PROCEEDINGS OF THE CHEMICAL DEPARTMENT. 209 



as nutriment for the plants. Ten thousand parts of soil are then 

 capable of yielding to water from 5 to 15 parts of mineral matter, 

 and even of this but a small proportion consists of those sub- 

 stances which are admitted to be most essential to plants. The 

 potash rarely exceeds 4 or 5 parts in 100,000, and there is no 

 phosphoric acid. 



When the soil is treated with acetic acid, the quantity of 

 matters dissolved is much higher, and amounts to from one-half 

 to one and a-half per cent., and to their number phosphoric acid, 

 which rarely appears in the watery solution, comes to be added. It 

 is not found in solution in all cases, but in some soils the quan- 

 tity dissolved is comparatively large, and sometimes reaches 

 half that which the solL contains. As a rule, the quantity of all 

 the substances dissolved is much larger than in the watery solu- 

 tion. This applies, as might be expected, in an especial degree 

 to lime, which, existing in most soils to a greater or less extent, 

 in the form of carbonate, is readily soluble in acetic acid. Ac- 

 cordingly, we find in some instances all the lime in solution, and 

 rarely less than half the total quantity. The difference in this 

 case must be attributed to the fact, that lime is in most cases an 

 artificial addition to the soil, and the whole quantity so added 

 must readily dissolve in acetic acid ; and hence it may be inferred, 

 that those soils in which the whole of the lime dissolves in 

 acetic acid must in their natural state have either contained little 

 or no lime among their mineral constituents, unless, indeed, it 

 was originally derived from some organic source. In Mr Hope's 

 soil, for example, where the lime is entirely soluble in acetic 

 acid, it is highly probable, indeed certain, that part of it is 

 derived from sea-shells. Magnesia, on the other hand, which is 

 not added to the soil artificially, except in those cases in which 

 the land is limed with a lime containing it, is never entirely 

 soluble, and though acetic acid takes it up to some extent, the 

 quantity dissolved rarely exceeds a fourth of that present. The 

 quantity of alkalies, and especially of potash, dissolved, is con- 

 siderable ; and phosphoric acid is also found in the solution in 

 large amount, a half and some times more than that being- 

 dissolved. 



Acetic acid takes up a smaller proportion of the subsoil, but 

 the solution contains the same substances. Phosphoric acid, 

 however, is more frequently absent than it is in the acetic solu- 

 tions of the soils. The quantity of soluble lime is also in general 

 perceptibly smaller, though this is not invariably the case. 



It may at first sight appear to many, that the quantities of the 

 different elements of plant-food taken up by acetic acid are so 

 small as to afford but an inadequate supply to the plants ; but a 

 very little consideration is sufficient to show that, though small 

 relatively to the weight of the soil, the quantity is absolutely 







