INDUSTRIAL A N D ENGINEERING CHEMISTRY PUBLISHED BY T H E AMERICAN CHEMICAL SOCIETY
W A L T E R J. M U R P H Y , EDITOR
Determination of the Boiling Range Chlorinated Hydrocarbons DWIGHT WILLIAMS, Research Department,
OF
Westvaco Chlorine Products Corporation, South Charleston,
W.
Va.
A study of the factors that affect precision in the determination of distillation temperatures of chlorinated hydrocarbons showed that thermometer calibration errors cause some variation. The effect of variations in atmospheric conditions, such as the ambient temperature and drafts, Is appreciable. The rate of distillation is important in some casts. The most important single factor is superheating of vapor. Because, over limited ranges, distillation temperatures are linear functions of the composition, it i s possible to determine the composition of most binary mixtures and some ternary mixtures b y this method.
above line of immersion, expansion chamber above bulb and above column, distance from bottom of bulb to top of lower expansion chambcr not over 3.8 cm. (1.5 inchcs), scale 40' C. in 0.1 O C. division~. Thermometers conformiiig to these specifications and covering any desired range may be purchased from Taylor Instrumerit Companies on special order. The thermometers are calibrated a t the boiling point of each fluid with which they are used, accordiiig to the procedure described below. TI1Icit(.\ioblETEitREADER.Central Scientific Company Catalog 19,520 or its equivalent.
S
The heater is clamped into the position in which it is t o be used during the distillation. A tight connection is made by mema of a cork between the vapor tube of the flask and thc condenser tube. Thc flask is adjusted so that its outlet extends into the condenwr tube 2.5 t o 5 cm. (1 to 2 inches). The thermometer, provided with a cork, is tightly fitted into the flask, so that it is in the middle of the neck of t h r Rttsk and the top of the exparision chamher is level with the inside of the bdttom of the outlet tube a t its junction with the neck of the flask. The immersion mark should be closc to the bottom of the cork. Water a t a p mximately room temperature is allowed to circulate throuyh the bath. The heatcr is turned on long enough before starting the dietillation to maintain a constant rate of distillation. The heater must be turned on at the voltage a t which it is to be used for at lemt an hour, or for a shorter time a t a higher voltage, btafore starting the distillation. The voltage required to give u. constant rate of distillation of 5 t o 6 ml. per minute is determined empirically for each fluid. A 100-ml. Rumple, which is approximately a t room temperoture, is measured i n a dry, 100-ml. graduated cylinder and transferred to the dry distillation fla9k. The thermometer is placed in the charged Hask and the flask is fitted t o the condenser. The flask must be carefully fitted onto thc hole in the refractory of the heatrr. The graduated cylinder is placed without drying under thc o u t k t of the condenser. Tlic tcmperature is read and thc time recorded when the first drop falls into the graduated rcwiver. The receiver is then movcd so thnt the tip of tlic condelistir touches the side of the recciver. Thc temperaturv is rend when the volume i n the raduate rc:tches 5 ml. and 93 ml., : i i d when the distilling flm\ just goes dry. All tcmperature readiiigs are made by mpans of the thermometer reader and arc recorded to the nearest 0.01 C. The time is recorded at the dry point. The time between the first drop and the dry point should be between 17 and 20 minutes. The barometer aiid the temperature alongside are read during thc course of the distillation. Thc pressure is corrected for brass scale as follows:
PROCEDURE
EVERAL years ago this corporation initiated a study of tho determination of boiling ranges of relatively pure commercial solvents such as carbon tetrachloridc and trichloroethylene. A study of the effect of numerous impurities on the boiling range of pure solvents showed that, over limited ranges, distillation ternperatures were linear funrtions of the composition. Thus, it is possible to determine the composition of most binary mixtures and some ternary mixturcs very simply from distillation temperaturcs. A study of the precision of thc dctermination of distillation temperatures &owed that it was possiblc to estimate relatively small coricentrations of impurities from such data. However, the precision was far poorcr than thc prccision with which a mercury-in-glass thermometer may be rend. This led to a study of the factors which affcct precision. Thermometer calibration errors caused some variation. A relatively simple piece of e q u i p ment was built for c-alibrating boiling range thermometers. The effect of variations in atmospheric conditions, such as the ambient tempcrature arid drafts, was studied and wm shown to be a p prcciable, at least under extreme conditions. The rate of distillation was shown to be important in the case of some sol\ m t s , but not others. The moHt important single factor contributing to lack of precision is probably superheating of the vapor. While no satisfactory solution to this problem has bcen found, it is still under investigation and it is planned to make this the subject of a subsequent paper. I t is believed thnt the present paper will prove of some interest, since methods of this type are in gcncral use for testing the purity of fluids. APPARATUS
The shield, condenser, distilling flask, and graduate are those specificd i i i A.S.T.M. Designation D86-38 for the determination of the hiling range of gasoline. The following apparatus differs from thut specified in the A.S.T.M. mcthod: HEa.ren. The heater sold undrr the tradc name Ful-Kontrol is uscd. The ripper refractory is 1.9 cm. (0.75 inch) thick and has a 2.5-cm. (I-inch) hole in thc center. The refractory is used plane side up. THEILMOMETER. Precision grade, length 40 cm. (16 inchrs), scale 23.8 cm. (9.6 inches), immersion 10 cm. (4 inches) including bulb 1.9 cm. (0.75 iuch) in length. Scale starts 2.5 cm. (1 inch)
Po = Pt
-
( t X Pr X 0.000160)
where POis the barometric pressure in millimeters of mercury a t 0 " C. and Pt is the pressurc at. temperature t . The distillation tempcraturcs arc corrected to 760-mm. prcssure as follows:
T i ~ l= Tob8.4- d T / d P (760
- Po)
where T ~ M and ) Toba.are the corrected and observed distillation temperatures, respectively. These formulas may be simplified in a given laboratory in the 157
INDUSTRIAL AND ENGINEERING CHEMISTRY
158 Table
I. Precision of Boiling Range of Carbon Tetrachloride under Best Conditions Temperature,
C.
Test
First drop
5 ml.
95 ml.
Dry
2 3 4 5 6 7 8 9 10
Av.
76.58 76.58 76.56 76.58 76.56 76.58 76.53 76.59 76,57 76.56 76.57
76.71 76.73 76.72 76.73 76.71 76.72 76.69 76.72 76.72 76.72 76.72
76.80 76.80 76.80 76.80 76.79 76.80 76.78 76.79 76.79 76.79 76.80
76.89 76.88 76.90 76.90 76.84 76.87 76.87 76.86 76.87 76.83 76.87
of group L U I o f method
t0.016 t0.054
+=0.011 k0.036
+0.008 -0.024
t0.022 k0.072
NO. 1
UI
interest of expediting routine work. formulqs are used in this laboratory:
-
Pa = Pr T 7 6 1
= Tobs.
(t
x
Range 0.31 0.30 0.34 0.32 0.28 0.29 0.34 0.27 0.30
0.27 0.30 t0.024 +0.081
The following simplified 0.122)
+ f (760 - PO)
The factorf is 0.044" C. per millimeter for carbon tetrachloride. Finally, the thermometer calibration correction is added. MATERIALS
With few exceptions the materials used in this work were the normal commercial products. It was assumed that a product of sufficient purity was being used when the specific gravity and the boiling point agreed closely with the accepted value found in the literature I n case the normal commercial product was not sufficiently pure, a selected product was obtained or the material was purified by rectification in the laboratory. EXPERIMENTAL
The precision of the boiling range method as PRECISION. applied to a number of fluids was determined according to the procedure outlined by Moran (8). Data for a typical solvent, commercial carbon tetrachloride, are shown in Tables I and 11. As was pointed out by Rloran, the high ratios of LU2:LU1(limit of uncertainty under routine conditions to limit of uncertainty under the best conditions) indicates a method having considerable personal and seasonal variations. Nevertheless, these data are useful in estimating the precision within which impurities in carbon tetrachloride and other solvents may be determined from boiling range data.
Vol. 18, No. 3
EFFECT OF IMPURITIES. The boiling ranges of trichloro-thylene to which known amounts of chloroform have been added are shown in Figure 1. These data are typical of those obtained for binary mixtures. By plotting the temperature of the 5-ml. point against concentration it can be shown that the chloroform concentration over the range 0 to 16 volume per cent is given by: c = 2.39 (86.93
- t)
where c is the concentration in volume per cent and t is the temperature in C. The LUI of the 5-ml. temperature for trichloroethylene is t0.036' C. and the LU2 +0.1lo C. Thus, under the best conditions, it would be possible to determine the concentration of chloroform in trichloroethylene within *0.09%, while under routine conditions the concentration of this impurity could be determined within *0.26%. Data for the calculation of a number of impurities in different solvents are summarized in Table 111. The carbon tetrachloride which was used in obtaining these data was the commercial product, since the boiling range data showed this product to be pure within the precision of the method. The trichloroethylene, perchloroethylene (tetrachloroethylene), and acetylene tetrachloride (1,1,2,2-tetrachloroethane) were rectified to obtain materials having narrow boiling ranges. The purities of the trichloroethylene and perchloroethylene were comparable to that of the carbon tetrachloride. The acetylene tetrachloride was somewhat less pure, the boiling range from the 5-ml. point to the dry point being 0.8' C. The concentrations of all low-boiling impurities were calculated from the temperature a t the 5-ml. point, while the concentrations of high-boiling impurities were calculated from the temperature a t the dry point. Low-boiling impurities have a somewhat greater effect on the first-drop temperature than on the temperature a t the 5-ml. point, but the precision of the latter temperature is greater than that of the former, and in general more than compensates for the lower slope of the temperature-composition curve. For example, the LUz of the first-drop temperature of trichloroethylene is three times that of the LU? of the 5-ml. point. In determining chloroform in trichloroethylene, the slope of the temperature-composition curve, expressed in degrees per per cent, is twice as large for the first drop as for the 5-ml. point. I n the determination of ethylene dichloride (1,2-dichloroethane) in trichloroethylene it is 1.4 times as great. I t is seen that the increase in slope does not compensate for the reduced precision. A further indication of the relative precision is a greater scatterO
Table
It. Precision of Boiling Range of Carbon Tetrachloride under Routine Conditions Temperature,
Date Jan. Feb. March
Figure 1.
'
VOLUME, ML. Effect of Chloroform on Boiling Range of Trichloroethy1er.o
1 1 1 1
June
3 3
Oct.
i
1
May
Sept.
I
1
2 2 3 3
Aug.
.I
1
April
July
I
Analyst
1 1
4
4
4
4
Nov.
5 5
Dec.
6
5 6
Av. mz of group L G z of group Ratio LL'z:LUi
First
drop
76.60 76.56 76.64 76.64 76.63 76,63 76.57 76.56 76,52 76.43 76.58 76.61 76.61 76.54 76.55 76.60 76.55 76.59 76.58 76.55 76.64 76.60 76.62 76.50 76.60 76.58 ~ 0 . 0 10.15 3.0
5 ml. 76.72 76,78 76.79 76.81 76.75 76.75 76 68 76,68 76.79 76 78 76.76 76,78 z6.79 (6.81 76.80 76.78 76.77 76.77 76.76 76.71 76.76 76,73 z6.77 (6.76 76,75 76.76 5 *0.035
C.
95 ml.
Dry
76.83 76.84 76.88 76.90 76.83 76.87 76.79 76.78 76.89 76.89 76.83 76.85 76.85 76.87 76.87 76.85 76.82 76.83 76.82 76,77 76.86 76.80 76,82 76.85 (6.81 76.84 k0.035
76.91 76,96 76.99 77,OO 76,90 76.94 76.86 76.86 77.01 76.99 76.90 76.90 76,90 76.94 76,92 76.92 76.90 76.88 76.89 76,83 76,88 76,86 76.88 76.92 76.88 76.91 10.05 t0.15 2.1
t0.11
==0.11
2.8
5.5
Range 0.31 0.40 0.35 0.36 0.27 0.31 0.29 0.30 0.49 0.56 0.32 0.29 0.30 0.40 0.37 0.32 0.35 0.29 0.31 0.28 0.24 0.26 0.26 0.42 0.28 0.33
t0.075 *0.23 2.9
March, 1946
ANALYTICAL EDITION
159
temperature of 85" C. could be maintained with a heat input of about 80 watts.' The standard thermometers were purchased from Taylor Instrument Companies, Rochester, N. Y., oc. OC. under the following specifications: precision grade, t0.036 10.11 length 45 cm. (18 inches), total immersion, with ice ~ 0 . 0 7 2 AO.15 t 0 . 0 7 2 1 0 . 15 point, expansion chamber a t top of column, length 10.072 ~ 0 . 1 5 of scale 30 cm. (12 inches), range 40" C. in 0.1' C. *0.036 10.11 divisions. The manufacturer supplied a laboratory 10.036 to.11 ~ 0 . 0 8 7 i o . 17 test certificate with each thermometer a t the ice *0.02 ... +=0.02 ~ . . point and each 5 " C. The ice points were checked *0.05 ... prior t o use. These thermometers were subsequently t0.05 ... calibrated by the Bureau of Standards. ... ... The following procedure was used for the cali... ... ... bration: The bath was adjusted to the temperature a t which the calibrations were to be made. The standard thermometers were placed in the bath with 2.5 C. emergent stem measured to the center of the cover. Theldistillation thermometers (several were calibrated simultaneously) were adjusted to their immersion ing of the points when the temperature-composition curve is marks. The heat input to the bath was adjusted by means of the plotted for the first drop than when it is obtained for the 5-ml. Variac, so that the temperature rose 0.1 'to 0.2 O C. during the time point. The precision of the measurement of the dry-point temrequired to make a set of readings, which was about 10 minutes. The thermometers were then read in rotation beginning with the perature is normally sIightly poorer than that of the 95-ml. temstandard. Two laboratory-grade thermometers, which were perature, but this slight decrease in precision only partially offused t o measure the stem temperatures of the standard and dissets the greater slope in the temperature-composition curve. tillation thermometers, respectively, were then read, after which The ranges over which linear equations apply are shown in the series was read in the reverse order. This cycle was repeated five times, makin a total of ten readings for each thermometer. Table 111. For thermost part, linear equations applied over the The average of t i e ten readings was calculated for each therentire range tested and presumably over even wider ranges. mometer. This average for the standard was corrected for I n general, one impurity, if present in significant amounts, emergent stem (about 0.03"C.) and for the calibration correction affects the entire boiling range. Thus, the boiling range method given by the manufacturer. The difference between this temperature and the average temperature calculated for the distillais generally applicable only for the analysis of binary mixtures. tion thermometer is the calibration correction for the latter. For example, the presence of chloroform, ethylene dichloride, or acetylene tetrachloride in carbon tetrachloride prevents the Thermometers were calibrated a t the boiling points of the fluids quantitative determination of any of the others. Chloroform or with which they were to be used. The maximum calibration ethylene dichloride may, on the other hand, be present in trierror observed was 0.17" C. The precisions of the calibrations chloroethylene without interfering with the determination of were checked under actual working conditions by making dishigh-boiling impurities. Ethylene dichloride does not interfere tillation ranges. The distillation ranges for carbon tetrachloride, with the recovery of either pentachloroethane or hexachlorousing calibrated thermometers, are shown in Table IV. Slight ethane from acetylene tetrachloride, nor do either of the latter differences are indicated between the several calibrated therinterfere with the former over the ranges given in Table 111. mometers. These data were taken over a period of several weeks I n general, commercial products contain both low-boiling and by one person. The precision of the entire series falls between high-boiling impurities and the identity of the impurities may not the LU, and LUS values given in Tables I and 11. A precision be known. While the boiling range cannot be used for either the of this order of magnitude is to be expected under these conditions. qualitative or the quantitative analysis of such fluids, it is useful It is therefore improbable that there is any significant difference in indicating the presence of both low-boiling and high-boiling between the distillation temperatures given by the calibrated impurities. Further, an indication of the difference between the thermometers. boiling point of the main component and that of the impurity can Variations in the emergent stem temperature will cause signifibe obtained from the rate of change of temperature with respect cant errors in apparent distillation temperatures. The temt o the volume. Possibly the most useful application of the perature of the midpoint of the emergent stem during the calimethod is in the study of intermediates. It may be applied to bration of thermometers a t the boiling point of trichloroethylene supplement specific gravity and refractive index data for the was approximately 10" C. above that of the room. The temanalysis of complex mixtures. As is shown in Table 11, very small perature of the midpoint of the emergent stem during distillation concentrations of impurities can be detected from boiling-range varied from 10" t o 20" C. above that of the room. Seasonal data in case of compounds which have a substantial difference in boiling points and even when the difference in boiling points is relatively small the method is reasonably sensitive. The smallest . difference in boiling points is that between trichloroethylene and Table IV. Distillation Ranges of Carbon Tetrachloride Using Calibrated Thermometers ethylene dichloride (4' C.). The data show that ethylene diCalibration Temperature, C. chloride may be detected in trichloroethylene in concentrations Thermometer CorLection, First as small as 0.5%. Where a wide difference exists between the No. C. drop 5 ml. 95 ml. Dry boiling points, as in the case of hexachloroethane in carbon tetra1,977,258 76.42 -0.09 76.61 76.70 76.77 76.41 -0.09 76.61 76.73 76 70 chloride, concentrations as small as 0.005% may be detected. 76.41 -0.17 2,172,778 76 62 76 70 76.76 76.41 -0.17 76 61 76 67 76.74 CALIBRATION OF THERMOMETERE. A coaxial constant-tem76.39 -0.09 1,977,259 76 61 76 69 76.77 erature bath similar to that used by the National Bureau of 76.41 -0.09 76 60 76 69 76.78 - 0 . la 2,284,595 76.43 70 65 76.76 76 73 tandards ( 1 ) was constructed for the calibration of thermom76.44 -0.13 76 65 76 72 76.77 eters. The bath consisted of a 25 X 45 cm. (10 x 18 inch) Pyrex 76.47 -0.13 76 60 76.77 76 72 76.44 -0.05 5,677 jar. The sides were covered with a 3.8-em. (1.5-inch) layer of 76 65 76.79 76 73 7 6 . 4 5 0 . 0 5 76 65 76 72 76.80 Fiberglas insulation and the bottom with a 5-em. (2-inch) layer 76.36 -0.05 76 66 76.83 76 74 of magnesia. The cover consisted of two circles of 0.6-cm. (0.2576.43 5,678 -0.02 76 65 76.79 76 71 inch) Transite bolted t o ether, one circle fitting inside and one 76.40 -0.02 76.81 76 72 76 64 5,679 7 6 . 4 3 0 . 0 8 76 68 76.83 76 7 4 outside the glass jar. T%e cover was split for convenience and 76.43 -0.08 76 66 76.83 76 75 slots were cut in it for insertion of the stirrer, heater, and ther76.39 5,680 76.82 -0.05 76.67 76 74 76.40 -0.05 76.67 mometers. The inside cylinder was a 7.5-em. (3-inch) metal 76.83 76.74 tube. The heat input was controlled by means of a Variac. A Table 111. Substance
Q
Calculation of Impurities in Solvents from Boiling Impurity Equation Range5 % 0 to 2 (1,2) CzHiC1: c - 8 (76.72 - t ) 0 to 1 c = 2.56 ( t - 76.87) CiHCla 0 to 1 . 6 C I . 0.077 ( t - 76.87) Czcli 0 . 0 3 1 ( t - 76.87) 0 to 0 . 0 2 'C CzCla 0 to 1 . 6 c = 2.39 (86.93 - t ) CHCla 0 to 4 (1,2) CzHaClr c = 5.71 (86.93 - t ) 0 to 1 c = 0.187 ( t - 87.05) czc14 1.26 (121.08 - t ) 0 to 1 c CClr 1.70 (121.08 - t ) 0 to 4 CiHClr c CzHClr c = 0.140 ( t - 121.34) 0 to 3 c = 0.069 ( t - 121.34) 0 to 2 CZClS 0 to 2 1 2 ) CiHaClt c - 0.71 (145.5 - t ) 0 to 8 L;Hcls c = 1.33 ( t - 146.3) c = 0.22 ( t - 146.3) 0 to 4 CZCIB Liquid impurities in volume % : solids in weight %.
Range Data LUI &L'z
I
.
.
O
E
160
INDUSTRIAL AND ENGINEERING CHEMISTRY
variations in room t e m p e r a t u r e of 15' C. are not 07.4 uncommon. T h u s , t h e tem87.2 p e r a t u r e of the emergent stem during use may 87.0 differ by 25" C. from that during calibration. The emergent stem of the particular thermometer which was used for this work ( r a n g e 70" t o 110°C.) measured about 20" C. during the distillation of trichlorocthylDISTILLATION RATE, MLJMlN. ene. Thus, errors up to 0.08" C. Figure 2. Effect of Rate on Distillation may result from Temperature of Trichloroethane this C R U Y ~ . If the top of the scale were used, this error would be twice this value. For the highest precision both the calibration and the distillation temperature must be corrected to the same emergent stem temperature. Since, however, this corrertion is subject to considerable uncertainty, tho most precise results would be obtained by using a thermometer with a shorter range, say 10°C. EFFECTOF CONDITIONS. From Figure 2 it is seen that the rate of distillation hits a marked effect on the distillation temperatures of trichloroethylene. I t was found that the rate has a significant but less pronounced effcrt on the distillation temperatures of perchloroethylene, h i t it has no detectable effect on the distillation temperatures of carbon tetrachloride. Thus it appears that the rate has a marked effect on some fluids and none whatever on others. In general it is desirable to maintain the rate as nearly constant as possible. I t is considered practical to maintain the rate constant R7ithin a range of about 1 ml. per miiiut,e. A rate of 5 to G ml. per minute was chosen in order to complete the analysis as rapidly as possible. To ensure that this rate is maintainad, it is necessary that the time of thc first drop and t,he dry point be recorded. No attempt is made to control the time betwcen the application of heat and the first drop, since this is automatically controlled by the heat input required to maintain the desired mte. The shicld which is specified in the A.S.T.M. method for the distillation of gasoline was normally used during this work. The temperature inside the shield was substantially above that of the room, owing to heat rayttiinted from the distillation heater. Calculation showcd that the efficiency of the heater was only about S%, the rcinaining 92y0 of the heat serving to raise the temperature of the shrrounding atmosphere. To csaggernte this effect a cover of asbestos paper was provided Tor the shield. Thus, the heater and flask wcre completely surroiiiidetl by the shicld. The distillation thermometer prot r u d d through :L holv i r i the cover. An ausiliary thermometer to IneLsurc the temperaturv of the spare inside the shield also extcndtd tlirough the cover. The bulb of this thermometer ww aboiit 10 cm. (4 inchcs) from the heater. This thermometer registered a tcmperatiirc of (50"to 70" C. durinx the time the distillat iori wits i n progress. This addit,ioual shit!lding raiscd the distillation temporuturc of trichloroethylene at the 95-ml. and dry points by 4 " aid 8" C., rcspectivcly. In Ltri cill'ort to r c d w c this effect, the preceding experiment was repentid oscclit tliat the neck of the distillation Hask was insulatctl by wralipiiig it with asbestos wicking. This rclativcly inefficient method of insulation reduced the effect on tho tem-
Vol. 18, No. 3
perature a t 95-ml. point and the dry point to 2" and 5" C., respect ivcly. The effect of drafts was greatly exaggerated by removing the shield and directing a fan on the distillation flask. This procedure reduced the rate of distillation to 2 ml. per minute in spite of the fact that the heat input was more than doubled. Except for the high dry point, the distillation temperatures were not affected. This experiment was repeated except that the insulated flask described above was used. A normal boiling range was obtained under these conditions. From these data it appears extremely doubtful whether the drafts which are normally present in the laboratory will have any significant effect on the boiling range of relatively pure liquids sueh as those tested in this work, even though the A.S.T.M. shield were omitted. Superheating of the vapors by the radiant energy lost from the heater occurs to a substantial degree and is magnified by any device which encloses the distillation flask within the same space occupied by the heater. While it cannot be definitely concluded that the shield is harmful, it appears extremely doubtful whether it serves any useful purpose. It appears probable that, if the elimination of the effect of atmospheric conditions is necessary, it should be done by insulating the flask and not by enclosing the flask and heater within a shield. The author recognizes that this and perhaps other conclusions drawn from this work are contrary to comm6nly accepted beliefs and are apt to arouse controversy. Such conclusions cannot be considered as final, but if they serve to stimulate further investigation their purpose will have been served. Since the most serious error is caused by the very low efficiency of the hcatm, the most promising method for improving the procedure would involve the design of a more efficient heater. Some work has been done along this line but a satisfactory solution has not been obtained to datc. Formed-in-place heaters similar to those described by Krantz and Hufferd (2) were built to fit a 100-ml. distillation flask. Heaters of this design 6.25 cm. (1.5 inches) in diameter appear to have entirely eliminatcd superheating. Heaters of larger diameter cause superheating. That superheating is eliminated is shown by the following facts: Using formed-in-place heaters, the rate has no efkct on the distillation temperatures of trichloroethylene and the range of distillation temppratures from the first drop to the dry point is less than that which was obtained a t the lowest rate a t which the Ful-Kontrol heater was used. The Ful-Iiontrol heater causes superheating of methylene chloride of as much as 10" C.near the end of the distillation, but there was no indication of superheating of methylene chloride when using a 3.75-cm. (1.5-inch) formed-inplace heater. While this type of heater appears to eliminate superheating entirely, it is difficult to construct and has n short life in the small size required for this work. Other types of heaters are being tested, but none has been found t o date which is considercd entirely satisfactory. This work is continuing and it is anticipated that a heater will eventually be found which is generally satisfactory. I t is planned to make this the subject of a subsequent paper. ACKNOWLEDGMENT
The author wishes t o express his appreciation to G. F. Foy, J. E. George, F. D. Heilldcl, and C. C. Meeker for the preparation of most of the experimental data and to R. F. Moran, chief chemist, and members of the Control Laboratory scaff for furnishing the precision data under routine conditions. LITERATURE CITED
(1) Busse, Johanna, "Temperature, I t s Measurement and Control in Science and Industry", p. 242, New York, Heinhold Publishing Corp.. 1941. (2) K r a n t r , 11. A., a n d Hufferd, R. W., IND.ENQ.CHEM.,ANAL. ED., 12, 753-3 (19.10). (3) Moran, R. F., Ibid., 15, 361-4 (1943).
