Aprnry—On the Reduction of Manganese Peroxide in Sewage. 249 
considerable quantity of heat, and would therefore constitute a 
source of considerable energy to the organisms, is evident from a 
consideration of the following thermal data taken from Thomsen’s 
‘¢Thermochemische Untersuchungen ”’ :— 
2[Mn,0,H?0] = 189,440 
2) (Mn Oe eEeOi = 232,660 
Loss = — 48,220 
COA] B 96,960 
[MnH?0?, CO?Aq] = 13,230 
110,190 
~ 43,220 
+ 66,970 
Freshly precipitated peroxide also suffers reduction to manga- 
nous carbonate when it is mixed with solid fermentable organic 
matters. I have recently been able to put this to test on a some- 
what large scale at some sewage purification work where manga- 
nate of soda is employed for treating the sewage. At the works 
referred to, the greater portion of the solid matters in suspension 
in the sewage are first separated by mechanical subsidence; the 
sewage is then mixed with a water solution of manganate of 
soda; the peroxide, which afterwards separates, is allowed to 
subside, together with matters remaining in suspension in sewage, 
to the bottom of the tank in which the operation is conducted. 
It is finally drawn off from the tank in the form of a mud. I 
obtained several hundredweight of this mud, and first drained it 
on a gravel-bed, and, when of sufficient consistence, I made it up 
into a large heap, and allowed it to slowly air-dry in a covered 
shed. After being left in this condition for about three months, 
I found the interior portions of the heap had assumed a grey 
colour, only these portions immediately exposed to the air had 
retained the original brown colour of the peroxide. 
I detached some small lumps from the heap, allowed them to 
