238 Dormant and Active Ingredients of the Soil. 
quence of the close union of the elementary matters of which it 
consists, and the compactness of its mechanical texture, might 
be as barren, and as incapable of imparting food to plants, as an 
artificial soil composed of pounded glass is known to be, notwith- 
standing the large proportion of alkali contained in it. 
Thus I have myself observed,* that the soil which covers the 
serpentine rock of Cornwall, although the latter is principally 
made up of a mineral consisting of — 
Silica . . .43-07 
Magnesia . . .40-37 
Alumina . . .0-25 
Lime . . .0-50 
Oxide of iron . . 1-17 
Water . . . 12-45 — Hisinger. 
contains, nevertheless, so minute a proportion of magnesia, that in 
an analysis of a small sample its presence had been altogether 
overlooked by me, in so great a degree may the mechanical con- 
dition of the components, and the state of combination subsisting 
between them, preserve a rock from the decomposing action of 
the elements which tend to set loose its treasures. 
Now it seems obvious, that whatever cannot be extracted from 
a soil by digestion in muriatic acid during four or five successive 
hours, must be in such a state of combination as will render it 
wholly incapable of imparting anything to a plant, for such a 
period of time at least as can enter into the calculations of the 
agriculturist ; and moreover, that all which muriatic acid extracts, 
but which water impregnated with carbonic acid fails in dissolv- 
ing, ought to be regarded as at present contributing nothing, 
although it may ultimately become available for its purposes. 
I have therefore thought proper to distinguish between the 
immediately available resources of the soil, and those ultimately 
applicable to the uses of the plant, designating the former as its 
dormant, and the latter as its active ingredients. 
The portion dissolved after digestion in muriatic acid will con- 
tain both the dormant and the active ; that taken up by water 
impregnated with carbonic acid will consist merely of the latter ; 
the difference in amount between the two will therefore indicate 
the dormant portion of its contents. 
The dormant and active portions may both be comprehended 
under the designation of its available constituents, whilst those 
which, from their state of combination in the mass, can never be 
expected to contribute to the growth ot plants, may be denomi- 
nated the passive ones. 
Every soil which is capable of yielding an abundant crop of 
* Lecture on the Application of Science to Agriculture, from the Journal 
of the Royal Agricultural Society of England, vol, iii. part i. 
