THE SMITHSONIAN INSTITUTION. 387 



A dilute solution of sulphate of zinc 0.0223 



Commercial nitric acid 0.0263 



Hankel lias published a more extensive series of experiments on 

 tliis subject, {Fog. Ann., LXIX, 255.) He found the resistance of a 

 concentrated solution of sulphate of copper (A) of tlie spec. grav. 1.17, 

 at different temperatures, as follows : 



0° 11.26 



11.9 7.33 



31.0 4.70 



66.4 3.12 



The resistance of 108.^ parts of the former solution (A) ivith 185 parts 

 ivas, at 



0° 22.87 



11 15.16 



25 10.5 



67.4 7.1 



The resistance of a concentrated solution of nitrate of copper teas, at 

 0° 4.89 



11.5 3.27 

 25 2.18 

 67.2 1.64 



The resistance of a concentrated solution (B) of sulphate of zinc ivas, at 



0° 13.05 



9.8 8.62 



27.4 4.55 



67.4 2.29 



TJie resistance of a mixture of "il parts of the solution (B) and 1 16 ^ar^s^ 



water loas, at 



0° 13.00 



11.1 8.82 



28.8 5.57 



65.1 3.51 



The unit to which these resistances were referred was arbitrary. 



The construction of the vessel holding the liquids used in these ex- 

 periments cannot be clearly understood from Hankel's description. 



On considering the result, we find that the decrease of resistance is 

 not proportional to the increase of temperature, as Becquerel supposes. 



For the concentrated solution of sulphate of copper, we have on an 

 average the following for a rise of one degree of temperatuTe : 



Limits of temperature. Decrease of 



resistance. 



0° and 12° 0.327 



12 '' 31 0.138 



31 " 66.4 0.044 



Thus for a given difference of temperature, the corresponding change 

 in the resistance of the liquids is greater, the lower the temperature. 



