The residues from the hydrogen peroxide treatment were examined
microscopically for evidence as to the nature of the undecomposed
organic matter. Occasionally particles resembling roots were observed,
but these particles seemed to be mere outlines and entirely
different in appearance from roots not treated with hydrogen peroxide.
In the Hagerstown loam, black particles, evidently charcoal, could
be seen. The black particles gather on the sides of the beaker during
the digestion. Charcoal can be distinguished by a test, devised by
J. G. Smith of this laboratory, which consists of drawing a spatula
firmly over a small quantity of soil material which has been placed
on a clean, white sheet of paper. Charcoal gives a characteristic
black streak. This may be confirmed by burning the black particles
and by microscopic examination. White and Holben (14) recommend
testing the soil for charcoal by stirring the soil in water; the
charcoal particles will then rise to the surface.