It is not possible to state definitely the nature of the carbonaceous
matter which resists decomposition by hydrogen peroxide in the
adopted procedure. It is quite certain, however, that all organic
matter of the nature of humus, crude fiber, and other cellulose material
is decomposed. This is shown in the preliminary tests of
these materials, and also by the fact that the residues from the peat
and mosslike peat were very small. Preliminary tests with the
adopted method indicate also a partial decomposition of charcoal
or coallike material. From the microscopic examination it seems
that a considerable part of the undecomposed organic matter in most
of the materials examined may be charcoal, and graphite in two of
the samples. In two cases a parafíinlike substance in the residues
was indicated by ignition. Prolonged boiling with hydrogen peroxide
also indicated that charcoal or a substance very high in carbon
contained practically all the carbon of the undecomposed residue in
one sample, and from one-half to one-third of the carbon in the
residues of two other soils. Apparently the organic residues obtained
from different soils contain different forms of carbon, and more
than one kind of carbonaceous matter may be present in a single
residue. In general, however, charcoal seems to be the most common
carbonaceous constituent.