278 AprnrEy—Dissolved Gases and Fermentative Changes. 
of experiment, with distilled water in the proportion of one volume of the former to 
nine of the latter, and used. The results were the formation of small quantities of 
carbon dioxide, and of nitric acid, the consumption of a part only of the dissolved 
oxygen, and the disappearance of all the ammonia originally present. 
In experiments 4 and 4a, it became necessary to employ, in addition to the 
portions of H which remained from previous experiments, some fresh solution of 
humus (/’), which had been prepared on February 26th previously, and had been 
kept since its preparation in a vessel freely exposed to’ the air. These experi- 
ments were made to examine the fermentative properties of the humus in the 
presence of a decided quantity of ammonia under more suitable conditions than 
experiments 2 and 2a were found to afford. In those experiments, the ammonia 
was present in unnecessarily large quantity, and prevented the certain detection 
of small quantities of nitric acid if formed. Accordingly, for experiments 4 and 
4a, a less quantity of ammonia was taken, and a longer time allowed for fermen- 
tation. The results of these experiments showed that, when the dissolved oxygen 
was insufficient for the complete oxidation of the ammonia present, both nitrous 
and nitric acids may be formed, and small volumes also of carbon dioxide. 
The conditions secured for the next and final experiments (5 and 5a) were 
arranged, so that oxygen should be present in just sufficient quantity for the 
complete oxidation of the ammonia, and in each experiment the oxidation of the 
ammonia to nitric acid was complete. These experiments also prove that a nitric 
fermentation of ammonia may be carried on in the presence of small quantities of 
humus, without any carbon dioxide being formed, there being some evidence 
(see 5a more especially) that a small quantity of carbon dioxide was actually 
“fixed.” Abundance of evidence of a similar nitric fermentation, in the presence 
of both fermented organic matters and of peaty colouring matters, will be found 
throughout my first communication. 
These experiments afford additional evidence, to that I have already published, 
to the effect that organic matters, which are themselves the result of bacterial 
fermentative changes, or a carbon-oxidation of fresh organic substances, take an 
active part in any subsequent fermentation of ammonium compounds with which 
they may be mixed, and determine the ziéric fermentation of those compounds.* 
In addition they extend our knowledge of nitrifiable organic substances to 
those which may be derived from cultivated soils, or, in other words, to the 
organic matters which may be more especially met with in waters that have 
passed through cultivated soils (spring and well waters); and they show that 
these organic matters in no way differ in general fermentative properties from 
those to be met with in waters holding peaty colouring matters in solution (upland 
* Loe cvt., pp. 593-613. 
