274 AprnrY—Dissolved Gases and Fermentative Changes. 
and rochelle salt, dissolved in distilled water, to which was added a little sodium 
phosphate and potassium chloride. 
We may therefore regard the chemical changes which took place in the-mixed 
solid sewage organic matters and peroxide of manganese, in the mass above 
described, as a true carbon-oxidation of the organic matters, the available oxygen 
of the peroxide affording the necessary supply of that gas to the living organisms, 
just as the dissolved atmospheric oxygen did in the solutions of the organic 
matter with which I carried out my experiments on carbon-oxidation of soluble 
organic matters.* 
I propose to give an experimental proof that the organic matters which 
resulted from this process of carbon-oxidation possess all the fermentative, besides 
the physical and chemical, properties which I have already shown fermented 
organic matters and peaty colouring to possess in common. 
Description oF EXPERIMENTS UPON THE FERMENTATION OF THE Humus. 
As will be gathered from the above ‘Table of Analysis, a portion of the organic 
matters present in the sludge was taken up by the acid employed for dissolving 
out the soluble portions of the substance. Practically, however, all was left undis- 
solved when the solution was evaporated to dryness, and the residue treated with 
hydrochloric acid, in the ordinary way, for the separation of silica if present. 
' The organic matters which were separated in this way were employed for the 
experiments I have to detail. They were brownish black in colour, and were 
slowly but completely soluble in a solution of sodium carbonate, The solution 
obtained was of a deep brown colour, indistinguishable from an extract of peat or 
of garden soil similarly prepared. ‘The ratio of organic carbon to nitrogen was 
6°84:1. They were therefore similar in these particulars to the organic matters 
contained in the extract of peat employed for the experiments recorded in Part II. 
of my first Paper. t 
I should add that the portions of the sludge which were undissolved by hydro- 
chloric acid, also yielded, on treatment with sodium carbonate solution, a deep 
brown solution. ‘The details of experiments with this portion of the organic 
matters of the sludge I must, however, leave to a future Paper, should they prove 
* Professor W. N. Hartley, F.R.S., has recently published a short interesting paper on ‘‘ The Cause and 
Nature of the Chemical Changes occurring in Oceanic Deposits,” in which he points out that the chemical 
changes which take place between the organic matter and the mineral salts in fresh- and sea-water mud are 
,0 be ascribed to the action of well recognized living organisms, and shows, by thermo-chemical equations, 
that, at each stage of change, there is heat evolution.—Proc. R. 8., Edinburgh, 1895-96, p. 25. 
} Loe, cit., p. 598. 
