V O L U M E 22. NO. 6, J U N E 1 9 5 0
837
mark on the scale with that an the reoord and nhotostatically
in more favorable regions. The reduced records (Figure 1) are mounted on 8.5 X 15 inch Kevsort cards (McBee Comuanv. Athens. Ohio) and
trmnspar&t Plexiglas and the top, bottom and one side are hinged t o permit dropping of cards after insertion of needles through the appropriate parallel slots a t front and back.
Figure 2.
Sorting Box for Keyeort Cards
taouine key is taDDed every 0.04 micron-i.e.. as evew other ediibra%on*mark bh the w&e-length dial cr&s the hairline. (Marking a t 0.OZ-micron intervals results in poor delmeation in some sueetrsl reeions.) When the calibration marks have
permsnently lttaohed t,o each reobrd by aligning the 15-micron
If adequate photostating service is av&il.ilable, the entire prooedure soon becomes a routine stsndmd practice which greatly enhanoes the utility of itn ever-increasing infrared library in day-to-day analytical work. ACKNOWLEDGMENT
The simple slit drive arrangement now in use was first suggested to the authors by W. C. Kenyon, Experimental Station, Hercules Powder Company, Wilmington, Del. R e c m v ~ nMay 10, 1949.
Improved Centrifuge Type of Ultrafiltration Apparatus ISAAC FELDMAN: ROBERT A. DANLEY, AND JOHN F. O'LEARY ,University of Rochester, 1 schooz H E first use of centrifugal farce to obtain ultrrtfiltration presTmre was described by de W w d (7) in 1918. A much improved technique was described by Rehberg (6),but the author's previous experience indicated that the membrane 8UppOlt of metal would probably introduce adsorption errors. In addition, specially made cellophane tubes were required. I n B previous ultrafiltration study ( 1 ) of beryllium solutions of very low concentrations, quantitative interpretations were impossible because of adsorption losses on the sppsrhtus employed. An improved npparatus of the centrifugation type has been devised which gives excellent reproducibility and an a b d u t e 817011 of about 6% and embodies the separate advantages of those previously described (2, 4, 6, 7). The new apparatus is of all-glass construction and employs the readily mailsble Visking seamless cellophane tubing as the inembrane
SEALED WRH SCOTCH TAPE
FRlTTEO DISK.
(bl CELLOPHANE BAG USED AS MEMBRANE
ppit t
APPARAWS
The upper part of the apparatus, shown in F i p e La, wm made by sealing the ball part of an 18/9 ball-and-socket p i n t ta a co8rse porosity, borasilicrtte glass fritted sealing tube, 25 mm. in diameter. The socket art of the joint connected to B bulb of about 4 ~ 1 1 1 .rapacity wwid n~ the rcGiver for ultraliltratr. A rellophanc b3g, k"Igure 1,b. mudc by tymgdouble knots in the ends oi B u m c of \ k k i w wamleSi rrlloohmc dialyzing tubing, I9
Figure 1. Apparatus
shown in Figure 1 c To keep eonts&inrtting dust out of the apparatus during t.he centrifugation, the top of the ultrafilter wm covered with a piece of cellophane and sealed thereto with Scotch ta e Sootoh ta e and fabric-covered wire were used to seal the bafjoint. The uptrafilter was wrapped withasheet of 0.125-inch (O.%cm.)spongerubber to make it fit snugly in the metal centrifuge tube. In an International centrifuge, size 2, eight ultrafiltrations of 25 ml. each can be run simultsneously. Te,mperature-eontrolled enoeriments can be Derformed. four a t a time. in the International kortsble Model PR-1 refrigeksted centrifuge.
Bolutions of beryllium were prepared b dilution of a stock solution (6). Suspensions of beryllium hydoldde (Tsble I) were prepared by the addition of 5 ml. of 0.125 M sodium bicarbonate t o each 20 ml. of the appropriate solution of beryllium. The resulting suspensions were allowed t o stand 2hours before ultrafiltmtiotion. It is understood that these suspensions were not pure beryllium hydroxide, but rather a mixtore of beryllium hydroxide and b a i c carbonates.
OF BAG IN ULTRAFILTER
I C 1 POSITION
MEI'HOOS
838
ANALYTICAL CHEMISTRY Table 1. Ultrafiltration of Colloids
Ultrafiltrate Colloid concentration yo of initial R.p.m. Hour8 Ml. concn. 2.5 1.0, 0 . 3 2.5 0.0.2 0.2 2.2 0.2 2.2 0.5 5 1.2 2.5 0,o 2.5 0:o Protein (Difco serum) 2.5 0: 0 2 2 1 0,1 Inulin (3.25 mg. %) 1 3 2.2 68,68,92 a Tracer method of analysis used for all Be(0H)n suspensions. Substance Filtered4
Centrifugation Rate/ 1000 Time
Volumo
Plasma was prepared by centrifu ing oxalated beef blood obtained at a local slaughterhouse. T i e 10% Difco serum suspensions were prepared from Difco Bacto dried beef blood serum, All other chemicals used were C.P. grade. Beryllium was determined either by the colorimetric method ( 6 ) or the tracer technique ( 1 ) . Protein was determined by visual comparison of the turbidity obtained upon the addition of 3 drops of 5% sulfosalicylic acid to the test solution and to known dilutions of plasma. Inulin was determined by the method of Kruhoffer (9).
of inulin were required thBt the probable error of the analyses was rather large. Accordingly, the values reported for inulin are of qualitative significanceonly. When solutions of beryllium, in concentrations ranging from a trace to 4.64 micrograms per ml. in 0.001 M hydrochloric acid, were centrifuged a t 1000 r.p.m. for 6 hours, the concentration of beryllium (94 * 1%) in the filtrate was equal to that remaining in the cellophane bag. The consistently low recovery probably is due to a slight adsorption on the cellophane bag. DISCUSSION
The all-glass construction of the new apparatus represents a real advantage in eliminating problems of adsorption and decontamination] permitting accurate studies of extremely dilute solutions. Furthermore, the temperature a t which the filtration is carried out may be conveniently controlled. In spite of a consistently negative absolute error of about 5% (with low concentrations of an adsorbable solute) the ultrafiltration technique described gave very reproducible results. The accuracy seems adequate to permit quantitative studies. Under the experimental conditions employed, the membrane was permeable to dissolved beryllium and a low-molecular weight colloid, inulin, but impermeable to protein and precipitated beryllium hydroxide.
RESULTS
LITERATURE CITED
The force and rate of ultrafiltration are, of course, related to the speed and radius of centrifugation and also are dependent upon the solution being centrifuged. Thus, a t 1000 r.p.m., 2.5 ml. of filtrate were obtained from aqueous solution in 3 hours and from blood plasma in 6 hours. At 2000 r.p.m., the time required for the collection of 2.5 ml. of ultrafiltrate was 1 and 2 hours for aqueous solutions and blood plasma, respectively. The filtration of solutions of Difco dried serum was very slow, probably because of clogging of the membrane. These data are presented in Table I. Table I also shows that the membrane is permeable to small colloidal particles such as inulin but impermeable to beryllium hydroxide and to protein. For this work, such dilute suspensions
(1) Feldman, I., Neuman, W. F., Danley, R. A,, and Havill, J. R.,
Univ. of Rochester Atomic Energy Project, Rept. UR-59 (1948). (2)
(3) (4) (5) (6)
Ferry, J. D., Chem. Reu., 18, 373 (1936). Kruhoffer, P., Acta Physiol. Scad., 11, 1 (1946). Nicholas, H. O., J . B i d . Chem., 97, 457 (1932). Rehberg, P. B., Acta Physiol. S c a d . , 5, 305 (1943). Underwood, A. L., and Neuman, W. F., Univ. of Rochester Atomic Energy Project, Rept. UR-19 (1948); ANAL. CHEM.,
21,1348 (1949). (7) Waard, D. J. de, Arch. n&erZad.physiol., 2, 530 (1918). R E C E I V ~April D 14, 1949. Based on work performed under contract with the United States Atomic Energy Commission &tthe University of Rochester Atomic Energy Project. Rochester, N. Y.
Improved Manostat and Manometer WILLIAM P. RATCHFORD AND M. L. FEIN Eastern Regional Research Laboratory, Philadelphia, Pa.
LTHOUGH many pressure controllers suitable for use in A vacuum distillations have been reported (6),it is believed that the manostat described here is better adapted to precision vacuum fractionation than those previously described. A novel feature is the use of a completely enclosed magneboperated screw, which permits rapid and precise adjustment to any pressure over a wide operating range. The manostat is substantially independent of small variations in room temperature or pump capacity. Moreover, it is small and light in weight, and may be clamped conveniently to the usual laboratory rack or ring stand. Its construction requires the services of a skillful glassblower. A manufacturer of scientific apparatus is now developing a model for commercial production. Because deviations from the controlled pressure depend not only on the pressure-sensitive element, but also on the rest of the system, Figure 1 gives a semischematic representation of the arrangement used to obtain the degree of constancy reported here. The modified 40 X 170 mm. borosilicate glass test tube, 13, has an %nun. sidearm, 10, and a 14/38 ground-glass neck, 9. It holds approximately 40 ml. of mercury. The amount is not critical, but should be enough to fill the central tube completely, in case tube 13 is allowed to come to atmospheric pressure.
The 8-mm. central tube, 12 (soft glass ground to size 14/38), extends to within a few millimeters of the bottom of tube 13 and terminates in a 0.5-mm. hole, 15. The u er portion, 12 X 160 mm., qontains two glass :abs, which h o 8 s t a d e s s steel bracket 7; thw bears two extensions, 25 and 8; 25 serve8 as a bearing for the stainless steel screw, 4 (50 threads per inch), and 8 serves as pivot for the screw. The upper end of the screw terminatas in a soft iron vane, 3. On the screw is threaded stainless steel nut 6 of such size that when the screw is turned the nut is prevented from turning with it b the bracket, and so must advance or retreat alon the screw. Kttached to nut 5 w a stiff tungsten wire lead, 11, w%ch is connected electrically to the outaide of the central tube a t the top through the nut, screw, bracket, and latinum wire 27,which is sealed through the tube. The centr8 tube also contains the platinum lead, 14, which is in contact with the mercury at all tunes and 18 held against the side by a thin glass tube tacked to the wall. Thia lead w also sealed through a t the top, thus making the second of terminals 1, 1 The seals a t the top are protected by thermoplastic cement, which also holds in place the metal guide, 26, on which rests the annular magnet, 2. As the magnet is turned, it turns vane 3 and thus screw 4. moving electrode axially - the ti0 of the tungsten within the tube. The terminals are connected to an electronic relay, 28, which operates solenoid 22 (IO00 ohms). Use of an electronic relay minimizes the probability of sparking at the contact between
