36 On Agricultural Chemistry, 



and the straw, both of barley and of wheat, being retained upon 

 the farm. We have in this case, by the sale of grain, a loss of 

 minerals to each acre of the farm of only 20 to 24 pounds of 

 potass and soda, and 26 to 30 pounds of phosphoric acid, in the 

 course of the rotation, or an average of 5 to 6 lbs. of potass and 

 soda, and 6^ to 7J lbs. of phosphoric acid per acre per annum. 

 In the sale of the animals there would of course be an additional 

 loss of phosphoric acid, though, especially if no breeding-stock 

 were kept, this would be even much less considerable than in 

 that of the grain ; and the amount of the alkalies thus sent off 

 the farm would, according to direct experiments of our own upon 

 Calves, Bullocks, Lambs, Sheep, and Pigs, probably be only about 

 one-fourth that of the phosphoric acid. It has, however, long been 

 decided in practical agriculture that phosphoric acid may be ad- 

 vantageously provided in the purchase of bones or other phosphatic 

 manures, though in practice these are not found applicable as a 

 direct manure for the wheat crop ; and as we have already said, even 

 when employed for the turnip, its efficacy is not to be accounted 

 for merely as supplying a sufficiency of that substance to be 

 stored up in the crop. 



Of the minerals then, to be supplied by external sources yet 

 to be discovered or developed, the question lies with the alkalies ; 

 and of these there will in the sales of corn supposed above, be, 

 under any circumstances, only 5 to 6 lbs. per acre per annum 

 required to be provided from the stores of the native soil by 

 annual decomposition, in order that the immediately available 

 supply of them, which has thereby been drawn upon, should be 

 undiminished. 



But we believe that few will maintain that the amounts of 

 produce above supposed are, in practice, exported, unless under a 

 system of purchased food for stock, or of such substances as rape- 

 cake as manure for turnips ; and by neither of these means could 

 the produce thus be raised, without bringing upon the farm more 

 of the alkalies than could possibly be exported, in the increased 

 produce of corn and meat arising from their use. Under such a 

 course, then, and this is what happens wherever land is well cul- 

 tivated, the demand upon the native soil for alkalies, by the sale 

 of corn, will probably be less than has been assumed ; and it is 

 even possible that in actual practice the available alkalies of the 

 soil will, from the two causes of import and disintegration, accu- 

 mulate rather than diminish. 



In justification of the supposition that cattle-food must be im- 

 ported, if the sales of corn and consequent export of alkalies are 

 to be thus kept up, it must be remembered that the relative price 

 of meat and corn, and that of manures to both, as fixed by the 

 laws of supply and demand, would at present, at least, preclude 



