AIDS FOR THE ANALYST test tube with a water aspirator, and then allowing air to reenter the tube. About 0.05 ml. of air should be allowed to remain in the bulb. Mercury rises in the capillary only a few millimeters over the first 80" rise in tem erature, but then more rapidly until at 135" it rises a few mzlimeters for each 1' rise in temperature. The variation in temperature during distillation is within 0.5" as measured with a thermometer. If the upper third of the bulb of the regulator extends above the resting sol;tion, the temperature during distillation is elevated about 1 . Differences in atmospheric pressure cause insignificant changes in the distillation temperature.
Automatic Control for Fluoride Distillation Adrian C. Kuyper, Department of Physiological Chemistry, W a y n e University College of Medicine, Detroit, Mich.
most generally used procedure for the determination of [Godfrey, P. R., Shrewsbury, C. L., J. Assoc. Ofic.Agr. Chemists 28, 335 (1945)l requires a preliminary ashing of the sample, steam distillation, and titration of the distillate. The most tedious part of this procedure is the distillation, which must be performed at 135'13' C. and requires the constant attention of the operator for 1 or 2 hours. The author has devised a simple temperature control which regulates the amount of gas delivered to the burner and maintains the desired temperature automatically. HE
Tfluoride
With the exception of the thermistor type of regulator, which requires an expensive resistance-operated electronic relay and adaptation for use with a solenoid valve, commercially available regulators have too large a heat-sensitive area and are usually not sufficiently long for use in the control of this distillation.
The thermoregulator is designed to have a small temperaturesensitive area, not much larger than that of a thermometer, which may be inserted into the narrow neck of a flask and immersed in a small volume of solution (Figure 1). The capillary tubing extends through a stopper on the distillation flask and the electrical contacts are made outside of the flask. The regulator owes its sensitivity to the rapid increase in the vapor pressure of a liquid as its boiling temperature is approached. The ethylene glycolwater mixture and the mercury may be introduced into the regulator by placing small amounts in a very large test tube, inverting the regulator and placing it in the test tube, evacuating the
In the control circuit (Figure 2) current passes from the 110volt line through a rectifier, a variable resistance, the thermoregulator, and a vacuum tube plate relay. The use of pulsating current of low amperage minimizes sparking at the thermoregulator contacts to the extent that it is rarely discernible. The resistance should be set so that there is a time delay of a few tenths of a second in the closing of the relay. This delay, together with the time delay on opening the relay, effectively prevents chattering. Closure of the relay causes closure of the solenoid valve, which clamps a rubber tube and stops the flow of gas to the burner. The solenoid is operated on rectified current in order to avoid the excessive chattering that occurs when it is operated on alternating current. A small amount of gas is allowed to bleed past the solenoid valve in order to keep the burner lighted when the valve is closed. If it is desired to control the distillation by introduction of cold water, connection to the solenoid is made through the opposite arm of the double-throw relay. The control circuitry may be easily mounted in a 6 X 9 X 5 inch cabinet.
LEADS TO RELAY
CAPILLARY TUBING, ABOUT 1.5 mm. B O R F
This equipment was developed for use in research supported in part by the National Institutes of Health.
ABOUT 0 . 0 5 m l . A I R
Antivibration Table for a Semimicro Balance D. G. G a g e and Patrick Sullivan, Naval Research Establishment, Dartmouth, Nova Scotia, Canada
ABOUT 0.1 rnl. ETHYLENE GLYCOLWATER MIXTURE B.P. 142. +-BULB,
elimination of vibration in tables for analytical balances T has often created problems, particularly in industrial laboratories or in buildings in which heavy machinery is used. A HE
ABOUT 13X 16mm.
table devised in this laboratory has very good vibration-damping qualities when used with the Mettler semimicro Gram-atic balance.
Figure 1. Thermoregulator for constant temperature steam distillation
I
The damping material is 0.5-inch heavy felt of the type commonly used in mounting lathes and milling machines in machine shops. In order to take full advantage of its damping qualities, it must be heavily weighted; the table top, therefore, is a granite plate weighing 165 pounds. In this case, an instrument maker's layout plate was used, but any flat plate of similar weight and dimensions should suffice. The dimensions of the plate are as shonn in the diagram, and there is a 2-inch ledge on all sides. Dimensions of the frame are dependent on those of the top plate. The frame and legs of the table are constructed of angle iron welded at all joints. The legs are braced on three sides with 1-inch strapping; the remaining side is left open as knee space. Leveling screws are provided on each leg.
CONTROL
L Figure 2. Control circuit for thermoregulator CI. 10-pfd. electrolytic capacitor CZ. 20-fifd. electrolytic capacitor Fi. 35-ma. selenium rectifier Fz. 200-ma. selenium rectifier H . Hoffman clamp L. Solenoid, Guardian 33073 110-volt a.c. continuous d u t y 15ounce lift. A solenoid vaive operating on 110-volt a.c. ma'y be purchased from Skinner Electric Valve Division, Skinner Chuck Co., New Britain, Conn. Ri. 5000-ohm 4-watt industrial control R2. 250-ohm 50-watt adjustable resistor SI. S P D T toggle switch, center off sa. 10,000-ohm S P D T plate circuit relay W . Stout wire clamp for closing rubber tubing
Some evidence of the vibration-damping qualities of this table was recently provided during alterations and new construction in the building in which it is housed. Keighings could be made on a semimicrobalance on this table while riveting and compressed air drillings were going on. An ordinary Gram-atic balance in the same room was mounted on a commercia! pattern balance table consisting of a Transite plate weighted vith a steel pendulum and damped 1%-ithsoft rubber. The scale of this balance 922
