Various Electrochemical Processes and Experiments

Posted By Richard Jefferson on 19 February 2015

Posted in The Vintage Machinery Almanac

This article was originally published in Electrochemical and Metallurgical Industry Publication of November 1907. Information within this article is therefore correct as of 1907. The publication of this material aims to provide historical insight on the subject and its place in industry.

Electrolysis of Fused Salts

An important paper by R. Lorenz in Zeit. f. Elektrochemie, Aug. 23, refers to the well-known fact that the efficiency of electrolysis of a fused salt of a heavy metal can be very considerably increased by the addition of a salt from an alkali. Such additions have often been recommended and used by practical men in the past, but Lorenz's paper throws an absolutely new light on the rationale of their effectiveness.
Lorenz had formerly found that one of the principal phenomena which diminish the efficiency is the formation of a mist or fog or schliere from the fused cathode. Thus in the electrolysis of fused lead chloride with a fused lead cathode, lead goes back into the fused lead chloride bath in form of a mist, which travels over to the anode and there recombines with the anion (in this special case, chlorine), thus undoing the useful work of electrolysis. Lorenz and Helfenstein had formerly found that this migration of the mist toward the anode could be counteracted by separating or en-closing the electrodes by diaphragms, such as perforated glass or porcelain vessels. But he found later that in the case of electrolysis in lead chloride, the simple addition of potassium chloride prevented the mist formation, and was just as effective in increasing the efficiency as the use of a diaphragm. He has now established the fact that this is a general expedient. The efficiency of electrolysis of lead chloride is greatly improved by adding either potassium chloride or sodium chloride or barium chloride; similarly the electrolysis of lead bromide by adding potassium bromide, the electrolysis of cadmium chloride by adding potassium chloride or sodium chloride, etc. In all cases the effect of the addition is to prevent the formation of the cathodic mist. Why the formation of mist is thereby prevented is not yet quite clear, but the following experiment may perhaps indicate the reason. If we have no electrolysis at all, but a fused bath of lead chloride, containing a mist of lead so as to be not transparent, then the simple addition of some potassium chloride suffices to precipitate the mist, and the fused bath becomes transparent. This phenomenon reminds one directly of the precipitations of colloids by addition of electrolytes.

Artificial Diamonds

In London Electrical Engineering of Sept. 26, we note a French patent, 375,669, granted to L. Bonnet, and relating to a method of obtaining amorphous, fused or black diamond. The process consists in fusing carbon with a high-tension electric current in a liquid or gaseous medium under high pressure. The apparatus consists of a thick vessel of bronze or any other suitable metal, containing two thick carbon electrodes, between which is placed a piece of pure rod carbon. Underneath this rod there is a dish containing carbon disulphide or other liquid which has no action on carbon, and which will readily evaporate and produce a high pressure. A current sufficient to evaporate the carbon disulphide is first passed, and when the pressure is sufficiently high a heavy current, which fuses the carbon, is passed for a few minutes.
The pressure may also be produced within the vessel by forcing an indifferent gas into the apparatus by mechanical means. In this connection reference should be had to an account by C. A. Parsons in the September issue of the Proceedings of the Royal Society of some recent experiments made by him on the effect of heating carbon electrically to a very high temperature and under strong pressure. The main conclusions to be drawn from his experiments are that at very high temperatures and pressures carbon is still a very good conductor, and that soft crystalline graphite is the resulting stable form of carbon after this treatment. Further, there has never been formed more than a suspicion of black or transparent diamond, and the inference is, therefore, that mechanical pressure is not the cause of the production of diamonds in rapidly cooled iron.

Image Credit: SMU Central University Library