1800
ANALYTICAL CHEMISTRY ACKNOW LEDGMEh 'I
The authors wish to acknowledge the assistance of Vincent T Almasy and S. Meredith Meyers, electronic technicians, in the development of the circuit. LITERATURE CITED
Debroske, J. AI. F., Crisp, L. R., Rev. Sci. Instr. 24, 547 (1953). Heftmann, E., Johnson, D. F., A N ~ LCHEM. . 26, 519 (1954). (3) Kegeles, G., Sober, H. A , Ibid., 24, 654 (1952). (1) (2)
Feed Mechanism for Automatically Capping Fraction-Cutter Tubes J. G. Kirchner' and W . L. Stanley, Fruit and Vegetable Chemistry Laboratory, Western Utilization Research Branch, Agricultural Research Service, U. S. Department of Agriculture, Pasadena, Calif.
automatic fraction cutters in which volatile Iin moving materials and substances sensitive to oxidation are collected banks of test tubes, it is desirable t o provide a system K OPERATIXG
for capping the tubes as they are filled. During a study of the volatile constituents of citrus juices, an automatic mechanism employing glass balls was developed for capping volatile fractions in test tubes collected from fractional distillations and elution chromatograms. A schematic diagram of the device is shown in Figure 1, and a three-dimensional diagram is shown in Figure 2.
1c
RESERVOIR
nism. h simple coneshaped reservoir cannot be used, because the marbles pile up a t the mouth of the cone and block off the opening. However, if a tube is used for the reservoir, it must be bent with an offset, so as to limit to three the number of marbles resting directly on the spring-loaded suspension points. having a diaFigure 2. Three-dimensional meter of 0.75 i 0.01 diagram inch are handled satisfactorily by this feeding mechanism. For marbles of this a17e the space hetneeri the suspension points should be 21/32 inch, as indicated in Figure 1. Minor variations in the height and diameter of the test tubes do not affect the operation of the feed mechanism. hbsence of tubes in the moving bank of collection tubes will not result in the complete discharge of marbles from the reservoir. hfter the dropping mechanism had been perfected, the next step was to test the efficiency of differently treated marblecapped tubes to use for maximum retention of lox-boiling solvents over evtended periods of time.
This was accomplished by setting up two sets each of five untreated tubes, one set of five tubes with greased lips, one set with beveled lips, and one set with beveled-greased lips. Beveling consisted of grinding the tube lips with water and a medium weight Carborundum powder, using one of the glass marbles The marble was carefully rotated so as to obtain a narrow bevel approximately 1 mm. wide around the inside of the tube lip. As long as the bevel around the lip is unbroken, small variations in tube roundness are insignificant. The beveled rims of one set of tubes were coated with grease. For h drocarbon solvents, a v-ater-soluble grease similar to that descriged by Meloche and Frederick [ J .Am. Chem. SOC.54,3265 (1932)l is satisfactory. Fifteen-milliliter portions of petroleum ether (boiling range 35" to 60" C.) were next pipetted into all tubes. One set of untreated tubes was sto pered with corks, the remaining tubes were capped n i t h marbes, and all tubes were immediately weighed. The corks were removed from the one set of tubes, and these open tubes and the capped tubes were allowed to stand a t room temperature (25' to 27' C.) for 26 hours. After this period the open tubes were again stoppered, and all tubes were reweighed. Efficiency of solvent retention was calculated by subtracting from 100 the product of 100 times the average weight loss from each set of five open tubes.
'Table I.
Figure 1.
Schematic diagram
The device consists of a storage reservoir connected from above to a chamber in which a marble is held on suspension points by t\yo spring-loaded, pivoted metal jaws. The pivoting jaws are opened and a marble is released when a test tube in the moving rack passes between the lower extensions of the jaws. As the marble is being released, blocking suspension points a t the opposite end of the j a m retain the marbles in the reservoir until the capped test tube has moved on. The jaws are then closed by the loading springs, causing the suspension points a t the bottom of the chamber to open and release another ball from the reservoir into the feed chamber.
A reservoir for coin-operated candy vending machines, or a long tube, can be used to supply marbles to the feeding niecha1
Present address, Tenco, Inc.,720 West Edgar Road, Linden, N. J .
Efficiency of Solvent Retention by Ball-Capped Test Tubes
Treatment of Tube Lip Pl-one Beveled Greased Beveled-greased
.4verage Weight Loss, Grams Capped tube. Open tube, .4 B 5 47
5 47 5 07 5 07
3.48 2.92 1 01 0.12
Retention Efficiency. 100 - 100 -B ..I
37 47 80 98
Table I indicates maximum solvent retention when beveledgreased test tubes were used. Similar results were obtained with other organic solvents. ACKNOW LEDGMEKT
The authors' appreciation is extended to L. F. htkinson of this laboratory, who contributed to the design and constructed this apparatus.
