New York Agricultural Experiment Station. 253 



The above figures show clearly that the phosphoric acid in the 

 iron ore waste had little availability. Moreover, the results cor- 

 roborate those previously given as to the inability of graminaceous 

 plants to utilize freely the ground untreated phosphates, such as 

 Tennessee rock. 



These tests, with some preliminary analyses, present some inter- 

 esting data regarding the chemical methods for determining avail- 

 able phosphoric acid. In planning the tests, it became necessary 

 to know the amounts of total P 2 5 in the different materials in 

 order to apply equal amounts in the different boxes. These deter- 

 minations were made by A. W. Clark, Assistant Chemist ; and he 

 also analyzed the samples for available P 2 5 by both the official 

 method and the Wagner method. These results are shown in the 

 last two columns of Table XIV. The official method gave little 

 P 2 5 in either the iron ore waste or the ground rock, yet the 

 barley made some growth on both. Rather hasty scrutiny showed 

 that the results by the Wagner method approached nearer to the 

 measure of utilization of phosphorus by the barley; and compu- 

 tations gave the data shown in Table XV. 



Table XV. — Relative Availability op Phosphoric Acid from Different 



Sources as Measured by Chemical Methods 



or Shown by Plant Production. 



Monocalcium phosphate taken as base. 



* The relation, expressed as percentage, which the amount of available phosphoric acid in these 

 boxes bears to that in the corresponding mono-calcium phosphate boxes. 



The increase of plant production was found by subtracting the 

 weight of dry matter produced on the check boxes from that 



