1895.] PUBLIC DOCUMENT — No. 33. 309 



In Experiment VII. 8.95 per cent, of available phosphoric 

 acid was obtained, with but 1.94 per cent, of insoluble acid 

 and .90 per cent, of nitrogen; the phosphate was also in 

 STood mechanical condition and gave no tannic-acid reaction. 

 The proportions of water, sulphuric acid, floats and leather 

 appear to be about correct, and the percentages of available 

 phosphoric acid and nitrogen as high as could be expected, 

 with floats as a dryer. 



Experiment IX. — In experiments III. to VIII. Philadel- 

 phia tankage was used as a source of leather. 



In this experiment pure fine-ground sole-leather was used, 

 to see if the sulphuric acid acted as strongly upon the pure 

 leather as upon the prepared article. To 30 grams of 50*^ B. 

 acid were added 9 grams of sole-leather, 20 cubic centimeters 

 of water and 60 grams of floats. 



The resulting phosphate weighed 98.5 grams. 



Analysis gave the following results : — 



Per Cent. 



Total nitrogen in tlie superphosphate, 710 



Total nitrogen after digestion, 220 



Total nitrogen digested, 69.000 



Nitrogen soluble in water 047 



Per cent, of soluble nitrogen, 6.620 



No tannic acid could be detected in this superphosphate. 

 The artificial digestion of the nitrogen was made by taking 

 5 grams of the substance, washing out the soluble phosphoric 

 acid with water, and proceeding in the usual manner. 



It is to be noted from the above figures that the nitrogen 

 in the sole-leather thus treated was as digestible as is the 

 average animal matter sold for fertilizing purposes. 



Practical Deductions. 

 The various experiments made would indicate that leather, 

 sulphuric acid, water and floats should be mixed in about the 

 following relative proportions : — 



Pounds. 



Sulphuric acid, 50^ B 2,000 



Ground leather, 600 



Water 800 



Floats, 2,700 



