OF THALLIUM, INDIUM, AND TIN 29 



With the idea of testing the effect of stannic chloride, but without much 

 hope of obtaining results fully corresponding to a quadrivalent ion, a 

 further attempt was made to measure a tin amalgam concentration cell, 

 using an electrolyte containing at first pure stannic chloride. Pure tin was 

 dissolved in aqua regia and the nitric acid was removed by boiling 

 repeatedly with fresh portions of hydrochloric acid. The solution was then 

 diluted with water, most of the free acid was neutralized with sodium 

 hydroxide, and the solution containing all its tin in the state of highest 

 oxidation was placed in the cell. 



No constant readings could be obtained with any of the tin amalgams 

 under these conditions. Evidence was obtained, however, that this electro- 

 lyte tended to give lower potentials than those obtained with stannous 

 chloride. For example, with a cell whose calculated potential would be 

 0.01605, if the tin were quadrivalent, and 0.0321, if bivalent, a value of 

 0.0262 was obtained. Clearly, as we had expected, ionized quadrivalent 

 tin is not in a state of electrochemical equilibrium with tin amalgam. 



Cady 28 supposed that he attained this equilibrium by using potassium 

 stannate as an electrolyte, but in our opinion it is extremely doubtful if in 

 a solution of a stannate, the quadrivalent tin ion is in reversible equilibrium 

 with a tin amalgam. Our practical experience confirms this conclusion. 

 We attempted to measure a cell with a solution of sodium stannate as its 

 electrolyte, but were unable to obtain anything approaching constant 

 potentials. 



We regret to state that another fact also points to the conclusion that 

 Cady's work with tin was questionable. Roozeboom and van Heteren 

 have shown that at 25 tin amalgams containing from 1.2 to 99 "atom 

 per cent " of tin give the same potential, there being present two phases 

 of invariable composition a liquid phase containing 1.2 "atom per cent" 

 tin and a solid phase of 99 per cent tin. But Cady supposed he had made 

 a tin amalgam of 1.73 per cent by weight or nearly 3 atom per cent, when 

 he used potassium stannate as electrolyte in the attempt to obtain the 

 potential of a cell in which tin behaved as quadrivalent. He calculated 

 the concentration ratio on the basis of his supposed percentage. 29 In 

 the light of the work of Roozeboom and Van Heteren this work is evidently 

 faulty, since the strongest liquid amalgam in the cell could not have 

 exceeded 0.8 per cent by weight of tin, and the more dilute amalgam 

 might have been affected by crystals of tin dissolved on dilution. Clearly 

 Cady's work on tin is without significance. 



28 Jour. Phys. Chem., 2, 551 (1898). Attention should be called to another serious 

 error in Cady's paper, of which due acknowledgment was made. (Ibid., 3, 107 

 [1899]). All this work of Cady's was done under the direction of W. D. Bancroft. 



29 Professor Cady has kindly looked up his data in his original note-books, and 

 finds that the mistake was not an error of proof-reading, but arose from lack of 

 knowledge of the solubility of tin in mercury. 



