534 THE ACTION OF SULPHIDE OF POTASSIUM UPON CHLOROFORM. 
An attempt was then made to obtain the free acid. A quantity of the lead 
salt was suspended in water, and sulphuretted hydrogen passed in in excess on 
filtering off the sulphide of lead and allowing the clear solution to remain 
exposed to the air till no sulphuretted hydrogen remained in solution. The 
liquid was found to be strongly acid, and contained scarcely a trace of HCOSH. 
While at the same time a large quantity of formic acid was present, recognised 
by odour and its reducing action on mercuric chloride and nitrate of silver. 
This method having failed to give the free acid, the barium salt was prepared 
by treating a mixture of barium carbonate and the lead salt suspended in water 
with excess of sulphuretted hydrogen ; the solution was evaporated in presence 
of excess of barium carbonate, filtered, and alcohol added. White pearly scales 
separated, which were dried and found to contain 
53'1 per cent. Ba. Theory, 52°9 per cent. Ba. 
From this it appears probable that when the thioformiate of lead is decomposed 
by H.,S, the thioformic acid decomposes with the formation of formic acid ; but 
if the thioformic acid is set free in the presence of a base, then decomposition 
does not take place. 
There remains only for me to give the probable formule for this reaction, 
which lead to the production of thioformiate of potassium when sulphide of 
potassium and chloroform act on one another. After the reaction was over, 
and chloroform was in excess, it was noticed that the solution was strongly 
alkaline, and contained sulphide or sulphydrate of potassium. In order to 
determine which of these two salts was present, a little iodide of ethyl was 
mixed with the liquid and mercaptan was formed; it was also found that 
alcoholic sulphydrate of potassium would not act on chloroform, while even a 
very dilute solution of sulphide of potassium acted at once. Any explanation, 
then, of the reaction must account for the residual sulphydrate. The following 
give the probable explanation :— 
HCCl, + 2K,S = 3KCl + HCSSK, this HCSSK comes in contact with 
water, HCSSK + H,O=HCOSK + HS, and H,S+K,S=2KHS. 
