32 Proceedings of Royal Society of Edinburgh. [sess. 
then a minus quantity— 9*2 units, and the thermal effect in (2) 
would result 
- 341*2 -9-2 + 269*6 + 69 
= -350-4 +338-6 
Total = - 1T8 heat units absorbed. 
This is, however, in respect to only one molecule of CH 4 , and there 
are three molecules involved in equation (1), and therefore, if we 
consider the two changes taking place simultaneously, we have 
+ 41'8-35 - 4= +6 - 4 heat units evolved. So that, whatever may 
be the condition of the sulphuretted hydrogen liberated, the 
ultimate effect is heat evolution. 
Let us take into account the oxidation of the sulphur and of 
the sulphuretted hydrogen ; presuming that the latter gas is in 
solution, then by equations on the preceding page : — 
(a) H 2 S (solution) + O = H 2 0 (liquid) + S (solid) 
-9-2 +69 
Heat evolved = 78*2 heat units. 
(b) S (solid) + 30 + H 2 0 (liquid) = H 2 S0 4 (solution) 
+ 141 heat units. 
Total heat evolution in (a) and ( b ) 
78*2 + 141 = 219-2 units. 
We know that this is the course of chemical effect by the life 
processes of some, if not all, of these sulphur-bacteria ; but let us 
suppose that there may be some organisms which act directly upon 
sulphuretted hydrogen in presence of oxygen without the separation 
of sulphur, it will be seen that the heat evolved under such con- 
ditions is nothing like so great as in the former case : 
(c) H 2 S (dissolved) + 20 2 = H 2 S0 4 (dissolved) 
-9-2 +141 
Heat evolved = 150*2 units. 
The difference between the changes in (a) and (b), taken together, 
as compared with (e), results in a difference of 69 heat units in 
favour of the former, and it is therefore in the highest degree 
probable that the former chemical change is actually that which 
takes place. 
