GAY-LUSSAC 181 



binations ; that it is the radicle of hydrocyanic acid and 

 cyanic acid ; and that prussic acid is a compound of 

 carbon, hydrogen, and nitrogen. Cyanogen, it may be 

 mentioned, plays an important part in many organic 

 reactions and compounds. 



Gay-Lussac observed that the action of chlorine on 

 hydrocyanic acid replaced the hydrogen forming cyanogen 

 chloride, or acide chlorcyanique of his day ; and he found 

 that when beeswax was bleached by means of chlorine, 

 it lost hydrogen and took up an equal volume of chlorine. 

 At a royal ball at the Tuileries, in the reign of Charles X. 

 (brother of Louis XVI. ), the guests were "much annoyed 

 by the irritating vapours which came from the wax 

 candles to illuminate the apartments." This was due to 

 the fact that the manufacturer had used chlorine to 

 bleach the wax, and the irritating vapours contained 

 hydrochloric acid. 



In 1816 " Gay-Lussac made the remarkable observation 

 that when a crystal of common potash alum is hung up in 

 a saturated solution of ammonia alum it grows exactly as 

 if it had been placed in the solution from which it was 

 originally obtained. From this fact he drew the con- 

 clusion that the molecules of these two alums possess the 

 same form." This was the beginning of Mitscherlich's law 

 of isomorphism, which was discovered in 1810. 



Gay-Lussac, by igniting potassium carbonate in iodine 

 vapour, or chlorine gas, obtained an evolution of oxygen 



