58 
ANALYSIS OF SOILS. 
other matter convertible into humus ; but we contend that these decomposable 
matters are adventitious— the products of vegetation, on the spot or remote, as the 
case may be, but in no degree constituents of native earth. 
Humus has been analyzed by Fourcroy, Davy, Chaptal, and Th. de Saussure, 
and treated of by numbers of their followers : hence we learn that certain elements 
have been revealed, which by no human art (it is avowed) can be again combined, 
so as to effect its ^-production. An agency therefore is wanting ; a link is 
broken, that is lost and cannot be discovered : and, consequently, the nature of 
humus (manure) is not perfectly understood. 
Humus, we read, is insoluble ; but no sooner does cultivation commence, than 
the air acts upon and decomposes it : one part it converts to carbonic acid, (carbon 
with oxygen,) another part to water, (hydrogen with oxygen,) leaving the 
remainder of the oxygen, hydrogen, carbon, and nitrogen in the condition of a 
" soluble extract," now capable of being conveyed into the absorbent vessels of the 
roots. This passes glibly from the pen, and reads well ; but the reader may be 
assured that the processes — the great natural phenomena — so detailed, have not 
been traced in the laboratory of the chemist, or investigated under the surface of 
the soil within the immediate range of the vegetative vital principle ; they are 
pure inferences. 
We will not affect to deny that carbonic acid has been detected, and its absorp- 
tion witnessed during experiments under inverted glasses, or by a pneumatic 
apparatus ; but we contend that the great laboratory of nature remains unexplored, 
that the entrance to it is barred, and that all the analytic experiments of the 
chemist upon living beings or their functions are subversive of nature, and tend at 
least to partial, if not to delusive conclusions. Vegetables decompose manures 
(humus) if properly prepared by incorporation with earth suitable to their several 
habits, by the energy of their vital principle ; and they thus impoverish land by 
depriving it of those manures, depositing, however, fibrous or other matter of their 
own in it. Hence, land always contains decomposable substances which partially 
enrich it for a cross, or rotation crop, but deteriorate or poison it for any individual 
species. But the native earths are unchangeable ; clays remain clays, sand sand, 
and so on ; and though a minute portion of each earth may be assumed by plants, 
yet its quality remains unaffected. 
We now contend that humus is neither more nor less than manure : its 
analysis has proved the great fact that it is entirely decomposable ; but beyond 
that, we can only infer that plants decompose it, and appropriate its elements 
according to natural laws. 
The analyst of soils therefore will not misapply his time and energies in adopt- 
ing Mr. Rham's mechanical method of investigation, which we now again advert 
to. He directs that metallic sieves of different fineness be provided, and gives a 
drawing of a compound vessel to facilitate the operation'of sifting. Thus " sieves 
may be made so as to fit into one another like the filterers in a coffee-biggin, the 
