ANALYTICAL CHEMISTRY
928
specially prepared filter paper pulp to help collect the silica, filter immediately through one of the specially prepared filter papers, and wash once with 1 to 99 hydrochloric acid. Put the paper containing the silica back in the platinum dish, add 5 ml. of concentrated nitric acid and 3 ml. of perchloric acid, cover with the cover glass, and heat gently to oxidize the paper. After oxidation is complete, wash down the cover and sides of the dish carefully with a small amount of water, continue the evaporation to dryness, and then ignite gently. Fuse the residue with 2 grams of anhydrous sodium bicarbonate, allow to cool, take up fusion with water, and then neutralize and adjust to pH 4.5 to 5.0 with a pH meter, using 6 N sulfuric acid. Keep dish covered while neutralizing, in order to avoid loss from spattering. I t was found by experiment that this pH will result in the optimum pH of 1.6 a t the point of formation of molybdisilicic acid (1). It will be necessary to have some silica-free ammonium hydroxide on hand to help in adjusting the pH a t 4.5 to 5.0. Heat the solution t o remove carbon dioxide, cool, and then dilute to 100 ml. The oxides of nickel that will be present soon settle and a clear solution can be pipetted off the top, or if desired, the solution can be filtered through one of the specially prepared filter papers and then diluted to volume. Suitable aliquots are treated as in the preparation of the calibration curve, and transmittancy measurements are made a t 820 mp after 20 minutes. Values are obtajned from the calibration curve.
Data. Table I indicates the accuracy of the method; the results are compared to those reported by other laboratories.
SUMMARY
Although to date this method has been used only for determining silicon in cathode nickel and a Iiational Bureau of Standards sample of aluminum alloy, it should be applicable to the determination of silicon in almost any metal or material that is acid-soluble, unless the major component is an element that interferes seriously with the color development. In that case, it would be necessary to wash the filter more thoroughly, determine the loss of silica for the necessary number of washings, and apply a correction in subsequent similar analyses. ACKNOW LEDGhIENT
The author wishes to express appreciation to Wendell L. Hummer, a former member of the analytical staff, for his iuggestions and generous assistance in preparation of the manuscript. LITERATURE CITED
(1)
Bolts, D. F., and Mellon, 31. G., IND.ENG.CHEM., A N ~ LED,, . 19,
873 (1947). (2) Bunting, W. E., Ibid., 16, 612 (1944). (3) Smith, G. F., “Perchloric Acid,” 4th ed., p. 18, Columbus, Ohio, G. Frederick Smith Chemical Co., 1940.
RECEIVED February 20, 1950.
Simultaneous Determination of Ethylene and Propylene Chlorohydrins W. A. CANNON Wyandotte Chemicals Corporation, Wyandotte, Mich. Ethylene and propylene chlorohydrins are determined simultaneously with an average error of 1.9% for ethylene chlorohydrin and 2.0% for propylene chlorohydrin. The mixed chlorohydrins are hydrolyzed to glycols by heating with sodium bicarbonate in sealed bottles. The glycols are oxidized with periodic acid and the acetaldehyde and formaldehyde are determined polarographically after a simple distillation. The method is applicable to mixtures
A
LTHOUGH several methods have been described for the quantitative determination of chlorohvdrins, none is applicable to a quantitative determination of ethylene and propylene chlorohydrins in the presence of each other. Trafelet (4) determined total water-soluble chlorohydrins by selective hydrolysis with sodium bicarbonate and titration of the chloride ions liberated. Other methods mentioned in the literature, such as Uhrig’s (6) method for determination of ethylene chlorohydrin, cannot be used to distinguish between ethylene and propylene chlorohydrins in mixtures. The method described in this paper consists essentially of hydrolyzing the chlorohydrin mixture with sodium bicarbonate to the corresponding glycols.
+ NaHC08 --+C H ~ O H . C H ~ 0+H KaC1 + CO, CHa.CHOH.CH&I + NaHC03-+ CHs.CHOH.CHzOH + NaCl + COS
of ethylene and propylene chlorohydrins in water solution or water-soluble solvents. The principal limitation to the method is that there must not be present or formed any volatile substances polarographically reducible at the same potential range as the aldehydes. The presence of monohydric alcohols or moderate concentrations of hydrochloric acid, aliphatic dichlorides, or dichloro ethers does not interfere with the determination.
+ HI04 +2HCHO + HI03 + Hz0 CHa.CHOH.CH20H + HI04 HCHO + CHaCHO + HIOs + HsO CHzOH.CH20H
.----f
The aldehydes produced are removed by distillation and determined polarographically according to the procedure described by Warshowsky and Elving (6) and Whitnack and Moshier (7‘). The acetaldehyde produced by periodic acid oxidation is a measure of the propylene chlorohydrin concentration of the mixture before hydrolysis. The ethylene chlorohydrin can be estimated by deducting the formaldehyde produced by the oxidation of propylene glycol from the total formaldehyde produced.
CHzOII.CH&l
After neutralization, the glycol mixture is oxidized with periodic acid to give formaldehyde and acetaldehyde according to the following equations:
MATERIALS AND APPARATUS
Periodic Acid, 0.5 N. A solution is pre ared by dissolving 11 grams of eriodic acid (G. Frederick Smitg Chemical Compan ) in distillexwater and diluting to 100 ml. This solution should
