476 PROFESSORS A. W. RE1NOLD AND A. W. RUCKER OK 
In the following table a few out of a large number of examples of the accuracy of 
this formula as applied to the liquid in mass are given :— 
Column I. gives the percentage of salt in the standard solution. 
Column II. p or the number of parts by volume of water or glycerine added to 
100— p parts of standard solution to produce the derived solution. 
Column III. gives the value of a obtained from the above rules. 
The other columns explain themselves. 
Table IY. 
I. 
X . 
11 . 
V- 
III. 
a. 
IV. 
l>-20■ 
V. 
t°. 
VI. 
pi (observed). 
VII. 
pt (calculated). 
3 
0 
0-0300 
2081 
16-8 
229 
228 
19-5 
211 
211 
3 
30 H,0 
0-0300 
176-0 
22-5 
160 
163 
5 
0 
0-0300 
135-0 
18-5 
142 
141 
0 
22-3 
125 
126 
5 
20 H,0 lost 
0-0355 
177-4 
18-2 
188 
189 
21-7 
167 
167 
5 
25 H,0 lost 
0-0390 
203-4 
14-9 
244 
244 
24-5 
172 
168 
It is unnecessary to quote experiments not made near the temperature limits of the 
observations on the films. With regard to the value of p. :o it was found that the 
addition of glycerine increased, of water (within certain limits) diminished, the specific 
resistance of a standard solution. If, however, the quantity of water added exceeded 
a certain amount, which varied with the percentage of the solution, further additions 
increased the specific resistance. As in all the instances of considerable change of con¬ 
stitution to be discussed hereafter, the specific resistance was greater than that of the 
standard solution, while the hygrometer showed that the air was drier than when the 
precautions to fill it with aqueous vapour at the tension of that given off by the 
solution were taken, it follows that, on the assumption also to be discussed hereafter 
that the specific resistance of the film and the liquid in mass are identical, the only 
case to be considered is that of a solution which has lost water by evaporation. 
A soap film, made from a standard solution, which has lost water by evaporation, 
may be considered as a mixture of another standard solution, containing a greater 
percentage of salt and of glycerine. 
If x and X be the percentages of the first and second standard solutions respec¬ 
tively, p the number of volumes of water lost in 100 of solution, 6' and g the number 
of volumes of standard solution and glycerine in 100 parts of the derived solution, of 
which the altered film is formed, respectively; then since a standard solution contains 
2 "2 volumes of glycerine to 3 of water 
