996 CYANOGEN COMPOUNDS. 



the escape of nitrous ether vapour, and precipitation of metallic 

 mercury; and soon fulminate of mercury is deposited in white 

 opaque granular crystals, which may be washed when cool, 

 and dried at the ordinary temperature. This salt crystallizes 

 from boiling water in fine, silky needles, and may thus be de- 

 prived of the free mercury with which it is accompanied. Ful- 

 minate of mercury detonates violently by percussion, or when 

 rubbed between hard bodies ; in the flame of a candle it defla- 

 grates with a feeble explosion. Mixed intimately with 6 times 

 its weight of saltpetre, it forms percussion powder, which is 

 introduced in the state of a paste with water, into the copper 

 capsules used with fire-arms. Fulminate of silver is prepared 

 like the salt of mercury, but with about twice as much alcohol. 

 It detonates even more violently by percussion than the salt of 

 mercury, and also by heat. This fulminate is deprived of only 

 half its base by an alkali, and a salt formed containing 1 atom 

 of alkali and 1 atom of oxide of silver as bases. Nitric acid 

 throws down an acid fulminate of silver, containing an atom of 

 water as the second base ; it is crystallizable and more soluble 

 than the neutral salt. The action of hydrochloric acid upon 

 fulminate of silver is attended with the formation of an acid 

 containing chlorine, chlorocyanhydric acid, of which the proba- 

 ble composition is H 2 -f C 2 NC1 5 (Gay-Lussac and Liebig). 



CYANURIC ACID. 



Formula of the acid crystallized from water : 3HO,Cy 3 O 3 -f 

 4HO. 



Cyanuric acid was discovered by Scheele and examined by 

 Serullas, but its true constitution was first ascertained by Liebig 

 and Woehler. It is formed in a variety of circumstances ; in 

 the decomposition of urea by heat, the distillation of uric acid, in 

 the decomposition of the solid chloride of cyanogen by heat, &c. 

 M. Liebig recommends its preparation from Melam (p. 1000). 

 A portion of melam is gently warmed in a little strong sulphuric 

 acid until dissolved ; the acid liquid is poured into about 30 

 parts of water, and boiled in a flask, with the occasional addition 

 of water for four or five days, till the liquid no longer gives a 

 precipitate of ammelide with ammonia. By evaporation the 

 fluid gives brown crystals of cyanuric acid, which may be made 



