% ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 63 
a surface of 300 of an acre, the entire rain-fall (dews, etc., 
included) for those years. Prof. Way, at that time chem- 
ist to the Royal Ag. Soc. of England, analyzed the waters, 
and found that the total amount of ammonia contained in 
them was equal to 7 lbs. in 1855, and 94 lbs. in 1856, for 
an acre of surface. These amounts were yielded by 
663,000 and 616,000 gallons of rain-water respectively. 
In the waters gathered at Insterburg during the twelve- 
month ending March, 1865, Pincus and Réllig obtained 
6.38 lbs. of ammonia per acre. 
Bretschneider found in the waters collected at Ida-Ma- 
rienhiitte from April, 1865, to April, 1866, 12 lbs. of am- 
monia per acre of surface. 
The significance of these quantities may be most appro- 
priately discussed after we have noticed the nitric acid of 
the atmosphere, a substance whose functions towards vege- 
tation are closely related to those of ammonia, 
§ 7. 
OZONE. 
When lightning strikes the earth or an object near 
its surface, a person in the vicinity at once perceives a 
peculiar, so-called “ sulphureous” odor, which must belong 
to something developed in the atmosphere by electricity. 
The same smell may be noticed in a room in which an 
electrical machine has been for some time in vigorous 
action. 
The substance which is thus produced is termed ozone, 
froma Greek word signifying to smell. It is a colorless 
gas, possessing most remarkable properties, and is of the 
highest importance in agricultural science, although our 
knowledge of it is still exceedingly imperfect. 
Ozone is not known in a pure state free from other 
bodies; but hitherto has only been obtained mixed with 
