14 
causing much less deflocculation of the clay, so that by ordinary 
filtration the solutions can be freed from all but traces of clay. Forty 
grams, after extracting with dilute hydrochloric acid, were treated 
with 2,000 cubic centimeters of 3 per cent sodium hydrate solution 
for a period of two days, with occasional shaking during the first day. 
The solutions were siphoned off and aliquot portions used in the 
studies. 
SEPARATION OF DIFFERENT FORMS OF NITROGEN IN HTJMTJS. 
A part of the humus can be precipitated from the alkali solutions 
by acids, and this method has been used for obtaining so-called pure 
humus. The amounts precipitated, however, vary with the amount 
of acid used. Shorey * has shown that after filtering out the pre- 
cipitate obtained by acidifying the humus solution a still further 
precipitate can be obtained by carefully neutralizing the filtrate, 
and that of the precipitates thus obtained each contains nitrogen. 
The humus extract made with a 2 per cent sodium hydrate solution 
was found to contain 0.0399 gram nitrogen per 100 cubic centimeters 
of solution. The hydrochloric acid filtrate he found to contain 0.0251 
gram of nitrogen per 100 cubic centimeters of the original solution, 
and on neutralizing this filtrate with caustic soda the precipitate 
formed was found to contain 0.0168 gram of nitrogen. 
In the work here reported hydrochloric acid was carefully added 
to 1,000 cubic centimeter portions of the humus solution (corre- 
sponding to 20 grams of soil) to apparent neutrality to litmus paper, 
then 20 cubic centimeters of 1 per cent hydrochloric acid was added, 
the precipitate formed was collected on a filter and washed. In this 
way the humus matter was roughly separated into two parts. The 
precipitates thus obtained were afterwards subjected to acid hydrol- 
ysis by boiling with 400 cubic centimeters strong hydrochloric 
acid for a period of 10 hours, and then filtering and washing the 
residue. The amid and basic nitrogen contained in the original 
humus solutions, in the filtrates obtained from precipitating the 
solutions with dilute hydrochloric acid, and in those obtained upon 
hydrolyzing the humus precipitates, have been determined. 
The following table shows the total nitrogen contained in the 
original humus solutions, and that in the portions obtained by the 
various separations: 
i Hawaii Sta. Rpt. 1906. 
