234 
gen in wheat, to 51.7, the quantity of humic acid united 
with the 2.3 of nitrogen, and which, at 57 per cent, of 
carbon, produces 29.4 carbon, introduced into wheat by 
means of ammonia. 
Atomic weight of Lime 28 
„ „ Potassa 48 
„ „ Soda 32 
3)108 
3G 
Then as 36 (the average atomic weight of lime, potassa, 
and soda) is to 315 atomic weight of humic acid, so is 1.3 
weight of lime, potassa, soda, &c., in the ashes, to 11.3, 
the quantity of humic acid, which, at 57 per cent., produces 
6.4 of carbon, introduced by means of the earths and salts 
in the ashes. 
Or, carbon of wheat 46.1 
Nitrogen, 2.3, united with 51.7 humic acid, which 
last contains 57 carbon 29.4 
Potash, soda, earths, oxides, — 1.3 uniting with 11.3 
of humic acid, or 57 per cent 6.4 
Total carbon introduced by humic acid... 35.8 
So that, if ammonia passes through the soil, the plant must 
receive at least 35.8 parts out of 46.1 of its carbon directly 
by the roots, or about three-fourths of the quantity con- 
tained in it. Practically speaking, it is immaterial how 
carbon does reach the plant, provided it does arrive, and 
that farmers do not believe all their care about straw to be 
ineffectual; yet upon this subject Liebig contradicts himself: 
he says, page 15, "It may be affirmed with positive certainty 
" that manure neither serves for the production of the 
" carbon, nor has any injiuence upon it." Yet, at page 47, 
he says, " Humus acts in the same manner in a soil perme- 
" able by air ; as in the air itself, it is a continued source of 
" carbonic acid. An atmosphere of carbonic acid, formed 
