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removal of the filtrate and as a means of maintaining the same atmosphere above and below the fritted disk when connected to the glass tube a t the top with Tygon tubing during centrifugation. The rubber stopper to fit on top should be cut out with a shoulder as shown. The apparatus is centered in the largest cup (Catalog S o . 373) for an International centrifuge, size 2, by use of the ring shown in Figure 1, B. This consists of a brass ring made from sheet brass, with wooden blocks of the proper size attached to keep the filtering apparatus in place. The hooks keep the ring from falling into the centrifuge cup. The solution to be filtered is placed in a piece of Visking seamless cellophane dialyzing tubing (1 ). I t was found most convenient to place in the apparatus the previously soaked tubing doubled so that both open ends are on top. After the tube is filled, the open ends are tied or doubled and clobed
I
35
- 0 INCHES I
NECK
FROM I
graph (Figure 2) v a s made of air volume t s . Figure 1. Precise Quiclireagent level. This graph Delivery Koch-Type Pipet will vary with the di1. Leveling bulbs of the apparatus mensions 2. Air reservoir 3. Manometer and with the density of Mirror the reagent. Before a Scratches 6. Capillaries series of measurements t. Tube 8. Supply hulh was made, the reagent 9. Drying tube level was noted and thc air volume adiusted to 2.5 nil. greater than the value indicated on the graph for this level. The weight of water delivered to a glass-stoppered volumetric flask varied with the density of the water and with the discharge rate. The density of the water varied between series with teniperatuie and with the amount of dissolved air. Typical v a l u ~ s are shown in Table I. The identical deviations at the two slower discharge rates may indicate that variable loss of water from the weighing flask was greater than the variation of the pipet. At either rate the pipet n as not a sprious cause of variations in iodine numbers.
I
I
blood plasma at speeds b p to 2000 r.p.m. In actual operation, the material collected during the first 15 minutes is discarded; this eliminate< any dilution that might be caused by surface moisture on the cellophane. The size shown will handle conveniently up to 20-nil. input, and for larger quantities a larger sealing tube may be constructed in the same manner. If an apparatus very much larger than the one shown is desired, it is preferable to start with a fritted disk funnel (Corning S o . 36060), which is made of much heavier glass. In the latter
U f
u
7
LITERATURE CITED (1) .4nderson, H. H., ANAL. CHEhf., 20,1241 (1948). (2) Florence, W. M., unpublished 5f.S. thesis, Kansas State College, 1951. (3) Holmes,F. E . , A N A LC . H E M . , 1526 ~ ~ , (1951). (4) Popjak, G., Biochem. J . , 46,558 (1950). (5) Rosenmund, K. W., and Kuhnhenn, W., 2. Untersuch. Xahr. u. Genusm., 2 1 , 6 3 (1935). COSTRIBCTION 488, Department of Chemistry, Kansas State College
Centrifuge Type of Ultrafiltration Apparatus. T. Y. Toribara, Division of Pharmacology and Toxicology, Department of Radiation Biology, School of Medicine and Dentistry, University of Rochester, Rochester, S .Y. study of the clearance of various ions in biological work, ultrafiltration is a very valuable technique. Feldman et al. ( 1 ) have described an all-glass centrifuge type of ultrafiltration apparatus which eliminates a number of undesirable features of other types (9-6). The apparatus described here maintains all the desirable features of the all-glass apparatus, and its one-piece construction makes it simpler to use.
I
N THE
APPARATUS
One end of a borosilicate glass straight sealing tube with coarse fritted disk (Corning No. 39570, 25-mm. diameter with 20-mm. disk) is sealed off and a 6-mm. glass tube is sealed on a t an angle near the disk (Figure 1,A). This tube serves as the outlet for the
B Figure 1. Ultrafiltration Apparatus A.
Apparatus made from straight sealing tube,
25 rnm. diameter with 20-mm. fritted disk
€3. Top and side views of centering device
case, a bulb is sealed onto the stem, which is thickened and enlarged for strength. This apparatus is also used without the cellophane bag for drying precipitates by centrifugation. LITERATURE CITED
(1) Feldman, I., Danley, R. A., and O’Leary, J. F., ANAL.CHEM., 22, 837 (1950). (2) Ferry, J. D., Chem. Revs., 18, 373 (1936). (3) Nicholas, H. O., J . Biol. Chem., 97, 475 (1932). (4) Rehberg, P. B.,Acta Physiol. Scand., 5 , 305 (1943). (5) Waard, D. J. de, Arch. nderland. physiol., 2, 530 (1918). BASEDon work performed under contract with the United States Atomic Energy Commission a t the University of Rochester Atomic Energy Project. Rochester, N. Y
