ELECTRICAL ACTIVITY OF ORE BODIES. 



357 



If now, e be the electromotive force of the two sohitions in contact, e that 

 due to the difference between the zincs alone, in the first position of the bags 

 A and B {A in water and B in the liquid to be tested), the apparent force 

 would be 



in the second position of the bags {B in water and A in the Hquid to be 

 tested), 



the connections themselves remaining unaltered. A mean of both measure- 

 ments gives e; half the difference, e. The following are some of the results: 



r Both bags in water 



! < Ba<is alternately in solution of Na* SO* and in water. 



{Both bags in water 

 Bags alternately in salt solution and in water. 

 Both bags again in water 



r Both bags in water 



I Bags alternately in Zn SCH solution and in water. 



It will be seen that in the different sets e is fairly constant. The value 

 of e is small, as anticipated, notwithstanding that nearly concentrated solu- 

 tions were used. In the case of zinc sulphate e is practically zero, as it 

 should be, the bags themselves containing this solution. 



The following table contains analogous experiments made in the mines. 

 Holes IX. and X., 600-foot level, were put in contact. Measurements were 

 made by a zero method: 



Water in both IX. and X I - 28 



Water in X. : concentr.ated brine in ZX- — 27 

 Concentrated brine in both IX. and X. . ! — 27 



Two other holes similarly treated gave: 



Apparently, therefore, large discrepancies are not produced in tliis way. 



