ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 75 
and the whole phenomena are explained. In support of this 
view Cameron showed that cotton and other absorbents behaved 
exactly like ‘‘acid’’ soils, slowly turning blue litmus red; the 
phenomenon was therefore a general property of a class of 
absorbents. 
Baumann and Gully applied this idea to the case of peat and 
showed that it fully explained all the known facts. 
In the first instance they pointed out that it was not necessary 
to assume that the ‘‘acid ’’ was a decomposition product because 
the original sphagnum was almost as ‘‘ acid ’’ as the peat. 
Secondly, the acid if it exists must be insoluble, because the 
water extract of the peat is practically neutral to litmus. 
It must, however, be very potent because solutions of neutral 
salts such as calcium chloride, sodium nitrate, etc., are decom- 
posed with liberation of free hydrochloric and nitric acids when 
treated with peat or sphagnum. 
Baumann and Gully argue that no acid of this character is 
known to chemists, and it involves less strain to conceive of a 
hysical adsorption of the base from the dissolved salt with 
iberation of the acid than to imagine an insoluble organic acid 
capable of decomposing simple salts in solution. 
The view that acidity of the mineral acid soils is due to pre- 
ferential absorption of the base was developed by Harris in an 
investigation of Michigan soils. The phenomena are substan- 
tially the same as for peat: the soil turns blue litmus red; an 
aqueous extract is neutral, while an extract made with a solution 
of a salt, e.g., calcium nitrate, is acid. We must therefore 
assume either an insoluble but very potent mineral acid, or a 
preferential absorption of the base over the acid. The latter is 
indicated because, as in the case of peat, the amount of acid 
liberated from equivalent quantities of different salts is not the 
same, as it should be in a chemical reaction. 
Daikuhara has applied this view to the case of the acid mineral 
soils of Japan and Korea, but he has modified the explanation 
and made it more easily intelligible to the chemist, who finds it 
difficult to understand why an unparalleled physical decomposi- 
_tion of a simple salt should be accepted, and the assumption 
of a difficultly soluble but potent acid rejected. Daikuhara shows 
that the development of acidity in the salt solution is due to an 
_exchange of bases and not to simple absorption of the base from 
the salt. If the acid solution is analysed it is found to be really 
a solution of an aluminium salt: aluminium being given up 
from the soil in amount approximately equivalent to the base 
absorbed. Aluminium salts, as is well known, turn blue litmus 
red, and therefore are indicated as acids. The phenomenon is 
still essentially an absorption, but the seat of the reaction is 
located. 
This view is supported by Rice’s experiments, which have 
demonstrated the substantial identity in hydrogen ion concen- 
tration of a solution of aluminium nitrate and the solution 
obtained by treating an “‘acid”’ soil with .potassium nitrate 
solution. 
