244 



DR. DAUBENY ON THE ROTATION OF CROPS, ETC. 



In the following Table the results are all reduced to one standard. 



1000 grains of the soil. 



For one cubic foot of the soil of the garden was found to weigh eighty-two lbs., 

 from which it follows, that an area of 100 square feet to the depth of three feet (which 

 is less than the average depth of the soil in the garden), would contain 24,600 lbs. of 

 soil, which at TO gr. to 1 lb. of soil would give an amount of phosphoric acid equal 

 to 3-5 lbs. 



Now it has been calculated (page 230) that the quantity of phosphoric acid extracted 

 from the soil in ten years did not exceed 1-84 lb., so that the permanent bed of barley, 

 which contains at present 0*8 of phosphate of lime, or 0-4 of phosphoric acid, would 

 not have possessed before the cropping more than 1*26 of phosphate, or 0-63 of phos- 

 phoric acid, in the 1000 grains. 



With respect to the alkalies, we shall find by the same mode of calculation that 



the medical garden contains in 100 square feet — 



lbs. 

 Potass 6-9 



Soda 2-9 



And as each permanent crop of barley in the average extracted no more than of — 



Potass 0-436 



Soda 0-064, 



(deduced from 1-18 of chloride of sodium) in 100 parts, there would be a supply of 

 potass equal to fifteen crops of barley, and of soda equal to forty-five crops. 



* Thus we perceive that a series of ten successive crops of turnips had added more organic matter to the 

 soil than it had abstracted. See Boussingault's late work, chap. vii. on the Rotation of Crops. 



