268 Mr. Mallet on the Physical Conditions 



Chloride of nitrogen. 



Iodide of nitrogen. 



Fulminate of silver. 



Fulminate of mercury. 



Fulminates of several other metallic bases. 



Pyroxyle, or gun-cotton. 



241. Gunpowder itself also differs much in the rapidity of its explosion 

 according to the density and mode of the charcoal having been burned, its 

 state of aggregation, the fineness oflevigation and intimate admixture of all its 

 constituents, and their relative proportion, the size, form, and density of the 

 grains, and highness of " glaze" of the powder, and its perfect dryness. When 

 all, or the chief of these numerous conditions, are united favourably in certain 

 gunpowders, their rapidity of explosion is so great, and their injury to fire-arms 

 so remarkable, that they are known in France as " poudres brisantes." This 

 property is still further exalted if the powder be slowly heated up to nearly the 

 highest point it will bear without decomposition, prior to ignition (as when 

 charged into a heated gun, in the way previously alluded to) (sec. 89). It is 

 stated that a temperature of IGO'Fahr. increases the effect of the explosion ^, 

 and that one of 400" nearly doubles it (Straith on Artillery, p. 554). This effect 

 is not so much due to increased tension of the gases evolved by elevation of 

 temperature, as to the state of unstable equilibrium into which the elements of 

 the compound are brought by its gradual increase, towards the verge of that at 

 which total subversion occurs, producing far greater rapidity in the explosion 

 when it does occur. 



242. A very simple and beautiful, though not very common experiment, 

 well illustrates this. If a common Congreve or Lucifer match (those made of 

 sulphuret of antimony and chlorate of potash answer best), be slowly and 

 cautiously heated up for a minute or two, nearly to its igniting point, by being 

 held close to a fire, or to a heated iron bar, and then ignited, it no longer catches 

 fire and blazes, burning gradually out, as when lighted in its ordinary con- 

 dition, bwt explodes suddenly, with a sharp loud report, and this, whether 

 ignition be in this state produced by friction only, or by contact of an ignited 

 body. 



The effect of the gradual exaltation of temperature, in either case, is to 



