An Adjustable Sensitive Thermoregulator J. Y. YEE
AND
R. 0. E. DAVIS, Bureau of Chemistry and Soils, Washington, D. C.
T
pressure against the plunger, thus preventing air from entering. The adjustment mechanism can be made to operate over a wide t e m p e r a t u r e range by varying either the bore or the length of the Jena KPG tube. The thermoregulator described here holds about 110 ml. of mercury and has a temperature range of 80" C. (20" to 100" C.).
HERE are a number of sensitive
thermoregulators described in the literature (I, W,3, 7) t h a t can maintain thermostats constant to *0.001' C. for long periods of time without much attention. Most of these regulators are either glass tubes filled w i t h t o l u e n e a n d mercury or metal tubes filled with mercury. Every time the temperature of the b a t h is changed over a wide range i t necessitates addition or removal of mercury in the regulator. In order to eliminate these operations, Parks (6) employed a tight-fitting rubber plunger in a side arm of the regulator. By raising or lowering this plunger, the temperature of the thermostat could be varied to within *0.02" C. of the desired temperature. The thermoregulator herein described is made of glass, filled with mercury. The adjustment mechanism is similar to that of Parks, but of permanent construction. With this regulator, the temperature of a 36-liter thermostat can be easily changed and maintained a t 25', 30', 35', and 40' * 0.001" C. For shorter periods (2 or 3 hours) sometimes no movements can be detected in the Beckmann thermometer.
As pointed out by Geer (3) and others, a n accurately c o n t r o l l e d thermostat requires more than just a sensitive thermoregulator. It depends just as much on the type of heater, the relay, the thermal i n s u l a t i o n of the bath, the regulator suspension, and the stirring. The modified r a d i o t u b e r e l a y system (6) used requires less than 2 microamperes through the regulator, so that there is no sparking at the mercury contact. Figure 2 shows a modified Heisig and Camerson (4)type of double-walled thermoregulator with indentations in the inner tube to increase the surf a c e a n d r e d u c e t h e wall thickness. This r e g u l a t o r has about the same sensiFIGURE 2 tivity as the one shown in Figure 1. but reauires less mzrcury (about 70 kl.). The inside and outside tubes being only about 3 mm. apart, i t requires some glass-blowing skill to make the upper and lower ring seals, while a n amateur glass blower can make one of the types shown in Figure 1 without difficulty.
This thermoregulator, shown in Figure 1, is made of thin-walled (0.8-mm.) Pyrex tubing, A (35-mm. outside diameter), with a number of large indentations, B, which are about 25 mm. wide at the opening and 25 mm. deep. The thickFIGURE 1 ness of the walls of these indentations is only about 0.2 to 0.3 mm. This accounts for the rapid response of this regulator to temperature changes in the bath. Extending inwardly in tube A , these indentations do not make the apparatus more fragile. To kee air from being trapped underneath these indentations when t f e regulator is being filled, they are pointed slightly upwards. The adjustment mechanism, directly sealed to tube C that extends almost to the bottom of tube A, consists of a piece of Jena KPG tubing (5.05-mm. bore, 50 mm. in length) with a very uniform inside diamter (*0.001 mm.). Attached with Picein cement to the top of this Jena tubing is a brass cap, E,through which passes a finely threaded brass rod carrying an Invar steel plunger, F. The diameter of the plunger is only slightly smaller (about 0.015 mm.) than the inside bore of the tube, but can be moved freely therein without using any lubricant. The top of tube G is fitted with another brass cap, H , through which passes a rod carrying a fine nichrome wire that makes contact with the mercury a t point I , where the fine capillary tube (0.7-mm. bore) opens into the upper bulb. Side arm J is for the other electrical contact. K and L are lock nuts. With the plunger removed, redistilled mercury is introduced into the regulator through a funnel with a fine capillary stem reaching to the bottom of tube C. The mercury rises very slowly in tube A , so that no air bubbles can be trapped therein. Care is taken to keep the stem of the funnel full during the filling operation; otherwise air is forced into the regulator. When the mercury reaches halfway up in tube D,the funnel is removed and the plunger carefully replaced. In so doing the mercury level in tube D is pushed downward while that in tube G rises. The pressure created by the difference in these mercury levels will soon completely force out all the air trapped between the mercury and the plunger. The plunger in tube D is not air-tight, although no mercury can escape, and therefore the bottom of the plunger should always be slightly below point I , so that there is a positive
Literature Cited (1) Beaver, D. J., and J. J., IND.ENQ.CHEM.,15, 359 (1923). (2) Ferguson, A. L., Van Leute, K., and Hitchens, R., Ibid., Anal. Ed., 4, 218 (1932). (3) Geer, W. C., J . Phys. Chem., 6, 85 (1902). (4) Heisig, G. B., and Camerson, A. E., IND.ESG. CHEnf., Anal. Ed., 5, 420 (1933). (5) Heisig, G. B., and Gernes, D. C., Ibid., 6, 155 (1934). (6) Parks, W. G., Ibid., 5, 357 (1933). (7) Wing, H. J., Ibid., 2, 196 (1930). RECEIVED August 17, 1936.
CORRECTION. In the article entitled "Quantitative Separation and Determination of Aluminum and Zinc" [IND.ENG. CHEM., Anal. Ed., 8, 349 (1936)l by F. H. Fish and J. M. Smith, Jr., no reference was made to the work published by H. A. Horan and J. B. Damiano [J.Am. Chern. Soc., 57, 2434 (1935)l. We sincerely regret the omission of this important reference. Reference 2 a t the end of the article should have read: Heyrovsky, .J., J. Chem. Soc., 117, 1013 (1920). F. H. FISH 477
Apparatus for the Fractional Distillation of Liquefied Gases ARTHURROSE The Pennsylvania State College, State College, Pa.
L
OW-temperature fractionating columns of numerous designs have been described by Frey and Yant (IO), Oberfell and Alden ( I 7 ) , Podbielniak (a@, Davis ( 2 ) , Bosschart ( I ) , and others (3,7,9, I d , 13,14,18,19, 21,23). These columns are all characterized by a partial condenser, and fractionation takes place in a closed system. McMillan (16) has recently patented an improved form of such apparatus. I n order to obtain a smooth boiling point curve, close and continuous attention must be given to the pressure inside the column and to the condenser temperature because of the effect of these factors on the boiling point observed. The successful operation of the columns requires considerable skill and experience, especially when the mixture being analyzed contains components boiling near one another. The apparatus described here is such that its operation can be easily mastered and it gives a boiling point curve that is smooth and independent of all reasonable variations in condenser temperature and heat input to the still. At the same time the apparatus is relatively inexpensive and simply constructed.
A packed glass fractionating column 310 mm. (12 inches) long and 6.3 mm. (0.25 inch) in inside diameter, fitted with a 25-cc. still and a condenser, is kept cold by placing it in a large Dewar tube 50 by 620 111111. (2 X 24 inches) in inside dimensions (Figure The condenser of the column is cooled by passing liquid air cold air through it. The cold air coming from the condenser is passed through the length of the Dewar tube 'and thus keeps
kk
the entire apparatus in an environment suitable for operation. The acked section is surrounded by a closely fitting but not actua7ly sealed outer jacket, which creates a dead air space and thus partially insulates the column from its environment. Since the column has no vacuum jacket, its construction involves only simple glass blowing. The large Dewar tube can be purchased complete at a cost only about three times that of a widemouthed quart-size Pyrex Dewar. Several different columns, each with certain special characteristics highly developed, can be inexpensively constructed and used with the same large Dewar tube and other accessory apparatus. The column is designed for total condensation, the product being taken off as a gas through a side arm just below the condenser, while the top of the condenser may be left open to the atmosphere. Variations of pressure in the column and the resulting effects on boiling points are thus entirely eliminated, even though the condenser temperature may vary widely. The condenser is purposely constructed with a large heat capacity, so that its temperature cannot change suddenly or vary rapidly to any great extent. It follows that the apparatus may be operated with only slight fluctuations in pressure and boiling point, even when the top of the condenser is shut off entirely from the atmosphere, as in vacuum or pressure distillation, or in the preparation of a pure substance when it is desirable to be absolutely certain that no contamination occurs. A simple semi-automatic device is used to control the rate a t which liquid air is supplied t o the condenser, so that the --x)
PRODUCT RECEIVER
F L E X I B L ~LEAD TUBING MANOMETER 7J OW^ DAESSdRE IU CON-!
OIL TO INDICATE WHEN AIR IS B E I N G DRAWN INTO COLUMN
hECTlhG TLBING AhD .h PRODUCT PECE VERI
CONDENSER-
MANOMETER TO SHOW PRESSURE INSIDE COLUMN
DETAIL OF UDPER PART OF CONDENSER
a GLASS TUBE THAT CAN BE RAISED M1 LOWERED -CONDENSER LARGE DEWAR' TUBE W I T H FRACTIONATING COLUMN INSIDE J
EXIT
CLOSE FITTING BUT NOT ACTUALLY
FIGURE 1. DIAGRAM OF APPARAT~JS 478
ON LlOUlD AIR IN
