THE ELECTRICAL RESISTANCE OF THIN LIQUID FILMS. 
477 
X 
r- 
300 
— ,C 300-5'2p’ 
_2-2 lOOjo 
“ 3 100 —/ 
5=100— g 
Solutions were made up in accordance with the numbers given by these formulae to 
represent films composed originally of a 5 per cent, standard solution, which had lost 
15, 20, and 25 parts of water respectively. The standard solution used had a specific 
resistance of 135 at 20°, somewhat lower than that given by other similar solutions 
which varied from 140 to 143. 
It was found that the specific resistances and parts of water lost were connected by 
the convenient formula 
jr=10(p—p')=10S 
where p is the specific resistance of a standard x per cent, solution. 
Table V. 
P= 135. 
P- 
V- 
p (calculated). 
135 
0 
00 
157 
15 
14-8 
177 
20 
20-5 
203 
25 
26-0 
XI. Results of the experiments. 
Specific resistance oj films .—The observations on the licpiid in mass showed, as has 
been already pointed out, that additions of water diminished, and additions of glycerine 
increased, the specific resistance. In agreement with this a large number of prelimi¬ 
nary experiments proved that the specific resistance of a soap film was higher in dry 
than in damp air, and that the changes due to variations in the hygroscopic state of 
the atmosphere were very much larger than any which might be due to the diminish¬ 
ing thickness of the film. As our latest experiments were however in several respects 
the most full and trustworthy, we confine ourselves in this paper to giving an account 
of them, premising only as the result of our preliminary work, that any large change 
in the specific resistance of a film might be safely attributed to the absorption or 
evaporation of water. 
The observations were made between September 13 and October 1 , 1880. Several 
films were rejected either because the insulation was found to be faulty, or because 
irregular masses of the black or white of the first order, which must have deflected the 
lines of flow, were collected at the top. Twenty-three films were observed without 
3 q 2 
