OCTOBER 15, 1937
ANALYTICAL EDITION
ceived, but can be easily rendered iron-free by one distillation through glass. Being very stable it can be stored indefinitely. It is manufactured by the Carbide and Carbon Chemicals Corporation and sold under the trade name “Methyl Cellosolve.” The price is considerably below that of the c. P. acetone, heretofore used in routine analysis.
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open test tubes a t average room temperature of 27” C. The values a t the end of 24 and 47 hours both showed the evaporation in 2-methoxyethanol to be 96 per cent less than in acetone. The acetone reagent (5) used in all the above tests was made by dissolving 10 grams of ammonium thiocyanate in 45 ml. of water and 200 ml. of acetone.
Experimental
Summary
The reagent solution is made by dissolving 10 grams of ammonium thiocyanate in sufficient 2-methoxyethanol to make 250 ml. The solution should be stored in the dark a t once and left for 24 hours before using. That length of time is necessary to allow decolorization of the initial pink color formed by the iron present in even the best grade of thiocyanate. The persistence of color from such a small amount of iron is excellent confirmation of the nondissociative nature of the solvent; in water the dissociation is instantaneous, no pink color being visible a t any time. The reagent thus prepared has only one disadvantage: It is subject to photochemical change, with the formation of a yellow color. This effect can be completely prevented by keeping the reagent away from light except when in use. It is also advisable to keep both the solvent and the reagent solution from contact with filter paper, cork, and rubber to prevent contamination with iron and organic materials. If the ammonium thiocyanate is sufficiently clean there will be no need to filter. In developing the ferric thiocyanate color 4 volumes of reagent are used to 1 of iron solution. For routine analysis the author has followed this plan:
2-Methoxyethanol is a superior medium in which to develop and compare the ferric thiocyanate color. It gives a color 85 per cent more intense than that developed in water. Compared with the most effective acetone-water mixture, it shows 27 per cent greater intensity of color and 96 per cent less evaporation. It is colorless, almost odorless, and can be rendered ironfree by one distillation through glass. Because of its low price and slight evaporation it is very economical. With ammonium thiocyanate it makes a clear colorless reagent which conforms to Beer’s law, and, having a low dielectric constant, it effectively inhibits loss of color through dissociation. Since this new medium makes possible the development of a ferric thiocyanate color of unusual intensity and stability, it should prove especially effective for determination of the minute amounts of iron in biological materials.
Pipet 2 ml. of unknown solution into a 10-ml. volumetric flask, add 2 drops of 0.1 N potassium permanganate, and when
Acknowledgment The author wishes to express his appreciation to Joseph P. Bain, Department of Chemistry, University of Florida, for valuable advice concerning organic solvents, and to thank W. H. Byers of the Department of Physics for his determination of the dielectric constant of 2-methoxyethanol.
decolorized run in the reagent t o volume. Develop the standard in the same way and make the color comparison in a Bausch & Lomb biological (semimicro) colorimeter using a 25-watt frosted bulb in a Bausch & Lomb dome-shaped illuminator. Have the Standard and unmirror at angle of maximum reflection. known iron solutions should contain sufficient hydrochloric acid to give a normality of 2.5. The most suitable concentration for the iron standard is 0.02 mg. of iron per ml.
Literature Cited Akerlof, G., S.Am. Chem. Soc., 54, 4125 (1932). Fowweather, F. S., Biochem. J.,20, 93 (1926). International Critical Tables, Vol. 6, pp. 78-96 (1929). Marriott, W. McK., and Wolf, C. G. L., J. Bid. Chem., 1, 451 (1906).
Miller, R. C., Forbes, E. B., and Smythe, C. V., J.Nutrition, 1, 217 (1929).
Under the above conditions, several tests were made to determine the relative intensities of color developed with ammonium thiocyanate in the three media under discussion: water, water-acetone mixture, and 2-methoxyethanol. Using the water solution as the standard, and reading immediately, the 2-methoxyethanol gave a comparative in20.0 tensity of 10.8 mm. With the acetone-water mixture as the 20 0
%
mm. Thus the instandard, the average reading was tensity of color developed in 2-methoxyethanol is 85.2 per cent deeper than in water and 27.4 per cent deeper than in the acetone-water mixture. I n order to test the optical clarity of the 2-methoxyethanol-ammonium thiocyanate solution, the following comparison was made: I n one flask a standard solution was used whichcontained 0.02 mg.of iron, and in theother flaskan equal volume of standard containing 0.04 mg. of iron. Both flasks were developed with the 2-methoxyethanol reagent under identical conditions. At different deDths the readinas were 10.0 15.0 20.0 25.0 30.0 =, T ~ 10.2, , i2.6,and -, thus indicating excellent con15.3 formity to Beer’s law. The boiling point of 2-methoxyethanol is so high that there is no loss in volume during the process of analysis. The developed solution will stand in an open test tube for weeks without pronounced loss of color or of volume. The evaporation loss from solutions developed by the organic solvent reagents was calculated from decrease in depth of column in
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Tarugi, N., Ann. chim. applicata, 16, 281 (1926). Walden, P., 2.physik. Chem., 147, A, 1 (1930). Weigert, F., Ibid., 10, B, 241 (1930). Williams, J. W., Chem. Rev.,6, 589 (1929). Wong, S. Y., J. Bid. Chem., 55, 421 (1923). RECEIVED August 16, 1937.
The Absolute Turbidity of Raw Sugars F. W. ZERBAN AND LOUIS SATTLER New York Sugar Trade Laboratory, New Yorlr, N. Y.
I
T HAS previously been stated by the miters [IND. ENG. CHEM.,Anal Ed., 6, 178 (1934); 7, 157 (1935); 9,229 (1937)] that the correction factorf(r) of Sauer can be used to calculate the absolute turbidity of white sugars, but that it is not applicable to raw sugars high in turbidity. A reexamination of the miters’ data on raw sugars has shown that the correction factor must be based, not on the extinction coefficient (-log T for 1 cm. thickness) of the turbid solution as has been done by Landt and Witte, but on that corresponding to the coloring matter alone. If this be done, the absolute turbidity of raw sugars is found to be directly proportional to the turbidity expressed in the system used by the writers. Details will be published later. RBCBNVED September 16, 1937.
