ANALYTICAL EDITION
92
C o m p a r i s o n of R e s u l t s O b t a i n e d by Various M e t h o d s METHOD BaSOa B Isolation C Titration D Temperature rise E Aniline
A
SLUDGEI Per cent 58~4 55.1 58.6 5s:7
59.5
form solution to light-oil sludge is pure aniline sulfate and only the free sulfuric acid in the sludge reacts. Acknowledgment
60:6 59.2
Acknowledgment is made to the Magnolia Petroleum Company for permission to present the results of this work.
I1 SLUDGE Per cent Per cent 50.6 49.0 50.0 56:4
Vol. 1, No. 2
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Chart of Indicators Useful for pH Measurements’ Clarke E. Davis and Henry M. Salisbury NATIONAL BISCUITCOMPANY, 85 NINTHAvE., NEWYORK,N. Y.
a
H E accompanying chart of the indicators has been found to be very useful in quickly judging the pH of solutions and of spot tests on dry materials. It was compiled by noting the cblor produced when 4 drops of each indicator we:e added to 10-cc. sets of the buffer solutions recommended by Clark and lLubs.2 Most of the indicators are of the Clark and Lubs3 series with the addition of a few others in common use. The one called Combination A is a 50-50 mixture of methyl red and bromothymol blue that has been found very useful because of its wide range in color changes from pink a t pH 4.8 through orange, yellow, green, and finally blue a t pH 7.4. Bromocresol green as suggested by Cohen4has been found to be very useful over its range. The parabolas and ellipses are used in this chart to show, by their overlapping, the blending of one color with another. Diminution or increase in color strength is shown by a decrease or increase of the vertical width of the parabola or ellipse. The indicators were made up as shown in the table. In using this chart to test solutions, 4 drops of the indicator are added to 10 cc. I 2 3 of the solution and the color is then compared with the colors noted on the chart. When used for a spot test on dry material only a very small amount of the indicator is applied directly to the material under examination and reference made to the chart after ti moment or so. C O N C N . OF
INDICATOR
Methyl red Propyl red Bromocresol purple Bromothymol blue Phenol red Cresol red Phenolphthalein Thymol blue (alkaline range) Cresolphthalein Thymolphthalein
SOLN. Per cent 0.10 0.04 0.04 0.02 0.02 0.02 0.02 0.04 0.04 0.02 0.02 1.00 0.04 0.02 0.20
SOLVENT PH RANGE
1% alcohol Watet Wafer Water Watei. 60 alcohol 60% alcohol Water Water Water Water 95% alcohol Wster 95% alcohol 957! alcohol
1 . 0 to 3.2 1 . 4 to 2 . 8 3 Oto 4.6 3.Oto 4.8 3.2 to 5.S 4 . 4 t o 6.0 4.8to 6.4 5 . 2 to 6 . 8 6 Oto 7.6 6.8to 8.4 7 . 2 to 8 . 8 7 . 8 to 8 . 5 8 . 0 to 9 . 6 8 . 4 to 10.0 9 . 4 to 10.0
ljVhere,possible, the use of several indicators is advised in ordei. to give a more accurate judgment of the pH. I n some l-Rec&ed December 12, 1928. Contribution No. 11 from the Research Labgatory of the National Biscuit Comeany. 2 Clarq and Lubs, J . B i d . Chem., 26, 479 (1916). 8 Clar6 and Lubs, J . Bact , a , 1, 109, 191 (1917). 4 Cohen, U. S. Pub. Health Service, Pub. Healfh Refits., 33, 199 (1923); 41, 3061 (1926).
parts of the pH range the pH can be judged with an accuracy of *0.2. The operator’s accuracy can also be increased by the use of buffer solutions for comparison.
5
6
i
8
10
PH
Electrical measurements on unknowns followed by the use of indicators will also help the operator t o judge the finer shades of color.
Errors in Nitric Acid Figures Editor of Industrial and Engineering Chemistry: A mistake in the correct amount of fuming nitric acid to use in the Carius determination of halogens and sulfur has been carried into recent editions of analytical chemistry. This mistake renders this determination dangerous. Corrections may have been issued on these, but a reminder to check your books, cross out the incorrect and write in the correct amount, may save time and accidents. Fresenius, “Quantitative Chemical Analysis,” Vol. 11, John Wiley & Sons, 1915, on page 118 states t h a t “to avoid explosions, 4 grams of nitric acid per 50 cc. of bomb should under no circumstance be exceeded.” Three to 5 cc. of fuming nitric acid are ample for all determinations. Scott, “Standard Methods of Chemical Analysis,” 4th ed., Vol. I, p. 145, D. Van Nostrand Co., recommends 30 cc. of 96 per cent nitric acid. Treadwell-Hall, “Quantitative Analysis,” 3rd ed., Vol. 11, p. 326, John Wiley & Sons, recommends 40 cc. of 1.5 sp. gr. nitric acid.
The writer has not checked other editions or books for this error. A. W. BESHGETOOR THB Dow CHEMICAL COMPANY MIDLAND, MICH. January 4, 1929
