Fig. 



_ — '—-Cu. 



Zn 



a,— =m? 



ih 



Polarization of Platinum Plates. 491 



small glass bottle, A A, was placed a weak 

 solution of zinc sulphate, which reached to 

 the level, a a. The bottle was closed by a 

 cork, through which passed two glass 

 tubes, B, C, of about |-inch bore, and open 

 at each end. C contained a strip of amal- 

 gamated zinc, which could be lowered into 

 the zinc sulphate or raised out of it as 

 required. The tube B contained a thick 

 copper wire, which was gutta-percha 

 covered (except for about half an inch 

 where it passed beyond the lower end of the tube), and 

 passed into a test-tube, D, through a cork, E. This test-tube 

 was filled up to the level a a with a saturated copper sulphate 

 solution, and the naked part of the copper wire was embedded 

 among crystals of copper sulphate placed at the bottom of the 

 test-tube. The level of the liquids was about half an inch 

 below the top of the test-tube. Scarcely any diffusion of the 

 liquids is possible ; and this form of the Daniell, though useless 

 as a means of producing currents, has a very constant electro- 

 motive force. 



Readings. — A series of experiments was made at the tem- 

 peratures. 40°, 60°, 80° C, and with the water in the bath 

 boiling. The readings were taken in sets, proceeding from 

 weaker to stronger currents and back again, so as to elimi- 

 nate the effects of possible leakage of the electrometer. The 

 galvanometer-deflections were corrected for torsion of the 

 suspending fibre, and the electrometer-readings for scale- 

 error. In the following table, E indicates the electrometer- 

 readings and 6 the deflection of the galvanometer-needle. 



Temp 



40°. 



Temp 



60°. 



Temp 



80°. 



E. 



Tan0. 



E. 



Tana 



E. 



Tan0. 



25-0 



•1187 



2295 



•1026 



22-5 



•1178 



270 



•1585 



249 



•1463 



24-15 



•1495 



28-9 



•2045 



28-3 



•2127 



260 



•1927 



31-45 



•2621 



319 



•2881 



28-1 



■2292 



351 



•3476 



36-6 



•3925 



30-25 



•2766 



38-9 



•4323 



40-4 



•4661 



330 



•3396 



41-5 



•5024 



44-25 



•5722 



36-7 



•4171 



44-8 



•5722 



496 



•6829 



39-2 



•4828 



48-0 



■6363 







414 



•5446 



520 



•7120 







45-0 



•6041 



54-8 



•7673 







530 



•7651 



5665 



•7999 







601 



•8S10 



