250 



results of a similar mutual attraction of the mercury and the ele- 

 ments of the liquid to those obtained by methods 1 and 2. The 

 mercury moves towards the cathode in acids because its positive end 

 has acquired, by the aid of the electric current, a stronger affinity for 

 the negative element of the liquid than its negative end has for the 

 positive element, and moves towards the anode in alkalies because 

 its negative end has acquired a stronger attraction for the positive 

 element of the liquid than its positive end has for the negative ele- 

 ment. I do not, however, give either this or the previous explana- 

 tion (34) as an ascertained fact, but merely as a temporary hypo- 

 thesis to aid further investigation. 



38. The amount of positive flow produced by the 3rd method in 

 strong aqueous hydrocyanic acid, or strongest solution of ammonia, is 

 comparatively small, apparently on account of their inferior electric 

 conductivity ; but if the smallest amount of ammonia is added to the 

 hydrocyanic acid, the positive flow obtained is very strong ; also, if 

 instead of ammonia a small quantity of caustic potash, soda, baryta, 

 strontia, magnesia, lime, or even alumina is added to the acid, similar 

 effects are produced : a little strontia or lime causes the nearest part 

 of the mercury to dart up the watch-glass more than half an inch 

 towards the positive electrode, if the battery is sufficiently strong. 

 Silica had no effect. The addition of oxide of zinc, dioxide or 

 protoxide of copper to the acid, reversed the direction of the flow, 

 and dioxide of mercury neutralized the positive movement and 

 diminished the conduction. The strongest positive flows obtained 

 by the 3rd method were with strong solutions of alkaline cyanides, 

 and the strongest negative flows with sulphuric acid. 



39. The behaviour of liquids upon mercury in V-tubes by the 

 three methods is not essentially different from their behaviour in a 

 watch-glass ; the former, indeed, may be safely predicted from the 

 latter. Sufficient pure mercury was placed in a V-tube of half an 

 inch bore just to fill it at the bend, then a strong solution of sulphate 

 of alumina poured upon it half an inch deep in each leg ; on con- 

 necting the platinum wires from twenty-two pairs of small Smee's 

 batteries with the solutions in the two legs, the liquid at once flowed 

 from the negative to the positive leg ; but by lowering the negative 

 wire into the mercury, it flowed from the positive to the negative leg : 

 no flow of the liquid was produced by placing the positive wire in 



