ANALYTICAL EDITION
September, 1946
has a vent-a tiny hole punched near the top of D suffices. (The vent is less helpful the smaller the volume to be filtered.) It is often possible to take advantage of nearly the full capacity of the bottle by removing some of the clear supernatant with a pipet before the filtration. Sometimes a few cubic millimeters of dry ice are added to a bottle three-fourths full just before pulling up the stick; the filtration is as rapid as through an open or vented filter. The rate of filtration through the T filters ground with 150-mesh Carborundum is very high, even though the length of the ground zone of contact is as much as 5 to 10 mm. X filter such a4 I (Figure 1)having 10/8 Tvas compared with a Corning 15 F fritted filter. Both were fitted with rubber collars and placed on receivers such as D, then charged with 10.0 of distilled wdter and centrifuged a t 1580 r.p.m.; both filters let through 8.5 cc. in 2 minutes. If the receiver had no vent the ground filter n-as dry in a total of 3 minutes but the fritted filter held 1 cc. for at least 5 minutes; if the receiver had a vent both filters were dry in 3 minutes. The holdup of the ground filter was 0.05 cc., of the fritted filter 0.15 cc. The retentiveness (in the centrifuge) of these two filters was comparable: both prevented the passage of any visible amount of barium sulfate when tested by the method of Scribner and Wilson ( 8 ); both readily allowed Staphylococcus aureus ( 1 1 dis (It is hoped that ground filters can be ameter) to p a ~ through. made which i t ill retain the Staphylococcus and other bacteria Experiments on this are being continued.) There is room in the No. 2 International centrifuge (100-cc.
bras3 cups) for a total length of filter plus receiver of 225 mm.
when these have outside diameter of 25 mm. or less. Filters of
585
type C 2 weighing 30 to 50 grams have been repeatedly carried by receiver D without breakage a t 1850 r.p.m. Still longer (larger capacity) filter bottles can be made for use with smaller capacity receivers in cases where much of the supernatant solution can be pipetted off before filtration. It would be wise to make them smaller and/or from lighter wall tubing if, for special purposes, speeds of 2000 r.p.m. or more are desired. The speed of 1580 r.p.m. has often given a holdup of only 20 mg, of mother liquor on 1 gram of moderate sized crystals. SUMMARY
Small (up to 30 cc.) all-glass filters are described in which filtration occurs between standard-taper rough-ground surfaces. These filters are equal to or superior to small Corning F fritted filters in the folloTving respects: they give equal rates of filtration, and have equal retentiveness; They have smaller holdup, are much easier to clean, and do not contaminate preparations with parkisles of glass. In adaptability of design they have distinct advantages over the filters described by Craig and Post. A new filter bottle is described which is particularly suitable for use in the centrifuge for determin,tions of solubility and for quantitative handling of rerrystallizations and precipitations. LITERATURE CITED
(1) Bush, Dickison, Ward, and dvery, J . Pharmacol., 85, 241 (1946). (2) Craig and Post, IND. ENQ.CHEY.,A N ~ LED., . 16,413 (1944). (3) Scribner and Wilson, J . Research Natl. Bur. Standards, 34, 453-8 (1945). FGNDB for carrying out this work were kindly supplied by the Mallinokrodt Chemical Works.
Solution Intake Unit for Improved Operation of the Flame Photometer A . T. MYERS, Fruit and Vegetable Crops and Diseases, Bureau of Plant Industry, Soils, and Agricultural Engineering, U. S. Department of Agriculture, Beltsville, Md.
IN
USISG a recent model of a commercial flame photometer, annoying drift and fatigue of the phototube n-ere encountered ( 1 ) . As a result one standard solution had to be run alternately with the sample solution tested. Bn improved solution intake unit has been added to the atomizing system which increases the speed and accuracy of operation. Figure 1 shows the original solution intake and the improved unit. K i t h this double capillary intake and the three-way stopcock, the standard solution can be left in the system continuously, changing only the beaker containing the sample solution, which is alternated with a beaker of distilled water for flushing the atomizing system. -4sample reading can be made very quickly, after setting the instrument on the 100-mark with the standard solution. I n other words, the time allowed for drifting of the
!
I Figure 2.
Four-way Stopcock for Solution Intake Unit
phototube has been kept a t a minimum. However, the most important improvement is the elimination of the extra operation of handling the standard solution which now stays continuously in the system. A further possible improvement is shown in Figure 2, vhere a four-way stopcock allows a beaker of distilled water to be added for flushing the atomizing system. This distilled water remains continuously in the system like the standard solution; thus the operator need handle only the beaker containing the sample solution.
THREE-WAY
ACKNOWLEDGMENT
I
The assist,ance of Jane L. Showacre in trying out the new unit is appreciated.
ORIGINAL
I
Figure 1.
1
Original and Improved Solution Intake Unit for Flame Photometer
LITERATURE CITED
(1) Barnes, R. B.,Richardson, D., Berry, J. W., and Hood, R. L., IND.ESG. C H ~ MANAL. ., ED., 17, 606-11 (1945).
