48

Scientific Memoirs by

both in the laboratory of the Assay Department of the Calcutta Mint and
in that of the Chemical Examiner to Government with the following results:—

      (1) Analysis in the laboratory of the Assay Department, conducted by
elutriation on samples which had been submitted to prolonged drying
at 100°C.—

      (2) Analysis in the laboratory of the Chemical Examiner to Government—

     It might at first sight appear as though the two analyses gave discordant
results in regard to the proportion of clay present in the soil. This, however,
is a mere matter of appearance, and is due to the fact that the method of
determination was different in the two analyses. In the first the method
employed was that of elutriation, which is a mechanical process of "separation
of substances by washing them in large quantities of water, so that the heavier
particles fall to the bottom, and the lighter ones, remaining some time suspended,
are gradually deposited in a finely-divided state"¹. What in it is styled clay is
not, therefore, equivalent to chemically pure clay, but merely to a mass of very
finely-divided particles to which the term mud would have been more strictly
applicable. In the second analysis the method followed was the ordinary
chemical one, and the proportion of clay is indicated by the amount of alumina.

     Even, however, were we to accept the mud of the first analysis as equivalent
to clay, which it certainly was not, the soil could not be correctly described as a
clay one. In Morton's Cyclopædia of Agriculture we find the following state-
ments regarding the classification of soils:—

     Soils in general consist of a mechanical mixture of the following four ingredients:—

                    1. Silica, silicious sand, and gravel.

                    2. Clay.

                    3. Lime.

                    4. Animal and vegetable remains (humus).

     There are few soils which consist of only one or two of these four substances; most
contain them all, but the relative proportion of each in different soils varies considerably,
A natural division of soils, accordingly, may be founded on the preponderance of one
of these four chief constituents.

     Upon this principle, soils may be conveniently classified as follows:—

               1. Sandy soils, containing above 80 per cent. of silicious sand.

               2. Calcareous soils, containing above 20 per cent, of lime.

       A Dictionary of Science, Literature, and Art, by Brande and Cox, 1872, p. 770.