Resistance of certain Amalgams ivith Temperature. 435 



is used the stirring necessary to keep it of a uniform com- 

 position throughout is liable to introduce air-bubbles. (2) 

 Those amalgams containing a high percentage of foreign 

 metal were not sufficiently fluid to run into the spiral except 

 at a high temperature, and it was found difficult to keep the 

 vertical wide limb dipping into the amalgam at a high 

 enough temperature for a time long enough for the spiral to 

 be filled with sufficient slowness. 



The most satisfactory method is the following : — The whole 

 spiral was placed in a sand-bath and kept at a suitable tem- 

 perature. The amalgam in a fluid condition was all placed 

 in one of the vertical limbs, which for this purpose was 

 specially wide, the other being temporarily closed by means 

 of a pinched rubber tube. The fluid mass was well stirred 

 and then, by opening the rubber tube, was allowed to quicldy 

 fill the whole spiral, the rapidity with which this took place 

 being regulated by opening or closing the rubber tube. 



If any air-bubbles were present, they generally made their 

 presence known if the substance was allowed to cool and then 

 had its temperature again raised ; it none made their appear- 

 ance the spiral was shaken while the amalgam was solidifying, 

 to keep the metals from separating into layers, and was then 

 allowed to anneal slowly. If this last precaution was omitted 

 the spiral was very liable to breaxs when it was again heated. 



Contact was made by thick amalgamated copper pieces put 

 in while the amalgam was fluid. To guard against any 

 changes in contact of these copper pieces the spiral was placed 

 in an oil-bath and heated several times to just over the highest 

 temperature to which it was intended to raise it in the actual 

 experiments. 



Good circulation of the oil in the bath by means of which 

 the temperature was raised, was secured by fastening three 

 small cork feet to the spiral, and keeping the bath well stirred. 



In all cases, of course, the spiral was well cleaned previous 

 to the introduction of the amalgam by frequent washing with 

 caustic potash, hot nitric acid, and finally distilled water. 



The change in resistance was measured by Carey Foster's 

 method. It may be mentioned here that no difference in the 

 variation of the resistance of the spiral could be detected in 

 the two cases when, immediately after solidification, it w r as 

 slowly annealed and when it was allowed to cool quickly 

 before an open window. 



§ 2. Results for Zinc Amalgams. 

 Observations were made on a series of zinc amalgams in 

 w T hich the proportion of zinc present varied between 41 per 

 cent, and 40 per cent. 



2H2 



