Action between Metals and Acids. 



839 



From whatever point of view the result may be regarded 

 there is no doubt that metallic contact between A and B 

 would reduce the amount of mercury salt in solution round 

 the former. If B were very large compared with A, the 

 amount of mercury left in solution round A would be very 

 small. Similarly if A were connected with a succession of 

 masses initially like B but small (each being removed before 

 another took its place), the amount of salt in solution round A 

 could be continuously lowered. 



Although it appears possible to obtain oxygen-free surfaces 

 of mercury (like B), they are usually in rapid motion and 

 very difficult to observe. It is easy, however, to study a 

 surface (like A) subjected to metallic contact with a suc- 

 cession of surfaces much more nearly oxygen-free than 

 itself. 



§ \). Experimental realization. — Mercury poured into a 

 vertical glass tube drawn to a fine capillary at the lower end 

 escapes in a narrow stream. Since the surface of the mercury 

 per unit mass is much greater in this than in the tube, a 

 considerable quantity of the mercury below the surface in 

 the tube must enter the surface in the jet. Thus a surface 

 film, upon the mercury originally, must become much thinner 

 in the jet. 



Suppose the stream to enter an acid solution as at J in the 

 figure. It will possess much less oxygen per unit surface 



Fig. 1. 



than mercury at rest. The concentration of oxygen may 



fall below the amount sufficient to raise a to the value 



required to satisfy (i. a), and therefore a small quantity of 

 hydrogen may form. 



3 L 2 



