J. A. Prescott 



117 



Ahsor'ption of acid radicals. 



The absorption of acid radicals has not been much discussed, chiefly 

 because the early workers invariably found as much CI, SO4, or NO3 in 

 all their solutions after as before treatment with a soil. In the case 

 of phosphoric acid the problem has been automatically removed from 

 the discussion because most soils contain sufficient lime to precipitate 

 soluble phosphates chemically. The soil phosphates have therefore 

 been divided up into available or unavailable classes according to 

 their solubility. Recent work however has shown that phosphoric 

 acid can be physically absorbed by a soil in the presence of excess of 

 acids like citric, nitric or hydrochloric acid. This absorption is discussed 

 elsewhere^. The absorption of oxalic and citric acids (see p. 124) has 

 been observed by the author to take place in the presence of nitric or 

 hydrochloric acids. U. Pratolongo^ has shown that there may be 

 two distinct processes — with soils containing no lime, absorption of 

 phosphoric acid from monocalcium phosphate solution is practically 

 instantaneous, with a soil containing much calcium carbonate there is 

 a further slow fixation of phosphoric acid after the initial absorption. 

 The immediate process is regarded as an absorption, the second as preci- 

 pitation. His results are as follows : 



The absorption of other acid radicals has not yet been observed in the 

 case of soils. 



Effect of Temperature. 



Small changes in temperature seem to be without appreciable effect 

 on absorption, but W. Schuhmacher^ found that at high temperatures 

 the absorption was usually less than at low temperatures. 



1 See Proc. Ckem. Soc. 1914, 30, 123, and this Journal, p. 05 

 - Le Stazioni Sperimentali Agrarie, 1915, 48, 457. 

 3 Ann. der Lanchc. 1867, 49, 322. 



