140 



Miss Klaassen, On the effect of Temperature on [Jan. 26, 



74-7 % 



Temperature Eesistance 



16-8° C 13-3 Ohms 



96-7 

 93-6 

 82-5 

 80-5 

 68-9 

 50-3 

 42-0 

 30-5 

 28-7 



3-2 

 3-3 



3-8 

 3-9 

 4-6 

 6-2 

 7-3 

 9-4 

 9-8 



30% 



Temperature Eesistance 



170° C 2-68 Ohms 



420 

 624 

 91-3 



84-0 



1-89 

 1-60 

 1-33 

 1-40 



HS0 4 



2 4 



Temperature Eesistance 



63-6° C 1-53 Ohras 



46-0 1-81 



15-8 2-7 



•6 3-67 



These observations are represented graphically in Plate IV. in 

 which Temperatures are represented by ordinates, and Resistances 

 by abscissae. 



The form of these curves is similar in type to that of the 

 corresponding ones for viscosity given by MLr D'Arcy in the Phil. 

 Mag., Oct. 1889. The curvature first increases with the tempera- 

 ture, reaches a maximum, and then decreases. 



In Plate V. are represented the isothermals for 18° C, 20° C, 

 30° C, 40° C, 50° C, 00° Q, 70° C, 80° G. and 90° C, drawn from 

 the curves in Plate III., resistances being represented by ordinates, 

 and the percentages of H 2 S0 4 by abscissas. Points marked are 

 taken from Kohlrausch's observations. 



The isothermal for 18° C. has been continued up to its minimum 

 point (30% H 2 S0 4 ) from the observations of F. Kohlrausch. 



This curve has a point of minimum resistance at about 

 92 % H 2 S0 4 , 

 the resistance then rises, reaching a maximum at 



84-5 % H 2 S0 4 (the hydrate H 2 S0 4 . H 2 0), 

 and then again falls. The isothermals for higher temperatures 

 show that this rise in the resistance gradually diminishes, up to 

 70° C, above which temperature the resistances are in descending 

 order of magnitude. The increased resistance due to the hydrate 

 has, however, not quite disappeared, for even in the isothermal for 

 90° C. there is a change in the sign of the curvature, although 

 there is no longer a point of maximum resistance. 



