INSTITUTE, PUSA, FOR 1919-20 35 



The results of experiments so far tried indicate that rapid 

 and accurate determinations may bcrnade by the Kjeldahl- 

 Gunning- Arnold, by Dyer's modification of Kjeldahl 

 method and by the Gunning method as followed at Pusa. 



Phosphoric acid. In all the methods tried the results 

 obtained were compared with the figures obtained by the 

 standard magnesia method. Mention may be made here of 

 the methods which appear to be promising amongst those 

 studied so far. The Pemberton-Kilgore method which is 

 the one in use in this laboratory gives accurate figures. In 

 the case of substances like superphosphate, ashes, etc., the 

 phosphoric acid can also be quickly and fairly accurately 

 determined by titration with standard alkali. The pro- 

 cess consists essentially in rendering the solution of phos- 

 phate just neutral to methyl orange, adding an excess of 

 neutral calcium chloride and then titrating until alkaline 

 to phenol-phthalein. The volumetric estimation of phos- 

 phoric acid by silver nitrate solution has its limitations but 

 it is capable of yielding good results under certain condi- 

 tions. 



VI. The retention of soluble phosphates in 



CALCAREOUS AND NON-CALCAREOUS SOILS. 



The investigations in regard to the retention of phos- 

 phoric acid in calcareous and non-calcareous soils referred 

 to in previous years' reports have now reached a stage 

 which has enabled Dr. Harrison to submit them. for publi- 

 cation. Consequently, a brief summary of the whole in- 

 vestigation is now given. 



It used at first to be maintained that the retention of 

 soluble phosphoric acid of superphosphate by the soil is 

 simply due to the precipitation of phosphate of lime and 

 later on of phosphates of iron and alumina. The precipi- 

 tated phosphate being exceedingly finely divided and being 

 thoroughly disseminated in the soil was accounted to pro 

 vide a -continuous supply of phosphoric acid to the roots of 

 the growing plant. Evidence, however, soon accumulated 



which tended to show that this simple explanation did not 



d2 



