* 206 SCIENCE PROGRESS. 



Can the method proposed be applied to soils containing 

 variable amounts of calcium carbonate, which will of course 

 neutralise the citric acid? If calcium carbonate is mixed 

 with a soil, of which the composition by the citric method is 

 already known, can the former result be again obtained by 

 extracting it with citric acid ? 



What is the solvent action on phosphates and potash of 

 citric acid of strengths below one per cent, when working 

 on a poor and rich Rothamsted soil ? Is the action of the 

 citric acid modified by the presence of calcium citrate in 

 solution ? 



For the further elucidation of the subject it is important 

 that some typical soils should be extracted with acetic acid, 

 and with ammonium citrate, as well as with citric acid. 



There are a number of very interesting and important 

 facts in Dr. Dyer's paper which we cannot now call atten- 

 tion to as they do not belong to our present subject. We 

 must not, however, end the present paper without referring 

 to the entirelv different view as to the condition of the avail- 

 able plant food in soil which has been proposed by L. 

 Grandeau. 



Grandeau was led by his investigations to believe that the 

 effective mineral plant food in a soil was always in combina- 

 tion with humic matter, and that this humic matter was the 

 indispensable vehicle necessary to transfer this mineral food 

 to a growing plant. Fertile soils, he said, offer their mineral 

 ingredients to plants in a state similar to that in which they 

 are contained in farmyard manure. His plan of analysis 

 was first to subject the soil to a preliminary extraction with 

 very dilute hydrochloric acid to decompose the humates and 

 remove basic matter, and then to extract the residual soil 

 with ammonia. The dark-coloured solution thus obtained 

 was evaporated to dryness, the residue ignited, and the 

 mineral matter left was determined by ordinary methods of 

 analysis. 



Grandeau's method has been submitted to a careful 

 study by O. Pitsch (Landw. Versucks. Stat., xxvi., i). 

 Having examined many soils by this method, but appa- 

 rently chiefly with regard to their richness in phosphoric 



