REVISION OF THE INDICATOR METHOD OF CLASSIFYING ACIDS AND BASES IN QUALITATIVE ORGANIC ANALYSIS DAVID DAVIDSON
T H E INDICATOR reagents recently recommended for use in qualitative organic analysis1 possess satisfactory stability over a period of a year except in the case of the B-I1 reagent. The difficulty in this case is due to the ease with which the less acidic sulfonphthaleins such as thymol blue undergo conversion t o dimethyl ethers by means of methanol.= It is now recommended, therefore, that the B-I1 iudicator reagent be prepared without thymol blue, 25 ml. of methanol being substituted for the 25 ml. of thymol blue stock solution previou* prescribed. The resulting change in the color chart of Table 5, page 225, involves the extension of the yellow zone of the weak bases to the right-hand edge of the chart since the red zone no longer appears. The thymol blue stock solution (0.1 per cent in
' DAVIDSON, J. Chem. Education, 19, 221 (1942).
ORNDORFPAND CORNWELL, I. Am. Chem. Soc., 48, 981 ~ ~ SHAPIRO, ibid., 46, 2856 (1924). (1926): O R N D O RAND
Brooklyn College, Brooklyn, New York
methanol) which is employed in preparing the A-I1 indicator reagent should be made up with sufficient 2 M potassium hydroxide (in methanol) to convert most of the indicator to its basic form (blue). 0.3 ml. per 100 ml. of stock solution is adequate. This opportunity will he taken to point out several typographical errors which occurred in the original article as well as in a companion artic1e.J Page 160, Example 2, last line. Read "weak" for "intermediate." P a ~ e160, Example 3, next to last line. Insert "ion" after "dipolar." Page 222, Table 1. Read "10-"" for 10-1." Page 224, Figure 2, horizontal axis. Read "14" for "4." Page 224, second column, line 17. Read "5.4" for "8.6." Page 226, first column, next to last paragraph. Read "sulfonimides" for "sulfonamides." a DAvIDsoN, 3. Chem. Education, 19, 154 (1942).
