Resistance of certain Amalgams ivith Temperatvre. 445 



is greater when they are cooling ; (b) that part of the cycle 

 at the higher temperatures is reversible ; (c) when allowed to 

 stand at the temperature of the room after being heated the 

 resistance falls. This fall is a great deal less, however, than 

 in the case of zinc amalgams, and it is completed in three days. 

 The curve in fig. 8 represents the results of measurements 

 made on the spiral after it had been standing for a week. If 

 the amalgam is heated, and then, immediately it has cooled 

 to the temperature of the room, is taken through a cycle, the 

 first part of the curve is much flatter, as for zinc amalgams ; 

 but two different curves cannot be obtained, for this flat 

 portion soon joins the other, after which they coincide. It 

 is interesting to note with respect to these resemblances of 

 zinc and cadmium amalgams that zinc and cadmium are 

 nearly related according to the periodic arrangement of the 

 elements. 



§ 6. Magnesium Amalgams. 



Only one magnesium amalgam was tried, owing to the 

 difficulty of preparation. It contained 1 per cent, of mag- 

 nesium. The curve obtained was practically a straight line 

 up to 110°, showing that up to this temperature the tem- 

 perature-coefficient was unaltered. At increased temperatures 

 the resistance increased at a slightly greater rate. The 

 resistance was the same at a given temperature, whether the 

 spiral was being heated or cooled. 



Under 1 per cent, of magnesium gives a solid amalgam 

 which melts at about 170°, so that these could probably be 

 best studied in the form of wires, which would have to be 

 protected from the air, as amalgamation renders magnesium 

 more active chemically, e. g. magnesium amalgam will de- 

 compose water at ordinary temperatures. 



§7. 



Experiments were next made to discover other physical 

 properties which presented any sudden variation at the 

 temperatures at which the resistance undergoes sudden 

 alteration. 



In the case of tin and cadmium amalgams this sudden 

 alteration in resistance accompanies a change in state. A 

 portion of the 10 per cent, tin amalgam was put in a thin 

 test-tube surrounding a thermometer-bulb; it was heated to 

 150° and then allowed to cool slowly suspended in a copper 

 vessel whose walls were kept at a constant temperature. 

 The temperature was read every 15 seconds, and a curve 

 plotted with time as abscissa? and temperature as ordinates. 



