends chiefly upon the rapidity with which the conversion of the explosive into gas takes place, and this depends on varying conditions, no ex- plosion being absolutely instantaneous. The primary condition is the rapidity with which the chemical reaction among the constituents takes place. Some, as nitrate and chlorate of potassa, require heat for their decomposi- tion; others are probably dissociated by the' vibrations produced by percussion or the ex- ploding spark, as nitro-glycerine and chloride