Constructing Apparatus for Electrodialysis JOHN RUSSELL
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R. ELIOT STAUFFER, Eastman Kodak Co., Rochester, N. Y.
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FIGURE 1. Two TYPES OF THREE-COMPARTMENT CELLS
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tight joint. A very satisfactory gasket can be cut from 0.05-cm. (0.020-inch) thick Eastman acetate sheet. Diaphragms, D, of any suitable membrane material are clamped between the three compartments of the cell in conjunction with the gaskets. The capacity of a cell constructed from 3.75-cm. (1.5-inch) piping is 225 to 275 ml. in the middle compartment, and 125 t o 200 ml. in the electrode compartments. The side limb of the center compartment is large enough in diameter to admit a glass stirrer and a Beckman glass electrode and reference half-cell with ease.
HE procedure of electrodialysis is of considerable value in many fields of scientific and technological activity. Various types of apparatus for use in electrodialyzing substances have been described from time t o time in the literature, and some of these are available commercially through laboratory supply houses. Almost all of these commercial outfits possess one or both of two serious drawbacks. In the first place, many are largely constructed of rubber or some similar material which is entirely unsuitable for use in electrodialytic operations on many substances. Most apparatus which is available is so limited in its flexibility of design that no modifications can readily be made in the size or arrangement of its essential features. I n the course of some work in these laboratories, the authors have had occasion t o use procedures involving electrodialysis. In a search for suitable apparatus for their purposes, they have devised a method of constructing electrodialysis cells, which they believe is novel and useful because of its flexibility of design and ease of manipulation. The important feature of their method of constructing electrodialysis apparatus is the use of stock fittings of Corning industrial flanged Pyrex pipe. These fittings, which are available in a wide variety of shapes and sizes, have been described in considerable detail (1). Figure 1 gives in one composite drawing two types of three-compartment cells which have been built and used b y the authors, and serves to illustrate the method of construction.
The Pauli type of arrangement has been used to remove electrolytes from colloidal silver preparations and to purify hydrophilic colloid preparations, such as starch derivatives. In addition to its use in colloidal preparations, the equipment is particularly suitable for lecture purposes. An interesting lecture demonstration of the migration of ions in an electric field can be performed with either type of apparatus. For this purpose, three dyes of different colors and different ionic character were chosen. Such dyes may be, for example, Safranine 0 (Eastman organic chemical No. 1753), which forms a red cation and a chloride ion; tartrazine (Eastman organic chemical No. P 1163), which dissociates into sodium ions and yellow dye anions; and Chicago Blue-6B (National Aniline Chemical Co., Niagara Sky Blue-GB), which dissociates into sodium ions and blue associated dye anions. If a mixture of these three dyes in solution is electrodialyzed in the above cell fitted with membranes of No. 600 0.0045-cm. (0.0018-inch) Cellophane swelled for 12 hours in distilled water, a clean-cut migration occurs. The safranine goes into the cathode compartment and tartrazine into the anode compartment, with retention of the Chicago Blue in the center compartment. The catholyte is tinted red and the anolyte yellow in from 5 to 20 minutes by applying a potential of 110 volts across the cell. Because of the tendency of the dyes to precipitate one another in certain concentration ratios, care must be taken in making up the mixed solution. This was satisfactorily prepared from the dyes on hand by making stock solutions of safranine containing 0.50 gram er liter, tartrazine containing 2.5 grams per liter, and Chica o Byue containing 0.25 gram er liter. Equal volumes of ea& were taken and were mixed gy adding the safranine to the tartrazine, and then adding the Chicago Blue to the mixture. The electrode compartments contained 0.001 N sodium chloride at the start of the demonstration.
The middle compartment, B, is a 3.75-cm. (1.5-inch) Pyrex Tfitting to which was sealed a stopcock to act as a drain for the compartment. Simple electrode compartments can be made in the form labeled A from 90" L-fittings of the same size by attaching a stopcock to act as a drain, or a somewhat more elaborate type of electrode compartment can be built as shown by C. This latter design, which is similar to the type of cell devised by Pauli (2), is particularly suitable for removing electrolytes from colloidal substances. Caps, P, for the electrode compartments, were made by drawing down a 15-cm. (6-inch) length of 3.75-cm. (1.5-inch) flanged Pyrex pipe. Three short pieces of 10-mm. Pyrex tubing were sealed to each cap to provide openings for the introduction of electrodes, gas delivery tubes, or funnels, as desired. The various parts of the apparatus are clamped together by means of the standard metal joint flanges, F , which are supplied for this purpose by the Corning Glass Works. Between the sections, gaskets, G, of various materials may be used to ensure a
Literature Cited (1) Corning Glass Works, Corning, N. Y., Bull. 814. (2) Pauli, Wo., Biochem. Z.,152, 355 (1924). COMMUNICATION No. 725 from the Kodak Research Laboratories.
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