Apr. a8,1923 Effect of Changing Reaction of Soils upon Azotobacier 295 
after being added or at the beginning of incubation. There are in soils 
organisms capable of utilizing many organic acids or their salts as food- 
This would cause the disappearance of the acid. 
TabliB VI .—Effect of adding acid to a soil containing Azotobacier {soil C)« 
Sam¬ 
ple 
No. 
Acid added to 200 gm. soil. 
Ph. 
Azotobacter 
cultures. 
Mar. 2. 
June 23. 
I. 
0.2 cc. iV/i sulphuric. 
6. 53 
+ 
+ 
2. 
i.o cc. Nji sulphuric. 
6. 73 
+ 
4 - 
3 . 
5.0 cc. iV/j sulphuric. 
S. 88 
+ 
4 ' 
4 . 
lo.o cc. iV/jsulphuric. 
5-29 
(?) 
5 . 
20.0 cc. NJi sulphuric. 
4 - 74 
+ 
6. 
.2 cc. Nji acetic. 
6. 42 
4 - 
4 - 
7 . 
1,0 cc. iV/i acetic. 
6. 61 
+ 
4 - 
8. 
5.0 cc. V/i acetic. 
6. 64 
+ 
4 “ 
9 . 
lo.o cc. Nji acetic. 
6. 74 
+ 
10.... 
20.0 cc. iV/j acetic. 
7. 10 
— 
(?) 
II.... 
.2 cc. V/j butyric. 
6.44 
+ 
4 - 
12... . 
1.0 cc. iV/r butyric.. 
6. 58 
+ 
4 - 
13.... 
5.0 cc. Nji butyric. 
6. 69 
-f 
4 - 
14.... 
10.0 cc. Nji butyric. 
6. 70 
— 
4 - 
15.... 
20.0 cc. Nji butyric. 
7 - 05 
— 
4 - 
16.... 
.2 cc. V/i hydrochloric. 
6. 41 
4 - 
17.... 
1.0 cc. iV/i hydrochloric. 
6.51 
4 - 
18.... 
5.0 cc. V/i hydrochloric. 
5. 58 
+ 
— 
19.... 
lo.o cc. iV/j hydrochloric. 
5-51 
-f 
— 
20.... 
20.0 cc. Nji hydrochloric. 
4. 51 
+ 
— 
21.... 
6. 50 
4 - 
4 - 
<* +== Presence of Azotobacter, 
—=Absence of Azotobacter, 
?=* Azotobacter indefinite. 
Experiment set up Feb. i6. Moisture content optimum. 
Acidity determined electrometrically. 
The increased growth of such organisms would bring about the ac¬ 
cumulation of protein in their bodies which, upon decomposition, would 
result in the formation of more ammonia and hence a possible decrease 
in the hydrogen-ion concentration. The initial high acidity might result 
in either the partial or total destruction of the Azotobacter flora. If 
only a few organisms survived they might escape detection by the 
methods used. As soon, however, as the reaction again became favor¬ 
able they would become abundant and be easily detected. This is prob¬ 
ably what occurred in samples 14 and 15 of Table VI. On the other 
hand, if all the Azotobacter were killed they would never reappear 
unless inoculation took place, and subsequent analyses would fail to 
reveal their presence even though the reaction were favorable. The 
rapidity with which the Azotobacter are destroyed probably depends 
upon the degree of acidity, while the completeness with which they 
disappear from an acid soil depends upon the length of time the organ¬ 
isms are in contact with the acid condition. In the examples just given 
their complete destruction would depend upon the initial acidity and 
the period that elapsed before the hydrogen-ion concentration was 
again reduced below the maximum tolerated. 
The data in Table VII show that with increasing quantities of organic 
as well as mineral acids the hydrogen-ion concentration increases. From 
