506 Mr. W. C. M. Lewis : Experimental Examination 
this way at the oil interface. The first experiments to be 
described were carried out with aqueous solutions of bile-salts. 
In order to make certain that no chemical or solubility 
effects existed between the oil and the solutions, the following 
tests were carried out : — 
(1) A portion of the oil was shaken up with water which 
was tested with phenolphthalein — neutral reaction, and 
therefore absence of* free fatty acid as impurity. 
(2) A portion of the oil was boiled for three hours with reflux 
N 
condenser with ~ methyl alcoholic potash — excess potash 
being titrated with standard acid. It was found that the 
acid required for neutralization was the same in amount as 
that for a blank experiment in which no oil was present. 
This proves the absence of fatty esters in the oil. 
(3) Some of the bile-salt powder was shaken up with the 
oil, the latter allowed to stand, filtered, and a "drop-number" 
taken with the pipette (see later) against distilled water. 
The same drop-number was obtained as with the untreated 
oil fresh from the stock. Since the tension is a very delicate 
test for the presence of the salt, the above shows fairly 
conclusively that there was no salt present in the oil after 
filtration, i. e., the salt is insoluble in the oil. 
(4) The oil was shaken up with a solution of the salt, the 
oil filtered off and a drop-number taken against water. The 
same result exactly was obtained as with the oil which had 
been simply shaken up with distilled water filtered off and a 
similar drop number taken against water. 
The above tests point conclusively to the fact that no 
effects of the nature of chemical combination or solubility 
take place between the oil and the bile-salt. 
Examination of the Bile-salt. 
A quantity of u sodium glycocholate " was obtained from 
Merck. On close examination, however, it appeared that 
this was far from pure. Besides sodium glycocholate there 
is also sodium taurocholate and other fatty acid alkali-salts. 
There were no inorganic substances such as sodium chloride 
or carbonate. Several determinations of the molecular 
weight (which is required, as will be seen later) by means of 
the lowering of freezing-point and rise of boiling-point of 
water gave as a result 140. Assuming complete dissociation 
iu water, this would give the undissociated molecular weight 
280. This latter was confirmed by a determination by the 
rise of boiling-point of alcohol, the result being 283. The 
osmotic molecular weight in water (viz. 140) is, however, the 
quantity required in the subsequent calculations. 
