72 
Skene .— The Acidity of Sphagnum and its 
Rindell criticizes from the physico-chemical standpoint, and finds the 
reactions explicable on the assumption of a mixture of more and less soluble 
humus acids. 
Oden and Ehrenberg and Bahr point out that it is scarcely permis¬ 
sible to apply fine methods, such as that of conductivity determination, to 
so coarse a mixture as that presented by ordinary peat. They attempt to 
isolate the humus acids by extraction with ammonia, precipitation with acid, 
and further purification. 
Conductivity determinations with a preparation thus obtained led 
Oden to the conclusion that its combination with ammonia is of the nature 
of a true salt formation. He roughly determined its equivalent weight and 
basicity. 
Ehrenberg and Bahr, with an improved preparation, confirmed these 
results. They also attempt to demonstrate the true chemical nature of the 
compound with ammonia, by observations on its thermic decomposition, 
and by comparing the adsorption of ammonia with that of sulphur dioxide. 
Their experimental results do not, however, seem capable of an interpre¬ 
tation on the assumption that only a simple chemical reaction is involved. 
They suppose that the compounds formed with bases go into solid solutions 
with uncombined humus acids, and so account for aberrant numerical results. 
This, however, seems to be an approach to the views held by Baumann and 
Gully. Very important is the fact that their insoluble preparation of humus 
acids is capable of decomposing tricalcium phosphate, so that it possesses one 
at least of the peculiar properties of the natural compounds. 
It is clear that in the view of chemists the theory of Baumann and 
Gully is by no means held to be proved ; but at the same time evidence 
as to the existence of insoluble alkaline salts of the humus acids is not 
forthcoming. The compounds of the artificial preparations with the alkalies 
are soluble ; in fact on this depend the various methods for their preparation. 
To account for the retention of the bases in the form of such salts by the 
peat or Sphagnum , some sort of adsorption must be called into play. 
Ehrenberg and Bahr admit as much when they invoke the aid of ‘ solid * 
solutions to explain their figures ; and, as a matter of fact, no one denies 
that the humus acids are colloids. Acids which are colloids will act both 
as acids and as colloids. The attempt to explain all their peculiarities on 
the basis of one only of these two properties is bound to lead to failure. 
In what follows the terms ‘acid’ and ‘humus acid’ are employed 
only because they denote most conveniently the chief property of the 
substances in question—their responsibility, direct or indirect, for an acid 
reaction ; this use does not imply agreement with the view that they do 
not act also as colloids. 
For the purposes of the ecologist it is sufficient to recognize that peat 
contains compounds capable of breaking up salts and liberating their acids, 
