A SEW CELL FOR ELEC TRODI.%LPSIS* BY HARRY S . HOLMES A S D .ILBLRT L. E L D E R * *
The usual apparatus for electrodialysis consists of three conipartmrnti. one for t h r solution to be dialyzed rind one for each of the electrodrs. 'Phi, electrode compartments are commonly as large as the center compartment. The apparatus described in this paper, constructed in line with a suggestion by I h y t that the electrode compartments be as small as possible, ha.; rrduced them to a mere moving film of x i t e r . D l s t I I led W a t e r
i FIG.I
-%PP-IR-4TV$. The appnratu. and electrical connections arc shown in Fig. I . 1) is t h e dialyzing cell, a cylinder of pyrex 9 cm. in diameter and 13 cni. in length with x hole H nt the top. Over the flanged ends of the glmj cylinder are stretched pieces of rubber tubing, such ar msy be used on Gooch cruciblcr. After these are given a light coating of vaseline, wet parchment paper.; a r r stretched over the ends and are tightly secured by means of long strings of rubber bands looped together somewhat like links in a chain. .%gainst each of the membranes are placed sheet; of filter paper (\Thatman S o . 44, ash content O . O O O I Z O g r , ) , These are cut to a point a t the tiottoni. The tops are folded over for about z cm. and \--shaped holes are cut in the folded edges.
* Contribution from Severance Chemical Laboratory of Oberlin College. * * The authors are indebted to Mi-. Elton S. Cook for some of the quantitative measurrrnents.
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HARRY N . HOLMES AND ALBERT L. ELDER
The electrodes E are cleaned carbon plates 13 cm. X 13 cm. X 6 mm. These are pressed lightly against the filter papers by means of ring clamps containing rubber stoppers, the clamps being supported by a rod fastened to a ring-stand (not shown in the figure). Distilled water from a 40-liter carboy is led through the tube Y, its rate of flow being regulated by the screwclamps s, and is allowed to drop through the tubes T, which are drawn to capillary tips, into the V-holes of the filter paper F. This device guarantees
Tima in Hours
FIG.2
the maintenance of a moving film of mater the thickness of the filter pdpers The electrodes must not be pressed too tight11 or the water will tend to go around the ends of the dialyzer The folding of the filter papers, giving greater thickness a t the top, also helps to prevent this The dialysate drops into the funnels G and is carried to the sink Through the hole H is led a tube B carrying a stream of COn-free air which acts as a stirrer, although some other mechanical stirrer may be used a t H -4heating coil C, enclosed in a pyrex tube, may be suspended through H if desired The electrical connections are self-explanatory, X being an ammeter, V a voltmeter, P a single-pole double-throw switch, R and R’ variable resistances For greater constancy of temperature, the whole apparatus, exclusive of the electrical instruments, is placed in a glass case.
A N E W CELL FOR ELECTRODIALYSIS
I353
Experimental The results obtained mith the apparatus are plotted in Figs 2 and 3 In all determinations the source of current was storage batteries or storage batteries in series Aith B-batteries The rate of flow of water over each electrode averaged 15 cc per minute Fig 2 , in which cmcentration of the solution in the dialyzer 15 plotted against time in hours, shows the removal of sodium and chlorine ion< from ?u' I O O S a c 1 I n each case j o o cc of the solution was used. Concentration of the solu~- tion in the dialyzer was determined by titrating 5 cc. samples with W I O O silC u r v o x 5 0 0 c c %o,,NaCI, ver nitrate, using saturated potassium 65'70', 150 v o l t s dichromate as the indicator. The legend Curve o 5oocc "Dlfco accompanying the figure explains the Gelatin ,55'-60', >150 volts curves. It will be seen that, using I j j volts and maintaining the temperature a t 5 5'-60°, no qualitative test for chloride ions could be obtained after I O hours, while a t room temperature and with no current flowing over I j o hours were required for such effective removal of chloride ions. Fig. 3, giving the results of dialyzing j o o cc. of SCc "Difco" gelatin a t I 5 5 volts and j5'-6oo. A curve for S I O O SaC1, is included for comparison. In these curves, current in milliamperes is plotted against time in hours. The rapid drop of current during the first four hours of gelatin dialysis will be noted. The gelatin a t this point still gave a t'est for sulfates. To remove this Tcme ~n Hour$ last trace of sulfat,e ion it was necessary FIG.3 to continue the dialysis in excess of 40 hours. Fsperiments were carried out using ?j I O O HCI. .It high voltages and high ternparatures it was found that the membranes were attacked with consequent leakage. The rcrnoval of adsorbed chloride ions from silica gel which had been treated with HC'I to dissolve out the iron was also tried. This could be accomplished satisfactorily but not in so short a time as by continuous nashing with warm water. Some esperiments u-ere tried using platinum electrodes consisting of pieces of fairly coarse gauze, 2 . 5 cm X 3 cm., backed with glass plates.
HARRY S . HOLMES AND ALBERT L. E L D E R
I351
The dialysis was not as efficient as with carbon electrodes. However, for the results t o be comparable, platinum electrodes of larger dimensions should be used. Heating t h e cell with a flame is not quite 50 good as heating with a resistance coil. Ilialgsin at 6;0-;0" is, of cnur,st! inore effective because ionic mowrnentq arc inorc rapid th:in :it rooiii teniprrriture..
Summary I.
.new, I inespcnsivc :ind efficient cell for electrodialysis has been
dcvribed.
It has been provcd t h t , using S 100 Tn('l! no test for chloride ions 2. i t 1 5 j volts and 6 jo-70'. can kJe obtaincd after I O hour- of tlialy The application of thi, cell to t h t rcmoval of salts from gelatin has 3. been shown.
