82 HOW CROPS FEED. 
command for experimental study, will establish or disprove 
them by suitable investigations. 
He believes, from the existing evidence, that free nitro- 
gen can, in no case, unite directly with water, but in the 
conditions of all the foregoing experiments, it enters com- 
bination by the action of ozone, as Schénbein formerly 
maintained and was the first to suggest. 
We have already recounted the evidence that goes to 
show the formation of ozone in all cases of oxidation, both 
at high and low temperatures, p. 67. 
In Zabelin’s experiments we may suppose that ozone 
was formed by the oxidation of the cellulose (linen and 
paper) he employed. In Schénbein’s experiments, where 
paper or linen was not employed, the dust of the air may 
have supplied the organic matters. 
The first result of the oxidation of nitrogen is nitrous 
acid alone (at least Schonbein and Bohlig detected no ni- 
tric acid), when the combustion is complete, as in case of 
hydrogen, or when organic matters are excluded from the 
experiment. Nitric acid is a product of the subsequent 
oxidation of nitrous acid. When organic matters exist in 
the product of combustion, as when alcohol burns in a 
heated apparatus yielding water having a yellowish color, 
it is probable that nitrous acid is formed, but is afterward 
reduced to ammonia, as has been already explained, p. 74. 
Zabelin, in the article before cited, refers to Schénbein 
as authority for the fact that various organic bodies, viz., 
all the vegetable and animal albuminoids, gelatine, and 
most of the carboliydrates, especially starch, glucose, and 
milk-sugar, reduce nitrites to ammonia, and ultimately to 
nitrogen; and although we have not been able to find such 
a statement in those of Schénbein’s papers to which we 
have had access, it is entirely credible and in accordanee 
with numerous analogies. 
If, as thus appears extremely probable, ozone is devel- 
oped in all cases of oxidation, both rapid and slow, then 
