~)'22 Mr. W. 0. M. Lewis : Experimental Examination 
Frenndlich's experiments owing to the presence of the solid 
phase, but considerable support would be given to the ad- 
sorption theory of dyeing if it were shown that dye solutions 
actually did lower the tension at the interface between the 
solution and an inert liquid. This liquid must of course be 
such as to exclude both chemical combination and solution. 
With this object further measurements were made with 
the hydrocarbon oil B already experimented with, which was 
to function as the substance to be i£ dyed.-" 
Aqueous solutions of various concentrations of the follow- 
ing dyes were prepared : — Congo red (sodium salt), methyl 
orange (sodium salt). 
It is hardly to be expected that in any of these cases there 
would be solution in, or chemical combination with, the oil. 
Congo Red. 
A preliminary trial with this substance showed that there 
w T as a distinct lowering of interfacial tension. The following 
table gives the results obtained for solutions of different 
concentrations. 
Table IV. 
Per cent. 
Concentration. 
Drop- 
number. 
Relative 
Tension. 
Tension in 
dynes, cm. 
o-o 
128 
10 
48 
02 
140 
0914 
4387 
005 
148 
0-865 
41-52 
01 
165 
0-775 
3720 
012 
165 
0-775 
C7-20 
0-2 
165 
775 
37-20 
025 
165 
0-775 
37-20 
The results of Table IV. are plotted in fig. 5 (lower 
curve). 
It will be noticed that after the concentration has reached 
O'l per cent, there is no further effect on the tension. This 
probably represents the maximum true solubility of the dve ; 
and the minimum value for the tension might possibly be 
made use of as a practical method of ascertaining the optimum 
concentration for the dye-bath. 
From the lower curve (fig. 5) we obtain the value of the 
coefficient -r- , for the curve itself is practically a straight 
line. We may proceed, therefore, to apply the adsorption 
