Glass Helices for Packing Laboratory Fractionating Columns ROBERT W. PRICE AND WILLIAM C. MCDERMOTT, University o f Vermont, Burlington, V t .
To draw a spiral of uniform fiber diameter it is essential that the glass rod be advanced a t a constant rate. This is accomplished as follows: A convenient length of Pyrex rod is closely wound from one end to a suitable length from the other with a length of soft cord. Sufficient glass is allowed to remain uncovered to extend from the top of the metal guide, E (a cork borer of the proper diameter mounted in a cork), to the steel mandrel. The free end of the cord is draped over the edge of the desk and held taut by means of a small weight appropriately fastened with a battery clamp. A slight downward pressure while slowly and evenly unwinding the cord from the glass rod causes it to advance at a uniform rate.
Procedure The tip of the Pyrex rod is fused to the glass ring on the anchor and using an air-blast flame about 7.5 em. (3 inches) long the mandrel is slowly turned to start the spiral. After a few turns the rate is increased to about 90 r. p. m. which is maintained to the end. As glass is drawn from the Pyrex rod it is slowly and FIGURE 1. DIAGRAM OF APPARATUS
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ECENTLY the need arose in this laboratory for a quantity of single-turn glass helices to be used as packing for a fractionating column. A survey of the literature failed to reveal a suitable process intermediate between a few rather arduous methods ( I , $ , 4) requiring considerable adroitness on the part of the operator, and the excellent but intricate mechanism of Stewart ( 2 ) . With very little practice the following method yields a uniform spiral which is easily withdrawn intact from the steel rod upon which it is wound, or broken into single-turn helices with negligible loss while still on the rod. Two operators are required and all materials, with the possible exception of the steel rod, are available in any chemistry laboratory.
Description of Apparatus The apparatus consists essentially of a suitably supported steel mandrel upon which is wound a spiral drawn from a 5-mm. Pyrex rod (Figure 1). In this instance the authors used a 120cm. (4-fOOt) length of 0.47-cm. (0.1875-inch) steel rod bent a t one end to form a small crank. Two loosely turned up rightangle clamps, A and B, and cork C serve as bearings and prevent swaying of the mandrel as it is turned. Cork D, tightly fitting on the rod, serves as an anchor for a small glass ring to which the beginning of each glass spiral is fused. Uniform spacing of the spiral is accomplished by tying a length of pliable cord to the crank and allowing this to wind up on the mandrel while turned by one operator. The front of the cord spiral thus formed runs against the side of clamp A and causes a displacement of the mandrel equal to the diameter of the cord for every revolution. The unused cord is conveniently draped over the top of clamp A and a slight tension maintained by allowing it to run through the thumb and index finger of the left hand. A loosely fitting cork handle on the crank facilitates smooth turning of the mandrel. S irals of widely varying pitches can be produced by using cords o?different diameters.
FIGURB 2. TYPICAL SPIRALS 289
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uniformly advanced by a second operator. The blast flame is so adjusted that the outer brush is tangent to the mandrel and the tip of the inner cone just touches the glass rod. When a spiral has been drawn the Pyrex rod is quickly withdrawn to part the glass. The mandrel is removed by unscrewing clamps A and B, and the spiral is broken away from the ring and slipped off. After replacing the mandrel and rod another spiral can immediately be drawn. One critical adjustment is necessary in the position of the Pyrex rod. The elevation from the horizontal makes little difference, but it is essential that the longitudinal axis of the rod intersect the axis of the mandrel and be about perpendicular to it. Using this method a uniform spiral 35 cm. long can be drawn, removed from the mandrel, and the apparatus reassembled ready for another spiral in about 4 minutes. Several suggestions have been made for breaking spirals into individual single-turn helices (1, 2, 4). The authors found that negligible waste resulted if the spiral were returned to the mandrel, and individual helices broken apart by twist-
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ing the blade of a spatula or other similar blunt instrument between individual turns. Nonuniform spirals are difficult to remove from the winding form and yield considerable waste upon being broken into helices. I n a typical operation 15 cc. of single-turn helices were obtained in 20 minutes from four 28-cm. spirals weighing 2.85 grams. Waste material amounted to 0.1 gram or about 3.5 per cent by weight. Spirals have averaged 5.9 mm. in outer diameter with an individual fiber diameter of 0.6 mm. A few typical examples are shown in Figure 2.
Literature Cited (1) Roper, E. E.,Wright, G. F., Ruhoff, J. R., and Smith, W. R., J. Am. Chem. SOC.,57, 954 (1935). (2) Stewart, W. W.9 IND.ENQ.CHEM.9 Anal. Ed., 8,451 (1936). (3) Wilson, C.D., Parker, G. T., and Laughlin, K. C., J . Am. Chem. Soc., 55, 2795 (1933). (4) Young, W. G., and Jasaitis, Z., Zbid., 58, 377 (1936).
Semiautomatic, Multiple, Electrometric Titration Apparatus MAURICE E. STANSBY, Technological Laboratory, United States Bureau of Fisheries, Seattle, Wash., G. A. FITZGERALD, Birdseye Laboratories, Boston, Mass.
An apparatus is described in which ten electrometric titrations can be performed simultaneously by one operator within nearly as short a period as is required for a single titration. The burets are controlled by solenoids and the progress of the titration is followed by a series of colored lights on a control panel. While the apparatus was designed primarily for use in a fishfreshness titration, it can be used for a wide variety of potentiometric titrations. When applied to the determination of the freshness of fish, the apparatus enables a single operator to conduct freshness tests on a mass scale which would require six to eight operators using the ordinary singletitration method. A practical application foreseen by the authors is the predetermination of the freshness of all fish landed on the Boston Fish Pier to enable sale price to be based upon quality.
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HE electrometric method for determining the freshness of fish, as proposed by Stansby and Lemon (6),was
studied further by Fitzgerald and Conway (1) to determine the practicability of its use in the commercial grading of fish. These studies showed an excellent correlation between freshness as indicated by electrometric titration and organoleptic tests conducted by expert fish buyers of long experience in judging the quality of fish. It was apparent, however, that if the method was to be applied in industry, certain
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modifications would be required to permit the handling of a considerable number of samples simultaneously. I n commercial practice, data on a large number of samples taken from different fishing vessels, and from different sections of the hold of each vessel, must be availabIe within a relatively short period. Accordingly, a multiple-unit apparatus has been constructed which allows an operator to handle up to 10 samples at a time. The apparatus is suitable for making a wide variety of potentiometric titrations and hence is described here in some detail.
Description of Apparatus The circuit consists essentially of 10 sample titration halfcells connected individually, one after the other, by means of an automatic switching arrangement through a galvanometer to a reference electrode. The principle employed is that of Treadwell and Weiss (6),whereby the reference half-cells contain a solution having a pH identical with the desired titration end point, a t which the galvanometer deflection will be zero. The automatic switch connects the titration cells into the circuit successively a t 3-second intervals. Thus, a galvanometer reading is obtained for each particular cell once every 30 seconds, and the progress of the titration followed accordingly. The presence of any one cell in the circuit is indicated by one of 10 flashing amber lights on a control panel. The titration burets are manipulated from the control panel and the flow of acid is controlled by solenoid cutoffs. When an end point for any cell is reached, as indicated by a zero deflection of the galvanometer a t the instant the cell is cut into the circuit, the operator can throw a switch which cuts off the corresponding buret. At the same tima a warning red light turns on, indicating that the particular buret has been turned off. A general view of the entire apparatus is given in Figure 1.
