INDUSTRIAL AND ENGINEERING CHEMISTRY
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with excess moisture from the air sufficiently to cause the alloy to burn. Upon re?ction with water, the alloy disintegrates into a fine powder and the sodium is effectively used quantitatively for drying. The convenience in handling, the efficacy of use, and the safety and ease of disposal of the residues more than offset the seeming drawback of handling a large amount of otherwise inert metallic lead.
VOL. 11, NO. 12
The alloy, ?;aPb, is made industrially as a n intermediate in the manufacture of tetraethyllead and is particularly easy to manufacture on a semiworks scale. It would seem, therefore, that if the demand would justify its production on a larger scale, it would be a n easy matter for the supply houses to stock the alloy and sell i t at a price which could compete with that of metallic sodium on the basis of available sodium.
Small Centrifuge Tube Filter THEODORE PERRINE AND WILLIAM KUMP Merck & Co., Inc., Rahway, N. J.
W
HEN working with relatively small amounts of sub-
stances using centrifuge technique, separation of solid material from liquid is sometimes troublesome, particularly when the solid has approximately the same specific gravity as the liquid. It is also often desirable to separate solid from liquid as rapidly as possible, as when working a t low or high temperatures. Various methods have been used to overcome these difficulties. The Skau tubes ( 2 ) A have the advantage of being completely closed, so that it is possible to work under anhydrous conditions, but they are expensive and perhaps not so convenient to handle as the ordinary 15-ml. centrifuge tube. The tube proposed by Cheronis ( I ) , while very inexpensive, h a s t h e disadvantage of having a rubber stopper in contact with the liquid. The filter described in this paper has several advantages. It is easily constructed from material which is relatively inexpensive and readily available. It conforms in dimenF sions to the ordinary centrifuge tube, and will, therefore, fit apparatus designed for use with centrifuge tubes. No substance but glass and filter paper comes in contact with the contents of the tube. The filter may be made moistureproof, and may be used a t low or high temperatures and withFIGURE 1 out danger of contamination with outside substances.
:I
CONSTRUCTION. An ordinary Pyrex ls-ml. centrifuge tube
is cohstricted a t E as shown in Figure 1. The constriction is so placed that chamber F will be of only slightly smaller ca acity
than chamber G. Filter plate D may be made from ffyrex tubing or molded. The disk should make a snug fit inside the centrifuge tube and should be ground to a rough seat on the shoulder, H . Filter stem C is made of 3-mm. Pyrex tube to reduce weight and t o permit equalization of pressure between
chambers F and G. Rubber stopper A has a 4-mm. hole bored incompletely through the center to support stem C loosely. (The stopper may also be made of glass and ground in.) The holes in the filter plate may be ground through or burned through with a hot tungsten wire. USE. Filter paper is cut with a cork borer to fit snugly inside the centrifuge tube, and with a small hole concentrically placed to accommodate the stem of the filter plate. Two or more such pieces of paper are slipped over the filter stem, pushed into lace with a small glass rod, then moistened if desired with a Ettle suitable solvent. The substance to be filtered is poured onto the filter, and after insertion of the stopper is centrifuged in the ordinary manner. After centrifuging, the residue on the filter is easily removed practically quantitatively by simply removing the filter from the tube, when the filter paper, if properly cut, acts as a scraper against the walls of the tube. The solvent is then removed or otherwise treated. The filtrate may be removed through the hollow filter stem by means of a long capillary dropper, without disturbing the preci itate. If it is desired to air-dry the precipitate, suction may {e applied to the filter stem. When using the filter a t above or below room tem erature, the substance, the filter, and the centrifuge tube shiePd are all preheated or precooled. Then the substance is rapidly transferred to the filter and centrifuged. Where it is desired to maintain the air about the centrifuge tubes at a low temperature (using a centrifuge with a guard bowl), it is convenient to place finely powdered solid carbon dioxide in the bottom of the guard bowl. When the centrifuge is run, the air within the bowl is soon filled with small particles of solid carbon dioxide, and the temperature is considerably lowered in a short time. The filter described has been used successfully to remove suspended charcoal from solutions, for the filtration of very soluble compounds, and for other uses where filtration is preferable t o a centrifugal separation.
Literature Cited (1) Cheronis, N. D., J . Chem. Education, 16, 31 (1939). (2) Skau, E. L., and Rowe, L. F., IND.ENG.CHEM.,Anal. Ed., 3,
147 (1931).
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