David F. Houston
Western Regional Research Loborotoryl Aibony, California
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I
Disposable Aluminum Weighing Dishes
Light-weight disposable dishes simplify the labor involved in weighing the many small residues for determination of weight distributions in counter-current or chromatographic processes. Suie able dishes can be made readily in desirable sizes from household-type aluminum foil by the procedure here described. A disc cut from the foil sheet is placed-approximately centered--on the peg shown in the illustration and is held in place by pressure with the stopper. The outer portion of the ground joint is forced upward to form the dish around the stopper and then is lowered. The formed dish is removed easily from the stopper. Discs can be stamped out with a cork-borer, or preferably a sharpened steel tube, from foil placed on a wood or plastic surface. Table 1 lists sizes of discs suitable for dishes of various capacities, the corresponding weights of 1-mil foil, and suggested standard stopper sizes. Table 1.
Foil
diameter' (mm)
Aluminum Dish Sizes
ADPCOX. Giight ( 4
APD~OX. .. vol. (ml)
Stoppel (std-taper NO.)
* These diameters correspond to cork-borer sizes The peg device illustrated is made conveniently from wood or plastic. It holds the disc centered for forming, provides a flat-bottomed dish, and allows easy 1 A laboratory of the Western Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture.
removal from the outer joint in which the dish other wise tends to stick. The joint and stopper usually are available from salvage of broken glassware.
Device for forming
dishes.
A is a tapered stopper Rtting outer port of a ground ioint B; C is o cylindrical peg inrerted in bore D; E is a foil disc.
Dishes formed from discs 30 mm or less in diameter can be weighed rapidly on a torsion-type balance of 50 mg capacity. Individual numbering is done simply by writing with a stylus or pencil on the bottom of the dish as it sits upright on a smooth solid surface. Dishes are handled with tweezers, and solutions can be evaporated quickly under a heat lamp. Some organic liquids tend to carry solution up and over the edge of the dish by capillary action in the wall creases. This problem can be reduced considerably by crimping the sides of the dish only lightly and by placing the solution-containing dish promptly on a prewarmed porcelain block under the heat lamp. Dishes formed with spherical ground joints are also less subject to this capillarity problem. I n this case the glass stopper is replaced by a spherical inner joint portion, the tube of which is plugged. Chloroform solutions of lipids have been handled adequately by these procedures.
Volume 39, Number 2, February 1962
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