of Gibbs's Theory of Surface-Concentration. 515 
a concentration 0318 per cent. After adsorption had oc- 
curred, a drop-number through the emulsion gave 459 
corresponding to a tension 13'U: dynes, which again cor- 
responds on fig. 2 to a concentration "295 per. cent. 
.\ Fall in concentration = '023 per cent. 
This was the general method adopted to determine change 
in concentration, it being much more delicate than any 
purely chemical means. It will be noticed that in the above 
the assumption is made that the emulsion particles them- 
selves would not affect the value given by the pipette for 
the tension of the solution in which the emulsion is suspended. 
Justification of this is afforded by the concordance between 
the results obtained for the adsorption by this method and 
by an entirely different method to be described later. 
Continuing: — 
Fall in concentration of '023 per cent. = '115 gram 
for the 500 c.c. solution employed. 
Hence the mass adsorbed per cm. 2 , L e. 
r= 'Ho 
31,553 
r = 3'6xl0- 6 gram. 
Similar determination ofT, using Oil B : — 
The solution made up gave a drop-number 531, corre- 
sponding on fig. 3 to concentration "317 per cent. 250 c.c. 
of solution were emulsified with '160 c.c. oil (density *900), 
and after emulsification the drop-number was 507, corre- 
sponding on fig. 3 to a concentration '290 per cent. 
Hence the fall in concentration = '027 p. cent. 
.*. Total mass adsorbed from the 250 c.c. soln. = *067 gram. 
Total adsorbing area = 11058 cm. 2 
.'. F=5'9 x 10~ 6 gram per cm. 2 
A further determination with a solution whose original 
concentration was *2 per cent, gave a value for the adsorption 
coefficient 
T = ±'7 x 10 -6 gram per cm. 2 
An estimation of the probable error of these values really 
depends on the estimation of the radius of the emulsion 
particle. As great care as possible was taken to obtain 
