Letts and Rea — The Chemistry of Foul Mud Deposits. 177 



(2). An apparatus was constructed so that hydrogen sulphide could be 

 passed into a vessel containing calcium carbonate and water, and when all the 

 air had been displaced, the vessel could be corked, the hydrogen sulphide 

 still continuing to enter the apparatus. After the experiment had continued 

 for some 24 hours, 10 c.c. of the solution were removed and the calcium 

 determined, when it was found that this contained calcium corresponding 

 with - 0109 grm. of the carbonate or 50 c.c. with 0"109 grm. of that 

 compound. Therefore the action of hydrogen sulphide on the carbonate is 

 slightly less when the carbon dioxide does not escape, as might be 

 expected. 



Action of Hydrogen Sulphide on Ferrous Bicarbonate. 



- 6676 grm. of crystallized ferrous sulphate was dissolved in 100 c.c. of 

 distilled water, and to this was added an equivalent amount (0-5087 grm.) 

 of crystallized sodium carbonate. 



Carbon dioxide was then passed through the mixture until the preci- 

 pitated ferrous carbonate had dissolved with formation of the bicarbonate 

 (a slight brownish precipitate was, however, left, probably ferric hydrate). 



A stream of hydrogen sulphide was then passed through the solution 

 for 20 minutes, a black precipitate forming immediately of ferrous sulphide. 



The current of hydrogen sulphide was stopped, the solution boiled, and a 

 stream of hydrogen passed through the mixture. 



The boiling was continued for five hours, but even then some hydrogen 

 sulphide continued to escape. 



The current of hydrogen was then interrupted, some hydrochloric acid 

 slowly added to the contents of the flask, the current of hydrogen again 

 started, and the escaping gases passed into standard arsenious anhydride 

 solution. The latter was then filtered from the precipitated arsenic sulphide, 

 excess of sodium bicarbonate added, the solution filtered and titrated with 

 N/10 iodine solution, when the following result was obtained: — 



Hydrogen sulphide actually produced. ... O'OIG grm. 



„ „ calculated, ... ... ... 0'014 „ 



The reaction proceeds quantitatively then, in the sense of the 

 equation : — 



Fe (HC0 3 ) 2 + H 2 S = FeS + 2H 2 + CO*. 



Examination of Foul Sewage Deposits. 



(1). Marine Mud. 



The first sample to be examined was obtained from Belfast Lough and 

 had probably been formed from rotting Ulva. 



