52 GENERAL PROPERTIES OF LIVING TISSUES 



and 1 metre posts of the rheochord, respectively. 

 Connect the zero post and the slider to the capil- 

 lary electrometer (Fig. 13). Turn the pole- 

 changer to pass the battery current through the 

 copper sulphate solution or " electrolyte." The 

 cation (copper) will be 

 partially de-ionized at 

 the negative pole, or 

 cathode, on which cop- 

 per will be deposited 

 in a fine film. The anion 

 (sulphion, S0 4 ) will pass 

 towards the positive pole, 

 or anode, where it gives 

 up its electric charge and 

 becomes the ordinary radical S0 4 . This radical 

 cannot exist uncombined in water, but forms sul- 

 phuric acid, setting free oxygen, which therefore 

 appears at the anode. 



The elements copper and oxygen deposited 

 respectively on the cathode and anode tend to 

 fly back into the ionic state ; and this ten- 

 dency, taken in connection with the opposing 

 osmotic force of the ions already in solution, 

 sets up an electromotive force equal to that 

 which caused the de-ionization, but in an op- 

 posite direction. Hence the polarization cur- 



Fig. 13. 



