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the soil, or rather its combinations with ammonia. Dr. Daubeny 
says that Liebig begins by showing, that vegetable mould 
contains m general two principles ; the first of these, which 
is soluble in alkalies and in certain of the earths, has been 
termed humic acid ; that humus, in common with all carbona- 
ceous substances which contain a small proportion of hydro- 
gen, when slightly moistened, undergoes a process of slow com- 
bustion, termed by him eremacausis ; that when acted upon by 
earths and alkalies it is converted into humic acid, and com- 
bines with them; that humus can only be dissolved by water 
when in union with an alkali or an earth. " Hence," says 
Dr. Daubeny, " the amount of humus, or humic acid, which 
" enters the vegetable tissue, must at least be limited by the 
" quantity of earthy and alkaline matters which are absorbed; 
" and how small that quantity is, may be seen by reference 
"to the statement I have already made, as to the weight of 
" ashes in a given portion of a plant." (Lecture IL, on Agri- 
culture, pp. 53 and 54.) 
But if lime, in combination with humic acid, enters into 
plants as humate of lime, which is on all hands agreed, surely 
ammonia, an alkali, must also unite with humic acid, and 
therefore be absorbed as humate of ammonia ; and this in 
proportion to their respective atomic weights. It will there- 
fore follow, that as all the carbonaceous or vegetable manure 
in a soil is continually being resolved into humic acid, so it is 
impossible for either caustic ammonia or the carbonate of 
ammonia, (the latter being the state in which the Professor 
erroneously says ammonia enters into plants,) to pass through 
any soil in which there is a trace of vegetable matter, without 
being converted into humate of ammonia. Now, the quantity of 
carbon in humic acid, according to Liebig, is from 57 to 72 
per cent., and the quantity of humic acid in some soils, 
according to Sprengel, is 45 per cent. It is therefore clear, 
that a very considerable portion of carbon must obtain 
