Mi\ E. A. Parnell on Sulphocyanogen. 257 



precipitate in solution of sulphate of copper. The precipitate is 

 decomposed by the hydrochloric, nitric and concentrated sul- 

 phuric acids ; also by sulphuretted hydrogen, 'the hydrothio- 

 cyanic acid being liberated. It is blackened by alkalies, an al- 

 kaline thiocyanide being produced : the black or brown sub- 

 stance remaining appears to be a subsalt. When the thio- 

 cyanide of copper is ignited in a tube, it gives off sulphur, 

 hydrated cyanic acid, and bisulphuret of carbon, leaving 

 a residue of sulphuret of copper. 



Lead. Solutions of hydrothiocyanic acid produce a yellow 

 precipitate in acetate and subacetate of lead, which is decom- 

 posed by the stronger acids, and by sulphuretted hydrogen, 

 the acid being reproduced unaltered in the last case. Nitric 

 acid instantly produces sulphate of lead. On being heated in 

 a tube, it gave rise to similar products as the copper salt ; 

 hydrated cyanic acid, sulphur, bisulphuret of carbon, and 

 sulphuret of lead. Like most insoluble salts of slightly solu- 

 ble acids (when prepared from solutions of the acid), this is 

 contaminated with a large excess of acid. Two combustions 

 by oxide of copper gave 



1. 8 '62 per cent, of carbon *49 of hydrogen. 



2. 8-72 -50 



For the lead : 1. 12 '3 grains treated with nitric acid gave 

 9*36 grains of sulphate of lead, equal to 51*96 per cent, of 

 lead. 



2. 10*77 treated in the same manner, gave 8*19 of sulphate, 

 or 51-93 percent. 



Calculated according to the formula They 4 Pb + 4 aq, it 

 should contain 7*90 of carbon, '5 1 of hydrogen, and 53*40 of 

 lead per cent. ; notwithstanding this difference, no other 

 formula could have been selected, in accordance with the ulti- 

 mate composition obtained for the acid. 



Like the copper salt, thiocyanide of lead is blackened by 

 alkalies, a subsalt being produced. 



Silver. The behaviour of the solution of hydrothiocyanic 

 acid with nitrate of silver is very peculiar and characteristic, 

 forming a test sufficiently delicate to detect one part of the 

 acid in 10*000 of water. On mixing the solutions a yellow 

 flocculent precipitate is formed, which on standing a short 

 time, or immediately on heating, aggregates, changing to a 

 black colour, without any evolution of gas or odour of cy- 

 anogen. The change is not hastened; by solar light. When 

 the black substance is treated with sulphuretted hydrogen, the 

 acid is reproduced, and sulphuret of silver formed. Concen- 

 trated sulphuric acid has no effect on it; if diluted, sulphate 

 of silver is formed, and the acid is liberated. It is soluble 



Phil. Mag. S. 3. Vol. 17. No. 110. Oct. 1840. S 



