A N A L Y T I C A L EDITION
April 15, 1941
on the exterior of the tube. The centering bearing, T,has four holes in it, in addition to the bearing hole for F , for the passage of the liquid refrigerant through the bearing piece. The actual expansion from liquid to gas, or to mist, takes place through the orifice -- _..-..in..V. . . A commercial refrigeration halide leak tester has been found an invaluable adjunct for working with such an experimental system.
Jv.
this description. IT, Rice aided in testing the initial operation of the new expansion valve. The actual construetion of the valve was effected by Alfred Gedies, the laboratory technician, to whom credit is due for his careful execution of the task add for certain suggestions, both factors contributing materially to the successfu~functioning of the instrument.
Acknowledgments
This work was done for Arthur B. Lamb in his laboratory and the author wishes to thank him for permission to publish
259
Literature Cited (1) Roper. TND. EXG.CHEX~., Anal. Ed., 12, 113 (1940).
An Improved Electrodialyzer F. E. BRAUNS The Institute of Paper Chemistry, Appleton, Wis.
E
LECTRODIALYZERS on the market consist of three glass cells, clamped together in a specially designed stand, and in which two parchment or cellophane membranes separate the middle cell from the outer cells. I n addition to the fact t h a t the middle cell has only a small capacity, the apparatus is somewhat difficult to handle, the dialyzing surface is small, and leaks may occur between the membranes and the cells. It was desired, therefore, to design a n electro-
dialyzer which would not only allow one to dialyze largerquantities of liquor, but would require little wash water for the electrodes-a distinct advantage when the material that dialyzes out is to be recovered by evaporation of the wash water. An electrodialyzer which permits dialysis of larger amounts of liquids in a relatively short time and has been found t o work satisfactorily is shown in Figure 1. The three cells required in any electrodialysis apparatus are formed by the glass vessel, A , and the two dialyzing bags, Bl and B,. The outside cell, formed by A and Bl, has a platinum gauze electrode, K , which is laid against the glass wall of A and is used as a cathode. K is separated from B1 by the glass tube spiral, C , which serves a double purpose. It prevents B,, after it has been filled with the liquor to be dialyzed, from coming into contact with K and thus soon rendering the bag defective; further, the wash water for K is passed into the outside cell through this spiral. The water enters the spiral at E and the outside cell at F. Inasmuch as the spiral lies close to K on one side and B1on the other, the water is forced to pass through the outside cell along the spiral between K and B1 and, in this way, causes a thorough G washing of the electrode. The water leaves the outside cell a t the overflow, D. The small distance between B1 and K reduces the resistance of the wash water. The spiral fills a considerable amount of the space between the electrode and the bag, thus reducing the amount of wash water and increasing the concentration of the mineral content of the outside Fash water. B1 is suspended on a ring, S, which, in turn, is fastened to a ringstand, R, by means of the screw clamp, G. The inner cell is formed by the dialyzing bag, B1, which is tightly fastened to the ring, H , which, in turn, is screwed to the ringstand, F , a t I . The glass tube, M , which is widened a t its lower half, is inserted in Bz and held in place by a three-hole rubber stopper, L. Around the outerside of the wider part of M , the electrode, N , is wound, the lead wire of which is led through and sealed in the capillary tube, 0. In order to prevent any contact between BI and N , the latter is protected by the glass ribbon spiral, P,the ribbon of which forms an angle of about 70" with the spiral axis. The wash water enters the inner cell at the bottom of M , is forced by the glass spiral to rinse N , and leaves the cell through the glass tube at &.
M
-==I $(l
N
~~
I
~~~~~~
FIGURE 1. DIAGRAM OF ELECTRODIALYZER
L,
K h e n hot water is passed through the outer and inner cells, the dialysis can be carried out at higher temperatures. The dialyzer can be used as a n ordinary dialysis apparatus by taking out the inner cell a t 1. On account of its relatively large dialyzing surface, the dialysis proceeds rapidly and may be further accelerated by stirring the liquor in the middle cell. Cotton cloth bags impregnated with viscose have proved most satisfactory as containers.
