AIDS FOR THE ANALYST A n All-Glass Rotary Film Evaporator Murray E. Volk, Nuclear Instrument and Chemical Corp., Chicago 10, Ill. 7EYERAL
devices have k e n described which utilize the prin-
S ciple ' of evaporat,ion from a rotating film under vacuum for concentrating solutions of heat-sensitive materials. A simple all-glass apparatus which employs this principle has been developed. I n this device connection is made from a rotating round-bottomed flask to a commercially available lyophilizing unit through a lubricated ball joint. Since the axis of rotation lies :~pprosimately 15 dpgrees from the horizontal, somewhat more than one half of the volume of the round-bottomed flask may be occupied by the solution when the evaporation is started without clanger of mechanical transfer. The turbulence induced in the liquid by the rotatory motion of the flask effectively prevents humping due to local superheatirg. Aqueous and ethanolic solutions in flasks of 2 liters in capacity have heen evaporated to dryness in 1 hour with this device. The figure illustrates the apparatus. The lyophilizing w i t , 11: 18 X 50 cm. in outside dimensions is firmly mounted on a tablc. Into one of its six outer 29/42 standard taper joints is fitted R short adapter, B , carrying the ball portion of a 35/20 ball joint. The hollow axle, C: is fabricated of 22-mm. outside dimension tubing and carries the socket part of the ball joint a t its ited end, and an inner 24/10 standard taper joint at its lower end, to which the round-bottomed evaporation flask may. be attached. The Kjeldahl trap, D , while included in the design, IILZS not proved essential to satisfactory operation. The entire hollow shaft is 29 cm. long. The bearing, E, consists of four rubher wheels mounted in pairs and serves to support the weight of the rotating aysembly and to absorb any vibration. The drive is a metal pulley, F , with a center hole bored somewhat larger than the glass shaft. The pulley is fastened to the shaft hy four -411en screws which make contact with a split-brass cylinder. The two halves of the brass cylinder are cushioned from the glass tubing by a layer of sponge rubber. A V-belt of suitable motor, G, dimensions drives the pulley. A '/l&orsepower equipped with a speed reducer turning at approximately 40 r.p.m., rotates the assembly. h variable source of power may he employed to control the speed of rotation, but its use has not been necessary. Only dpiezon ?; has proved suitable as lubricant for ,the rotating ball joint. A vacuum pump capable of maintaining prespure below 0.5 cm. of mercury is adequate for operating the apparatus. During operation, the pressure differential is sufficient to hold the evaporation flask to the rotating d e , although spring clips may be used. This design for a device for the concentration of heat-sensitive materials using evaporation from a rotating film under vacuum possesses several points of superiority over others previously described. The apparatus of Craig, Gregory, and Hausmann [ANAL.CHEX.,22, 1462 (1950)l requires the rotation of both the evaporation flask and the condenser bulb. The inherent high
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inertia of this system makes accidental breakage of the apparatus during operation very possible. Partridge's device [Partridge, S. &I., J . Sci. Instr., 28, 28 (1951)] rot,ates a longnecked flask and employs only a single hearing, but the vacuum take-off is complicated, requiring special machining and packing of the vacuum gland. Only the single hollow shaft and the evaporating flask rotate in the device presented here. Use of a lubricated ball joint as the rotating vacuum connector makes construction simple and straightforward. The entire apparatu? can easily be fabricated Lvithout outside nssiPtance using available standard components. -4condenser of spherical shape such as employed in the apparatus of Craig and coworkers performs its function in a relatively inefficient manner. The ratio of condensing surface area to total volume of the condenser is minimal. The work of this laboratory involves the concentration of solutions containing considerable quantities of radioactivity. The lyophilizer used in the authors' apparatus has been found to act as an efficient condenser which ensures that any radioactivity in solution, which might be carried mechanically into the condenser, is trapped and does not escape into the pumping system and 1)ossibly contaminate the laboratory. Khile a commercial lyophilizing unit such as this device employs is a relatively expensive piece of equipment, it is in use in many laboratories working with biological extracts and other heat-sensitive materials. The alternative function suggested hew, as a condenser for a liquid concentrating device, which use in no way interferw with its original purpose, serves t o increase its usefulnesp. ACKNOWLEDGMENT
The autlior's appreciation is extended to F. E. Icelsey 01 thc University of South Dakota and to R. H. Delgado of this company, who contributed to the design and construction of ihe apparatus.
Matched Test Tubes in the Beckman DU Spectrophotometer Bernard E. Saltzman, U. S. Department of Health, Education, and Welfare, Division o f Special Heath Services, Cincinnati, Ohio
sets of matched test tubes are a great convenience for L colorimetric analysis. Tedious rinsing of photometer cells is no longer required when a dry tube is available for each sample ARGE
or standard color. The light path of 2-cm. length which may be obtained with 10 ml. of solution is more convenient in many cases than that of the usual I-cm. cells. Little time or expense is required t o prepare such tubes, and the accuracy of analysis is not noticeably affected by the slight variation of 2 or 3 parts per thousand in the diameters of the tubes of any one set. Only a single day's time was required t o produce four matched sets comprising 200 tubes. The installation of the tube holder does not require the removal of the regular cell holder and does not impair the use of the instrument with the regular cells. I n this latter case, a blackened cork is used to seal the test tube opening. This report describes the adaptation of the Beckman D U spectrophotometer for this purpose, and a simplified method of matching the tubes. The tube holder was prepared from a hardwood board by boring holes as shown in Figure 1. Care was taken t o maintain true alignment and accuracy, and the two large surfaces were made plane and parallel. The size of the hole may be adjusted t o fit the tubes at hand snugly and yet freely. The lower part of the tube was centered by its round bottom resting on the ledge a t the bottom of the hole. The lower 5/8-inch hole provided 1207
