Resistance of certain Amalgams with Temperature. 449 



100 ohms resistance. The readings obtained are thus inde- 

 pendent of the change in resistance of the amalgam. The 

 junction was heated several times to ensure against changes 

 in the surface of the metal wire before readings were taken. 

 If a new compound is formed at the hot junction at a given 

 temperature, we may expect a change in the E.M.F. at that 

 junction between the metal wire and the amalgam, but this is 

 not the only effect that would be produced, lor, going from 

 the hot junction, we come to amalgam that is at a lower 

 temperature, and which is therefore unaltered in composition, 

 and this being in contact with the altered amalgam, and the 

 temperature not being uniform along the tube, we might 

 expect another E.M.F. to be set up between contiguous 

 portions of the amalgam if they differ from each other 

 chemically or physically, and this may increase or decrease 

 the effect which it is wished to observe at the junction. The 

 thermo-E.M.F. between different metals and the amalgam 

 measured in this way was found to increase uniformly with 

 the temperature, so that if a new zinc-mercury compound is 

 formed its thermo-electric effect introduces a change too 

 small to be measured. As the change in E.M.F. would 

 necessarily be small if it were present, care was taken to get 

 rid of other thermo-E.M.F. s in the circuit by having all 

 contact-makers and wires in the circuit of the same material 

 and kept as nearly as possible at the same temperature. 



The same result was obtained when a circuit was formed 

 by the W-shaped tube and a galvanometer only. The tube 

 being wide its resistance may be neglected if that of the 

 galvanometer is a few ohms, and so an increase in the current 

 through the galvanometer arising from a fall in the resistance 

 of the amalgam in the neighbourhood of 70° will not be 

 observed, and any irregular change in the current will thus 

 come from a change in the thermo-E.M.F. at the hot junction, 

 but no such irregularity was noticed. 



The rise in temperature effected in equal times when the 

 amalgam was placed in an inclosure whose walls were kept 

 at a constant high temperature was next examined. 



The inclosure used was a heater used in calorimetry. The 

 two ends of the cjdinder were plugged up to avoid draughts, 

 and a good supply of steam was passed through the outer 

 double walls. The amalgam was first cast on a thermometer 

 bulb, and the stein of the thermometer passed through a cork 

 at the top of the heater, but this was unsatisfactory, for a 

 laro-e thickness of the substance under examination could not 

 be put on the bulb for fear of fracturing it, and with the 



Phil. May. S. 5. Vol. 48. No. 294. Nov. 1899. 2 I 



