812
INDUSTRIAL AND ENGINEERING CHEMISTRY
The various possible effects of atmospheric pressure, while all are not pertinent to the efficiency of the system, are nevertheless interesting. The water in H rises until its level is the same as that obtaining inside the reservoir. If the reservoir were 40 feet above the water bath and the barometric pressure were 32 feet of water, the water in H would rise to a level 32 feet above the water in the bath. At this point a balance would be reached between atmospheric pressure and the weight of the column of water in H , and the two would offset each other. Inasmuch as the si honing action in tubes M and K is dependent upon the ability ofatmospheric pressure to force water to a height equal to the height to which these tubes extend above the level of the water in C and/or B, any nullification of the effects of atmos heric pressure stops the flow of water through the system. &ch a nullification may be complete, as in the case just cited, or it may constitute a nullification of the “atmospheric head”, as is the case during normal operation a t heights less than about 30 feet. By atmospheric head is meant that portion of atmospheric pressure which is required to raise the level of the water in H to the same height as the level in the reservoir. The lower portion of H should be of fairly large diameter to eliminate surface tension interferences. When sufficient water has been lost from the bath by evaporation to lower the level below the opening of H, air enters H and water runs down H into the bath. This results in a lowering of the water level in H , which usually empties, and the siphoning action in tube Jf begins. Since the level in C is thereby lowered, the siphoning action in K sets in. The complete cycle takes place about every half hour in actual practice. Inasmuch as the automatic emptying of H is accompanied by considerable agitation, this tube should be fastened securely in such a position that its open end is kept a t the optimum level for the water in the bath. A convenient location for the entrance of H into the bath is through the smallest of the usual four sets of concentric rings. Tube L is a glass T held in place by rubber tubing. As is shown in Figure 1, H opens into vessel 2, which is a modification of the Berzelius beaker suggested by Holmes (6). This vessel consists of a 1-liter conical glass percolator, the bottom opening of which is connected by rubber tubing to a glass capillary of 1.5-mm. inside diameter. The percolator is fastened in place so that approximately its upper two thirds extends above the opening of H . Z accomplishes two things. First, if, as Holmes (6) states, a large flask immersed in the liquid of the bath is abruptly removed, the level of the water in 2 is lowered so slowly (by virtue of the fact that the water must drain out through the small capillary) that the water outside of 2 will revert to its original level before all the water in H runs out and allows the air pressure within the reservoirs to rise to atmospheric. The entrance of air into H lowers the water in H and increases the air pressure within the reservoirs slightly-just enough to start the flow of water into the bath and maintain it until the level is brought back to normal-but even if there were a sufficient lowering of the bath level to allow all the water in H to run out, the presence of 2 makes it run out in slowly repeated small increments. The chances of such a large beaker being removed from the bath as to interfere seriously with the stabilizing action of Z are very remote, The disadvantage of allowing the air pressure within the reservoirs to rise to atmospheric rests in the fact that water will not stop flowing into the bath until the water again rises in H to the same level as that obtaining in the reservoirs. From the time water begins to flow back into H until these equilibrium levels have been reached, water continues to flow into the bath, and when this finally ceases, the water in the bath is likely to be undesirably high. This condition is prevented by 2. If the bath is small, or changes of volume of the water are small, or if larger changes in level due to siphoning of water into the bath through M a r e not objectionable, Z may be omitted. Secondly, in pumping water into the reservoirs from A , 2 has sufficient water to stabilize the action of the H tube, through which excess air escapes during the filling process. At the conclusion of this pumping, in order to prevent the air pressure within the reservoirs from rising to too great an extent, the stopper in A should be removed, allowing all the water in J to flow back into A , the stopper should be replaced, F should be closed, and G should be opened, in this order. It is the use of L in place of the Mariotte arrangement of Gerdel ( 4 ) which permits refilling of the reservoir. If it is desired, only one 5-gallon bottle may be used as a reservoir; on the other hand, more than two may be used, de ending on the length of time the operator wishes the bath to \e without attention.
’overThis6 months, apparatus has been in daily use in this laboratory for and has been satisfactory in every way. The
Vol. 14, No. 10
apparatus is of simple construction, requiring no glass blowing, but only the usual laboratory equipment such as standard tubing, bottles, etc. The literature contains a considerable number of articles on constant-level devices for water baths (1-3, 6, 7-14). T h e writer is indebted t o the authors of all these papers for their several valuable contributions in tracing the history of constant-level devices up to the present time, T h a t paper which reports a device most closely approximating the writer’s is the one by Gerdel (4).
Literature Cited Brooks, Richard, J. Chem. SOC.(London), 125, 1546 (1924). Eddy, C. W., Chemist-Analyst, 18, 20 (1929). Fouque, G., Bull. soc. chim., 41, 115-16 (1927). Gerdel, R. W., IXD.ENQ.CHEM.,19, 50 (1927). (5) Holmes, F. E., IND.ENG.CHEM., ANAL.ED., 12, 483-5 (1940). (6) Holmes, F. E., private communication. (7) Meyer, Lester, Chemist-Analyst, 20, No. 2, 16 (1931). (8) Robertson, J. H., J. Chem. Education, 10, 377 (1933). (9) Stannard, W. S., Pharm. J., 118, 245 (1927). (IO) Vinycomb, T. B., and Vogel, A. I., J. C h m . SOC.(London), 1932, 2088. (11) Tilde, H. D., IND.EXQ.CHEM.,16, 904 (1924). (12) Wilson, N.F., and Carleton, R. K., J . Chem. Education, 6, 13356 (1929). (13) Wing, H. J., IXD. ENG.CHEM.,17, 630 (1925). (14) Yohe, G. R., and Keckler, C. G., J. Chem. Educetion, 11, 462 (1934).
(1) (2) (3) (4)
A Simple Thyratron Circuit SIDNEY GOLDEN The George Washington University, Washington, D.
c.
ANY circuits which employ a thyratron in conjunction with thermostat regulation have been described. While no particular claim of originality is made, the circuit shown in the figure is very simple. The values of the resistors employed are not critical and may be varied somewhat. The relay unit, although not essential for the operation of the thyratron, is included in order t o prevent damage to t h e thyratron following periods of line failure, while in operation. With line failure, the relay opens the circuit and must be closed mechanically t o reapply power, after t h e anode switch is opened. The usual procedure is follomed of allowing the cathode to come to operating temperature before closing the anode switch, which takes about 5 minutes. The low current at the thermoregulator contacts (measured a t 14 microamperes with the suggested resistor values) suggests other
uses where such an on-off cont r o l m a y be used. It is important that the secondary and primary of the transformer be
FG 57
I
e .
AN&
bA.C.d
swITCH
I
connected so that measurem e n t of t h e alternating current voltage between t h e two free ends shows a greater voltage t h a n t h a t across the primary.
