58 



but arbitrary, calcium bicarbonate concentration. An empirical 

 relationship has been found which enables such an interpolation 

 to be made from a single experiment. The Hutchinson-Mac- 

 Lennan method can give no indication of the intensity of soil 

 acidity, but it will serve a useful purpose in showing the amount 

 of lime needed to reduce this acidity considerably ; it gives guid- 

 ance as to the amount of lime to apply, where pH measurements 

 and other tests and observations have shown that lime is needed. 

 The interaction of soil with calcium acetate and dicalcium phos- 

 phate give results of the same type as those given with calcium 

 bicarbonate. Calcium carbonate suspensions, containing phenol 

 red or cresol red, show an almost instantaneous colour change 

 when poured on air-dry acid soil, owing to the decomposition of 

 some calcium carbonate. The interaction of acid soil with calcium 

 carbonate and water in full bottles liberates an amount of total 

 acid, as carbonic acid and calcium bicarbonate, which is greater 

 than that estimated by the Hutchinson-MacLennan method. Still 

 greater quantities of acid are liberated when water is percolated 

 through intimate mixtures of acid soil and calcium bicarbonate. 

 These differences are to be explained by the higher pH values of 

 the liquid at equilibrium, and the conditions approximate more 

 closely to those obtaining in the field. (See paper LXII.) 

 See also Paper LVI. 



XXXI. T. Eden. " The Edaphic Factors Accompanying 

 the Succession after Burning on Harpenden Common/' 

 Journal of Ecology, 1924. Vol. XII., pp. 267-286. 



The floristic survey of Harpenden Common shows the suc- 

 cession of vegetation after the periodical fires to be Rumex 

 acetosella, Holcus lanatus, Agrostis. Of the soil factors influenced 

 by burning those of soil reaction (in terms of the Hutchinson- 

 MacLennan Lime Requirement and pH measurement) and humus 

 content show a gradation accompanying the progress of the suc- 

 cession. The nature of the acidity and its probable relation to 

 the succession, the formation of humus and to burning are 

 discussed. 



(e) CHEMICAL PROPERTIES OF SOIL. 



XXXII. H. J. Page and W. Williams. " Studies on Base 

 Exchange in Rothamsted Soils/' Transctions of the 

 Faraday Society, 1925. Vol. XX., pp. 573-585. 



The content of exchangeable bases in the soil of certain plots 

 on Broadbalk field, and the Grass Plots, Rothamsted, has been 

 determined by Hissink's method. The results show that in the 

 soil of Broadbalk field, containing excess of chalk : — 



(a) The relative proportions of the different bases vary con- 



sistently with the manuring. In all the soils about 90 

 per cent, of the exchangeable bases (in equivalents) con- 

 sists of calcium. 



(b) The total content of exchangeable bases can be correlated 



with the amount of fine inorganic material (diameter of 

 particles less than 0.005 mm.) and of organic matter. 



