by Contact of Liquids with Powdered Silica. 307 



1881, pp. 397, 398). Pockels states that the surface of water 

 has greater solvent power than the mass, and that a thin disk 

 of camphor partly immersed in a vertical position in water 

 having the cleanest possible surface is cut through in the 

 course of a few hours {ibid. March 12, 1891, p. 439). We 

 know that plates of metal partly immersed in a vertical 

 position in corrosive liquids are frequently cut through at the 

 air-contact line : this is often the case with anodes in electro- 

 lysis; and I have observed, whilst electrolytically depositing 

 pure grey antimony from its solution, the deposit spread from 

 the cathode over the surface of the liquid as if the surface 

 conducted better than the interior of the liquid. Mens- 

 brugghe, speaking of the cause of surface-tension and evapo- 

 ration of liquids, concluded that the molecules of the surface- 

 layer of a liquid are farther apart than those of the mass 

 (ibid. March 2, 1893, p. 428) ; he also observed that the 

 boiling-point of carbon bisulphide contained in the pores of 

 finely-divided carbon was higher than that of a mass of the 

 free liquid (Phil. Mag. July 1877, p. 43). I have shown that 

 when the molecules of a solid or liquid conducting substance 

 are separated farther apart by solution or dilution, they 

 acquire greater electromotive force due to increased mole- 

 cular volume ("A Relation of Electromotive Force to 

 Equivalent Volume and Molecular Velocity of Substances," 

 Proc. Birrn. Phil. Soc. 1892, vol. viii. pp. 63-138). 

 J. J. Thomson states that, with saline solutions, in some 

 cases the surface-film of the liquid contains more and in 

 other cases less salt per unit of volume than the interior ; 

 and that permanganate of potassium is removed from its 

 aqueous solution by trickling through pure silica (* Applica- 

 tions of Dynamics to Physics/ pp. 191, 192). It has long 

 been known that vinegar is to a certain extent separated from 

 water by pure quartz sand, and that when potato-brandy is 

 filtered through that substance, water passes through first, 

 then alcohol, and finally alcohol plus fusel-oil, as unaltered 

 liquid (Gmelin's ' Handbook of Chemistry/ vol. i. p. 114). 

 Further, in a recent research on the " Decomposition of Liquids 

 by Contact with Powdered Silica," I have found that on agi- 

 tating various aqueous solutions of acids, alkalies, and salts 

 with finely precipitated pure silica and allowing the pow 7 der to 

 subside, the latter substance in many cases abstracts a larger 

 proportion of the dissolved compound than it does of the 

 water, and in a number of cases less (see Proc. Birm. Phil. 

 Soc. 1894, vol. ix. part 1, pp. 1-24), and that in some 

 instances it abstracts more than 80 per cent, of the dissolved 

 substance. 



It is generally recognized by physicists and chemists that 



