1895.] PUBLIC DOCUMENT — No. 33. 311 



extended from the top to the bottom of the pot, connecting 

 at the base with a second tube of the same material, one 

 inch in diameter. This latter tube extended along the bot- 

 tom of the pot and was perforated with small holes. The 

 object of these tubes was to supply water partially from the 



bottom. 



The Soil. 



In order to test the availability of different sources of 

 nitrogen, the soil to be used for such a purpose should be as 

 poor in this ingredient as possible. If not naturally in such 

 a condition, it should be rendered so by previous cropping. 

 As we had not an ideal soil at hand for such a purpose, a 

 sandy subsoil was selected that was poor in all of the several 

 ingredients of fertility. It had the following composition : — 



Per Cent. 



Moisture when tested, 14.25 



Phosphoric acid, . .13 



Potassium oxide, , OS- 



Nitrogen, 09 



The Fertilizers used. 



In order to turn the nitrogen to the very best account, 

 phosphoric acid and potash must be supplied in excess. 



The sources of nitrogen were nitrate of soda, dissolved 

 leather and Philadelphia tankage. The Philadelphia tankage 

 has already been described. The dissolved leather was pre- 

 pared as follows : to 210 grams of c. p. sulphuric acid of 

 50° B., heated to 80° C, were added 63 grams of finely 

 ground sole-leather. The mixture was thoroughly stirred, 

 and allowed to stand for half an hour ; a dark pasty mass 

 resulted. Forty-nine grams of water were added to thin the 

 paste somewhat, and then finely ground calcium carbonate 

 (marble) was added, to take up the excess of sulphuric 

 acid, and enable us to secure a dry, easily handled material. 

 We used the carbonate instead of the phosphate of lime as a 

 dryer, in order to avoid an excess of phosphoric acid. After 

 standing twenty-four hours the substance had dried out 

 sufficiently to be easily handled and ground. 



Double superphosphate was used as a source of phosphoric 

 acid, and the potash was applied in the form of the double 

 sulphate of potash and magnesia. 



