i8 



is here meant the soluble organic matter extracted with a 2 per 

 cent solution of ammonia, after treating the soil with a dilute 

 solution of hydrochloric acid. The "humic phosphoric acid" is 

 the phosphoric acid present in the extractive material. Humic 

 phosphoric acid proved to be one of the most valuble forms. 



Dumont 1 investigated the absorbing power of several organic 

 soils containing humus and lime. Mono-calcium phosphate was 

 applied in aqueous solution before and after calcination of the 

 soil. Calcination seemed to decrease the immediate, but increased 

 the final absorption of phosphoric acid. These results were con- 

 strued as proving the combination of humus with phosphoric 

 acid. The quantities of lime present appeared to have same 

 effect on the absorption, but the relationship of lime, humus, and 

 phosphoric acid was not well defined. Mono-calcium phosphate 

 was also applied to precipitated humus. Absorption took place 

 in the ratio of humus 10, to P 2 O 5 i. Precipitated humus was not 

 defined. 



The use of ferrous sulphate in agriculture, has not been the 

 object of much experimental enquiry. Griffiths 2 , however, ob- 

 tained some very interesting practical results by its use, and his 

 work is taken up here because of its bearing on the behavior of 

 phosphoric acid in the soil. 



The material was applied at the rate of 50 Ibs. per acre. 

 Among the crops grown were hay, mangels, beans, potatoes, and 

 wheat. Applied with farmyard manure, its action was injurious, 

 the poisonous effect being due to the formation of ferrous sul- 

 phide. The crops in nearly all other cases were increased largely 

 and the percentage content in phosphoric acid was increased in all 

 cases. The ferrous sulphate was not oxidized rapidly in the soil, 

 its presence being proven six weeks after application. Ferrous 

 sulphate was used in conjunction with superphosphate in all tests. 



The subject was taken up a little later by Delacharlony and 

 Destremx 3 . They found that the sulphate was productive of in- 

 creased yields only when the soil contained small quantities of 

 iron, the increase ceasing when the ferric oxide reached 3 per 



1 Compt. rend., 1901, 132, 435. 



2 Jour. Chem. Soc., Trans. 1884, 71. 1886, 114, 1887, 215. 



3 Bied. Centr., 1889, 9. 



