Dormant and Active Ingredients of the Soil. 
243 
garded as an exceptional case, I might have referred to Sprengel, 
who states that the per-centage of phosphoric acid in the soils he 
analysed varied from 0 • 024 to 0 • 367 ; and in the subsoils from 
about 0 007 to 0-2. 
I detected many years ago phosphate of lime in several secondary 
limestones chiefly taken from the oolitic formation, and Mr. 
Schweitzer of Brighton has determined the proportion of that 
ingredient in the chalk near Brighton, to be not less than one 
grain in the 1000. We need not therefore resort to South Ame- 
rica for bones, if means could be found for extracting this in- 
gredient economically from the rocks of our own country. 
3rdly. These facts place in rather a new light, although one, 
it is conceived, not less striking than before, the importance of 
taking care of the various excrementitious matters at our disposal, 
whether proceeding from animal or from vegetable sources. 
Such substances indeed contain the products which nature has, 
with so large a consumption of time, and by such a number of 
complicated operations, elaborated from the raw material con- 
tained in the soil, and has at length brought into the condition, 
in which they are most soluble, and therefore best fitted to be 
assimilated by the organs of plants. 
To waste them is therefore to urdo what has been expressly 
prepared for our use by a beautiful system of contrivances, and 
to place ourseh'Cs under the necessity of performing, by an ex- 
penditure of our own labour and capital, those very processes 
which nature had already accomplished for us, without cost, by 
the aid of those animate or inanimate agents which she has at her 
disposal. 
4thly. The analyses above reported may suggest caution as to 
the inferences which some might be disposed to deduce from cer- 
tain researches lately announced, with respect to the power which 
a plant possesses of substituting one alkali, or one earth, for 
another in the processes of vegetation. 
This substitution indeed, however brought about, is a fact 
which hardly admits of being questioned, supported as it is by 
the testimony of men so eminent as Saussure and as Liebig ; and 
indeed many of the analyses detailed by me in the Philosophical 
Transactions might be appealed to in corroboration of its truth. 
Thus we find, that whilst the amount of bases agreed pretty 
nearly in the three crops of the same plant which had been ana- 
lysed, the proportions between them often varied considerably. 
This is particularly seen in the case of the lime and magnesia, the 
deficiency in one of these earths being often made up by an ex- 
cess in the other. 
In like manner a deficiency of potass is found to be compen- 
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