Properties of some Liquid Metals. 399 



ture of the hot junction was not altered by more than ^ 

 of a degree. As the leading-in wires were hotter, when 

 warmed by the flame, than the melted lead, y^- degree was 

 greater than the greatest error introduced during the experi- 

 ments by the heat-insulating capability of the asbestos 

 paper. 



Each of the copper wires with its thermo-element junction 

 was melted into the metal in its respective limb, and held in 

 the centre of the tube by asbestos paper. One limb of the 

 W was heated in a sand bath, and the other was kept cold in 

 melting ice. 



The two standard copper wires and the two free wires from 

 the temperature-determining thermo-element were led to a 

 paraffin switch-block, so that either pair could be connected, 

 through a reversing key and a resistance, to a reflecting gal- 

 vanometer. This resistance was so great as to render no 

 correction necessary for the resistance variations, due to heat, 

 in the circuit. For each reading the temperature of the hot 

 junction was made nearly constant ; then, using each thermo- 

 electric combination alternately, galvanometer deflexions 

 were noted with the current direct, and the current reversed. 

 After the necessary correction, the mean of the readings of 

 the platinum -platinum -rhodium thermo-element gave the 

 temperature, and the mean of the readings of the thermo- 

 element under test gave the E.M.F. in arbitrary units. 

 After each complete experiment, the constant of the tempera- 

 ture-measuring thermo-element was determined by removing 

 the crucible containing sand, putting in its place one contain- 

 ing melted lead, and allowing the lead to cool, meanwhile 

 taking readings. 



The curves for copper-lead, copper-tin, and copper-bismuth, 

 which were obtained by this method, are given in figs. 1, 2, 

 and 3 respectively. The abscissae are temperatures and the 

 ordinates E.M.F.'s in arbitrary units. These curves will 

 be discussed when the mercury experiments have been de- 

 scribed. 



The W-shaped tube was not suitable for the application of 

 a freezing-mixture, and so in the mercury experiments the 

 junctions were each in a small test-tube about half filled with 

 the metal. An inverted U-tube also full of mercury, with 

 one end dipping into the metal in each of the test-tubes, 

 connected the two. One of the test-tubes was surrounded by 

 melting ice, and the other was cooled with a mixture of solid 

 carbon dioxide and ether. A mass of copper wire was 

 wrapped round the tube to be cooled, in order that it might 

 warm up slowly after the evaporation of the carbon dioxide. 



2 H 2 



