CHAPTER II 



THE ELECTRICAL APPARATUS IN COMMON USE IN 

 PHYSIOLOGICAL WORK 



Batteries. A voltaic element or cell usually consists of two metals 

 e.g., zinc and copper immersed in a fluid such as dilute sulphuric 

 acid, and the changes (movements of ions) which occur under these 



Anode. 



Copper. 



Kathode. 



Zinc. 



Dilute sulphuric acid. 



FIG. l. VOLTAIC COUPLE. 



circumstances in the fluid produce a disturbance of electrical equili- 

 brium in the cell which manifests itself as a difference of electrical 

 potential or pressure at the metals. If wires are connected to these 

 it is found that the end of the wire connected with the copper or 

 electronegative metal is charged with positive electricity, and that 



connected with the zinc or electropositive metal is charged with 



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