522 ANNUAL REPORT OF THE Off. Doc. 



FEKTILIZEKS ANALYSES AUGUST 1 TO DECEMBER 31, 1915. 



Since August 1, 1915, there have been received from authorized 

 sampling agents eight hundred and fifty-four fertilizer samples, of 

 which three hundred seventy-one were subjected to analysis. Prefer- 

 ence was given to those which have not been recently analyzed. In 

 cases where two or more samples representing the same brand were 

 received, equal portions from several samples were united, and the 

 composite sample was subjected to analysis. 



The samples analyzed group themselves as follows: 233 complete 

 fertilizers, furnishing phosphoric acid, potash and nitrogen; 33 dis- 

 solved bones, furnishing phosphoric acid and nitrogen; 47 rock-and- 

 potash fertilizers, furnishing phosphoric acid and potash; 39 acidu- 

 lated rock phosphates, furnishing phosphoric acid only; 19 ground 

 bones, furnishing phosphoric acid and nitrogen, and 7 miscellaneous 

 samples, which group includes substances not properly classified 

 under the foregoing heads. 



The determinations to which a complete fertilizer is subjected are 

 as follows: (1) Moisture, useful for the comparison of analyses, for 

 indication of dry condition and fitness for drilling, and also of the 

 conditions under which the fertilizer was kejit in the warehouse. (2) 

 Phosphoric acid — total and insoluble; the latter is that portion not 

 soluble in water nor in warm ammonium citrate solution (a solution 

 supposed to represent the action of plant roots upon the fertilizer), 

 which is assumed to have little immediate food value. By difference, 

 it is easy to compute the so-called "available" phosphoric acid. (3) 

 Potash soluble in water — most of that present in green sand marl and 

 crushed minerals, and even some of that present in vegetable mate- 

 rials such as cotton-seed meal, not being included because insoluble 

 in water even after long boiling. (4) Nitrogen — This element is 

 determined in such a manner as to ascertain its total quantity and 

 also, the quality of the organic nitrogenous material present in the 

 finished fertilizer. The fertilizer is washed thoroughly with water, 

 which removes the nitrates, ammonium salts and almost all of the 

 cyanamid nitrogen, and the soluble organic nitrogenous mate- 

 rials. These are not separately determined, but are grouped 

 under, the name "water-soliihle nitrogen." The quantity of 

 water -insohihle nitrogen is directly determined, and by difference 

 between its amount and the total nitrogen, the water-soluble 



