78. Mr Johnston on a solid form of Cyanogen. 



and that the black deposit is simply carbon. From what 

 follows, I think it more probable that the deposit in both cases 

 is the hi-carburet of azote I have above described. 



When cyanogen is passed into alcohol over mercury, it is 

 absorbed with great rapidity. According to Gay-Lussac, 

 alcohol in this way absorbs twenty-three times its volume of 

 the gas. If a solution thus saturated be left in contact with 

 cyanogen over mercury for twenty-four hours or upwards, a 

 further absorption takes place, amounting in all to thirty or 

 forty volumes — the solution like that of potash becoming brown, 

 then brownish red, and gradually deepening in colour as it 

 stands. Of cyanogen which had stood over mercury for 

 twelve hours, I found the alcohol of the shops on one occasion 

 to dissolve forty volumes in a few minutes, becoming at the 

 same time of a dark reddish brown colour ; in general, however, 

 it requires a much longer period. If now drawn off and set 

 aside in a close vessel for several days, this solution deposits 

 a sediment black by reflected and reddish-brown by transmit- 

 ted light. The alcohol passes through the filter colourless, 

 but on being set aside a second deposition of the black sedi- 

 ment frequently takes place, which, after a few days, may be 

 separated in the same manner. 



When the matter collected on the filter is washed with dis- 

 tilled water, the washings pass through of a yellow colour, 

 showing that in this state it is partially soluble in water. Dried 

 in a glass capsule at first by a gentle heat, and afterwards by 

 the flame of a spirit lamp, one portion heated with chlorate of 

 potash gave 



Carbonic acid = 2.9^ inches 

 Azote = 1.502 



where the carbonic acid is to the azote nearly as 2 to 1. 



A second portion, without any previous washing with water, 

 was carefully dried at a heat not exceeding 212°, In mass it 

 was of a shining black, in powder of a deep chocolate colour. 

 Of this 7 grains were heated with 5 grains chlorate of potash. 

 The gas given off* amounted to 4.7 inches, and the loss of 

 weight to 2.6 grains. The gas consisted of 



