[shutt] 



NITRE CAKE AND SUPERPHOSPHATE 



143 



citric acid and shaken for 5 hours in a mechanical shaker and filtered. 

 The phosphoric acid as determined in the filtrate is denoted in the 

 tables of analyses as "1 per cent citric soluble." Determinations 

 of the water soluble and ammonium citrate soluble phosphoric acid 

 were also made according to the official methods of the Association 

 of Agricultural Chemists, generally adopted on the American continent 

 in the official analysis of fertilizers. 



The composition of the Florida pebble phosphate and the Can- 

 adian Apatite used in the experiments, is as follows: 



Analysis of Florida Pebble Phosphate and Canadian Apatite 



Canadian Apatite 



Total phosphoric acid 



equivt. to tricalcic phosphate. . . 

 One per cent Citric sol. phos. acid. 



equivt. to tricalcic phosphate. . . . 

 Citrate soluble phos. acid A.O.A.C. 



equivt. to tricalcic phosphate. . . . 

 Water-soluble phosphoric acid. . . 



39-40 



86-05 

 6-06 

 13-24 

 nil 



Discussion of Results 



Tables I. and II. set forth clearly the results obtained in this 

 investigation and will need but little explanatory text. The per- 

 centages of phosphoric acid as rendered available in the several mixes, 

 as determined by treatment with water and 1 per cent citric acid 

 solution and by the A.O.A.C. methods, are stated and the percent- 

 ages of the total phosphoric acid in the mixes so converted are also 

 given. Certain of the more important results maybe briefly emphasized 

 as follows : 



Table I. — Florida Pebble Phosphate 



Dry Mix: The highest percentage of available phosphoric 

 acid, as obtained by using water and 1 per cent citric acid solution 

 as solvent, resulted from the 1 to 1 mixture. This product contained 

 15-77 per cent, of which 6-83 per cent was soluble in water. This 

 indicates that of the total phosphoric acid in the mix, 97-6 per cent 

 had been converted into more or less available form. This is closely 

 followed by the mix, 0-5 nitre cake to 1 F. P. Phosphate, which by 

 the same analytical method is seen to contain 15-38 per cent of avail- 

 able phosphoric acid. Since the percentage of total phosphoric acid 



