Resistance of certain Am ilg a >ns with Temperature. 439 



Curve A. The spiral was heated to 120° four times on one 

 day, and a cycle taken on the following day. The resistance 

 still falls with increasing temperature, but the part of the 

 curve representing this fall is nearer a straight line than in 

 the previous case. The most important feature is that at a 

 temperature 63° there is a sudden fall in resistance instead 

 of an interval of temperature in which the resistance scarcely 

 alters, as in the previous case. Also between 70° and 100° 

 the heating and cooling parts of the curve coincide. 



Curve B was obtained after the spiral had been standing for 

 five weeks. It shows abrupt changes in direction at the 

 points marked P, Q, R, corresponding to temperatures 37°, 

 7-4°, and 27° respectively. At these temperatures therefore 

 the rate of variation of resistance with temperature is rapidly 

 altering. 



Fu 



3. — Resistance of an Amalgam containing - 23'9 per cent, of Zinc. 



a Q 



In fig. 3 B represents the results obtained from an amalgam 

 containing 23*9 per cent, zinc after it had been standing for 

 several weeks. 



As it is typical of all the curves pertaining to amalgams 

 containing more than 10 per cent, of zinc, which were 

 obtained after the spiral had stood for some time, its chief 

 points will be noticed. 



It starts with a portion MS, nearly a straight line, followed 

 by a more sharply curved part SP. Along this latter part, 

 when the experiments are in progress, the resistance does not 

 attain its final value immediately the temperature of the bath 

 has become steady, but it has to stand in some cases fifteen 

 minutes before a reading can be taken. At P, corresponding 

 to a temperature 36°, there is a sudden change in direction. 

 The temperature corresponding to this sudden change in 

 direction is the same for all the amalgams which were tried 

 having percentages of zinc higher than 9'5. 



Along PQ the resistance quickly attains its final value, and 

 this part of the curve is very approximately a straight line. 



