306 AGRICULTURAL EXPERIMENT STATION. [Jan. 



One hundred and thirty-six grams of superphosphate were 

 obtained, which gave no tannic acid reaction. 



Experiment II. — To 30 grams of 50° B. sulphuric acid, 

 heated as above described, were added 12 grams of leather. 

 A dark, thick paste was obtained, to which were added 

 25 cubic centimeters of water and 33 grams of bone ash. 

 Seventy-three grams of superphosphate were obtained. 

 The reaction of tannic acid was not strong. 



Analyses of the two products were made as follows : — 



Per Cent. 



ir. 



Per Cent. 



Moisture,. 



Soluble phosphoric acid, 



Reverted phosphoric acid. 



Insoluble phosiohoric acid, 



Total phosphoric acid, 



Nitrogen, 



15.59 



11.80 



1.50 



3.38 



16.68 



1.20 



Experiments III, IV.., V., VI. — The previously described 

 Philadelphia tankage was used in these experiments, and 

 South Carolina floats in place of bone ash. The objects in 

 view were to see (a) how much leather could be used with- 

 out giving a tannic acid reaction, (6) to note, if possible, to 

 what extent the leather interfered with the action of the sul- 

 phuric acid upon the floats, (c) to notice the approximate 

 percentage of available phosphoric acid and nitrogen result- 

 ing, (d) to see if any nitrogen in the resulting superphos- 

 phates was soluble in water, (e) to note the amount of nitro- 

 gen in the superphosphate artificially digestible by Stutzer's 

 solution. To make this latter estimation (e), 5 grams of 

 superphosphate were stirred with water, filtered, and washed 

 till the wash water was no longer acid. The portion not 

 soluble in water was treated with pepsin solution. 



Experiment III. — To 30 grams of 50° B. sulphuric acid, 

 after heating, previously described, were added 12 grams of 

 Philadelphia tankage. A thick, black dough resulted. It 



