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XLII. The Tin- Chromic Chloride Cell. 

 By S. Skinnek, M.A* 



A CELL consisting of a tin and platinum couple in a 

 solution of the green chromic chloride was described 

 by W. E. Case in the Proc. R. S. 1886, p. 345. The tin is 

 dissolved by the chromic chloride at a high temperature only, 

 and when the solution is cooled the tin is precipitated. The 

 chemical changes are represented by the following state- 

 ment : — 



Cr 2 Cl 6 + Sn— fc SnCl 2 + 2CrCl 2 . 



As the reaction is reversed on cooling, the cell has the 

 interesting feature that at the end of a hot and cold cycle it 

 is in the same chemical condition as it was at the commence- 

 ment. It thus offers a method of deriving electrical energy 

 directly from heat. The author of the account gives a curve 

 of electromotive force, and finds that it is zero at 60° F., and 

 increases to about J volt at 200° F. I shall show that the 

 E.M.F. is not zero at the ordinary temperature, but is about 

 £ volt ; however, the cell will not give any current at these 

 temperatures on account of polarization. It appears that 

 the curve given by Mr. Case is not an E.M.F. curve, but one 

 which was probably obtained by using a wire voltmeter, and 

 therefore really represents the current the cell is capable of 

 producing. 



The tin is precipitated in small crystals from the cooling 

 solution of CrCl 2 and SnCl 2 , and does not then form a satis- 

 factory electrode. I have therefore arranged the cell with an 

 amalgam of tin in place of the solid rod. The precipitated 

 crystals fall into the mercury and dissolve so as to reconstitute 

 a suitable electrode. My construction of the cell is very 

 much like that of a Clark cell. 



A test-tube with a platinum wire through the base has 

 fluid amalgam in it, and this is covered with a solution of 

 pure Cr 2 Cl 6 , made by dissolving violet sublimed Cr 2 Cl 6 in 

 water with the aid of a fragment of tinfoil. A platinum plate 

 and wire form the positive pole of the cell. 



Connecting such a cell at 15° C. with a galvanometer, 

 there is a sudden deflexion which very rapidly becomes less 

 until some small steady value is reached. On warming the 

 cell the deflexion increases until it is relatively large. These 

 observations show that the cell cannot produce a continuous 



* Communicated by the Physical Society : read February 8, 1895, 



