52 Mr. W. H. Preece. Effects of Temperature on [Feb. 22 r 



the fact that whereas the temperature of the zinc cell rose faster than 

 that of the copper cell while being heated up, the former cooled faster 

 than the latter while cooled down from a high temperature [say 

 ]00° C.]), tend to indicate that the diminution in the electromotive 

 force of the cell at the beginning of the experiment was greatly, if not 

 chiefly, due to the thermo-electric action which must have been set up 

 in the circuit. 



(b.) The Bichromate Cell. — It will be seen from the Tables IV and 

 V that the electromotive force of the bichromate (both the double- 

 fluid and the single-fluid cell), diminished regularly when the tempe- 

 rature was made higher and higher, and increased regularly when 

 the temperature was made lower and lower. The regular diminution 

 by rise and regular augmentation by fall of temperature of the electro- 

 motive force (at least when the range of temperature was between 

 0° C. and 100° C), was very much greater in the case of the single- 

 fluid bichromate than in the case of the double-fluid bichromate. In 

 the case of the first, the electromotive force at 100° C. was as much 

 as about 6 per cent, lower than that at about 14° C. ; whereas in the 

 case of the second, the electromotive force at 100° C. was only about 

 1*6 per cent, lower than at 19° C. 



(c.) The Leclanclie Cell. — The Table VI shows that the electro- 

 motive force of the Leclanclie varied, when the temperature was varied,, 

 so slightly, if at all, that it was difficult to observe the variation by 

 the method used. 



(II.) The Internal Besistance. 



The results obtained for the resistances of the various kinds of cells 

 are more striking and more interesting than those for the electro- 

 motive force, as will be quite evident from the tables. They will, 

 however, be understood more readily from the graphical representa- 

 tions of the results by means of curves (in the Diagrams I, II, and 

 III) in which the abscissae are proportional to the resistances in B.A. 

 units, and the ordinates to the temperatures in degrees Centigrade. 



(a.) The Daniell Cell. — The curves in the Diagram I represent the 

 results for the Daniell, the curve ABODE corresponding to the case 

 (Table II) in which the copper sulphate solution was kept saturated 

 at all temperatures, while the zinc sulphate solution was kept constant 

 in strength, and the curve abode corresponding to the case (Table III) 

 in which both solutions were kept unaltered in strength during the 

 experiments. The directions of the arrows indicate the order of the 

 experiments. For instance, in the curve ABODE the portion AB 

 represents the result obtained while the cell was being heated up from 

 about 11° C. to nearly the boiling point of water, the portion BC that 

 obtained while the cell thus heated up was being cooled down 

 from 100° C. to about 12° C. ; and, lastly, the portion DE that 



