THE ELECTRICAL RESISTANCE OP THIN LIQUID FILMS. 473 
The circuit was now broken, ancl the potential difference of the points a, a' again 
determined. The temperature at the beginning and end of each set of observations 
(which occupied about four minutes) was noted. Two sets of observations were always 
made at each temperature. The mean liquid-deflection derived from (1) and (3) 
was then divided by the resistance-deflection, after the proper corrections (already 
described) had been applied to both, and the quotient multiplied by the value of the 
resistance in the box of coils. 
Calculation, based on Joule’s law, showed that the rise of temperature of the 
liquid in the tube, due to the passage of the current, could not in an extreme case, 
supposing the current to flow continuously for 10 minutes, exceed the one-thirtieth of 
a degree Centigrade. 
A series of experiments was carried out with the view of determining how far the 
resistance of liquids measured by the electrometer method were in agreement with 
those obtained by other methods. Since the determinations of the electrical con¬ 
ductivities of liquid, made by Kohlrausch, and by Kohlrausch and Grotrian are 
more complete, and their results more consistent and trustworthy than those of other 
observers, it was resolved to test the electrometer method by comparing the resistance 
of a liquid furnished by it with that of the same liquid given by Kohlrausch. 
Sulphuric acid was selected for the purpose, and three solutions were prepared, their 
specific gravities at 18° being 1 1993, 1*4119, and 1*611. A new tube was made, the 
radius of which was about O'15 centim. Pieces of the larger tubing were fused to the 
ends for the insertion of electrodes and thermometers. The distance between the 
small holes made in it for the reception of thermometers was 12*742 centims., and the 
7 tV^ 
constant — was determined to be 0*00563376. 
I. Sulphuric acid, spec. grav. at 18° =1*1993, computed from determinations made 
at 12°*5 and 17°. 
Temperature. 
Specific resistance 
(=P). 
Centigrade. 
15-38 
20-61 
21- 46 
22- 78 
26-26 
Ohms per cub. centim. 
1-48235 
1-36730 
1-32820 
1-32450 
1-24865 
These values were plotted down on a piece of curve paper. From the curve so 
obtained the specific resistance at 18° was found to be 1*4198. 
Kohlrausch (Pogg. Ann., Bd. 159, p. 233) gives for sulphuric acid 
