n 



Foreign Metals on the Electric Conducting Power of Mercury. 173 



mercury was sufficiently purified by the process we subjected it 

 to, was proved by comparing it with some distilled mercury, 

 which after distillation was treated with dilute nitric acid and 

 dried in a current of hydrogen. The experiments were made as 

 follows : — 



Thermometer-tubes were fused on to wide tubes and bent, as 

 shown in the figure. The length of these 

 was about 300 millims. Into the wide 

 tubes dipped well-amalgamated copper 

 wires (5 millims. thick), which reached 

 to the bottom of the tubes at a, thereby \ ^ 

 closing, as it were, the ends of the 

 thermometer-tubes with a plate of copper. It was found that 

 the height of the mercury in the wide tubes made no difference 

 in the results obtained. The weight of mercury taken for each 

 determination was 50 grammes. 



To obtain concordant results, the precautions taken were : — 

 I. The amalgam was made in the tube itself. This was filled 

 with the requisite quantity of mercury, and its resistance deter- 

 mined : this was always repeated twice, to be sure no air-bubbles 

 were in it ; and either the solid metal was added, or, as in the 

 case of the poorer amalgams, a certain weight of an amalgam 

 of known composition, and then heated for a quarter to half an 

 hour over a Bunsen-burner, during which time the mercury was 

 allowed to flow continually from the one arm to the other, at 

 the same time taking great care that the thermometer-tube 

 remained always full; for if it became empty, the amalgam 

 would leave a tail in it, and thereby injure the continuity of 

 the column. The thick copper wires were heated before being 

 dipped into those amalgams, which partially solidified on cooling. 

 It is almost superfluous to add that the tubes were, after they 

 were emptied, well washed with nitric acid and distilled water 

 and carefully dried, and that the ends of the copper wires were 

 cleaned after each determination, and, when necessary, reamal- 

 gamated. 



II. As the conducting power of mercury is known, and as the 

 resistances of the tubes filled with that metal were always deter- 

 mined, it was not necessary to measure the length or diameter 

 of the tubes ; for we obtain more concordant results, when expe- 

 rimenting with the different tubes, by comparing their resist- 

 tances with that of the tubes filled with mercury, than if we had 

 measured their respective lengths and diameters and brought 

 these data into calculation. 



III. The metals used for the experiments were pure. 



IV. During the determination the tube filled with the 

 amalgam was placed in a trough filled with water, the tempera- 



