RECENT WORK IN AGRICULTURAL SCIENCE. 



CHEMISTRY. 



On the chemical determination of the agricultural value of dif- 

 ferent natural phosphates, G. Paturel {Ann. Agron., 20 {1S9-I), 

 No. 7, 2)p. Hl()-348). — After briefly reviewing tlie work of other investi- 

 gators on the assimihibility of x)ho«phoric acid in soils and i)hosphates, 

 the author reports in detail investigations relating to the action of the 

 acids contained in the roots of plants, particularly citric acid, and acids 

 contained in soils, especially acetic acid, on natural phosphates. 



These experiments were undertaken principally to determine what 

 basis there is for the preference given h\ practice to the Boulonnais 

 phosphates as compared with the Somme phosphates. 



In preliminary experiments it was found that citrate and oxalate of 

 ammonia did not give reliable indications as to the assimilability of the 

 natural phosphates in the soil. The weak acids (acetic acid proposed 

 by Deherain and citric acid proposed by B. Dyer) appeared to give 

 results to some extent comparable with those produced by the acids of 

 the soil and of the roots of plants. 



The acid reaction is very general in vegetable substances, especially 

 in roots, but the study of tliese acids is accompanied by the difficulty 

 of securing a sufficient amount of the roots for extraction. By using 

 potato tubers, however, the author obtained an acid extract which was 

 found to contain citric acid. This extract was used for the purpose of 

 testing the extent of the action of the root acids upon various mineral 

 substances, such as marble, apatite, etc., and the results were found to 

 fully confirm those reported by Sachs. 



When the Boulonnais and Somme phosphates were treated with citric 

 acid solution the quantity of phosphoric acid dissolved was much higher 

 in the case of the former, a result which conforms to the preference 

 given to this phosphate in practice. However, it appears that the 

 difference in assimilability was not due to the difference in hardness 

 of the two materials, but to a difference in coutentof carbonate of lime, 

 the Boulonnais phosphate containing 7 per cent of this substance 

 while the Somme phosphate contained .'53 per cent. 



Q'he difference in assimilability of phosphoric acid can not be explained 

 by simple saturation of the citric acid by the carbonate. The latter 

 appears to x^resent a special obstacle to solution, for a .'^mall quantity 



187 



