Continuous Dialysis under Reduced Pressure GILBERT C . H . STONE City College, college of the City of New York, New York City
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HEN dialyzing a colloidal dispersion to free it of diusible substances, the solution is usually placed in a semipermeable membrane, and the sac immersed in running water. The process is continued until all traces of the dinsing substances bave disappeared from the outer liquid. This usually takes days, depending on the concentration and the rate of diffusion of the material coming out of the sac, as well as on the efficiency of the method for bringing the liquid in the interior of the bag near the surface of the membrane. Usually the dialysate is discarded and its large volume presents no problem.
During the course of some work with ragweed pollen extracts, the author found i t necessary to dialyze one of the protein-containing solutions. Since both the dialyzed solution and the dialysate were wanted for testing purposesinjection into ragweed-sensitive patients-a large volume with great dilution of dialysate was undesirable. It would have necessitated a prolonged evaporation to bring the volume down to a manageable quantity. This might bave resulted in mechanical loss of some of the dialysate, as well as a possible inactivation or contamination of the material. The problem was further complicated by the protein-like nature of the diffusing and nondiusing substances. Temperatures would bave to be kept comparatively low to minimize putrefaction and denaturation. Violent agitation of the solutions would have to be avoided to prevent excess foaming. Many and various dialyzing devices have been described. None seemed completely satisfactory for use in this case. The apparatus described below was devised with a view to eliminate cork and rubber, to keep all volumes comparatively small, to maintain low temperatures, and yet to provide for continuous and exhaustive dialysis. The use of interchangeable ground glass joints served to eliminate all non-glass connections and stoppers. Cellophane tubing, obtainable from the Visking Co. in various diameters and thicknesses, provided uniform, strong, narrow bags which gave efficient and rapid dialysis. With such materials and a blast lamp the dialyzing apparatus can easily be assembled. From the diagram it will be noted that the device works underreduced pressure,making itpossible tomaintain temperatures of 25% or lower. The solution to he dialyzed is placed in a piece of Visking cellophane sausage wrapping of appropriate diameter. Toluene or other preservative may be added. The tubing is closed a t either end by careful knotting or the use of screw-clamps. The sac F is then immersed in distilled water in the chamber E. It is kept from sinking to the bottom and stopping up the water inlet by means of several indentations in the glass tube a t S. The top of the tube E is ground to take an interchangeable glass joint. By means of two male glass joints sealed to a piece of bent glass tubing, the dialyzing chamber is connected to the boiling flask D. A steam plate, C, provides the heat for boiling the liquid in the 3-neck, round-bottom flask. Through one neck of the flask is a capillary, J,and the gas drawn throueh i t first mav be made to ass throuph toluene
a series of condensers L, K, and K'. The condensed water is conveyed through the tube I to the bottom of the dialyzing chamber E. Thus a fresh supply of distilled water is constantly flowing past the sac F. The volume of the dialysate is kept constant and small. To prevent loss of water and to prevent flooding, each bulb condenser, K and Kt, should be a t least 500 mm. long and arranged a t an angle rather than placed vertically. The rigidity of this all-glass apparatus is
minimized by the use of a semiball joint, H, a t the point of maximum strain. If i t is not essential to eliminate all rubber, tube A may be made of two pieces, rubber-connected, to reduce rigidity. Also, stopper B may he of rubber. The introduction of the tip of a small buret through a hole in a rubber stopper a t B allows toluene or caprylic alcohol to be introduced into the system more efficiently than through the capillary J.
