446 



The Tin- Chromic Chloride Cell. 



given in the following- 



tables. The first cell contained tin- 



amalgam, and the second cell contained a tin rod. Both cells 

 had not been used for producing current within the 24 hours 

 immediately preceding the measurements. 



Cell No. 1. 



Tin-amalgam. 



Temperature. 





E.M.F. 



15-5° C. 





•44 volt. 



20-5 





•45 



49-0 





•43 



75-0 





•41 



93-0 





•40 



96-0 





•40 



97-0 





•40 



20-0 





•44 



Cell No. 2. Tin rod. 





Temperature. 



E.M.F. 



16° 





•52 volt. 



30° 





•52 



97° 





•45 



Connexion was made and a current allowed to flow for 

 1 minute, and then the cell was allowed to rest for 1 minute : 



97° | -08 volt. 



At end of second minute : 



97° | -11 volt. 



At end of third minute : 



97° | -11 volt. 



These results showed that the cell had polarized, and was 

 only slowly recovering its electromotive force. 



When a solution of the green chromic chloride at the ordi- 

 nary temperature has silver nitrate added to it, only two- 

 thirds of the chlorine is precipitated. This, according to the 

 theory of ionisation, indicates that only two atoms out of 

 three act as negative ions, the other atom apparently being 

 part of the positive ion. On the other hand, if a solution of 

 chromic chloride near 100° be treated with silver nitrate, the 

 whole of the chlorine may be precipitated. This indicates 

 that at the higher temperature all the chlorine atoms behave 

 as negative ions. 



Taking this into account, the Grotthus chain representing 



