51 



from what physical observations the required distribution curve 

 may be derived, and verifying- Oden's formula. 



(tt) A criticism of Schloesing's sedimentation formula. 



(Hi) The development of practical methods for the statistical 

 treatment of the readings of the automatic balance in order to 

 derive the required curve of size distribution. 



(iv) An examination of the degree of accuracy obtained in a 

 duplicate experiment carried out on Rothamsted soil, by the 

 Physical Department ; and of the incidence of random and 

 systematic errors in this experiment. 



(v) A discussion of the causes of error in the current 

 technique, and of the means of control of the fluid motions to 

 which they appear to be due. 



(b) PHYSICAL PROPERTIES OP SOIL. 



XVIII. B. A. Keen. " Recent Advances in Soil Physics/' 

 Proceedings of the Fourth International Conference 

 on Soil Science. (Int. Inst, of Agric, Rome, 1924.) 



A review of work in this subject since 1900, and a critical 

 discussion of some outstanding problems. 



XIX. E. M. Crowther and J. R. H. Coutts. " A Dis- 

 continuity in the Dehydration of Certain Salt 

 Hydrates/' Proceedings of the Royal Society. A., 

 1924. Vol. CVI., pp. 215-222. 



During a preliminary study of the evaporation of water from 

 soils and colloidal material, experiments were made with the 

 simplest solid systems, viz. ? crystalline hydrates, using the auto- 

 matic balance (paper XVI). In the evaporation of water from 

 CuS0 4 .5H 2 and BaCl 2 .2H 2 at 100°C, a marked discontinuity 

 was noticed. The evaporation proceeded rapidly up to 

 the formation of the definite hydrates CuSO^.SHjO and 

 BaCl 2 .lH 2 0, but was almost completely interrupted at these 

 points. After varying periods the evaporation recommenced and 

 proceeded rapidly to the formation of CuSO d . 1H 2 and BaCl 2 . 

 A tentative explanation is advanced, based on Langmuir's treat- 

 ment of actions at surfaces. 



XX. B. A. Keen. " On the Moisture Relationships in 

 an Ideal Soil." Journal of Agricultural Science, 1924. 

 Vol. XIV., pp. 170-177. 



This paper consists of a critical examination of a portion of 

 Wilsdon's theoretical investigation on moisture relationships. 

 Wilsdon's investigations appeared to show that the maximum 

 moisture holding capacity of an ideal soil (i.e., one built up of 

 uniformly packed solid spheres all having the same radius) was 

 23.46 per cent. Further, his experimental and theoretical work 

 indicated that the total amounts of water held by the soil colloids, 

 as distinct from the i( free " or interstitial water was 4.7 x (Hygro- 

 scopic Coefficient). The total moisture holding capacity of an 

 ordinary soil would therefore be : — 4.7 x (Hygroscopic Co- 

 efficient) + 23.46, which is remarkably close to Briggs' well 



