THE ELECTRICAL RESISTANCE OF THIN LIQUID FILMS. 475 
The experiments with sulphuric acid were not carried further, as they were intended 
merely to test the trustworthiness and accuracy of the method. Tabulating the above 
results, we have— 
Sulphuric Acid. 
Specific resistance at 18°. 
Spec. grav. at 1 8°. 
By electrometer. 
Deduced from 
Kohlkausch’s 
experiments. 
Difference. 
I. 
1-1993 
1-420 
1-426 
Per cent. 
0-44 
II. 
1-4119 
2-001 
2-000 
0-05 
III. 
1-6110 
4-725 
4-687 
0-80 
The agreement of the resistances measured by the electrometer, with the values 
obtained for similar solutions by Ivohlrausch by a totally different method, is suffi¬ 
ciently close to justify us in placing reliance upon this method for the investigation of 
other liquids. 
X. Relations between the specific resistance, temperature, and constitution of a liquid. 
A number of experiments were made at different times, by the method just des¬ 
cribed, on standard and derived solutions of different constitutions. Each liquid was 
observed at several different temperatures, and the results were plotted down in curves. 
Between the limits of temperature at which the observations on the films were made 
(17° C. to 22° C.), these curves were very approximately straight lines, and the 
equation to any of these might be expressed by the formula 
/ 3 = P2oC 1 + a ( 2 0 — t)} 
where p 20 is the specific resistance at 20° C. 
The quantity a varied only between the limits 0'027 and 0'032 for standard solutions 
containing 3, 5, and 7 per cent, of salt respectively, and for derived solutions to which 
not more than 100 per cent, of water had been added. Addition of glycerine to the 
standard solution increased the value of a, but, within the range of the change of 
constitution observed in the films, it did not exceed 0'039. The mean value for all the 
standard solutions studied, viz. : 0'03, was therefore taken as correct for all others 
differing but little from them in composition. For the five films mentioned in 
Section XI., which lost considerable quantities of water, a was taken equal to 
0-03 + 0-00013S 
where 8 is the difference between the specific resistances of the solution and of the 
standard solution from which it was derived. 
MDCCCLXXXI. 
