PAPERS OX CHEMISTRY AND PHYSICS 



309 



It is interesting to note that according to these esti- 

 mates, rock phosphate is worth $3.20 a ton, while acid 

 phosphate is priced at $16.89 a ton. In spite of this 

 difference in price, acid phosphate ordinarily contains 



8 s 



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 0.0 



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43.5 



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Percant EeccTery 



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Fig. 1. Percent phosphorus recovery from Tennessee rock phosphate 

 and double acid phosphate after different soils were treated with 

 these substances in proportion of 4 nigs, of phosphorus per 23 gms. of 

 soil; normal fifth nitric acid was used for extraction. 



only one-half of the amount of phosphorus found in rock 

 phosphate from which it is being prepared. 



It is a mooted question among soil workers as to which 

 of the two phosphatic fertilizers is hotter and the more 

 economical to apply to the soil for crop production and 



