ELISHA MITCHELL SCIENTIFIC SOCIETY. 



125 



In the foregoing experiments the quantity of soil is constant ; 

 i. e., 32 times the content of soluble phosphoric acid in the super- 

 phosphate. It was thought desirable to ascertain if by increas- 

 ing the quantity of soil the precipitation would be correspond- 

 ingly increased, and to what extent this would take place. 



Soil Xo. 2, with 28.125 per cent, ferric oxide and alumina, 

 was taken for these experiments, because the change in soluble 

 phosphoric acid would be more marked on account of the larger 

 content of ferric oxide and alumina than in either of the other 

 three. 



The same acid phosphate was taken. The mixtures were made 

 in t he same way as previously but in different proportions, and 

 analyzed after seven weeks. 



Mixture A. — 1 gram acid phosphate to 4 grams soil Xo. 2 (as 

 in previous series), corresponding therefore to 1 part soluble 

 phosphoric acid to 32 parts soil. 



Mixture B. — J gram acid phosphate to 3 grams soil, corre- 

 sponding thus to 1 part soluble phosphoric acid to 96 parts soil. 



Mixture C. — \ gram acid phosphate to 4 grams soil, corre- 

 sponding therefore to 1 part soluble phosphoric acid to 128 

 parts soil. 



Mixture D. —\ gram acid phosphate to 6 grams soil, corre- 

 sponding to 1 part soluble phosphoric acid to 192 parts soil. 



The results obtained are recorded in Table IX, in which the 

 percentages of insoluble phosphoric acid arc corrected by sub- 

 tracting the quantity of phosphoric acid present in the varying 

 amounts of the soil. 



TABLE IX. 



SHOWING ACTION OF VARYING QUANTITIES OF SOIL No. 2 (WITH 28.12:. PER 

 CENT. OF FE 2 '»3 AND AL 2 r > 3 ) ON ACID PHOSPHATE (WITH 12.72 PER CENT 

 BOLUBLE PHOSPHORIC ACID AND 0.89 PER CENT. LNSOLUBLE PHOSPHORIC 

 \< il>) AT THE END OF SEVEN WEEK8. 



