234 DR. DAUBENY ON THE ROTATION OF CROPS, ETC. 



On the other hand, the shifting crops of barley, which in ten years amounted to 

 421 lbs., and which, taking as our criterion the amount of ash yielded the last year 

 (1844), had drawn from the land 26*31 lbs. of inorganic matter (the sand, charcoal, 

 and peroxide of iron, drawn from other sources having been deducted), would have 

 abstracted from the soil in ten years, as follows : — 



Sand and charcoal") ^ ^ ,^r 



. , „ . > extraneous . . 6* 1 75 



Peroxide ot iron J 



Silica 9-300 



Phosphoric acid 2370 



Sulphuric acid . 0*600 



Carbonic acid 0*366 



Chloride of sodium 0*364 



Potass 4*220 



Magnesia . . ^ 0*915 



Lime 1*960 



26*270 



Proceeding now to the second case, that of the potatoes, we find the amount of 

 the produce, in the case of the permanent crop, in nine years to have been 620*8 lbs., 

 yielding 7*37 of ashes, of which, however, about 1*37 were extraneous. Consequently 

 during that period the inorganic constituents, abstracted from the soil, and contained 

 in 6 lbs. of real ash, would be as follows : — 



Silica 0*11 



Phosphoric acid .... 0*80 



Sulphuric acid .... 0*27 



Carbonic acid .... 0*80 



Chloride of sodium . . . 0*20 



Chloride of potassium . . 023 



Potass 2*80 



Magnesia 0*52 



Lime 0*27 



6*00 



On the other hand, we find, in the case of the shifting crop, the average of nine 

 years' produce to be 89*1, or nearly 802 lbs. for the whole period, yielding of ashes 



about 7'3 lbs. 



from which must be deducted, as extraneous matter, about. . . . . . 0*7 



Leaving for real ash . . . . 6*6 



