INDUSTRIAL AND ENGINEERING CHEMISTRY
578
With arsenious oxide Lang's procedure, as described below, was used except that 0.3- to 0.6-gram samples were taken.
Procedure for Standardizing 0.1 N Potassium Permanganate with Arsenious Oxide Accurately weigh ap roximately 0.25 gram of the dried oxide and transfer to a 400-mf beaker. Add 10 ml. of a cool20 per cent solution of sodium hydroxide, free from oxidizing or reducing substances. Let stand for 8 to 10 minutes stirring occasionally. When solution is complete, add 100 ml. o i water, 10 ml. of hydrochloric acid (sp. gr. LlS), and 1 drop of 0.0025 M potassium iodate or potassium iodide. The titration can be followed potentiometrically or visually. POTENTIOMETRICALLY. Titrate with the permanganate solution to the maximum value of the ratio, A E / A V , change in potential per unit volume of solution added. Add the last 1 to 1.5 ml. dropwise, allowing equilibrium to be reached before the AEreading is taken. In the potentiometric titration the blank is negligible, provided the reagents are free from interfering substances. VISUALLY.Titrate with the permanganate solution until a faint pink color persists for 30 seconds. Add the last 1to 1.5 ml. dropwise, allowing each drop to become decolorized before the next is introduced. Determine the volume of permanganate required to duplicate the pink color of the end point. This is done by adding permanganate to a solution containing the same amounts of alkali, acid, and catalyst as were used in the test. The corrections should not amount to much more than 0.03 ml. The end point can also be taken with ferrous phenanthroline indicator. In this case, add 1 drop of a 0.025 M solution of the indicator as the end point is approached. Then add permanganate slowly until the pink color of the indicator changes to a very faint blue. The blank correction should average about 0.02 ml. The normalities indicated for two approximately 0.1 N solutions of potassium permanganate are shown in Table I. The data indicate t h a t the recommended procedures yield results of a very satisfactory order of precision and that the standardizations of permanganate solutions b y the use of the
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TABLE I. NORMALITY OF POTASSIUM PERMANGANATE (Comparison of the normality of approximately 0.1 N KMnO4 as indicated by titration of AszOa and NazCzOd) t Difference Average from Normality Number of Deviation from NazCzO4 by AszOa Determinations Mean Value Catalyst
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Series 1. Normality by NazClO4 = 0.10015'J 0.10016 3 0.022 0.01 KIOa 0. lOOl8b 3 0.029 0.03 KIOa 0.002 0.10019 2 0.04 KIOaC n. ion19 3 0.028 0.04 KI ..~. 0.10391" Series 2. Normality by NaaCzO4 0.10387 1 0.04 KIOsd 0.03 KId 0.10388 1 4 o:oi5 0.10390 0.01 KIO3 0.10389 2 0.015 0.02 KI a Normality as indicated by Fowler and Bright's method. I n the first series the value is the avera e of 8 determinations (average deviation from mean = 0.014 ner cent), a n f i n the second, the average of 7 determinations (average deviation = 0.0JO per pent). ' b 0.6000 gram of arsenious oxide used, all othera 0.3000 gram. C KMn04 added slowly, about 7.ml. per minute. d End point with o-phenanthroline.
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National Bureau of Standards' standard samples of sodium oxalate No. 40c and arsenious oxide No. 83 should agree within one part in 3000.
Literature Cited (1) Fowler and Bright, S. Research Natl. Bur. Standards, 15, 493 (1935). (2) Kolthoff, Laitinen, and Lingane, b. Am. Chern. Soc., 59, 429 (1937). (a) Lang, R., 2. anal. Chem., 152, 197 (1926). RBCEIVEDOctober 21, 1937. Published by permission of the Director, National Bureau of Standards, U. S. Department of Commerce.
A Simple Electrodialyzer I
DOUGLAS B. ROXBURGH AND MARSCHELLE H. POWER The Mayo Foundation, Rochester, Minn.
I
N THE course of certain investigations in this laboratory involving the purification of serum proteins, a simple and fairly easily constructed electrodialyzer has been developed. It is similar in some respects to that described recently by Bartell (1) but seems t o offer advantages as regards ease of construction and use. The a paratus used is illustrated in Figure 1. It consisted of a centrafglass cylinder, a, 46 mm. in outside diameter and 60 mm. in length, and two glass cylinders, b, each 49 mm. in inside diameter and 60 mm. in length, These cylinders were cut with a rotary saw from thick-walled Pyrex glass tubing; the ends were carefully ground and then fire-polished. The cylinders, b, were closed with No. 11 soft-rubber stoppers each carrying a glass tube, into which was sealed a coil of platinum wire, and small glass ubes, g and h, for inflow and outflow of distilled water.
fi
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The glass tubes, j , were bent as shown and filled with mercury, into which wires leading from a bank of B batteries were inserted. The apparatus is assembled and prepared for use as follows: A square of Cellophane (du Pont No. 300, plain transparent) is placed over each end of cylinder a and held in lace by gathering the edges under the rubber band, d. The encfof the cylinder is dipped into water and the moistened paper then is adjusted until it ib smooth and tight. The ercess aper can be trimmed off even with the rubber band. The cylinsers, b, are now forced carefully over the ends of the smaller cylinder and the joints made water-tight by means of a second rubber band, e. The rubber bands, d, 10 mm. in width, and e, 20 mm. in width, were cut from ordinary Gooch crucible tubing having a flat outside diameter of 3.1 cm. (1.25 inches). With the Cellophane membranes, m, in place, the capacity of a was about 100 cc.
With this apparatus it was found that a sodium sulfate solution of protein which had previously undergone simple dialysis, could be electrodialyzed, in 6 t o 8 hours at 220 volts, to the point at which the speczc conductivity was of the order of 1 X lo+, as determined b y a standard method. When the conductivity was of this order a milliammeter inserted in the circuit indicated t h e passage of a current of 0.5 t o 1.0 milliampere through the apparatus.
Literature Cited I
d
i
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e FIGURE 1. DIAGRAMOF ELECTRODIALYZER
t
(1) Bartell, F. E., IND.ENQ.CHEM.,Anal. Ed., 8, 247 (1936). RECEIVED October 29. 1937.
