April 15, 1942
ANALYTICAL EDITION
TABLE IV. EFFECT OF ACIDCONCENTRATION Ternary Mixture KI Kz Acid Acetyl Propionyl Butyryl
Acid Concentration0.10N 46.20 21.70 r Found Mole Per Cent 17.2 16.5 29.8 30.5 53.0 53.0 0.06 N 46.10 21.85
Taken
16.0 30.6 53.4
Coefficient ki
Propionic
kr kz kl
Butvric
N. G. Baumer, and M. Van Graafeiland in carrying out the analyses and tests reported in this paper.
7 -
0.12 N 45.85 21.50
16.6 29.4 54.0
TABLEV. EFFECTOF ACID CONCENTRATIOS ON PARTITION COEFFICIENTS Acid Acetic
297
k3
.
k6
0.06 N 0.846 0.574 0,583 0.256 0.285 0,092
0.10 N 0.844 0.573 0.579 0.254 0.278
0.12 N 0.844 0.573 0.579 0.252 0.273
0,090
0,090
0.12 N , and the results are shown in Table IV. The best agreement between the observed analyses and the amounts taken was obviously obtained with the 0.1 N solution, and poorer results were found using the other solutions. The six k values for acetic, propionic, and butyric acids were also measured a t these same three concentrations (Table V). It is apparent that the accuracy must suffer as the normality of the test solution deviates from the normality of the known acid solutions used in measuring the partition coefficients. For this reason, it is suggested that the normalities of the distillates be adjusted to within the range of 0.08 t o 0.12.
Extractants Tested Partition coefficients for acetic, propionic, and in some cases butyric acid were measured between water and each of the following organic solvents: Ethylene dichloride Propylene dichloride Carbon tetrachloride
n-Propyl acetate n-Butyl acetate Ethyl n-butyrate
E t h y l ether Isopropyl ether Butyl ether Amyl ether
Heptane Pentane Ligroin
Benaene Cyclohexane Decahydro naphthalene
n-Propyl and n-butyl acetates were found to give the greatest spread in numerical values for the three acids, and have been selected as the most satisfactory for this purpose.
Summary The partition (or distribution) method has been found to be practical and satisfactory for the analysis of mixed esters of cellulose, and particularly for cellulose acetate propionates, acetate butyrates, and acetate propionate butyrates. Details of manipulation are given together with limits of applicability, precision, and accuracy of the method. Necessary variations in the procedure are described for esters of higher acyl content and of nonvolatile acids. Commercial cellulose acetate propionates and acetate butyrates can be analyzed with a precision of about *O.l weight per cent acyl and an accuracy of about h0.2 weight per cent acyl. The effects of some of the variables have been measured. Acknowledgment The authors gratefully acknowledge the assistance of J. W. Mench, H. M. Barden, J. V. Fleckenstein, M. L. Townsend,
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Correction In the article on “Determination of Particle Size Distribution” [IND. ENG. CHEM., ANAL. ED., 14, 10 (1942)] several errors occur on page 12. Column 1, paragraph 4, the last word in the line should be “liquid” instead of L 1 ~ ~ l i d ” . Column 1, paragraph 8, PZ in the numerator of the fraction should be p 2 . Column 2, Sample Cnlculation, in the expression for p1 the numerical factor should be 1.0001. Column 2, the explanation in small type “For 40p at 20 cm.’ t r o = 9.75/9 = 1.2 minutes” should be “For 4 0 ~ at 20 cm.’ t g o = 9.75/8 = 1.2 minutes”. W. 0. HISKLE)
