1894.] Thermo-electric Properties of Salt Solutions. 371 



Let di, d 2 , d 3 be the changes in the resistance of ft in the three 

 observations, R the resistance of the platinoid coil 7, d the current 

 in the first, C that in the latter two observations. Then we have the 

 following equations, since we may take d it d 2 , d 3 proportional to the 

 changes in the temperature : 



RCf = d,K 

 AC 2 +HC = d*K 

 AC 2 -HC = dK 



2HC = (dt-dJK 



TT _ dzda C, 2 p 

 ~2dT ' C" ' 



is is open to the objection that the heating not being the same in 

 each case, the loss of heat will not be the same in each. 



An improvement on this method which was afterwards adopted 

 ensures the loss of heat being steady, and the same for all the obsei 4 - 

 vations. This was to so adjust the current that the change in the 

 resistance of ft should be the same, whether the current passed 

 through the liquid, so as to heat the electrode , or whether it passed 

 so as to cool , and at the same time passed through the coil 7. 



If C is the current which gives these equal differences, we have 



AC J + HC = dK = AC 2 -HC + RC 2 , 

 H = iRC. 



The following observations were obtained with these methods, or 

 combination of them, using a 15 per cent, solution of copper sul- 

 phate, for which the value of was equal to 6*8. The current is given 

 in terms of potentiometer readings and the change of resistance in 

 bridge divisions. 



Current 311 through 7 gives d = 49'6. 

 Current +315 through liquid gave d = +11. 



-315 d = -39, -39-5, -40, -43, 



and 46. 

 Mean, 41*5. 



Mean of first three, 39*5. 



+ 11 and -41-5 give H = 0'1992. H/f = 6-94x10-*. 

 + 11 and -39-5 H = 0-1927. H/* = 6'72 x 1Q-*. 



Current 311 gave the same change of resistance as current +306 

 through liquid a coil 7, 



VOL. LV. 2 D 



