236 



DR. DAUBENV ON THE ROTATJON OF CROPS, ETC. 



Silica . . . . . . . . 0-165 



Phosphoric acid . . . 0540 



Sulphuric acid . . . . 0*470 



Carbonic acid .... 0430 



Chloride of potassium . 0*270 



Potass 1*930 



Magnesia . . . . . 0*255 



Lime 0*520 



4*580 



The next crop I shall consider is hemp, of which the permanent crop, according to 

 the statements given in the first part of this paper, would have amounted in nine 

 years to 271*25 lbs., or 30*13 lbs. per annum, yielding of ash 16*27 lbs. 

 For as 100--6*0— 271*25— 16*27. 



Now 16*27 lbs. of ash would contain 

 of extraneous matter about 2*27 



leaving 14*00 of inorganic principles belonging to the plant, 

 which would consist of — 



Silica 1*30 



Phosphoric acid .... 0*70 



Sulphuric acid .... 0*17 



Carbonic acid .... 3*07 



Chloride of sodium . . . 0*06 



Soda 0*08 



Potass 1*10 



Magnesia 1*40 



Lime 6*12 



14*00 



Now the average of the shifting crops for seven crops was 40 lbs., and as the ash 

 obtained was about 7 per cent, its whole amount would have been 2*8 lbs. 



lbs. 



Or in seven years (2*8x7)=l9*6 



Of which the extraneous matter would be about 2*3 



Leaving of inorganic principles extracted from the earth in seven years 17*3 



Or, if in seven years — 17'3 — nine years . . 22*17 



Now 17*3 lbs. of inorganic principles consist of 



2*19 

 1*52 

 0*18 

 5*10 

 0*15 

 0*04 

 1*90 

 1*29 

 9*80 



17*20 2217 



