330 Mr. S. Bidwell on the Generation of 



The action is almost certainly of the same nature as that 

 which occurs in an ordinary voltaic cell. 



(2) It appeared desirable to construct a cell which, though 

 unsuitable for experiments with light, would have a much 

 smaller resistance than one of the form last described. A 

 plate of copper 3 centim. square was heated, and upon it was 

 spread a mixture consisting of 5 parts of sulphur and 1 part of 

 sulphide of copper. A plate of silver previously heated was 

 then laid on the melted mixture and the two plates squeezed 

 together, thus forming a sandwich-like cell. The thickness 

 of the copper plate was 2'75 millim., of the silver plate '60 

 millim., and of the completed cell 3'65 millim.; the thickness 

 of the layer of sulphur was therefore *3 millim. When this 

 cell (after cooling) was connected with the galvanometer, the 

 spot of light was violently deflected off the scale. Dr. Fleming 

 was kind enough to make a very accurate measurement of its 

 electromotive force by comparison with one of his standard 

 Daniell cells. It was found to be *0712 volt, and its internal 

 resistance was 6537 ohms. As in the case of the former cell, 

 the direction of the current is from silver to copper ; and there 

 can be no doubt that it is of a voltaic nature. At the time of 

 writing, the cell has been in existence nearly seven weeks, and 

 it is now, I believe, quite as powerful as at first. 



(3) It was thought that the internal resistance might be 

 further reduced by adding a larger proportion of sulphide to 

 the sulphur. Another cell was therefore constructed similar 

 in all respects to that last described, except that the sulphur 

 and copper sulphide were mixed in equal proportions. Its 

 internal resistance was enormously lower, being only 13 ohms, 

 but its E.M.F. was also lower, being *0071 volt. 



(4) A layer of precipitated sulphide of copper was placed 

 between plates of copper and silver which were squeezed 

 together in a screw-press. The resistance of this arrange- 

 ment was a small fraction of an ohm ; but when connected 

 with the galvanometer, it gave no indication whatever of a 

 current. It seems, therefore, that a certain amount of free 

 sulphur is necessary for the generation of an electromotive 

 force by cells containing copper sulphide. 



(5) Two parts of copper sulphide were mixed with one of 

 sublimed sulphur, and the powder was compressed between 

 plates of copper and silver. This cell gave a very small 

 current, indicated by a galvanometer-deflection of 2 or 3 scale- 

 divisions. The deflection was reversed as often as the con- 

 nections with the binding-screws of the cell were reversed ; 

 and the existence of a real, though very small, electromotive 

 force was undoubted. The internal resistance was *088 ohm. 



