1879.] 



Metals in Solutions of Salts of Potassium. 



39 



capillary electrometer, the quantitative differences of electromotive 

 force between each two consecutive metals, and thus to construct a 

 series of tables of electromotive forces of the particular solids and liquids 

 employed. But as after making many attempts I was unable to construct 

 such a form of that electrometer as might be relied upon as an accu- 

 rate measuring instrument, I abandoned the object of measuring the 

 electromotive differences, and proceeded no farther than simply deter- 

 mining the order of such differences in each particular solution. 

 Although I have not been able to carry out the examination as far as 

 I intended, I venture to submit the results to the Royal Society, in 

 the hope that if published they may be of use to other investigators, 

 as similar tables upon a less extensive scale have already proved. 



As the true electrical relations of metals in liquids depends largely 

 upon the purity of the substances, I beg to state that the metals and 

 salts employed were, in nearly all cases, the purest obtainable. The 

 tellurium, mercury, and antimony were very highly purified by me ; 

 the silicon was prepared by fusing some fine crystals, which I had 

 previously digested with pure hydrofluoric acid, hydrochloric acid, 

 and nitric acid separately. The gold, silver, platinum, palladium, 

 iridium, rhodium, cobalt, tin, and cadmium, were obtained from 

 Messrs. Matthey and Co., and were the purest they prepare. The 

 nickel was refined by Sir J. Mason, and was of a high degree of 

 purity ; it had been rolled into a thin strip. The carbon was a rod of 

 a Jablochkoff's candle. The indium was a portion of one of the 

 ingots exhibited at the Paris Exhibition by its discoverers. The 

 gallium was presented to me by M. Lecoq de Boisbaudran, and 

 said to be " nearly pure except traces of zinc." The thallium was 

 supplied to me by Messrs. Hopkin and Williams. The magnesium 

 was probably very pure, and was obtained from the Magnesium Metal 

 Company, from whom I also obtained the bismuth, said to be " highly 

 purified." The aluminium, copper, lead, iron, and zinc wires were of 

 the ordinary qualities. 



The salts employed were of considerable purity, and in every case 

 were dissolved in distilled water. To remove any trace of free iodine 

 or acid from the solutions of potassic iodide, or any trace of soluble 

 sulphide contained in those of cyanide of potassium, they were pre- 

 viously well stirred with a rod of aluminium or magnesium. 



Every investigator who has made experiments of the present kind 

 is aware that temporary reversals of the current frequently occur in 

 such cases. When the reversals took place immediately upon immer- 

 sion, the first current was not regarded, because it was probably due 

 to a momentary change of surface tension or of temperature, caused 

 by the physical contact of the solid and liquid prior to chemical action. 



A sufficient number of different strengths of solution of each salt 

 were employed to supply a large number of determinations, so as to 



