A Low Temperature Vacuum Drying Apparatus D. H . COOK School of Tropical Medicine, San Juan, Puerto Rico HE USE of dried plasma has stimulated the cement. The two ends of the wire were secured to development of apparatus for drying frozen ma- 0.125 inch brass bolts for the cement connection. terials or the evaporation of water from unstable This heater was supported on two paratlined plywood solutions a t a low temperature. In 1939 Greaves and rockers so that when the assembly was inserted into the Adair (1)made a critical study of the drying of solutions of proteins from the frozen state and designed efficient but elaborate apparatus for this purpose. Previously Stevens (2) had developed a relatively simple apparatus for drying protein solutions a t low temperatures but under the present conditions even his equipment would be difficult to obtain. Having the problem of concentrating small volumes of enzyme solutions we have constructed an apparatus from parts available to almost all laboratories; an apparatus that can handle 100-150 cc. a t a time and remove that volume of water in 24 hours. A piece of four-inch internal diameter galvanized pipe, six or eight inches long which fitted snugly into the lower tray compartment of an electric refrigerator was found in the junk pile. A piece of galvanized sheet iron 16 gage was soldered to one end giving a vacuum tight seal, and the sheet iron was cut to a semicircle of the outside diameter of the pipe, leaving a flat edge for a foot to keep the pipe from rolling. The other end of the pipe was pound flat and smoothed off by rubbing on N O . ~ O O A emery paper laid on a flat plate glass surface. A five-inch disc of d a t e class was cut for a pipe the upper face of the transite strip containing the heating element was about one and one-half inches window and vacuum seal foithe oven end of the vive. the lower inside surface of the pipe. A piece of transite two inches&byfive and one-half Two 0.3225-inch holes were drilled in the pipe, 180 inches was made into a heater by laying ribbon nicrome degrees apart and about one inch from the front end. wirein on one surfaceuntil 30 inches bad been used. This was cemented down with a thin layer of alundum (Continued on @age 434.)
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A LOW TEMPERATURE VACUUM DRYING APPARATUS (Continued from page 427.) 1.6 amperes, respectively, and from the heat formula: These holes were set 45 degrees from the vertical line so IaR Calories = that the short lengths of 0.3225-inch copper tubing 4.18 soldered to them and given right angle bends would come a t the upper and lower corners of the square we thus obtained 1.7 and 3.0 cal. per second. The following table indicates the results that could be refrigerator compartment when the pipe was inserted. obtained with this simple equipment. The upperkube is for the vacuum line connection and the lower tube carries two No. 18 rubber-covered wires TABLE 1 to bring current to the heater. These wires were sealed Tlm9rrolurc vnruvm vacuum tight by pouring a hot cement of rosin and of Pmsurr, Lorr 8.0 Molcrbl Scricr L i t h f Soldion, 'C. Mm. 961 hour asphalt into the copper .. tube. The details can be seen inthe figure. Dintilled water The whole assemhlv is inserted into the trav com- 10% smcrose 150 W 5-4 5-6 5.6 10-11 8-9 8.3 200 W ~ a r t m e n t :the vacuum and electric lines can be run uo ' 150 W &rough holes drilled in the floor of the refrigerator. 10% sodium chloride 5-10 4-5 7.4 A glass dish of 125-cc. capacity one and one-quarter inches wide by five inches long was found in a ten cent store and served as the evaporating tray when placed on In all cases with the 150-watt light in series the the heater. A tiny two-inch thermometer off an old evaporated water froze out on the walls of the pipe. Tycos hair hydrometer was held upright by means of Sometimes when using the 200-watt light all of the rubber bands in the evaporator to measure solution water did not freeze out but collected in a pool in the temperatures during the evaporation. The five-inch circular glass plate was placed over the bottom of the pipe. The temperature of the tray comground edge of the pipe which had previously been partment of the refrigerator controls to a great extent the efficiency of the apparatus and with good cooling smeared with stopcock grease, the vacuum and electric and low vacuum, five grams of Hz0 can he evaporated lines were connected, the pump started, and the reper hour a t a temperature of 2OC. or less. frigerator closed. Since the heating unit has a resistance of five ohms i t LITERATURE CITED is used in series with a lamp socket into which various lamps can be screwed to change the current. With (1) GREAVES AND ADAIR, 3. EX., 39, 413 (1939) 150-watt and 200-watt lights, the current was 1.2 and (2) STEVENS, 3. Lab. C h . Med., 23,978 (1938).
