70 J. A. EWING AND J G. MACGREGOR ON CERTAIN SALINE SOLUTIONS. 

1:3 
ep 
Y ae? 
or 
1°3 
R=65 +4 : 
D—1 
Calculating the resistances which this formula gives for the various densities, 
we have— 
Specific Resistance. Specific Resistance. 
—— SSS a 
Observed. Calculated. Observed. Calculated. 
WIG) - : A 194°9 536 . ‘ : 53°9 
L502" : ; 154°4 448. . ; 44°2 
OG ; : 101°3 30°00) = : E 35°3 
OO : : 81°5 29°69) ‘ : 29°6 
60°44. 3 : 62°7 F 
In conclusion, we give the following table for purposes of comparison :— 
Specific Resistance, B. A. Units. 
Sulphate of zinc, saturated ote ale : : 3 33°7 at 10° C. 
Do. do. (minimum) . ; 4 : ‘ 28°3 do. 
Sulphate of copper, saturated . ; , : ; 29°3 do. 
Sulphate of potash, _— do. : : : : ; 16°6 do. 
Bichromate of potash, do. : : : ; : 29°6 do. 
Mercury* ; : ‘ : : : . 0009563 at 0° C. 
It only remains that we should express our thanks to Dr Crum Brown and 
his assistants for the trouble they took to provide us with pure salts, which it 
seemed impossible for us to obtain without their help. The above experiments 
were made in the Physical Laboratory of the University of Edinburgh during 
the winter session 1872-73. We are particularly indebted to Professor Tarr 
for direction ana advice throughout the whole course of our work. 
* Report Brit. Assoc. 1864. 
