Nitrogen Fixation 47 
convert the nitrogen of the liquid excreta of the households into 
nitric acid which may be recovered in the form of potassic nitrate. 
In the case of the Chile saltpetre we have no definite evidence 
regarding the source of the nitrogen and as a result we have a va¬ 
riety of theories to account for its presence in such extremely large 
quantities in the form of nitrates. Almost every conceivable source, 
the droppings of great herds of animals, guano or the drop¬ 
pings of birds, marine vegetation, etc., have been suggested. 
These sources attribute the formation of the nitrates to the action of 
nitrifying bacteria on nitrogen of animal or vegetable origin. I 
know that this has not always been stated in just this way. Another 
source which has been suggested is the atmosphere. It has been 
claimed that the hydrated oxid of iron has the power to induce 
the oxidation of ammonia salts and that other basic compounds, the 
alkaline carbonates, for instance, have the power under certain con¬ 
ditions of inducing the oxidation of atmospheric nitrogen. Again 
the electric discharge has been suggested as the cause of the union 
of the oxygen and nitrogen of the atmosphere to form nitric acid, 
which falling to the earth as a dilute solution of ammonic nitrate 
in rain water may have reacted with the carbonates of the alkalis 
or alkaline earths which would then be carried with the waters to 
natural basins from which the waters have subsequently evaporated 
leaving the nitrates in their present form and place. 
The facts which I have found obtaining in such large districts 
in Colorado suggest the possibility that the atmosphere is the source 
of the nitrogen in these nitrates but that the agency which has 
transferred it from the atmosphere to the fixed form of the nitrates 
is not the electric discharge nor the action of alkaline carbonates 
on the nitrogen of the air in the presence of oxidizable matter, but 
to that of those micro-organisms, the azotobacter, which have the 
power of converting atmospheric nitrogen into nitric acid, respec¬ 
tively ihto nitrates, especially if there be enough calcic or other 
carbonate present to prevent the soil from becoming acid. 
We have in miniature a great many analogies to the occur¬ 
rences of Chile. In the lower parts of small basins we have de¬ 
posits of sulfate of soda, above this zone we have one rich in ni¬ 
trates. I have been told that in Chile they sometimes find calcic 
chlorid but usually sodic chlorid. We find samples in which calcic 
and magnesic chlorid together constitute 48.5 per cent of the water 
soluble portion. Others in which sodic chlorid constitutes 44.5 per 
cent of the water soluble. The amount of nitrates, dealt with in 
this bulletin, is surprisingly large. We have as the highest per¬ 
centages of nitrates found, 5.628 and 6.541 per cent of the air dried 
samples. These samples were gathered from the surface soil and 
were not taken to any depth, perhaps the one showing 5.628 per cent 
