306 



Mr. H. A. McTaggarfc on the 



Zr(N0 3 ) 4 . 



Time. 



Charge. 



10~ 9 .5 



Seconds. 

 23 





IO -8 



— 







10~ 8 .5 



95 



+ 



10- 7 



35 



+ 



10~ 7 .5 



30 



+ 



The positive ions Th and Zr not only neutralize the 

 negative charge but they give the surface a large positive 

 charge. The thorium salt is the most remarkably active in 

 this respect of all the salts used. 



Two tetravalent chlorides were tried but they showed very 

 slight effects : — 



PtCl 4 5 H 2 0. 



Time. 



Charge. 



io- 9 



Seconds. 

 16 





io- 7 



17 



- 



10" 6 



26 



- 



10" 6 .2 



40 



- 



SnCl a 8 H 2 0. 



Time. 



Charge. 



10~ 9 .7 



Seconds. 

 19 





10~ 8 .3-5 



28 



— 



10~ 8 .7 



32 



— 



10~ 7 .l-4 



25 



- 



In these cases it is likely that the metal forms part of a 

 complex ion, and is therefore not free to exhibit the full 

 effect of its valency (Whetham, 'Theory of Solutions,' 

 p. 196). 



Hexavalent chromium in Cr0 3 gave results of a similar 

 kind : — 



