26 



The amount of phosphoric oxide actually determined by the analyst 

 is, therefore, not the true amount dissolved, but the difference between 

 these two wholly different actions. 



It is now obvious why the amount of "available Phosphoric Oxide " 

 determined by extraction with dilute acids shows such great variations 

 in different methods of analysis and so little correlation with the actual 

 quantities obtainable by the crop. In no case do they stand for any 

 single quantity, but only for a difference between a direct action and 

 an adsorption which varies with the nature of the acid and the con- 

 ditions of the experiment. 



So long as they are confined to the same type of soil, however, any 

 of the acids investigated would have given useful results, but difficulties 

 would arise directly an attempt was made to compare dissimilar soils. 

 The proper way to use a soil analysis is in conjunction with a soil 

 survey. 



A diffusion method is described in which the reverse reaction is 

 eliminated and which therefore gives a true measure of the direct 

 action. But until we have had more experience with it we are not 

 prepared to say what value it has for soil analysis. 



IX. " The Phenomenon of Adsorption in its Relation to Soils." 



James Arthur Prescott. Journal of Agricultural Science, 

 1916. 8, 111-130. 



A resume of the subject in which the voluminous literature is 

 critically examined and summarised. Several directions are indicated 

 in which more investigations are needed. 



X. " Note on the loss of Phosphoric Acid during Fusion with 



Ammonium Fluoride. W. A. Davis and J. A. Prescott. 

 Journal of Agricultural Science, 1916. 8, 136-138. 



Considerable loss of phosphoric acid may occur when salts or 

 minerals containing this substance are ignited with ammonium 

 fluoride in the ordinary process of analysis of silicates. It seems 

 possible that the phosphorus is volatilised as a fluoride. The loss is 

 least in the case of salts containing an alkali metal, but is greater for 

 phosphates of the alkali earth metals, such as apatite and other calcium 

 phosphates. 



XL The Recovery of Ammonium Molyhdate used in phosphate 

 Estimations. J. A. Prescott. The Analyst, 191 5. 40, 

 390-391- 



The mixed residues are acidified if excess of acid is not already 

 present and evaporated to small bulk. The yellow precipitate of 

 molybdic acid which separates is filtered off, washed with cold water, 

 dissolved in ammonia and freed from phosphoric acid by means of 

 magnesia mixture. The filtered solution is concentrated, keeping 

 ammonia present in excess, and allowed to crystallise. 



If the solution is blue owing to the presence of lower oxides of 

 molybdenum it is treated with hydrogen peroxide. 



XII. " Studies of the Lime Requirements of Certain Soils. Henry 

 Brougham Hutchinson and Kenneth MacLennan. 

 Journal of A(^ri<ultural Science, 1915. 7, 75-105. 



