20, 1 Del Rosario and Valenzuela: Acetylsalicylic Acid 19 
OC-0-CHs C-O—CHs 
CeHy 
- 
. goGe 
Moreover, in the examination of this wrongly named ester, 
which is rather a keto-acid, we determined the free acetic and 
free salicylic acid by methods which, if not accurate, at least 
give us the ratio among the samples examined. . 
The methods used by us were: 
1. The titration of our group of samples dissolved in 15 cubic 
centimeters of alcohol rendered neutral with 0.2 N sodium 
hydroxide using phenolphthalein as an indicator. 
2. To this neutral solution 50 cubic centimeters excess of 0.2 
N sodium hydroxide is added, boiled under a reflux condenser 
for half an hour, and titrated back with 0.2 N sulphuric acid. 
The amount of sodium hydroxide used in both titrations for 
the acid and the saponification values ought to be the same. 
3. The identification of salicylic acid by the bromine test 
is based upon the fact that four hydrogen atoms are replaced 
by bromine; of these four bromine atoms only one (that of the 
chain) and the excess of the solution react upon the potassium 
iodide solution, thus: 
OH _—- OBr 
CoH + 8Br ——> CsHBre— + 4HBr 
COOH COOH 
OBr OK 
CsHBri OK) ==44 GHB 4+ KBr + 21 
“~cooH —~_ coon 
It is, therefore, evident that for each molecule of salicylic acid 
(molecular weight 138) three atoms of bromine (3 < 79.92=— 
239.76) are fixed. The number corresponding to sample 0 in 
Table 2 (which is theoretical) for the 0.2 N bromine solution is 
calculated for a one-gram sample. 
4. As to free acetic acid, we used a method that gives only 
a relative content of the sample. 
The method consists in washing a gram of the sample on a 
plain filter with small portions of distilled water at 15° C., up 
to a total of 25 cubic centimeters. The filtrate is then titra- 
ted with 0.2 N sodium hydroxide. 
