gas can be directed over the solution with a stopcock. The upper part of the compartment has a wider diameter to allow use of a stopper large enough to hold the capillary, gas exit tube, etc. If desired, a ground-glass stopper can be used to give an all-glass cell. Compartment B if3 provided with a ground-glass stopper to minimize flow of the bridge solution between compartments. Compartment C contains a platinum contact at the bottom for use with an exterc.al mercury pool, massive calomel, or similar reference electrode. Resistance of Celll. Resistance of the cell when it was filled with a number of aqueous and nonaqueous solutions of typical background elec-
trolytes was measured with a conductance bridge t o indicate the magnitude of the resistance t h a t might be expected under the usual conditions of operation. The values, tabulated in Table I, represent the resistance between a dropping mercury electrode and a mercury pool electrode in compartment A (1.5-cm. separation), and a dropping electrode in A and a mercury pool in C. When the resistance was measured between a dropping mercury electrode in compartment A and a mercury pool in compartment C, all three cell compartments were filled with the same solution. No attempt was made to use a particular reference electrode in compartment C for the resistance measurements. I n general, use of a
reference electrode solution in compartment C would result in a lower cell resistance because of the high electrolytic concentration in such solutions. ACKNOWLEDGMENT
The authors thank D. I. Myers for his cooperation in manufacture of the cell. LITERATURE CITED
Komyathy, J. C., Malloy, F., Elving, P. J., ANAL.&EM. 24, 431 (1952). (2) Zagorski, 2. P., in “Progress in Polarography,” P. Zuman, ed., pp. 549-68, Interscience, New York, 1962. WORK supported in part by the U. S. Atomic Energy Commission. (1)
A Versatile Solubility Apparatus
R. L. Coffin, L. Stoller, and D. B. Wetlaufer,’,
Department of Biochemistry, Indiana University Medical School,
Indianapolis 7, Ind. EXPERIMENTAL arrangements have been described for equilibrating solids with their saturated solutions (2). While the present apparatus was designed f i x this purpose, it has also proved convenient for gasliquid and liquid-liqui d solubility equilibrations. It permits isothermal phase separation for samp,ing and is easily adapted for use with inert atmospheres. I n addition, it is compact, inexpensive, and easily contructcd in borosilicate glass. As shown in Figure 1, the apparatus is composed of an upper and lower chamber, joined by a 24/40 ’$ joint, appropriately sealed. Equilibration of solid or liquid with solvent occurs in the lower chamber, when the assembled apparatus is immersed in a thermostated bath to a depth such that only about 3 cm. of the upper chamber is above the surface of the bath liquid. Agitation is by magnetic stirring-such a stirrer with external rheostat can easily be encased in a submersible, water-tight copper sheath. As many as six such equilibration vessels c m be stirred simultaneously with one h i v e unit below. It is also sometimes convenient to stir single samples from :he side, with the drive unit outside the (nonmagnetic) thermostat wall. The upper chamber and sidearm may be closed with serum stoppers during equilibration. After separate tests have proved equilibrium, saturated solution is forced through the filter stick into the upper chamber by UMEROUS
To whom correspcindence should be addressed. * Present address, Department of Biochemistry (Medical Sciences), University of Minnesota, Minneapolis 14, Minn.
applying gentle air pressure to the sidearm. The shaft of the filter stick is of thick wall capillary for ruggedness. I n the case of volatile solvents or solutes, the saturated solution can be forced directly into a rubber-tipped pipet placed snugly against the opening in the
T
23mm
bottom of the upper chamber. A pipet such as that used by Eberz and Lucas ( I ) is helpful in sampling volatile materials. For measuring the solubilities of gases in liquids, we lead the gas into the solvent through the filter stick, which now serves as a gas disperser. The gas efflux escapes through the side-arm. At moderate bubbling rates, hydrocarbon gases saturate aqueous solvents in less than half an hour. The saturated solution can be forced up into the sampling pipet by causing the gas in question to flow in the side-arm. When one is equilibrating two partly miscible liquids, the stirring must be controlled so that none of the less dense phase becomes attached to the sintered glass, or the liquid forced into the upper chamber is likely to contain microdroplets of the other phase. With the dimensions indicated in the sketch, a sample volume of about 15 ml. is conveniently handled. The design can easily be modified for special requirements. LITERATURE CITED
(1) Eberz, W. F., Lucas, H. J., J . Am.. Chem. SOC. 56, 1230 (1934). ( 2 ) Mader, W. J.,. Vold, R. D., Vold, M. F.. “Solubility.” in “Physical
Methods of Organic’ Chemistry,” 3rd ed., Part I, A . Weissberger, ed., p. 655, Interscience, Kew York, 1959.
INVESTIGATION supported in part by U. S. Public Health Service Research Grant GM 10900, Division of General Rledical Sciences. One of us (L.J.S.) was supported on an USPHS Medical Student Figure ratus
Exploded view
Of
appa-
Summer Research fellows hi^ (1961). Another (D.B.W.)gratefully achodedges support by an USPHS Senior Fellowship, SF-505. VOL. 36, NO. 3, MARCH 1964
699
