In some cases the ignition loss indicates which result is nearer the
true value. In any case the ignition loss should exceed the quantity
of organic matter, since it includes the combined water of the inorganic
colloidal material and part of the sulphur and chlorine. The
Florida peat has an ignition loss of 95.6 per cent. In this case the
ignition loss must be nearly the correct value for organic matter,
since very little water can be combined with inorganic material.
Here the combustion value for organic matter, though obviously a
little high, is more nearly correct than the hydrogen peroxide value.
The ignition loss of the mosslike peat, 96.5 per cent, shows that, in
this case, the hydrogen peroxide value is the more accurate. Moreover,
the fact that there is very little carbon in the undecomposed
residues from this peat is another indication that the hydrogen
peroxide value is very nearly correct. The muck subsoil has an
ignition loss of 13.24 per cent, which is probably the correct value for
organic matter, since the muck appears to be a mixture of quartz
sand and organic matter, little or no water being combined with the
organic material. The combustion value here is certainly too high,
and the peroxide value is too low. In the case of the Hagerstown
loam, the difference between the percentage of organic matter lost
through ignition (9.52 per cent) and the percentage obtained by combustion
(9.22 per cent) is only 0.30 per cent. This soil would contain
ordinarily about 2.50 per cent of water combined with th^ inorganic
colloidal material, since it contains 25 per cent of colloidal matter
which averages 10 per cent of combined water. The ignition loss
indicated in this case is 7.02 per cent of organic matter. The combustion
value seems to be too high, therefore, by a difference of 2.20
per cent, and the peroxide value too low by a difference of 2.10 per
cent. The ignition losses would seem to indicate that in one determination
the combustion value is the more accurate, that in another
determination the peroxide value is the more accurate, and that in
two cases there is no choice between the two methods.