An Adjustable Vapor Thermoregulator J. Y. YEE, Bureau of Plant Industry, U. S. Department of Agriculture, Beltsville, Md.
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vapor chamber having a bottom tube, B , about 65 cm. long and of 12-mm. bore, with a ring seal at C to hold the liquid ether in A . Tube D, about 95 cm. long and of 4-mm. bore, extends through A to the bottom of B. The adjustment meclianism is connected to D a short distance above A . E is a piece of Jena KPG tubing (of 8.04-mm. bore and 50 mm. in length) with a very uniform inside diameter (*0.001 mm.). (Pyrex tubings with uniform inside diameters are now obtainable.) To the middle of E a mercury reservoir, F , is carefully attached, so that, except a t the seal, G , the inside diameter of E above and below is not disturbed. Inside E is a Fernico alloy plunger, J , the diameter of which is only very slightly smaller (about 0.015 mm.) than the inside diameter of E, so that it can be moved freely therein by means of a rod connected to a brass bellows, K (250 mm. in diameter), without using any lubricant. The metallic bellows is soldered with ordinary solder to one end of a Fernico tube, L,the lower end of which is sealed to the Pyrex tubing above E. The upper and lower solder joints of the bellows as well as the one to the Fernico tube should be gas-tight. Both the Fernico alloy and the KPG Jena tubing can be sealed dirertly to Pyrex glass. By turning the thumbscrew T,the bottom of the Fernico plunger in E can be raised above point G or lowered beyond that point. G should be about 15 mm. below contact point H , so that the mercury always exerts a little pressure against the bottom of the plun er. After the system has been thoroughly cleaned an! dried, mercury and ethyl ether are introduced into the system in the following manner: With stopcock M opened to bulb N, the system is evacuated with a mercury pump and then sealed off a t 0. Before sealing a t &, enough mercury is distilled over from flask P t o fill tube B to a point a little below &. Now cup R is filled with dried ethyl ether, about 5 ml. of which are caref4ly.introduced into bulb N. Then about 2 ml. of the liquid are distilled into A by slightly warming bulb N. Some of the ether condenses and remains in tube B. The ether in A is then cooled with dry ice to reduce the ether vapor pressure in the system before sealing off at
REEN and Loring (1) described a method for construct-
ing an ether vapor thermostat and gave the advantages of using it for room temperature control. They pointed out that the regulator, as described by them, must be constructed at the place where it is to be used. The modified ether vapor thermoregulator described in this paper has given very satisfactory results for about a year in regulating the temperature in a small room. With a proper relay and heating system, a temperature variation of .t0.02" C. at the thermoregulator can easily be maintained. Its design not only overcomes the objection pointed out b y Green and Loring, but also makes it easily adjustable over a temperature range of 20" C. (20" to 40' C,), It can be readily made t o cover a much wider temperature range, if desired, by simply lengthening the mercury column. The vapor thermoregulator, shown in Figure 1, is made of Pyrex glass except for the adjustment mechanism. A is a 500-ml.
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After removing the dry ice bath from A , the instrument is ready for use. Thumbscrew T i s turned so that the bottom of the Fernico plunger in E is a little above G. As the thermoregulator C. for exbegins to warm up to the desired temperature-30' am le the vapor pressure of the ether in the system increases a n a f z e s the mercury in B to rise in D. Since there is enough mercury in this instrument to operate a t 20" C., the excess mercury oes into reservoir F. When the room temperature is about 0.5" below the desired temperature, the plunger is lowered below G by turning the thumbscrew to cut off the mercury in the reservoir from the main column. I n this respect, the plunger acts as a stopper. It also serves as the final adjustment for the temperature control, which is accomplished by gradually lowering the plunger still further in E , so as to force the mercury into the upper part of D, until it barely reaches contact point H , when the room temperature is exactly at 30' C. Then the distance between H and the mercury surface in tube B is 63.48 cm., which is the vapor pressure of ethyl ether at this temperature. The room temperature can easily be raised from 30" t? 35" C., by moving the plunger above G, to let more mercury into the reservoir P , as the temperature in the room is increased. As in the previous operation, the plunger is lowered below G again when the room temperature reaches about 0.5" C. below the desired temoerature. The final adjustment of the temperature is carried out as before. To lonrer the room temperature from 35" to 25' C., the plunger is again raised above point G , but this time the mercury in reservoir F is allowed to flow back into the system as the room is b+ng cooled, until the roqm temperature reaches the desired point. The final adjustment is the same as before.
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The thermoregulator is flexible.
Although contact point
H is sealed in a n evacuated chamber, this thermoregulator (unlike most adjustable thermoregulators of this type) does not require setting in a bath of the desired temperature when changing from one temperature setting to another.
Literature Cited (1) Green, J. B., and Loring. R. A., Rw. Sei. Instruments, 11, 41 (1940).
FIGURE 1
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