xii THE HALOGENS 245 



"This acid, compared with the animal substances, is 

 distinguished by the great quantity of azote which it contains, 

 by less hydrogen, and above all by the absence of oxygen. 

 Its acidifying properties cannot depend on hydrogen, which 

 has an alkaline influence, but on carbon and nitrogen. It 

 must be considered as a true hydracid, in which carbon and 

 nitrogen replace the chlorine in hydrochloric acid, the 

 iodine in hydriodic acid and the sulphur in hydrosulphuric 

 acid" 1 (Ami. de Chimie^ 1815, 95, 155). 



Gay-Lussac regards prussic acid as a derivative of 

 the " compound radical " cyanogen. Gay-Lussac found 

 that prussic acid, when acted on by potassium, liberated 

 half its volume of hydrogen and gave a salt, just as 

 hydrochloric and hydriodic acids did in similar circum- 

 stances. He therefore suggested that it contained a 

 COMPOUND RADICAL, CYANOGEN, which acted the part of the 

 simple radicals, chlorine and iodine : 



"There is, then, a very great analogy between prussic 

 acid and hydrochloric and hydriodic acids : like them, it 

 contains half its volume of hydrogen, and like them it has 

 a radical which combines with potassium, and forms a com- 

 pound quite analogous with the chloride and iodide of 

 potassium : only this radical is compound, where chlorine 

 and iodine are simple." 



" It seemed to me to be necessary to create a new name 

 to designate the radical of prussic acid. That of cyanogen 2 

 having seemed most suitable to the chemists of this capital, 

 I have adopted it and shall use it in this memoir. Ordinary 

 prussic acid will then receive the name of hydrocyanic acid 

 and the prussiates that of hydrocyanates. The compounds 

 of cyanogen with simple substances, when it plays the same 

 role as chlorine in the chlorides, will be designated by the 

 name of cyanides " (Ann. de Chimie, 1815, 95, 161, and 

 162-163). 



Gay-Lussac's view of the nature of the cyanogen-compounds 

 was vindicated by the discovery of CYANOGEN GAS, which he 



1 i.e., sulphuretted hydrogen. 2 Greek KVOVOS, blue. 



