SECTIONAL TRANSACTIONS.— B, C. 325 



Dr. N. V. SiDGWiCK, F.R.S. — Di-pole association in liquid mixtures. 



The molecular polarisation of a polar substance in a non-polar solvent 

 varies with the concentration, usually being greatest at infinite dilution, but 

 rarely (alcohols) rising to a maximum and then falling. This phenomenon 

 is called di-pole association. It may be due either to an orientation of the 

 molecules by the di-pole forces, or to their polymerisation. Its correct 

 interpretation is important as throwing light on the relations between the 

 molecules in a liquid. 



The marked case of nitrobenzene, whose molecular polarisation is five 

 times as great at infinite dilution as in the pure liquid, has been investigated 

 both electrically and cryoscopically by various authors. The ' degree of 

 association ' x can be calculated on the hypothesis that non-polar double 

 molecules are formed. In benzene the values of x obtained electrically and 

 cryoscopically agree roughly up to about 2-normal solutions {x by polarisa- 

 tion 0-46, by F.P. 0-57). But the mass-action association 'constant' 

 rises considerably (at ts normal 0-26 ; at 2-normal 0-39 and 0-77 respec- 

 tively). This shows that the association is not due to a definite polymerisa- 

 tion, but to an orientation of the polar molecules which diminishes their 

 activity. 



Dr. J. A. V. Butler. — Free energies of normal aliphatic alcohols in water. 



SECTION C— GEOLOGY. 



Thursday, September 1. 



Mr. C. E. N. Bromehead.^ — The geology of the York district and the 

 excursions. 



Reports of Research Committees. (See pp. 284, 299.) 



Miss E. W. Gardner. — Some problems of the Pleistocene hydrography of 

 the Kharga Oasis, Egypt. 



Kharga Oasis, 100 miles W. of the Nile, is a depression 300-400 metres 

 below the level of the Libyan Plateau . Eocene and Cretaceous rocks form 

 scarps on the northern and eastern sides. 



The Scarp.— Tuia is found along the eastern scarp and is of two types : 



(a) Plateau tufa, a massive rock practically devoid of life. 



(b) Wadi tufa, a softer, more cellular type of wider distribution. It 

 contains seven kinds of plants, and eight land and eight fresh-water 

 gastropods. It is considered to have been formed by chemical aggradation, 

 in a manner similar to tufa deposition at the present day in Brazil, and called 

 there ' Catinga ' type. 



Associated tools date the wadi tufas to three different periods : 

 (i) Lower Palaeolithic — Acheulean. 



(2) Transitional — Acheuleo-Levalloisean . 



(3) Middle Palaeolithic — Pre-Sebilian. 



Of these (2) was the longest and most important. 



The Floor of the depression was supplied in Pleistocene times by ' mound ' 

 springs, which are associated in groups. They have been formed by water 

 under pressure breaking through Cretaceous clays. 



The structure of the mounds suggests periods of relative quiescence and 



