17 
formed upon acidifying with acetic acid. The nitrogen recorded as 
precipitated on the seventh and ninth days, therefore, was not in the 
form of casern but was contained in the bacterial cells that were held 
up by the filter paper. 
From the foregoing it is apparent that bacterial hydrolysis of 
casein precedes ammonification and that the former takes place con- 
siderably more rapidly than the latter. 
EFFECTS QF BACTERIAL ACTION ON DIFFERENT GROUPS OF 
NITROGEN COMPOUNDS. 
In the preceding experiments maximum ammonification usually 
took place in from four to six days. Of the substances tested casein 
was the most completely ammonified, but as stated above, usually 
not more than 60 per cent of the nitrogen was converted into ammonia. 
The following experiments were made for the purpose of studying 
the effects of bacterial action on the different groups of organic nitro- 
gen compounds. Two gram portions pf the substances were mixed 
with 100 grams of silica sand, soil infusions added and incubated for 
definite periods. Then the sand mixtures were transferred to 1,000 
cubic centimeter Kjeldahl flasks, 400 cubic centimeters of hydro- 
chloric acid added, and the whole boiled under reflux condensers for 
10 hours. After filtering and washing the residue with hot water, the 
filtrates were diluted to 1,000 cubic centimeters and aliquots used in 
the determination of the amid, basic, and nonbasic groups of nitrogen 
compounds, employing the same methods as were used in previous 
work on the organic nitrogen of Hawaiian soils. 1 
In every case the residues left after filtration were practically free 
from nitrogen, showing that all the nitrogen present went into solu- 
tion, but a smaller amount was generally found than occurred in the 
original materials. This was probably due to the loss of ammonia 
by volatilization during the course of bacterial action, and to the 
decomposition of nitrates, and therefore, will be considered as having 
been converted into ammonia. It is possible, however, that some 
denitrification also took place. The length of time that the different 
materials were exposed to bacterial action varied, the purpose being 
to allow decomposition to continue no longer than was necessary to 
insure vigorous ammonification. Ammonia was determined in 
separate portions by direct distillation with magnesia. The original 
materials were also subjected to acid hydrolysis and the group deter- 
minations made as above. All determinations were made in 
duplicate. 
The materials studied include casein, dried blood, soy bean cake 
meal, cottonseed meal, and linseed meal whose nitrogen contents 
i Hawaii Sta. Bui. 33 (1914). 
