912 
Journal of Agricultural Research 
Vol. V, No. ao 
amount of ammonia-soluble matter in a soil. Comparisons of the color 
of the ammonia extracts with their content of dissolved matter show 
that this relation is variable for different depths in the same field and 
for the same depth in different localities (2, p. 13). 
The large number of soils referred to above were analyzed, using the 
ammonia extract and magnesia, without finding any in which the humus 
contained as much as 10 per cent of nitrogen. A later critical study of 
the method showed that the results were not reliable, the amount of 
humus nitrogen found being affected by the extent to which the solution 
was concentrated before adding magnesia and also by the time of diges¬ 
tion with the latter. One result of this was that, while parallel deter¬ 
minations gave concordant results, those run one after the other, using 
the same ammonia solution, gave widely varying results. 
The extraction of the humus by the Hilgard-Jaffa method (10) in the 
case of many soils, especially those of very fine texture, is extremely 
tedious, being in this respect similar to the Hilgard method for the deter¬ 
mination of humus, for which in the case of some soils 10 days or even 
longer is necessary (7, p. 320). For this reason we sought to devise a 
more expeditious and convenient method. Using two representative 
soils, one a silt loam from the Nebraska Experiment Station farm con¬ 
taining 2.41 per cent of humus and 0.245 per cent of total nitrogen, and 
the other a clay loam from Indian Head, Saskatchewan, Canada, with 
1.56 per cent of humus and 0.248 per cent of total nitrogen, we tried 
shaking 10 gm. of dry soil with 500 c. c. of a 4 per cent potassium- 
hydroxid solution for periods of 0.5, 1, 2.5, 5, 9, 12, and 24 days. During 
the working portion of the day the glass-stoppered bottles containing the 
mixtures were shaken at intervals of about one hour. With both soils 
the amount of nitrogen dissolved ceased to increase at the end of nine 
days. Repeated extraction of the same soil with fresh alkali solution, 
which might have given different results, was not tried. 
This method was then compared with that of Hilgard and Jaffa (10), 
using in the case of five arid soils from California (Table I) both a 4 per 
cent potassium and a 6 per cent sodium-hydroxid solution. 
