31 
especially nitrates, while occurring in relatively small amounts, have 
long been considered to be of great importance to plant growth. 
For the purposes of this investigation two courses of procedure 
were open. First, a study of the changes that take place in the indi- 
vidual nitrogen compounds occurring in soils; second, a study of the 
group changes — that is, the effects of the treatment on the relative 
amounts and proportions of the large groups included under the 
amids, monamino acids, and' diamino acids. The latter of these was 
chosen. 
EFFECTS OF HEAT ON NITRATES. 
The soils used in this investigation were taken from various locali- 
ties in the islands and represent a wide range of types and conditions 
of formation. Some of the samples were taken from arid sections, 
some from intermediate, and still others from extremely humid sec- 
tions. The method of heating differed somewhat from that employed 
in the work already reported. The time of heating was 2 hours, 
and the temperatures used were 100, 150, 200, 250° C. and steam heat 
in an autoclave at 2 atmospheres pressure. One hundred gram por- 
tions of air-dried soil placed in porcelain dishes were heated to the 
desired temperatures in an air bath, or autoclave. Nitrates were 
determined colorimetrically by use of the phenol disulphonic acid 
method, and ammonia, from separate portions, by distillation with 
magnesium oxid in the usual way. It should be remembered that 
the ammonia thus obtained probably occurred in part as amids. 
Distillation with magnesium oxid is known to liberate ammonia 
from amids. In a lew instances the modified method of Schloesing, 1 
which consists in leaching the soil with dilute hydrochloric acid and 
then distilling the ammonia from the filtrate with the use of mag- 
nesium oxid, was employed. The results were very similar to those 
obtained by direct distillation. The following table shows the effects 
of heat on the nitrate content : 
The effects of heat on soil nitrates. 
[Nitrate nitrogen expressed in parts per million of air-dried soil.] 
Temperature. 
Soil 
No. 9. 
Soil 
No. 290. 
Soil 
No. 292. 
Soil 
No. 329. 
Soil 
No. 335. 
Soil 
No. 407. 
Soil 
No. 411. 
Soil 
No. 428. 
108.0 
95.0 
57.0 
5.0 
5.4 
94.0 
18.0 
18.6 
12.5 
6.5 
.5 
10.5 
17.6 
13.0 
23.5 
3.5 
1.4 
12.5 
197.0 
1.58.0 
61.5 
1.3 
3.5 
148.0 
3.3 
2.0 
3.0 
.6 
1.0 
L8 
0.7 
.7 
.6 
.5 
.4 
.6 
56.0 
60.0 
1.7 
1.5 
.5 
48.0 
70.0 
100° c 
70.0 
150°C 
49.5 
200°C 
.8 
250°C 
.5 
Steam pressure 2 at- 
46.0 
These data i 
on soil nitrates 
ire of interest 
. In most in 
as showing the destructive effect of heat 
stances the nitrates underwent considera- 
i Referred to by Todidi, Michigan Sta. Tech. Bui. 4, p. 1L 
