210 PKOCEEDINGS OF THE CHEMICAL DEPAKTMENT. 



large. Taking the soil of Boysack, which I select as an example 

 because it is of fair quality, and yields, even without manure, a 

 crop of upwards of 12 tons of turnips, it is found to contain 

 01 01 per cent, of phosphoric acid in the acetic solution. Now, 

 as the upper 10 inches of the surface, which is assumed to repre- 

 sent the soil, weighs at least 1000 tons to the acre, this percent- 

 age gives us rather more than a ton of phosphoric acid, which 

 is equivalent to nearly 2 - 2 tons of phosphates, or it contains 

 as much as 4^ tons of bones. It is manifest that here, suppos- 

 ing the plants can really get possession of it, there can be no 

 deficiency of that constituent, especially if it be taken into 

 account that a crop of 12 tons of turnips only contain 20 lbs. of 

 phosphoric acid. A similar calculation applied to any of the 

 other elements of plant-food leads to similar conclusions ; and we 

 are forced to admit, that in every one of the soils analysed, there 

 is a superfluity of the requisite substances. 



How is it, then, that certain of these soils in their natural state- 

 fail to produce a crop of turnips ? and why should the addition of 

 a quantity of manure, containing only 56 lbs. of phosphoric acid 

 to the acre, a quantity absolutely trifling compared with that it 

 already contains, cause so great an increase in the produce in the 

 great majority of instances ? The question is one to which we 

 have at present no sufficient answer, and its thorough solution is 

 attended with difficulties which it is only possible to overcome 

 by repeated and long continued experiments. We require espe- 

 cially some information as to the reason why the same manure 

 produces a much greater effect on some soils than on others. 

 There are very remarkable examples of this to be found among 

 the experiments made on these soils. As an illustration, we may 

 select the effects produced by dissolved coprolites and bone ash 

 on the farms of Drylawhill, Boysack, Saltcoats, and Dirleton. 

 These particular manures gave to the acre of land 56 lbs. of phos- 

 phoric acid, and the average increase which they yielded per acre 

 over the produce of the plot which got no manure was as 

 follows : — 



TONS. CWTS. 



Drylawhill, 1 14 



Boysack, . . . 3 16 



Saltcoats, . . . 6 10 



Dirleton, . . . 9 17 



So that the same manures produced nearly six times as great an 



effect at Dirleton as at Drylawhill, and three times as much as 



at Boysack. Even under the most favourable circumstances, the 



increase contains but a small part of the valuable matters which 



the manure was used to supply. The extra produce on Dirleton 



must have contained about 16 lbs. of phosphoric acid, while the 



manure contained 56, so that little more than a fourth of it became 



