ANALYTICAL EDITION
January 15, 1942
in 1000 ml. of hydrochloric acid made by diluting 100 ml. of concentrated acid with water. The procedure employed in the titration of hydrazine sulfate was employed in the titration of 25.00-ml. portions of phenylhydrazine solution, except that beakers were employed and the iodate oxidation was followed potentiometrically (8). The internal indicator procedure then was applied in the same manner, except that 0.5 ml. of indicators 184, 185, and 246 was added after the reaction of the oxidation of iodine was almost complete. The results of a series of titrations are given in Table VII. Table VI1 shows that for the determination of both hydrazine and phenylhydrazine the Andrews-Jamieson procedure and the use of internal oxidation indicators give essentially the same results. Indicators 184 and 185 are preferred in the determination of hydrazine and indicator 185 is preferred in the determination of phenylhydrazine.
Summary The dyestuffs Amaranth, Brilliant Ponceaux 5R, and Naphthol Blue Black, having British Colour Index numbers 184, 185, and 246, respectively, may be used as oxidation indicators. They are not destroyed by high concentrations of
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hydrochloric acid in the presence of small amounts of iodine or iodine monochloride, but are readily destroyed by a trace of iodate under the same conditions. No indicator blank is required for sufficient amounts of indicator solution to give vivid end-point determinations. The determinations by the new procedure follow the established hdrews-Jamieson iodate-iodine monochloride reactions, except that chloroform or carbon tetrachloride is not required for use as immiscible solvent type of indicator.
Literature Cited (1) Andrews, L.W., J . A m . Chem. SOC.,25, 756 (1903). (2) Boettger, W., “Newer Methods of Volumetric Analysis”, tr. by Oesper, Part 4,New York, D.Van Nostrand Co., 1938. (3) Heisig, G.B.,J . A m . Chem. SOC.,50, 1687 (1928). (4) Jamieson, G. S., “Volumetric Iodate Methods”, New York, Chemical Catalog Co., 1926. ( 5 ) Smith, G. F., and Bliss, H. H., J . A m . Chem. SOC.,53, 2091 11931). ,--, (6) Ibid., 53, 4291 (1931). (7) Smith, G. F.,and May, R. L., IND. ENG CHEW,ANAL.ED., 13, 460 (1941). (.8.) Smith, G. F,, and Sullivan. V. R.. J . SOC.Chem. I n d . . 41, 104 T (1937). (9) Willard and Young, J . A m , Chem. SOC.,52, 38 (1930).
Colorimetric Determination of Phenothiazine H. L. CUPPLES Bureau of Entomology and Plant Quarantine, U. S. Department of Agriculture, Washington, D. C.
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MALL amounts of phenothiazine, such as may be encountered in the examination of insecticidal spray residues, may be determined colorimetrically by measuring the intensity of the red color produced by addition of bromine to the alcoholic solution of the phenothiazine (2). The same colorimetric measurement is employed for the analysis of commercial samples of phenothiazine (3). In describing certain modifications and improvements in the method as applied to the analysis of both foliage samples and commercial samples of phenothiazine, Dawsey (1) mentions the fact that the color development does not run its usual course with “high” concentrations of phenothiazine in the alcoholic solution, a green compound being formed in place of the desired red compound, but he gives no definite concentration a t which the green compound first makes its appearance. Other workers have noted that off-colors are sometimes obtained with concentrations of phenothiazine within the photometrically measurable range. I n applying the bromination method to the determination of phenothiazine in spray residues, the writer encountered considerable difficulty of this nature, and found the variation in visual color to be accompanied by a substantial change in the photometric reading. This was true for measurements with both a visual and a photoelectric photometer. The off-colored solutions had a purple hue and to the eye were darker than the normal-colored ones, but in the photometers they gave lower readings (absorptions). Investigation disclosed that off-colors could be produced a t will by adding the bromine water drop by drop, whereas a quick addition tended t o produce the normal red color. Three experimentally controllable factors were found to favor the formation of the normal red color: quick addition of the bromine water with rapid stirring, addition of the phenothiazine solution t o an excess of bromine water, and having the solutions warm when developing the color. I n addition, where the solution contains plant extractives, i t is
necessary to allow some time for bromination and to make sure that bromine is present in excess. With the aid of this information it was found possible to standardize the conditions of bromination so that consistent results were obtained mith known amounts of phenothiazine. The procedure adopted was t o add 5 cc. of saturated bromine water quickly t o 50 cc. of 95 per cent ethyl alcohol containing up t o 4500 micrograms of phenothiazine contained in a 100-cc. volumetric flask and previously warmed t o 60” C. The stoppered flask was allowed to stand 15 minutes in an oven at 60” C., and then a second 5 cc. of saturated bromine water was quickly added. After the flask had stood 10 minutes longer, the excess bromine was boiled off and the solution was cooled,diluted to definite volume, and filtered through a folded filter, the funnel being covered to minimize evaporation. Photometric measurements were made on the filtrate, after the first 25 cc. had been discarded. The precision of measurement is approximately one-tenth division a t the mid-point of the photometer scale, amounting to *2 per cent. With absorption cells 1, 3, and 10 cm. in length, satisfactory photometer readings may be made on solutions containing from 100 to 3000 micrograms of phenothiazine per 100 cc. The following data illustrate the accuracy of determination of known amounts of c. P. phenothiazine, as read from the appropriate calibration curves: Phenothiazine Taken
Phenothiazine Found
Micrograms
Mtcrograrn8
150 450 703 1200
140 430 730 1170
Error % -6.7 -4.4 f3.7 -2.1
Literature Cited (1) Dawsey, unpublished manuscript.
C. W., and De Eds, Floyd, Food Research, 2,305(1937). mith, L.E., IND. ENG.CHEM.,ANAL.En., 10,60 (1938).
