164 HOW CEOPS GEOW. 



sential, and what are really accidental ingredients, or what 

 amount of any given ingredient is essential, and to what 

 extent it is accidental. Wolff, who appears to have first 

 suggested that a part of the ash of plants may be acci- 

 dental, endeavored to approach a solution of this question, 

 by comparing together the ashes of samples of the same 

 plant, cultivated under the same circumstances in all re- 

 spects, save that they were supplied with unequal quantities 

 of readily available ash-ingredi6nts. The analyses of the 

 ashes of buckwheat-stems, just quoted, belong to this in- 

 vestigation. "Wolff showed that, by assuming the presence 

 in each sjpecimen of buckwheat-straw of a certain excess 

 of certain ingredients, and deducting the same from the 

 total ash, the residuary ingredients closely approximated 

 in their proportions to those observed in the crop which 

 grew in an unmanured soil. The analyses just quoted, 

 (p. 163,) are here " corrected" in this manner, by the sub- 

 traction of a certain per cent of those ingredients which 

 in each case were furnished to the plant by the fertilizer 

 applied to it. The numbers of' the analyses correspond 

 with those on the previous page. 



12 3 4 5 6 



SOp.c. 20j7. c. 25 7). c. 8.5??. c. 16.6^, c. 



Chloride Carbonate Carbonate Sulphate Carbonates 



After deduction of of of of of lime and 



of NofMng. potassium, potash, potash, rrutgnesia. maonesia. 



Potash 31.7 ST.O 33.5 33.5 30.6 28.0 



Chloride of potassium. 7.1 9.1 1.0 3.9 7.4 11.8 



Chloride or sodium 4.6 3.8 4.0 4.7 3.7 1.9 



Lime 15.7 17.3 16.0 14.5 15.3 14.6 



Magnesia 1.7 2.4 4.1 1.7 2.3 2.9 



Sulphuric acid 4.7 3.5 3.4 5.4 2.1 4.1 



Phosphoric acid 10.3 11.7 8.1 11.2 11.8 11.7 



Carbonic acid 20.4 20.1 25.9 19.8 21.6 19.3 



Silica 3.6 5.2 5.2 6.3 5.2 6.1 



100.0 100.0 100.0 100.0 100 100.0 



The correspondence in the above analyses thus " cor- 

 rected," already tolerably close, might, as Wolff remarks, 

 (loc. cit.) be made much more exact by a further correc- 

 tion, in which the quantities of the two most variable in- 



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