Researches with the dropping mercury cathode. Part IX. Tin

Abstract

This investigation of the electrodeposition of tin was undertaken to complete the table of the deposition potentials of metals at the dropping mercury cathode and to examine the basic and acidic properties of stannous hydroxide, similar to the experiments performed by Miss Kadlcova on the amphoteric hydroxides of zinc and lead I).T o prevent hydrolysis it has been found necessary to use distinctly acidic or alkaline solutions containing the tin-compound and, in either instance, to keep the solutions out of contact with atmospheric oxygen, Only freshly prepared solutions were used, to avoid as much as possible the ageing effects of the hydroxide. The solutions were prepared by dissolving pure "Kahlbaum" tin in pure redistilled hydrochloric acid, the tin being joined to a platinized platinum foil in order to lower its overvoltage and thus bring it into solution. Another method adopted was the deposition of tin from stannous chloride solutions (also a "Kahlbaum" specimen) by means of metallic aluminium, the spongy tin obtained being dissolved in acids. All these operations were carried out in an atmosphere of hydrogen. The tin content was estimated by iodometric titration or calculated from the known weight of the metal dissolved. The usual type of electrolysis vessel was used. 1.The following table contains the results of electrolysis in acidic solutions. Here c denotes the number of gram-molecules of stannous chloride per litre, E the observed decomposition E.M.F., r0 the observed potential of the anode, z' the deposition potential (= zo -E) and zN the "normal deposition potential" of tin, i.e. the potential at which a solution containing one gram-ion of tin per litre would begin to deposit tin.