306 AGRICULTURAL EXPERIMENT STATION. [Jan. 



One hundred and thirty-six grams of sxiperphosphate 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 culiic 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 : — 



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

 Philadelphia tankage was used in these experiments, and 

 South Carolina floats in place of ])one ash. The objects in 

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

 out giving a tannic acid reaction, (b) 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 artiticially digestible by Stutzer's 

 sohition. 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 

 solul;le in water was treated with pepsin solution. 



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

 after heating, previously described, Avere added 12 grams of 

 Philadelphia tankage. A thick, black dough resulted. It 



