Relation to Chalk and Mineral Salts . 71 
4. Reference to Table III shows that the amounts of the acids set free 
from different salts are widely different. It is found that, for a series 
of salts with the same base, acids are liberated in the following order : 
(a) hydrobromic, hydriodic, hydrochloric, nitric ; (b) sulphuric ; (c) acetic, 
the last named in largest quantity. This corresponds to the activity of 
the acids in various colloidal reactions. 
5. As regards the bases, bivalent bases are adsorbed more actively 
than monovalent, potassium more than sodium. 
6. It is possible to wash out a large portion of the adsorbed base with 
distilled water, especially if it contain carbon dioxide. By this means the 
original acidity of the Sphagnum may be almost completely restored. 
Baumann and Gully conclude that the old ‘humus acids’, 1 to which 
the acidity of acid soils in general, and of peat in particular, was ascribed, 
are non-existent: the acidity is in reality due indirectly to the presence of 
negatively charged colloidal compounds; these break up any salts present 
in the soil, and the acid of the salt produces an acid reaction in the soil. 
They regard the colloids in question as being chiefly located in the hyaline 
cells of the Sphagnum leaf. 
Since the publication of Baumann and Gully’s paper a number of others 
have appeared supporting or criticizing their conclusions. 
Czapek (’ll) agrees with the authors in all their deductions. Wieler (T 2 ) 
also supports the colloid hypothesis. 
On the other hand, a number of chemists have attacked these views, 
and sought to refer the reactions to ordinary chemical processes with 
typical acids. The most important papers are those of Tacke and 
Suchting (’ll), Tacke, Densch, and Arndt (’ 13 ), Rindell (’ll), Oden (T 2 ), 
Ehrenberg and Bahr (T 3 ). Gully (T2) has replied to some of those 
criticisms. The matter is really one for the physical chemist and it is 
impossible to go into details, but a few of the more important points may 
be summarized. 
Tacke and Suchting dispute some of Baumann and Gully’s experi¬ 
mental data ; refer the phenomena with tricalcium phosphate to interaction 
between humus acids, phosphoric acid, and the phosphates ; find that drying 
to 130° C.,and consequent serious diminution of the colloidal adsorptive surface, 
has no influence on the amount of acid liberated ; that peat can invert cane 
sugar, and give off hydrogen with iron—two typical acid reactions; and 
they can find no parallel to the reactions using other typical colloids, such 
as starch and gelatine. Colloid action is to be observed only in the 
adsorption of colloidal ferric hydroxide ; all the other reactions are to be 
referred to the action of humus acids as such. 
1 The form ‘humus’ is preferred to ‘ humous’ or ‘humic’, as the terminations of these are 
associated with definite chemical constitutions. 
