AMMONIA IN AIR. 107 
anything of a soluble kind existing in the air 
through which it fell. When this water has been 
allowed to stand a day or two, we then find it 
begins to smell rather disagreeably, and a good 
nose might detect a faint odour, something like 
that of smelling-salts, proceeding from it. This 
smell is partly due to the presence of a small 
quantity of a substance called ammonia, which is 
composed, as the chemists tell us, of two gases, 
—nitrogen and hydrogen. Now ammonia easily 
dissolves in rain; and as it could not of course 
have come from the roof of the farm-house, or 
from the water-butt, it must have been obtained 
from the air,—and the rain having fallen from 
the clouds, must have dissolved it, and thus 
brought it to the earth. 
Now we are approaching the true answer. 
Since we are quite sure that the element nitro- 
gen in plants was not got from the gas nitrogen 
composing the air, and since there is no other 
substance in the air but ammonia which is com- 
posed of nitrogen, it is only fair to conclude that 
this part of the food of plants, for such it is, 
was obtained from the ammonia floating in the 
air. And this is the true reply. 
