CHAPTER II 



The Electrical Apparatus in Common Use in 

 Physiological Work 



A VOLTAIC element or cell consists, in its simplest form, of two metals, 

 e.g., zinc and copper, or of zinc and carbon, immersed in a suitable fluid 

 such as dilute sulphuric acid; the movements of ions which occur 



Anode. 



Copper. 



.*..... Kathode. 



. Zinc. 



- Dilute sulphuric acid. 



FIG. 1. Voltaic couple. 



under these circumstances in the fluid produce a disturbance of elec- 

 trical equilibrium which manifests itself as a difference of electrical 

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

 parts of these outside the fluid it is found that the end of the wire 

 connected with the copper is charged with positive electricity, and that 

 connected with the zinc is charged with negative electricity ; these 

 ends are called the positive pole, or anode, and the negative pole, or 

 kathode, respectively. The anode is said to be in a condition of higher 

 potential and "the kathode in one of lower potential, and when they are 



