The Soil. 
35 
finer, until it reached its maximum in the dust and clay. The con¬ 
tinued treatment with pure water, used in small portions at a time, 
yet relatively large compared with that acting upon the same 
amount of soil in the field, may act more energetically upon the 
feldspar than the soil waters do, but in considering this the pres¬ 
ence of carbonic acid in the soil is not to be neglected, as it 
strongly tends to increase the solvent action of water upon this 
mineral. 
§ 75. The analyses of the water-soluble portion of these soils 
show, as a rule, very much more silicic acid than is present in the 
residues from the ground waters. This fact, together with the 
higher percentage of potash which the water-soluble portions 
uniformly contain, suggest that the reaction itself is either primarity 
different or that there is a subsequent reaction between the ground 
water solution and the soil. The known ability of soils to remove 
potash from solutions seems to make it probable that such secondary 
reaction takes place. The more exact nature of this reaction is not 
known. I believe, however, that such a reaction would account 
very largely, if not wholly, for the accumulation of the potash in 
the very fine portions of the soil, among which these newly formed 
and highly reactive compounds are included. 
THE WATER-SOLUBLE PORTION OF THE SOIL. 
§ 76. The following tables exhibit the composition of the 
water-soluble portions of the first and second two inches of the soil. 
They give us an idea of the differences which exist in the salts of 
the different layers of the soil, but no correct idea of the distribution 
of the alkali, for the samples were taken on different dates. 
That which has already been said in regard to the order in 
which the acids and bases, oxids, have been combined probably 
needs to be emphasized. The order adopted seems to be the most 
convenient one for the majority of cases, and approximates the facts 
in these cases, but is not always correct. Phosphoric acid, when 
found in these residues, has been combined with magnesia. While 
this may be correct, it is more probable that it was in combination 
with lime. Its quantity, however, is so small that no great violence 
is done to our knowledge or to the facts. 
