Harti—Ooncentration of Soap Solution on Surface of Liquid. 57 
soap, to settle, and then filtered off into a large airtight reservoir 
of two gallons capacity. A weak solution of standard CaCl, was 
also made by mixing 10 c.es. of the standard CaCl, solution with 
200 ec.cs. of distilled water. A large Winchester bottle, of a 
couple of gallons capacity, was cleansed thoroughly, and about two 
quarts of the soap solution introduced, and shaken up vigorously 
until the rest of the bottle was full of froth. The bottle was 
then put aside to allow the small bubbles to rise, and then the 
solution was filtered from the froth, and the froth allowed to 
settle in the bottle, which was corked tightly to prevent oxidation. 
The solution poured off was now titrated with the CaCl, from a 
burette by the usual method for determining the strength of soap 
solution. The condensed froth was likewise titrated, and the 
following results obtained :— 
First EXPERIMENT. SECOND EXPERIMENT. 
25 oeumitneut 25 c.cs. condensed 25 €.€S. solution. 25 eves scoucensed 
c.cs. CaCl. c.cs. CaCl,. c.cs. CaCl,. c.cs. CaCly. 
6°65 7:2 6 6-2 
6-4 7:3 5-4 6-1 
6°65 73 5:2 6°25 
6-7 6 6-3 
a7 6-2 
a) 
5:8 
Mean, 6-6 Mean, 7:26 Mean, 5°65 Mean, 6°21 
The third experiment was made, and a large amount of froth, 
from a couple of gallons of solution left to settle all night in a 
closed vessel. 
On titrating next day it was found to be of less strength 
than the solution from which it had been filtered, and which 
had been titrated at time of filtration. Evidently this was due 
to oxidation, and so another experiment was made, the filtered 
