188 6, j On converting Heat Energy into Electrical Energy. 345 



100° C. ; for most hard drawn wire, however, the temperature of 

 minimum internal friction is below 0° C. 



(/.) The temporary change, whether of the nature of increase or 

 decrease, wrought by alteration of temperature in the internal friction 

 of metals, is in most cases enormously greater than the corresponding 

 change in the torsional elasticity. 



IV. " On a New Means of Converting Heat Energy into Elec- 

 trical Energy." By Williaed E. Case, of Auburn, New 

 York, U.S.A. Communicated by W. H. Preece, F.R.S. 

 Received April 14, 1886. 



It was shown by M. Henri Loewel (see " Th* Chemist," Part VIII, 

 p. 476) that the addition of a solution of chromous chloride to 

 stannous chloride caused a precipitate of metallic tin, the reaction 

 forming chromic chloride. 



On heating the solution to the boiling point, 212° F., it was found 

 the precipitated metal was in a great measure redissolved, forming 

 the original solution, chromous chloride and stannous chloride, with- 

 out the liberation of hydrogen. 



On cooling this solution the tin was again precipitated, the action 

 continuing as often as the solution was heated and cooled. 



As chromous chloride has a great affinity for oxygen, it is necessary 

 the air should be excluded from the solution, otherwise the chromous 

 chloride would be reduced to oxy chloride of chrome, as Loewel states, 

 and the reactions would cease to take place after a time, the stannous 

 chloride formed during each heating remaining in solution. 



I constructed, in the form of a simple galvanic cell, a small element 

 with this solution, chromic chloride,* as the electrolyte, using tin as 

 the positive, and platinum as the negative metal. 



At 60° F. this element gives no electromotive force, although in 

 this case, when the cell was first set up, it gave 0*0048 volt, owing 

 probably to the presence of some foreign substance. 



On the elevation of its temperature by the application of heat, the 

 electromotive force rose and fell, as indicated in the diagram ; the 

 curves A, B, C, D, E, represent its increase during the rising tempe- 

 rature, and the curves F, Gr, H, I, J, its fall while cooling. 



The irregularity of the curves A, B, C, D, E, was probably due to 

 unequal heating. 



At the termination of the experiment, when .the cell had cooled 

 down to 60° F., no electromotive force was observed, as indicated on 



* The solution used was made by combining chromium trioxide with hydro- 

 chloric acid, and heating. 



