34 Proceedings of Royal Society of Edinburgh. [sess. 
3. Sulphuretted hydrogen is not oxidised simply by atmospheric 
air to sulphuric acid at ordinary temperatures. 
4. Sulphur-bacteria secrete sulphur which they separate from 
sulphuretted hydrogen, a compound which is essential to their life. 
This sulphur is then oxidised by the bacteria to sulphuric acid, 
which acts upon the carbonates and again forms sulphates. 
5. The formation of manganese carbonate appears to be due to 
an action on manganic oxide similar to that which operates on 
sulphates in presence of cellulose undergoing fermentation. 
Note . — The process of sulphur fermentation was first noticed by 
me in 1870. It occurred in stagnant water which filtered through 
a bed of new red sandstone after it had passed through mud highly 
charged with vegetable c!4bris. In 1872, when studying the life- 
history and chemical changes caused by the bacteria , called at that 
time vibrios , I found that beer was capable of undergoing a very 
powerful sulphur fermentation. It was not then suspected of 
being due to bacteria, but believed to be the effect of an abnormal 
fermentation caused by the common forms of yeast ( saeckaromyces ). 
On the publication of Cohn’s paper in 1875, giving an account of 
a bacterium found in well-water, which evolved sulphuretted hydro- 
gen, an explanation was afforded capable of application to all the 
facts known at the time. 
It may easily be shown by thermo-chemical equations that 
neither organic matter nor carbon itself can reduce sulphates such 
as calcium sulphate to sulphides except at a high temperature, 
because the thermal effect results in an absorption of heat under 
the most favourable conditions for such chemical changes. 
W. K H. 
February 13th , 1896. 
