Resistance of certain Amalgams with Temperature. 4o7 



temperature, so that in the curve the part pertaining to 

 decreasing temperature lies below the other. It cuts the 

 latter, however, at 28°, and the final resistance is very slightly 

 greater than that at the beginning of the experiment. In 

 most cases this slight increase in the resistance for curve A 



Fig. 1.— Resistance of an Amalgam containing 4-8 per cent, of Zinc. 



is found ; this is owing to the repeated heatings taking place 

 one day and the cycle being taken on the following day, the 

 small increase represents therefore the amount by which the 

 resistance has fallen during the interval. 



The separation of the heating and cooling parts of the 

 curve cannot be explained by a lag in the temperature of the 

 spiral behind that of the thermometer placed in the bath, 

 for before the final reading was taken the bath was kept at 

 a temperature varying only hj one-fifth of a degree for 

 several minutes. The spiral was then allowed to stand for 

 four weeks, when another cycle was taken. Curve B was 

 plotted from these readings. 



Curve B. An entirely different curve is here obtained. 

 Whereas in A the resistance falls with increased temperature 

 up to about 30°, and then reaches a flat minimum, in B it 

 increases rapidly up to about 40°, after which the curve is 

 nearly parallel to the corresponding part of A. The figure 

 also shows that the difference between the initial and final 

 resistance in B is very much greater than in A : it also shows 

 the relative amount the resistance fell between the two cycles. 



The next day after B was obtained a further cycle was 

 taken ; the curve obtained was similar to A, and was very 

 nearly coincident with B above 40°. After standing for 

 several weeks the resistance had returned to a value which 

 differed somewhat from that shown at P in curve B. when 



