59 



(c) There is probably a gradual conversion of exchangeable 



potash to a non-exchangeable form, or vice versa, 



depending on whether potash manures are used or not. 



In the acid soil of the Grass Plots, from which chalk 



is absent, the soils are all unsaturated, and the amount 



of exchangeable calcium can be correlated with the pH 



of the soil. 



The bearing of these results on current theories of base 



exchange in soils, and on the relation between soil acidity and 



ionic exchange, is discussed. 



XXXIII. N. N. Sen Gupta. " Dephenolisation in Soil, 

 Part II." Journal of Agricultural Science, 1925. 



Soils possess the power of destroying" phenol under conditions 

 precluding the possibility of biological action. This power, which 

 is greatly increased by preliminary acid-treatment of the soil, 

 varies greatly from soil to soil. It is shown that this chemical 

 dephenolising power of soils depends upon the presence of an 

 oxidising agent, and that most of the action is due to the presence 

 of manganese in the soil, probably in the form of manganese 

 dioxide. 



(/) CHEMICAL ANALYSIS. 



XXXIV. T. Eden. " A Note on the Colorimetric Estima- 

 tion of Humic Matter in Mineral Soils." Journal of 

 Agricultural Science, 1924. Vol. XIV., pp. 469-472. 



An application to mineral soils of the method worked out 

 for peat soils by Oden. 



XXXV. H. J. Page. " On the Perchlorate Method for the 

 Estimation of Potassium in Soils, Fertilisers, etc." 

 Journal of Agricultural Science, 1924. Vol. XIV., 

 pp. 133-138. 



The presence of chloric acid in the perchloric acid used for 

 the estimation of potassium in soils, fertilisers and plant material 

 by Davis's method gives rise to very erratic and erroneous results. 

 Every sample of perchloric acid should, therefore, be tested for 

 freedom from chloric acid before being used for the estimation 

 of potassium. 



In the application of Neubauer's method of treatment of the 

 soil extract to a soil deficient in carbonates, it is sufficient to add 

 only 0.1 gm. of calcium carbonate to the extract instead of the 

 0.5 gm. generally used. A considerable economy of perchloric 

 acid is thereby effected. 



XXXVI. E. M. Crowther and W. S. Martin. " The 

 Volumetric Determination of Total Carbonic Acid in 

 Dilute Solutions of Calcium Bicarbonate." Journal of 

 the Chemical Society, 1924. Vol. CXXV., pp. 1937- 

 1939. 



In the course of studies on soil reaction (papers XXVII- 

 XXX), it was found that the standard method for the deter- 

 mination of total carbonic acid (excess barium hydroxide and 



