Confined Spot Filtration Apparatus. Jack L. Lambert', Thomas E. hIoore, and Paul Arthur, Oklahoma -4. & 31. College Stillwater, Okla.
With the arrangement descnbed, all but those coarse precipitates that rapidly settle out under the influence of gravlt? gi\e uniformly colored spots. Fine suspensions are deposited evenly over the surface from center to edge by the uniform pressure differential through the barium sulfate m a t , filter paper, and sintered disk. If the colored spot thus formed was washed with a saturated solution of magnesium sulfate, the fragile barium sulfate mat, after drying, was cemented both t o the colored surface layer and t o the filter paper
described by Franke and coworkers (1) for Tthe apparatus colorimetric comparison of spots formed by the deposiHE
tion of small amounts of colored precipitates onto a suitable background material has been modified for greater convenience of operation. I n attempting to use Franke's apparatus for the determination of trace quantities of selenium ( 2 ) , two difficulties were encountered: t,he filter paper had to be cut to the esact size needed, and much care had to be taken to avoid damaging the colored spot while removing the filter paper from the ap: paratus. The apparatus illustrated all on^ the use of filter paper of varying sizes and shapes, and is easily disassembled to remove the filter paper and spot after it has been formed. The support for the filter mat is a porous borosilicate glass disk, D,formed in one of two 18/9 borosilicate glass socket joints, E, by sintering powdered borosilicate glass (passed by a 100-mesh, but retained b y a 1 4 0 - m e s h screen) in a 2- or 3-mm. layer. A plug of asbestos wool, pressed into the joint wet and then dried in an oven, holds the powdered glass while it is being sintered. C The asbestos can be easily removed after the porous disk has been formed by s o a k i n g n i t h water and loosening with a wire probe. The sintering is done with the socket joint in an upright Figure 1 Doeition, using a hIeker-tvpe burner which provides a flame hot enough to sinter the pondered glass but not hot enough to deform the joint. I t is best to build up the disk in thin layers, making certain that it is firmly welded to the inside surface of the socket joint. -125 x 100 mm. borosilicate glass test tube, -4,was xvelded as close as possible to t,he other socket joint B . The lips of both joints were ground flat and smooth on a Carborundum stone to make a tight seal t o the filter paper when clamp F is put in place. Each joint then had an inside diameter of 18.0 mm. Decreasing the diameter of the filtration area would increase the sensitivity, but, use of smaller socket joint,s would cause the constrict.ion to be smaller where joint B is attached to test tube A . By using the 18/9 size socket joints, the effect of the constriction upon the filtration of fine precipitates is made negligible. Although several qualities of filter paper were tried, the most successful was Whatman's S o . 50. With a dense, hard. smooth paper such as this, the air leak around the edge was negligible even \?-hen strong suction ivas applied. Barium sulfate is the most generally useful background material upon which to deposit colored precipitates because of its inertness, white color, and small particle size when freshly precipitated from dilut'e solut,ion. A mat of precipitated barium sulfate was prepared by mixing 10 ml. of 0.5% barium chloride solution with 10 ml. of 0.2570 sulfuric acid and filtering with suction through a moistened piece of Whatman's No. 50 filter paper, C, in the apparatus described (Figure 1). This mat will retain on its surface fine precipitates formed in the procedures for confined spot methods of analysis. Other materials can be used to form the mat and where adsorption or chemical reaction can be employed, substances of a colloidal or ionic nature may be removed from solution. 1 Present address, Department of Chemistry, Kansas State College, Manhattan, Kana.
ACh.1OW LEDGMEYT
T'he research, of which the development of this apparatus formed a part, was made possible by a grant from the Xational Institutes of Health, United States Public Health Service, through the Research Foundation of the Oklahoma A. I% hI. College. LITERATURE CITED
( 1 ) Franke, Burris, and Hutton, (1936).
ISD. ENG.CHEM.,AXAL.ED , 8, 435
(2) Lambert, Moore, and Arthur, .ISAL. CHEM.,23, 1101 (1951).
Automatic Test Tube Washer. R. E. Parks, Jr., G. Pi-, Kidder, and Virginia C. Dewey, Biological Laboratories, Amherst College, Amherst, Mass.
4 clean glassware problem faced by laboratories employing chemically is the time involved in the cleaning of test
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MAJOR
tubes with acid-dichromate cleaning solution and the subsequent rinsing. Jordan (IsD. ENG.CHEX., ASAL. ED., 17, 250 (194531 lias described an automat'ic pipet washer, now in common use in many laboratories, which rinses pipets thoroughly by means of repeated fillings and drainings of the tank in which the pipets are placed. This is performed automatically through a siphon system. 1-nfortunately. this type of device cannot be used for the rinsing of test tubes, because the tubes are not open on both ends. If the tubes are placed in a horizontal po:.ition in a pipet a-asher, only slight variations from the exact horizontal would allow either air or acid to be trapped in the tubes. The authors have recently developed an apparat'us (t,he Amherst automatic test t,ube wacher 1 which accomplishes thorough cleaning and rinsing of a large number of test tubes \i-ith a minimum of handling. The nen' feature of this device consists of a swinging tray suspended in a rinsing tank in which a hasket containing t'he test tubes is placed. By means of a float the tray and basket are rocked backward when the tank is filling and forward ivhen it is draining, thus allowing the tubes to fill and drain completely. The filling and draining are controlled by a siphon system as in the Jordan pipet washer: this could be accomplished. perhaps more efficiently, by meam of a solenoid valve. The apparatus, all parts of whirh are made of stainless step], is shown in Figure 1 wit'h the side of the tank removed to shoiv the swinging tray and basket a p if the tank were full. T h e rinsing tank, 10.5 X 13 inches, has a water inlet and siphon system. The siphon is constructed of an outer pipe 16 inches long and 3 inches in diameter, A , the top of which is sealed by a 0.5-inch dome and the bottom of which has a 0.75-inch opening into the bot,tom of the tank. Inside the lower end of A is a threaded collar. Through this collar and into the outer pipe fits a 23-inch section of 1.5-inch outer diameter pipe, B. An elboiv sleeve with a tapered rnd covers the lo\ver end of the inner pipe to improve the operation of the siphon; the $winging tray, C, 5.5 X 7 x 12 inches, has an attached float, D ,and adjustable bearings, E. The
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ANALYTICAL CHEMISTRY
bearings fit into bearing cylinders of thin tray supports, F , which suspend the tray in the rinsing tank; the basket, G, 11.75 X 5.375 X 12.25 inches, is made of perforated stainless steel with flanges to take a sliding screen, H , the top of which is provided with a handle with three notches. This basket holds about 400 15 X 125 mm. tubes; the stainless steel tank, 8 X 13 X 18 inches, contains the acid-dichromate cleaning solution.
Cell for Rapid Polarographic Analysis. Louis JIeites and Thelma ?\kites, Sterling Chemistry Laboratory, Yale I-nivereity, S e w Haven, Conn. of deaerating a solution rapidly, and the possiT bilitydifficulty of introducing cont,aminants from the agar bridge. HE
have led many polarographers t,o forego the use of H-cells (3’ in favor of less versatile cells with mercury pool anodes. Based on the cell design of I d i n e n and Burdett ( 2 ) in which the gas stream is dispersed by a fritted-glass disk, and the older design by Carritt (1‘1which eliminated the effects of contact with the agar plug, a modified H-cell which is free from these disadvani ages has been designed. Referring to Figure 1, the gas ent,ering a t a enters the solution through a sintered borosilicate glass gas dispersion cylinder, b, which brings the gas stream into intimate contact with the solution. IVhen deaeration is complete, the gas is diverted over the solutio11 in compartment c, and tube d is filled by suction a t a. Any reaction then occurring a t the agar-solution interface is isolated from the main body of the solution until the reaction prod.ucts diffuse through the entire length of d , and contamination of the solution is thereby effectively prevented. The iK correction corresponding to t,he resistance of the solution in d may gmerally be ignored, 01’ it may be detcirmined arid applied in precise work. When contact with an agar bridge is not harmful. a more conventional design is used, in which t,he gas-entry tube of the usual €€-cell ( 3 ) is replawd by a gas-dispersion cylinder, ringsealed through the wall of the solut’ioncompartment oppwite the I)ridge, tlnd positioned as show1 in Figwe I .
Figure 1.
The tubes are placed in the basket with their mouths toward the open side. The screen is slipped into place and the basket I‘ immersed in the tank of cleaning fluid, inclined so that the tubes will fill without trapping air. After the required soaking time, the babket is lifted from the cleaning solution in an inclined posltion, snd the fluid is allowed to drain from the tubes. This operntion is most easily accomplished by means of a hook attached to i~ chain rigged from a pulley above the tank. The three notches in the handle of the basket are designed t o allow the different inclinations while the basket is being immersed or removed from the cleaning tank. The basket is now lowered into the swingirig tray. The tray bearings have been adjusted previously, so that the mouths of the tubes are downward when the tank is empty. The water is started flowing into the tank. The water level raises the float, tipping the tray and basket backward, thus allowing the tubes t o fill without trapping air. As the water level resches the siphon height, all the tubes are full. At this level the siphon starts and the tank is drained rapidly. As the water level falls, the tray tips forward so that all the tubes dlain. The siphon “breaks” and the tank starts filling again. Thls cycle will repeat itself indefinitelv. After ten or more cycles have been completed, a few millifiters of saturated sodium hydroxide are added and the tank is filled to a point just below that a t which the siphon starts, After sufficient soaking, the water inflow is resumed for the desired time. Distilled water may be poured into the tank for the final rinses. The basket is removed from the tank, drained, and placed in a drying oven with the mouths of the tubes downward.
I n practice it is efficient t o have two or more baskets; a second basket may be filled with tubes while the first is being washed. The dimensions noted are those necessary for the cleaning of 15 X 125 mm. test tubes. If tubes of other sizes are employed, the dimensions of the apparatus should be adjusted accordingly.
Figure 1. Modified H-Cell a. Gas-entry tube, 4 - m m . outside diameter
b. Corning 39533 12C gas dispersion cylinder Solution compartment, 45 mm. outside diameter X 12 cm. d . 9 mm. outside diameter X 18 c m . total length e. Corning 39570 2031 fritted disk f. 25 m m . outside diameter X 3 c m . 4. Reference electrode compartment, 22 m m . outride dianieter X 12 c m . Length of arrow corresponds t o 10.0 c m . c.
Khen i 5 nil. of air-saturated 3 M potassium chloride in a cell like that shown in Figure 1 were deaerated by a rapid stream of hydrogen, the diffusion currents a t -1.6 volts us. the saturated calomel electrode indicated t h a t oxygen removal was 84% coniplete in 20 seconds and 9Sw0 complete in 10 seconds: oxygen could not be detected after 1 minute. LITERATURE CITED
(1) Carritt, D. C., Ph.D. thesis, Harvard University. 1947. (2) Laitinen, H. A4., and Burdett, L. W.. AF.AL. CHEM.,22, 833 (1950). (3) Lingane, J. J., and Laitinen, H. A , ISD. END.C H E W.,~ N . < I . .ED.,
11,504 (1939). Work supported by Contract AT(30-1)-842 between the Atomic Energy Commission and Yale t-niversity.
