132 



caastic ammonia or caustic potash, after heating to redness, had the 

 same composition. The black matter from solution of cyanogen m 

 alcohol may be obtained in large quantity, by saturating the same 

 portion of alcohol with cyanogen gas day after day as the odour of 

 the gas disappears ; a pint of alcohol being capable of absorbing the 

 whole of the cyanogen given off by four or five pounds of bicyanide 

 of mercury, becoming black and thick like treacle. The deposit 

 collected on the filter dissolves readily in solution of caustic potash, 

 and is precipitated by acids of a dark brown colour. In this state 

 it appears to have the composition represented by H+N.C.v When 

 heated to redness in close vessels, it gives off carbonate of ammo- 

 nia, and leaves paracyanogen, according to the formula 

 HN.C, + 2 HO = NC, + (H3N + CO, 0- 

 The paracyanogen dissolves in sulphuric acid giving a dark brown- 

 ish-red solution, from which water precipitates it unchanged. Boil- 

 ed in the acid, carbonic and sulphurous acids are given off, and a 

 partial oxydation of the paracyanogen takes place. Nitric acid, 

 either cold or hot, acts very slightly on the paracyanogen from bi- 

 cyanide of mercury, but dissolves readily in the cold, that prepared 

 by the other processes, giving a dark reddish-brown solution, from 

 which water precipitates the paracyanogen apparently unchanged. 

 Hot nitric acid, however, dissolves the black substance from cyano- 

 gen in alcohol, &c. with evolution of copious red fumes, givmg a 

 bright reddish-yellow, or a pale amber-yellow solution, from which 

 water precipitates a beautiful bright yellow powder. This yellow 

 snhst&nce h paracyanic cund. 



This acid is chiefly characterized by its great stability. It dis- 

 solves in nitric and sulphuric acids, and is very easily decomposed, 

 even when boiled in these menstrua. When heated in a close ves- 

 sel it gives off carbonic acid and nitrogen, and leaves paracyano- 

 gen Another very marked character is its affinity for the oxides 

 of mercury. A solution of the paracyanic in concentrated nitric or 

 sulphuric acid is precipitated largely and immediately by nitrates 

 and sulphates of mercury. The salt of mercury, too, is on y par- 

 tially decomposed by boiling in these acids. The salt of silver is 

 „,ore soluble, but may also be obtained by adding dry nitrate of 

 silver to a solution of the acid in concentrated nitric acid. These 

 salts constitute yellow powders more or less bright; they seem also 

 susceptible of crystallization. From the analysis of the acid and its 



