RESEARCH METHODS IN STUDY OF EOREST ENVIRONMENT. 127 
misnomer to call this a " humus determination." On the other hand, 
the amount of humified material is important as a possible source of 
nitrogen, it being, according to Hilgard (125), " wholly uncertain to 
what extent the unhumified material will ultimately become humus, 
from the nitrification of which plants are presumed to chiefly derive* 
their nitrogen." 
Loss on ignition. 
Loss on ignition, as has been said, may be of interest in connection 
with water-holding properties. It is readily determined by placing 
approximately 100 grams of the soil in a shallow earthen or platinum 
dish, in which it will first be oven-dried and weighed and then heated 
to red heat in a gasoline or electric oven, with a moderate current of 
air passing over it. Providing lumps have been broken down at the 
outset, the oxidation may usually be completed in an hour. After 
this the sample is again weighed, the ignition loss is calculated, and 
the percentage of loss is based on the oven-dry weight of the sample. 
In the case of soils containing considerable lime or magnesium car- 
bonate, the error through the breaking down of these on ignition ma}^ 
be largely eliminated by a preliminary treatment with dilute hydro- 
chloric acid, as in the humus extraction method. 
The ammonia-soluble humus. 
The ammonia-soluble humus, or matiere noire of Grandeau (122), 
is the aim of all of the more recent methods of extraction. Lime and 
magnesia are first removed by washing the soil with dilute hydro- 
chloric acid. Grandeau mixed the washed soil with coarse sand 
and placed it in a funnel at the bottom of which were fragments of 
glass or porcelain. The whole mass was then moistened with dilute 
ammonia and allowed to digest for three or four hours, after which 
the solution was washed through with water or water containing a 
little ammonia. The filtrate was then evaporated to dryness, weighed, 
ignited in a platinum dish, and weighed again. The loss on ignition 
is the measure of the extract able humus. The residue is termed 
humus ash. 
Hilgard 19 modified the Grandeau method by placing the soil in a 
paper filter, covering it with a disk of filter paper, and here perform- 
ing both the acid washing and the ammonical extraction. The latter 
is accomplished with 4 per cent ammonia water until the filtrate comes 
through colorless. 
Others have attempted to improve on Hilgard's method in order 
to expedite the process ; but, as shown by Alway. Files, and Pinekney 
(101), they have introduced serious error through including in the 
ammoniacal extract considerable amounts of colloidal clay which, on 
19 In Bulletin 38, Bureau of Chemistry, United States Department of Agriculture, 1893. 
