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Centrifuge Tube Agitator
R. F. REITEMEIER, U. S. Regional Salinity Laboratory, U. S. Department of Agriculture, Riverside, Calif.
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The handle of the valve grinder has been replaced by a bolt, by which the body is mounted upside down in a wooden saddie, which in turn is fastened to a wood base of dimensions 26 X 11 X 1.5 65 X ~ .inches . . . 28 X 3.8 cm.). A 6.25-inch hardwood Vpulley replaces the grinder crank.' This is turned elookwise by a 0.5-inch V-belt 30 inches long which also encircles a 1.25inch V-pulley on the shaft of a 0.25-hp., 110-volt, 1425 1.p.m. electric motor. (A 0,125-hp. motor of the same speed probably would he adequate.) This pulley combination fixes the speed of the wooden pulley a t 265 r.p.m., which is somewhat faster than the grinder would usually he turned manually in grinding valves. The body of the grinder is filled with light grease. The ordinary 15-ml. and thick-walled 12-ml. conical centrifuge tubes used by the author are held in a tramparent Lucite plastic holder fashioned from I-inch Lucite rad. A detailed picture of the holder is shown in Figure 2. The main inside diameter is 45/64 inch, which is barely sufficient for the broadest tubes. The upper 0.25 inch of the opening is tapered to a maximum diameter of 0.875 inch at the to which permits the use of a hand of thin Gaoch ruhher t u h n g stretched over the opening to hold the tube during its aeit,xt,ion. - ~ " ~The~ hand ~ is~ 0.9375 inch wide and 0.625 inch long: pinholes in the horizontal portion assist the escape of sir from the holder when a tube is inserted. Below the 45/64inch section, which is 3.5 inches long, extends a boring of 0.3125-inch diameter and O~.Li-inrh The tanered Dortion of the tube rests on .. ...... dsnth. --r~ the rim of this smaller hole, khere6y the tube is supported and centered. A niale threaded Lucite stud 0.75 inch long, fashioned on the base of the holder, holds i t securely in the threaded chuck of the Rrinder. The center of this stud is offset0.0625 inch from the center of the holder to provide a greater radius of gyration. The over-all length of the holder is 5.375 inches. A similar holder can he prepared from flared glass tubing cemented to a hsse and threaded stud of brass. To facilitate titrations directly in the centrifuge tube, a buret assembly is mounted on the wooden platform. Athin brass tube slides over a brass rod screwed into s base plate fastened to the platform; a hook at the top of this tube engages * guide pin located 1inch from the top of the rod. The microhuret, supported hy two thermometer clampa, moves vertically. and horizontally with the brass tube. With the hook on the guide pin, the tip of the buret is inserted into the centrifuge tube, the wooden pulley turned by hand, and the brass tube moved honeontally until the buret tip clears the tube during the rotation. A setscrew, 4 inches nbove the bottom of the tube. is then tightened. As an illumination aid, a dass plate 7 X.12 inphes,~towhich is cemented s sheet of thin white t h i n g paper, IS mounted in a wood support dirktly behind the agitator and the buret assembly. An inexndencent lieht bulb behind the paper screen furnishes sufficient diffusedlight far titrations and &her color observations. Agitation increases the height of a n aqueous solution in a centrifuge tube about 0.5 inch. Centrifuge tubes of 12- and 15-ml. nominal capacity can accommodate approximately 11 and 12 ml. of liquid, respectively, without loss of tube contents. Agitation for 5 to 10 seconds usually suffices for complete mixing.
ANY quantitative and qualitative semimicroanalytical procedures require the agitation of individual small centrifuge tubes during the addition of reagents, mixing of tube wntents, and titrations. Manual tati ion of tubes usually inkdves various motions such as shaking, angular swinging, stirring with small rods, and reciprocating rotation between the palms of the haods. Some disadvantages of these techniques. are: (1) discomfort to fingers and hands when handling hat tubes; (2) frequent Im of tube contents; (3) nonuniform agitation of the various tubes within an andytical aeries; .(4) tedium of repeated shakings during titrations; (5) extended time required for thorough mixing; and (6) errnrs involved in the handling and washing of stirring rods. T o avoid these difficulties, mechanical eantrivances have been investigated. Figure 1 shows a successful one.
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The essential component of this device is the actuatina mechanism of a manual valve grinder (Sioux valve grinder model 400, manufactured by Aibertson and (h., Sioux (:it!', fown). The e e ~ mi n the bodv of this tool are desiened 30 that when fhc crank turned in one"direction the chuck moves 213 revolution clockwise, then 1 revoIutioii minterclocknisr, and repeats thi' movement. Thus, the mrnfion of a ccntriiugc rube tliat rotates with 11,e h.w .... r.. -k winewhat rcsemblps l i a 1 of a tuhr rotatrd between the palms of the hands; when the crank is turned rapidly, the tube is agitated sufficiently to provide rapid mixing of the tube's contents. ~~
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This apparatus has been employed successfully in various operations of qyantitative semimicroanalytical methods preoxalate viously published (I), including precipitation.of.ddand titration with bexaperehlorato cerate, precipitation of magnesium aa magnesium ammonium phnsphate, precipitation of pdtassium sodium cobaltinitrite and development of cobalt ferrocyanide color, and precipitation of benzidine sulfate and sodium uranyl zinc acetate. ACKNOWLEDGMENT
J. D. Fletcher misted in the construction of the appwatus. and Milton Fireman and Dewey C. Moore in the photography. LITERANRECITED
(1) Reitemeier,
F i g u r e 9. Gos Seaion of Plastic Figure 1.
Agitator and Titration Assemblv
R. F.. I m . ENO.CHEM.,ANAL.ED.,15, 393 (1943).
Coxmrsa~ronfrom the U. S. Regional Salinity Laboratory. Bureau of Plant Indmtry. Soils and Agricultural Endneering. Agricultural Reaeareh Administration..!.I S. Department of Amicultura. Riverside, Calif.. in coopustion with the eleven westem state and the Territory of Hawdi.
Centrifuge Tube Holder
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