Properties of some Liquid Metals. 405 



observed for different pieces of bismuth are largely due to 

 this same cause. With tin the effect was less marked, and 

 with lead it was unnoticeable. In the mercury experiments 

 it was not possible to regulate the rate of cooling ; but the 

 two most widely differing curves obtained are given in fig. 4. 



As this effect of its previous treatment upon the metal 

 rendered accuracy impossible, the experiments were repeated 

 with three of the metals, viz. tin, lead, and bismuth, with a 

 method so arranged that the whole mass of the metal to be 

 tested was in a molten state, and thus homogeneous. 



The apparatus is shown in fig. 5. The metal was con- 

 tained in a U-tube A A x A 1 A, and was heated by a current of 

 electricity in ger man-silver wires HHH. The metal was 

 introduced into the tube by means of a glass pipette, both 

 tube and pipette being-warmed in a bunsen flame. The part 

 of the glass tube where the junctions were to be, A A, was 

 covered with copper to render the heat distribution more 

 uniform. The german-silver wire was insulated with 

 asbestos paper, and wound spirally round the tube in two 

 sections, M M l3 Mj M 2 . Over this were wrapped several 

 layers of asbestos paper and asbestos string, DD. The 

 connexions of the heating circuit are shown in fig. 5. In 

 the paraffin switch-block, P 4 , if T C and T x C\ were connected, 

 the same current from the heating battery passed through 

 both ammeters, G 1 Gr 2 , both resistances, W\ W 2 , and both 

 sections of the heating coil. This caused a saving in current 

 when it was merely required to melt the necessary con- 

 nexions into the metal, or to burn out the asbestos insulation. 

 If, however, T was connected the current passed through 

 the ammeter G 1? the resistance W 1? and the long section of 

 the heating coil ; and if Tj Oj was connected the current went 

 through the other ammeter, resistance, and heating-coil 

 section. By adjusting the resistances W x and W 2 the tempe- 

 ratures at the junctions could be varied as required. The 

 diameter of the german-silver wire was 0*5 mm., and the 

 largest current required was 4 amperes. The U-tube is 

 shown about one half actual size. 



For measuring the temperatures a platinum-silver thermo- 

 element was employed, as this gave E.M.F/s of the same 

 order of magnitude as those to be measured. This element 

 had three junctions, as shown in fig. 5, so that either the 

 temperature of one of the junctions or the temperature- 

 difference between the two junctions of the thermo-couple 

 under test could be measured. The thermo-element was 

 calibrated with linseed oil up to 288° C. ; and one point on 

 the calibration curve, at 441°*4 C. ; was determined with 



