226 



ORIGIN OF THE NITRATES. 



compounds is of great importance. Before the author's experi- 

 ments it was entirely unknown. It is a remarkable circum- 

 stance that this combination takes place equally well with the 

 highest and even the lowest electric tensions, contrary to what 

 happens in the case of oxygen and hydrogen. The products, 

 moreover, vary according to the greatness of the electric tensions. 

 14. Hydrocyanic acid. In allowing the voltaic arc or the 

 electric spark to act directly upon gases, the author has observed 

 that acetylene and nitrogen combine directly at equal gaseous 

 volumes, forming hydrocyanic acid. The same reaction takes 

 place with every hydrocarbon gas or vapour capable of forming 

 acetylene under the influence of the spark. This formation of 



Fig. 36. Action of the silent discharge on mercury. 



hydrocyanic acid constitutes the best defined positive character 

 of nitrogen and is the easiest to show. 



If a series of strong sparks be passed into a mixture formed 

 by the two pure gases, the gases assume almost immediately 

 the characteristic odour of hydrocyanic acid. 



After a quarter of an hour, or even less, if the sparks are 

 long and strong the reaction is already well advanced. It is 

 then sufficient to agitate the gas with potash to change the acid 

 into alkaline cyanide and to manifest the reactions which are 

 characteristic of it (Prussian blue, etc.) 



Under the circumstances just described the formation of 

 hydrocyanic acid is accompanied by that of carbon and hydro- 

 gen, formed in virtue of a distinct but simultaneous decomposi- 



