-572 Dr. G. E. Allan 



on 



even when the surface-layers become saturated, so that the 

 solute separates out in a solid form. 



The results of these experiments do not support this view. 

 In the first place, the rate o£ surface separation varies in an 

 irregular manner quite inconsistent with the above theory. 

 Secondly, there is no sign of equilibrium even after a pro- 

 longed period. Thirdly, this theory does not explain the 

 initial thickening and subsequent thinning of the surface- 

 layer, which occurs in the case of strong solutions of peptone 

 ■and albumin. 



The results indicate that the process is of a much more 

 complex character than simple " capillary-osmotic " action. 

 It is possible that the substance of the surface-layer differs 

 chemically from the original solute. This view was put 

 forward by Metcalf * as the result of experiments on surface- 

 films formed by allowing a drop of peptone solution to spread 

 over a water surface. At present I am engaged on a series 

 of experiments on surface-layers formed at the interface 

 between solutions of saponine, peptone, and albumin, and 

 hydrocarbon oils. This case, though more difficult to inves- 

 tigate practically, possesses theoretical advantages due to the 

 absence of evaporation and chemical action between the two 

 media. 



The University, Leeds. 

 Dec. 21st, 1908. 



LI. Magnetism of Basalt. ByG.E. Allan, D.Sc, Lecturer 

 on Electricity, Pure and Applied, and Assistant to the Pro- 

 fessor of Natural Philosophy , in the University of Glasgow^ . 



IN a previous paper J it was shown that bars of basalt 

 heated in air undergo a magnetic change, partly tem- 

 porary and partly permanent. In general the permanent 

 effect consists in a loss of magnetic susceptibility. Some 

 instances of an increase have, however, been observed. The 

 temporary effect is, roughly, similar to that in magnetite ; 

 the bar reaches a state of maximum strength, which is 

 followed by a state of minimum strength at a temperature 

 which is not the same for all, but is, for the majority of cases 

 examined, in the neighbourhood of 600° C. 



In order to obtain further information as to the behaviour 

 of such material, tests were carried out on new bars of 



* Zeit.fiir Phys. Chem. vol. lii. p. 1 (1905). 

 t Communicated by Professor A. Gray, F.R.S. 

 X Phil. Mag. January 1904, p. 45. 



