54 Mr. W. H. Preece. Effects of Temperature on [Feb. 22,, 



increases, but increases at a greater rate than it decreased while being- 

 heated ; in other words, the resistance of a Daniell cell at any tempe- 

 rature (at least between 0° C. and 100° C.) is smaller before it is 

 heated up to a high temperature than afterwards, provided the 

 heating and cooling be done not very slowly. 



3°. That if the cell thus cooled down be left undisturbed at a certain 

 temperature, the resistance of the cell gets less and less, till, at last, at 

 the end of a certain period (which will be from about 40 to 50 hours), 

 it gets down to the value which it had before being heated up at all. 



4°. And, lastly, that the resistance of a Daniell cell is considerably 

 less when the solution of the copper sulphate is more concentrated 

 than when it is less concentrated, at any temperature, and under- 

 otherwise exactly similar circumstances. 



(6.) The Bichromate Cell. — The results for the bichromate are not 

 quite so remarkable, nor are they so interesting as those for the 

 Daniell cell, as will be seen on comparing the curves in the Diagram I 

 with those in the Diagram II, but the fall of resistance is 

 nevertheless very striking. In the case of the double-fluid bichromate 

 the curve HK of resistance obtained while the cell was being 

 heated up, differs so slightly from the curve KL obtained while 

 it was being cooled down, that the one is hardly distinguishable from 

 the other. The differences in fact may be attributed more to errors 

 of observation than to anything else. Yet, if there should be any 

 difference in the resistance in the two cases, it is one opposite in 

 character to that found in the case of the Daniell cell. 



The probability of the existence of this difference, as indicated by 

 the curve HKL, is supported by the results shown by means of the 

 curve hlh, for the single-fluid bichromate cell. Every point of the 

 portion hi- of the curve obtained while heating the cell up, lies con- 

 siderably higher than the corresponding point in the portion hi 

 obtained while cooling it down ; that is to say, the resistance of the 

 single-fluid bichromate cell at any temperature is greater before than 

 after it has been heated up. 



(c.) The Leclanche Cell. — Yery little remains to be said of the 

 curve PQR in the Diagram III, which represents the results for 

 the Leclanche cell. The general character of the curve PQR bears a 

 strong resemblance to the curve HKL ; in other words, the resistance 

 of the Leclanche diminishes with the rise and increases with the fall 

 of temperature at nearly the same rate as the resistance of the double- 

 fluid bichromate cell does. And, moreover, it is a matter of difficulty 

 to say with certainty, in the case of the Leclanche as in the case of 

 the double-fluid bichromate, whether or not the curve of resistance 

 obtained while being heated up coincides with the curve of resistance 

 obtained while being cooled down, because the part RQ is so nearly 

 coincident with the part PQ of the curve PQR, that any slight errors- 



