NOVEMBER 15. 1938
ANAL1 TIC 41, EDITIOS
With the spiral bottle, the amounts of water removed per liter of nitrogen a t the gas rates of 0.6, 1.4, 2.8, 5.6, 9.9, and 15.3liters per hour were 0.01~7,0.0187,0.0180,0.0173,0.0173, and 0.0173 gram, respectively. K i t h the Drechsel bottle, the amounts removed at the same gas rates were 0.0177, 0.0172, 0.0169, 0.0175, 0.0184, and 0.0185 gram, respectively. The saturator temperature was 20" C., the pressure within the saturator was 754 nim., and the volume of the nitrogen was converted to 20' and 760 mm. The theoretical amount of water was 0.0178 gram.
TABLE I. ABSORPTION EFFICIENCIES .4T COSSTAKT GAS RATE .4SD DIFFEREXT CAUSTIC CONCENTRATIONS Weight
K??H
Total Cog Passed Dreohsel Spiral Grams Grams 1.096 1.200 1.119 1.132 1.119
1; D
4 3 2
1.119 1.114 1.105 1.115 1.119
Unabsorbed C o r Drechsel Spiral Gram Gram 0.0419 0.1161 0.1399 0.2042 0 4263
0.0010 0.0018 0.0018 0,0143 0.2093
E5ciency Drechsel Spiral
%
%
96.2 90.3 87.5 82.0 61.9
99.9 99.9 99.: 98.i 81.3
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Improved Vacuum Regulator CLAYTON W. FERRY Burroughs Wellcome & Co., Tuckahoe, X. Y.
0
F THE several devices designed to maintain a con-
stant pressure for vacuum distillation, that described by Ellis (1) has proved to be the most satisfactory. However, at pressures of 3 mm. or less, even the small variations in pressure that this regulator allows cause appreciable changes in the boiling point of materials being distilled, and some distillations tend t o build up pressures in the portion of the system beyond the capillary. This capillary, while equalizing and smoothing out variations in pressure caused by the intermittent operation of the pump, also slows up the evacuation of the distillation system, occasionally causing a lag after the distillation is started.
The following method was finally adopted: A mixture of about 99 per cent of nitrogen and 1 per cent' of carbon dioxide was passed through 100 cc. of caustic in the bottle being tested and the weight of carbon dioxide escaping absorption was determined. The setup is shown in Figure 2. The gas in cylinder A was passed at constant rate through bubble-counter B into the caustic in bottle C. The exit gas from C was dried by calcium chloride D and by Anhydrone E, and the carbon dioxide was absorbed by Ascarite F and G. The water vapor from the Ascarite was retained by Anhydrone H , whence the gas passed through protector tube I containing Anhydrone, Ascarite, and calcium chloride, and finally through meter J. The absorption tubes were weighed against a counterpoise with the usual precautions. Anhydrone H was necessitated by the vapor pressure of Ascarite. The average weight increase of Anhydrone H w&s 0.0098 gram, corresponding to a vapor pressure for Ascarite of 0.16 mm., which is significant when large volumes of gas are involved. Table I present's data on the relative efficiencies of the two bottles, using different concentrations of caustic. The nitrogen-carbon dioxide mixture contained 0.01736 gram of carbon dioxide per liter of nitrogen (20" C., 760 mm.). The gas rate was 3.8 liters per hour and approximately the same volume of gas was passed in each experiment (63.5 liters of exit nitrogen; 20' C., 760 mm.). Volume of caustic was 100 cc. in each run.
TABLE11. ABSORPTIOSEFFICIESCIESWITH 4 PER CEKT PoTASSIUY HYDROXIDE AT DIFFEREST Gas RATES Gas Rate Liters/hr. 3.8 7.6 11.5
Total COz Passed Drechsel Spiral Grams Grams 1.119 1.228 1.228
1.105 1.243 1.226
Unabsorbed COz Dreohsel Spiral Gram Gram 0.1399 0.1830 0.2033
0.0015 0.0050 0.0072
Efficiency Drechsel Spiral
%
%
87.5 85.1 83.4
99.9 99.6 99.4
Table I1 presents data on absorption efficiencies at the same concentration of caustic b u t with different gas rates. The nitrogen-carbon dioxide mixture used a t the gas rates of 7.6 and 11.5 liters per hour contained 0.01943 gram of carbon dioxide per liter of nitrogen (20" C., 760 mm.).
-4cknowledgmen t The authors express thanks t o F. L. Hayes for the glass blowing and to William Cerveny for analytical work.
Literature Cited (1) Friedrichs, Chem. Fabrik, 4, 203 (1931). (2) Keller, Chem-Ztg., 47, 506 (1923). (3) Martin, IKD. Eh-c;. C H m f . ,Anal Ed., 8, 395 (1936). (4) Martin and Green, Ibid.,5, 114 (1933). (5) Milligan, Sczence, 63, 363 (1926). (6) Shaw, ISD. EXG.CHEM.,Anal. Ed., 6, 479 (1934). (7) Weaver and Edwards, J. ISD. ESG.C m v . , 7, 534 (1915) ; B , erin-
stof-Chem., 18, N 9 1 (1937). RECEIVED Tu15 24, 1938
The first of these objections can be overcome by tilting the arm of the regulator, in which contact between the mercury and the electrode is made, from vertical to almost horizontal, as is shorn in the accompanying sketch. This causes the meniscus to travel a greater distance per unit change in pressure. Tubing 4 to 5 mm. in inside diameter is small enough to decrease any tendency of the mercury column to oscillate. If larger tubing is used, i t is advisable to p u t a constriction in the bottom of the U-shaped portion. The mercury terminals for the mires leading t o the relay are designated by a and b, xhile c leads to the pump and d is a pivot for the mounting board. As mercury tends to stick to the platinum or tungsten wires generally used for these contact electrodes, thus reducing the sensitivity, i t n-as necessary to use Chromel wire for the actual contact. T o facilitate the making of a good glass seal, the Chromel nire was soldered to a piece of tungsten nire, which v-as in turn sealed into the side arm. d condenser across the electrodes of the regulator reduces sparking and prevents fouling of the Chromel contact. To operate, evacuate with the stopcock open until approximately the desired pressure is reached, close the stopcock and make the fine adjustment by tilting the assembly board on it; pirot 9s desciihed by Ellis. The hasp of a Bunsen
648
INDUSTRIAL A S D E S G I S E E R I S G CHEMISTRY
burner, or better yet a Hoke valve, makes an easily adjustable bleeder in the system to keep the pump operating a t reasonable intervals. With this arrangement, the capillary between the two reservoir bottles (1) can be removed entirely, and pressures below 30 mm. are so constant that no variation can be detected on a manometer read with a reading glass. For pressures much above this value, there is a minute variation due to the effect of the extra stroke of the pump after the circuit is broken. If the same absolute constancy of pressure is desired a t these higher levels, it is necessary to use a large
I-OL. 10, KO. 11
reservoir system or resort to an arrangement in which the pump runs continuously, a glass capillary bleeder of the proper capacity being opened and closed by means of a rubber cap on the relay arm.
Literature Cited (1) Ellis, L. M., Jr.,
ISD. ESG. C H E M . ,Anal. Ed., 4, 318 (1932)
RECEIVED March 18, 1938. This device was developed i n the course of work done at The Johns Hopkins University under the John 11. Hancock Fellowship for S o r t h Dakota.
A Small Low-Temperature Rectifying Column J. H. SIMONS The Pennsylvania State College, State College, Pa.
T
HERE is frequently a need for a small loJ\--temperature which can be readily moved from place to place in the laboratory and does not require elaborate pressure or temperature controls or a vacuum system for its operation. Small quantities of gases are often generated in chemical reactions, and such a fractionating device mould be of value for their purification and determination. Figure 1 shows a design of such a column. I t has a capacity of about 5 cc. of liquefied gas, is small enough to fit into the usual commercial 0.95liter (1-quart) vacuum flask, is secured on a laboratory ring stand and so is readily portable, and requires for its operation only the addition of a potentiometer for temperature measurements, a source of electric current for a small heater that may be dry cells or a 110-volt line with rheostats, and an ordinary la bo r a t o r y wat er-suc t ion pump. K is the liquid container with a volume of about 5 cc. This contains a protruding nipple, L, wound wit'h a heating coil of asbestos-covered Nichrome wire, B. & S. No. 26. I n this nipple is a reentering thermocouple tube containing a copper-constantan couple. In the column section, J , glass-ring packing, held in place by a small cross bar, is contained in an inner taube of about 9-mm. outsidediameter with a dropping tip on the end. The condenser, H , consists of three concentric tubes: The innermost is of 0.47-cm. (0.19-inch) copper tubing, the middle is of 11-mm. glass, the closed lower end of which terminates in a dropping tip, and the outside tube is 20 mm. in diameter. At the lower end of the condenser a 7-mm. take-off tube, I , enters through the wall. Into this a reentering thermocouple tube carries a copper-constantan couple. The liquid-air reservoir above the condenser is double-walled and contains a center tube, F , through which extends the copper tube, G. G is notched at the top to allow free access of air and is held in place by a small rubber ring. A glass bell, E, rests on the top of G . A board fastened to the
A
top of the liquid-air reservoir holds the entire device, and to it are fastened the necessary stopcocks and terminal binding posts (not shown in the diagram). The column fits into a quart-size Pyrex glass unsilvered vacuum flask, Jf,which is surrounded by a radiation shield, N . of aluminum sheet containinn slots cut into it for observation of the important pa& of the column. The tubes to the stopcocks are 5 mm. in outside diameter. In operation J and K are first used as a trap to receive the material t o be distilled. With M removed and J and K immersed in liquid air or other suitable condensing medium, the gas is admitted through stopcock D, with stopcock B open to permit escape of air. Flask M , which has been chilled with liquid air but is em ty, is then replaced, D is closed, and !( is connected to a water-suction pump. Two glass traps to act as receivers are connected with rubber tubing t o the two outlets of the three-way stopcock, A , and are immersed in vacuum flasks containing suitable condensing medium. Liquid air is placed in the reservoir, and air is drawn into the condenser when C is opened. This air is both dehydrated and cooled as it is forced to travel over the surface of the liquid air, and it cools the condenser. The amount of cooling can be regulated by the volume of air admitted. When the condenser is cold, heat is supplied with A closed and B open. Observation enables adjustments t o be made until reflux is obtained and equilibrium established. B is then closed and A opened to one of the receivers. The amount of take-off can be regulated by adjustments of both the amount of heat supplied to the pot and cooling supplied to the condenser. Temperatures of both the pot and top of the column can be obtained by a potentiometer, and receivers can be changed at will. This device is a total condensation column operating a t constant pressure. The receiving traps must, therefore, he open to the atmosphere. A column of this design has been used successfully with liquids boiling a t -130", -80", and -50" C.
FIQURE 1
RECEIVED July 26, 1938.
