Apparatus for Determining Distillation Ranges at Reduced Pressures C. E. WATTS', JOHN A. RIDDICK,
L
AND
FRED SHEA, Commercial Solvents Corporation, Terre Haute, Ind.
OW- and medium-boiling liquids and solvents are frequently evaluated b y subjecting them to the A. S. T. M.
LINE
I
method for distillation range. Both the apparatus (which is supplied b y all the chemical supply houses) and the procedure (A. T. M. D268-41) are recognized as standard by the important producers of solvents, and are incorporated as requisites in many commercial specifications. The advent of a number of new solvents whose distillation ranges cannot be easily or readily obtained at atmospheric pressure has necessitated the development of apparatus for determining distillation ranges at predetermined and uniformly maintained reduced pressures. Such a n apparatus has been developed in this laboratory and has given very satisfactory results over a period of several years for control work in the manufacture of high-boiling liquids.
I86
s.
2 3 4 5
FJLAMENT
PLATE SCREEN CONTROL CATHODE
GRID
TABLE I. DISTILLATION RANGES Volume Distilled
lM1.
2-Mm. Pressure 1 2
c.
10-Mm. Pressure 1 2 Temperatures
c.
c.
188.0 190.0 192.0 194.0 197.0 198.2 200.0 201.0 201.5 202.5 203.0 204.0 206.0 206.0
First drop
!
10 20 30 40 50 60 70 80 90 95 98 (dry)
50-Mm. Pressure 1 2
c.
c.
187.0 188.0 192.0 194.0 196.5 198.0 199.2 200,o 201.0 201.5 202.5 203.0 205.0 206.0
224.0 226.0 230,O 233.0 236.0 237.0 239.0 239.0 240.0 241.0 242.0 244.0 244.2 248.0
1 1
c.
LOAD
225.0 228.0 231.0 234.0 236.0 237.0 239.0 240.0 240.0 241.0 242.0 244.0 244.2 249.0
FIGURE 2 housed in a white-pine box with a front panel 30 cm. (12 inches) high and 22.5 cm. (9 inches ) wide. The electrical equipment is mounted on a 4.7-mm. (0.1875-inch) piece of Masonite which fits into the box on supports giving a 6.88-cm. (2.75-inch) clearance from the bottom. The folloaing components are connected as shown in Figure 2: One BSBF8G2 Dunco relay; coil resistance, 3500 ohms (Struthers Dunn, Inc., 139NorthJuniperSt., Philadelphia, Penna.) One No. 43 radio tube and socket One 40-watt lamp and receptacle (approximate resistance, 250 ohms) One 500,000-ohm, 0.5-watt resistor One 50-ohm, lo-watt resistor One 2-microfarad, 450-volt paper condenser One 6-volt door-bell transformer One 6-volt, 2-coilfdoor bell or buzzer
APPARATUS. A 250-ml. distilling flask with glass tube sealed in as shown in Figure 1. This tube may be fitted with a fine glass capillary for the control of bumping or flooding. The authors have used a capillary with 0.175-mm. opening delivering about 1200 ml.of air per hour. This air intake can be reduced or eliminated entirely by applying a rubber tubing with a screw clamp when desirable in any particular distillation. An all-glass condenser (Figure 1) with the same size of condensing tube as the A. s. T. M. distiUation apparatus. A vacuum receiver which consists of a 100-ml. graduated cylinder modified by the addition of a side tube, as shown in Figure 1. A vacuum control which utilizes a vacuum tube to reduce the current at the mercury contact to 0.01 milliampere. The unit is 1
Present address, 3525 Pope
St., S. E., Washington, D. C.
THERMoNETERA ,E50ml.
r V A C U U U REGULATOR
DISTILLING FLASK
~
FINE CAPILLARY PLUG
VACUUM PUUP
I
eo00 .I BOILINP F L A S I
t
RHEOSTAT--) L V A P O R TRAP
CYLINDER
FIGGRE 1. DIAGRAM O F APPARATUS
FIGURE 3 506
ANALYTICAL EDITION
June, 15, 1942
The load leads are connected to the primary of the transformer. and the secondary is connected directly to the coils of the bell. The bell and clapper are cut off. the interrupter contacts are removed. and a piere of smooth rubber is cemented to the nrmature, as shown in Figure 3. The pressure-adjustment tube and the manometer are of convenient size. and are made, mounted, and connected as shown in Figure 3. A dry-ice trap is used to collect vapors and prevent them from entering the vacuum pump.
507
Determinations are carried out in the same manner as in the standard A. 8, T. M. distillation procedure, exceptthat the system is under reduced pressure. Uniform and reproducible pressures as low as 2 mm. can be obtained, as sho\Tn by Table 1. Readings were taken during the distillation of 1oo-ml. portions Of a large sample of methyl oleate at three different pressures.
A Study of the Electric Hygrometer R . S. EVAA-S A N D J . E. DkVENPORT Research Bureau, Consolidated Edison Company of New York. Inc., Brooklyn, ' I .Y.
I
N A previous paper (5) on the determination of water in
insulating oil, use was made of the electric hygrometer developed by Dunmore (3). This device appeared promising as a rapid field method for determining water in oil, and was likely to have other general applications wherever small amounts of water were a vital factor in industrial or laboratory operations. It seemed important, therefore, t o study the mechanism by which the electric hygrometer functioned. The effects of such factors as time of approach to equilibrium, temperature, inert gas pressure, mass of mater present, mass of hygroscopic salt on the unit, and resistance of the unit were studied. During the course of the study, a modified design of the hygrometer unit was developed and has been used throughout in the experimental results given below.
3Iodified Hygrometer The hygrometer unit described by Dunmore consisted of
KO.38 AWG palladium wire wound on an aluminum cylinder coated with polystyrene and with a polyvinylacetate film containing different percentages of lithium chloride, A similar unit was constructed in this laboratory and tried out in the determination of water in oil, without further investigation of its characteristics. It was calibrated by employing oils of a known water content as determined by the combustion method (4). After several weeks of successful operation, the behavior of the coil became erratic. It was felt that the movement of the wire in the film due to the solvent action on the polyvinyl acetate by the oil vapors, especially by the chlorinated hydrocarbon type of insulating oil, may have contributed t o this phenomenon. Accordingly, a new hygrometer was constructed. A No. 20 S. T. Pyrex male ground joint with 5-em. tubulations on b o t h e n d s y a s selected. The closed tubulation from the smaller end of the ground surface was dipped in paraffin and threadlike bifilar markin s in the paraffin exposing the gfass were made in a lathe. The exposed glass was etched for 30 minutes in a sulfuric-hydrofluoric acid mixture. After removal of the paraffin, the entire glass cylinder with its spirally etched grooves was coated with commercial platinizing solution and heated to a dull red appearance. After cooling, the cylinder was sandpapered, whereupon the platinum was removed from the ridges, resulting in two spiral threads of platinum baked on the glass 0.062 em. apart and 90 cm. long. The finished coil had a diameter of 1.5 em. and was 2.5 em. long. A substitute for glass sealed FIGURE1. MODIlead-in wires was effected by paintFIED ELECTRIC HYGROMETER ing two stripes on the ground surface
of the male joint and extending them to the end of the other tubulation (Figure 1). At these points copper wires were soldered on with ordinary soft solder. The hygroscopic film was put on by merely immersing the coil in an alcoholic solution of the desired salt, allowing the alcohol to evaporate in the air. The removal of an impaired film could thus very simply be accomplished by immersion in water. Before application of the salt film, the coil was subjected to 100 volts direct current to reveal any possible electrical bridges or other imperfections. Measurements were carried out with 3 volts alternating current on the coil. Later it was found that almost all the conduction took place in the first quarter of the coil. Therefore, the recommended length of the coil is one fourth that given above.
Relation between Resistance and Water Vapor Pressure A knowledge of the relation between the water vapor pressure and resistance of the coil was obtained through a study of the behavior of the coil under three experimental conditions-namely, an approximate mass of water vapor, the pressure of which was varied b y changing the volume with a mercury piston; the humidity of saturated salt solutions; and the formation of water from the explosion of a known volume of a hydrogen-oxygen mixture. I n Figure 2, a schematic diagram of the combined apparatus is shown. In buret B a prepared known mixture of hydrogen and oxygen is stored and introduced into the explosion pipet, A . The combination manometer-buret containing mercury had an inside diameter of 15 mm. in order to reduce to a minimum the sticking of the mercury column which was read with a cathetometer. The water vapor volume was chan ed by evacuating or applying pressure to the reservoir at the %ase. The entire apparatus was evacuated to a pressure of less than one micron at the start of an experiment and the hygrometer unit chamber at D was isolated by means of the three-way stopcock. The following data on a single quantity of water were obtained: (1) mass of water from the known hydrogen-oxygen mixture and a check of this value with that obtained from the product PV; (2) distribution of the water from (1) between the vapor space and the lithium chloride film; (3) partial pressure of water in equilibrium with the hygrometer unit; and (4)resistance of the hygrometer unit.
In the changing volume method, a suitable quantity of water vapor was introduced into the buret and, after the pressure and volume were read, was expanded into the previously evacuated hygrometer cell chamber. The difference between the calculated reduced pressure and the measured reduced pressure enabled one to estimate the micrograms of n-ater absorbed on the coil. The results are shown in Figure 3 for two hygroscopic salts, lithium chloride and potassium acetate. The observed mater vapor pressure where the sharp rise in the curve occurred corresponds to that of a saturated solution of the particular salt as given in International Critical Tables (6). Thus, in the vertical section of
