148 Generation of Sulphur in 



hydrogen makes its appearance at all. The reaction is very 

 simple : 



FeS + 2HC1 = FeCl 2 + H 2 S 



and H 2 S + Fe 2 Cl 6 = 2FeCl 2 + 2HC1 + S 



.-. by addition FeS + Fe 2 Cl 6 = 3FeCl 2 + S 

 because the 2HC1 appears on both sides of the equation, and 

 is in fact unnecessary. A trace of free acid is no doubt necessary, 

 and it is turned over and over again in the reaction of indefinite 

 quantities of FeS on Fe 2 Cl 6 , after the manner of a catalytic action. 



The same reaction takes place if we use ferric sulphate 

 in place of ferric chloride. 



It is evident, therefore, that if we have a sample of mud 

 containing sulphide, and we mix it thoroughly with a solution 

 of Fe 2 Cl 6 or Fe 2 (SO 4 ) 3 , we shall have in the ferric salt reduced 

 a measure of the decomposable sulphide present. The ferrous 

 salt can be readily determined by permanganate of potash 

 or otherwise. It will be seen from the above equation that 

 one molecule FeS decomposes one molecule Fe 2 Cl 6 with the 

 formation of three molecules FeQ 2 , so that the FeS in the mud 

 is one-third of the ferrous salt found. 



In order to make some preliminary experiments, a mixture 

 of 100 grms. alum and 30 grms. ferrous sulphate were dissolved 

 in about - litre of water and precipitated with ammonia and 

 sulphide of ammonium. The precipitate was thoroughly 

 washed by repeated decantations, the flask being always 

 filled up to the neck, and corked and allowed to settle. When 

 it was completely washed the surplus water was poured off, 

 and the precipitate, suspended in about J litre of water, was 

 preserved in a well-stoppered reagent bottle. The precipitate 

 consists of alumina and sulphide of iron, and may therefore 

 be taken as an imitation of a simple form of mud. I made 

 some experiments to see with what amount of agreement 

 in the results one could titrate a number of different samples 

 of the same mud. 



Three flasks were placed side by side, and into each 

 50 c.c. suspended FeS mud were measured. The mixture of 

 FeS + A1 2 O 3 was thoroughly shaken up, then run into a narrow 

 graduated cylinder, holding 50 c.c., which was emptied into 



