1905-6.] Electrolysis through Precipitation Films. 
447 
Electrolysis through Precipitation Films. Part I. By 
W. S. Millar, M.A., B.Sc., Carnegie Research Scholar, and 
Dr W. W. Taylor. Communicated by Professor Crum 
Brown. 
(Read July 13, 1906. MS. received October 31, 1906.) 
In a paper on the aluminium anode by one of us, in con- 
junction with Inglis,* it was pointed out that if the suggested 
theory of the aluminium anode is correct, a precipitation film of 
aluminium hydroxide should diminish the conductivity of salt 
solutions to very different extents depending upon the ions present, 
and that, e.g., the diminution in the case of potassium chloride 
might be expected to be slight, in the case of potassium bromide 
somewhat greater, and in the case of potassium sulphate to be 
very considerable. Preliminary experiments to measure these 
differences directly were not successful, almost certainly, as was 
stated at the time, because of the difficulty of freeing the pre- 
cipitation membrane from the concomitant soluble impurities. 
The experiments described in the present paper conclusively 
prove that the anticipated effect does exist ; and, though the 
quantitative agreement is fairly good, we hope to further improve 
the method in certain respects and so obtain exact measurements. 
That diaphragms may affect ions to a different extent was 
recognised by Hittorf, when he discarded the use of parchment 
paper or other diaphragms in his classic investigations on the 
migration ratios of ions. Tammann t found that in some cases 
osmotic pressure membranes offered considerable resistance to the 
passage of the ions which form the membrane, but that generally 
the resistance offered by the membrane was very small. Morse,]; 
in the preparation of osmotic pressure membranes by electrolysis, 
observed that an efficient film offered a very great resistance to 
the ions which form the film. 
* Taylor and Inglis, Phil. May., March 1903. 
t Tammann, Zeit. f. Physikal. Chem., vi. p. 237, 1890. 
t Morse, Amer. Chem. Journal , xxix. p. 173, 1903. 
