laboratory low Temperature Fractional Distillation Optimuilz Distillation Rates and Fraction Cut Points C. E. STARK, JR., J. S . ANDERSON, AND V. >I, DAVIDSON Esso Laboratories, Esso Standard Oil Company, Louisiana Division, Baton Rouge, La. In a previous paper (1)the results of a stud) of opti~ n u mcharging rates were reported. The present
paper contains the results of a continuation of this qtud? in which optimum distillation rates and fraction cut points have been determined. Two samples were emploj ed: one was a plant stream containing appreciable amounts of noncondensables and Ci. CZ, Ct. C4, and C , hjdrocarbons, and the other contained the same components, but the CI was present in on11 minute quantity. After charging and refluxing for a proper amount of time, the distillations were made at several different rates, and the heart cut of each fraction was analjzed h?
I
S A previous paper (4)on low temperature distillation studies, the results of a n investigation of optimum charging rates werc reported. In that ptudy it was shown that the precision for the tletc~rrnination of major fractions was only slightly different for vtlr'y fast distillation rates than for the s l o w r rates recommended i i i the literature ( I , Sj. The precision obtained a t high distillation i':it (bs could be due to compensating effects of contamination of ca:ich fraction by t,he nest higher and lower boiling components. The present study was initiated to determine the estent to which this phenomenon occurred under different conditions a i i d to drtt~i~mirie optiniuni conditions for minimizing these effects. I n the usual complete analysis of gases rniploying low tenipvrature distillation, the niisture is charged to the distillation cv)lumn, which is maintained at a low temperature by the use of licluid nitrogen: and the noneondensable portion is taken overIic.ad, measured, and submitted to chemical niiiiution of individual constituents. The re poi,tion is fractioiially distillfd, :md groups of hydrocarbons COIIt:iininp the sanie number of carbon atoms und boiling in the same r:iiigc :ire removed together for subsequent :mal, c.oiistituc~nts. As chemical and physical methods for the :tnalysc~( i f thrse fractions generally only identify types of compounds. .iicli as saturates, unsaturates, etc., it is necessary that cont:iniin:ition of one fraction with that of another of different carl i o n nunibrr be very small in oi,dei. to ohtain :iccuratr rwults foi, iiidividual component^. 111 the present study, t w o gas samples have been distilled at sc~vei~:d different rates and the Fractions analyzed to determine th(3 csstent of contamination of one fraction by another. Portions txkeii overhead between major boiling points have been :iiiaIyzed t o determine the optimum cut points to tx c~mployed. EQUIPMENT AND SAMPLES
Thc. equipment used in this study consisted of a Podbielniak Hyci-Robot dist,illation apparatus (5), a Consolidat,ed Engineering special sampling bottles, and ('orporation mass spectrometer (j), conventional laboratory equipment. T w o gases ~ v e r eemployed i n this st,udy. Sample 1 was a product gas stream from a fluid catdyst cracking unit, and its approsimat,e composition was 14% ~ ~ o r i c o n d ( ~ n ~ a34% b l e , methane, 12% CB,22% C,, 15% Ca, and 3W C':, Sainplr 2 contained approsinlately 15% hydrogen, 15%
mass spectrometer for contamination by lower and higher boiling constituents. Analyses were also made of total major fractions and fractions taken between major boiling points to determine if generally accepted cut points were optimum. It has been found that distillation rates as high as 100 cc. per minute may be used with negligible amount of contamination. If the column is operated properly, the amount of hydrocarbons distilling between boiling points is small and the contamination of one fraction with another, using generally accepted cut points, is negligible. The contamination is usually due to the lower boiling fraction.
methane, 10% C?, !ess than 1% C,, ai$ 60% Cd. This gas was analyzed to determine the contamination to be expected of a gas where one of the major components was either missing or present in only minute quantities, causing a large spread in boiling points between succeeding fractions. T h e samples were retained in a 25gallon cylinder a t a pressure below the dew point of the heavier hydrocarbons. GENERAL DISTILL.ATI0.Y PROCEDURE
The column was charged according to the procedure outlinetl in a previous paper (4).When sufficientsample was condensed in the still pot, the entering line and stopcock were sealed with mercury, and the pot heater was turned on and set, to deliver 2 watts of heat. The escess liquid nitrogcxn around the still and in the column was removed by blowing air up the column until all of the liquid nitrogen was removed. hfter the removal of the fisrd gmcs from the column and still, indicated by approsimately 150 cc. overhead on the methanix plateau, the column was placed under total reflux until the receivers could lie changed. The amount of heat supplied to the stili while taking overhead on a plateau was sufficient to maintain thc indicated rat.e of take-off and, at thc same time, to require reflus cooling a t 8- to 10-second intrrvals. As the column was under total reflus while changing rcccivors a t thv cut point,s, t.he heat, w a s removed to prevent flooding. The distillation rate was automatically slon-td a short distancc I d o r e the cut point and did not esceed 3 to 4 cc. pelr niinutcl during the "hrcak" from one plateau t o nnothw. DISTILLATION RATE STUDY
Determination of Precision of Total Fraction Analysis. The nominal distillation rates employed were 25, 50, and 100 cc. per minute. Fractions were segregated employing the usual cut points-i.e., C1-G at - 120" C., CY-C.3 a t -60" C., C&-C, :it - 2 7 " C., and C4-C; a t +18" C. (or - 6 " C:. :it 300-111l11. absolute pressure). The fr:tctionx were analyzed by mass spectrometer, ~ n the d results are shown in Table I. The data shown in Table I indicate the amount of contarnilltition of each fraction by the nest higher and lower boiling conipoiients when using the indicated distillation rates and the usual cut points described above. I n general, the major portion of the contamination is due to the loner boiling components Ivhich have not hreri completely removed in the previous fraction. -1lthough this cont:uninntion :imounts to a8 much as 2 to 370 in the larye 1197
1198
ANALYTICAL CHEMISTRY Table I.
Effect of Distillation Rate on Total Fraction Contamination
Mole (ro of Fraction (M.S. Analysis)
____
R a t e dist. cc./min.
~
-~
Mole % of T o t a l Sample
S A M P L E1 a
CI fraction 48% 25 (34% CH4, 25 14y0 non50 condens50 ables) 100 100
100.00 100.00 99.92 100.00 100.00 100.00 CHI 1,12 1.40 1.12 1.65 1.95 1 36
C? fraction 12%
25 25 50 50 100 100
Ca fraction 22%
25 25 50 50 100 100
, . .
0 :35 0.02
...
0.47 CaHe
25 25 50 50 100 100
CSfraction 3%
0.07 '
0 .'i2
..
...
CaHs 0.94 0.71 1.20 1.34 2.90
8.98 2.76 2.44 1.96
CZHE 64 63 63.50 63.94 64.12 64.89 64.11
C3H6 0.03
CJHS
0.33 0.12 0.24 0.24
0.'08
...
30% (15% CH4, 15% Hz) C2 fraction 10%
25 50 100 25 50 100
C1III
CI fraction SOT,
CHI 1.85 1.36 2 44
25 50 100
0.19 0.05 0.09
77.64 78.44 81.14 C2Hn 0.36 0.13 0.30
C3H8
7.12 7.49 7.55 7.58 7.66 7.50 C3He 12.59 12.39 12.04 12.16
... ...
0.04 0.01 0.03 0.03 C3Hs 9.64 9.61 9.90 9.55
Iso-C4Hia
...
0.14 0.11 0.18 0.20 0.44
5.09 4.41 4.79 4.54 4.24
1.20 1.13 1.22 1.01 1.12
8.61 9.37 8.84 9.93 9.35
CaHs
CsHm
CHI 0.12 0.17 0.13 0.19 0.23 0.16
..
...
43 05 56.16 0.02 43.28 55.81 0.04 44.80 54.47 0.07 43.60 55.54 43.07 0 .O? 56.23 41.80 5 G . 27 ... I s o - C ~ H I On-CqHlo CIHS No 11,s.analysis 33.73 7.97 57.17 29.20 7 47 62.08 31.74 8.10 R8.55 29.84 fi.64 fi1.36 28.05 7.31 61.52
S o 11,s.analysis 32 16 34.41 4.45 N o 1I.Y. analysi58,40 34.98 3.86 55.87 37.19 4.42 57.21 36.23 4.44
CH4 100.00 100 00 09.93
C?Hs
3.76 4.14 4.07 4.02 3.88 4.01 C2H8 0.16 0.18 0.07 0.18
..
...
CIIIS 0 03 0.06
C2H4
... ...
0.08
...
0.04
...
0.21 0.68
faHir
C3Ha
0.12 0 43 (1.19 0.33 0.15
0.01
0 .'l'l 0.10 0.29 0.07
...
0.02
...
.. , .
.., CaHa
...
... ... ...
0.01
..
..,
0.01 0.02
...
0.'08 0.16
...
Iso-CsHlz n-CsHI?
...
0.13
...
.. ... ..
0'. 09 0.08 0.07
1.93 1.84 2.06
1.15 1.23 1.30
0.13 0.15 0.16
0.01
CHa 0.19 0.14 0.24
13.0 13.8 11.1 C?HI 7 92 7 92 7 9.5
0.01 C?He 2 08 2 03 1.80
C3Hs 0.01 0 01 0 01
C2H4 0.12 0.03 0.06
0.22 0.08 0 19
0.56 0.31 0.18
8.41 7.86 8.23
...
...
C4Ha 0.01 0 01 0 ,Ol 0 05 0.15
0.Oi 0.02 0.04 0.01
0 02 0:06 0.03
0.08
0.02
Cs+
1'.03
(
.
.
...
2 0
0.0;
0.90 0.49 0.28
,
.
1.56
,..
..
C~HB
,.
0.27
C~HI
CzHa 20.43 20.09 16.34
CzHs
0.10
CsHio
SI\tPLH
CI fraction
CzHa
,..
C4Ha 25 25 50 50 100 100
0.03
0.08
CzHi
Ca fraction 15%
C~HI 34.22 35.10 34.53 34.11 32.92 34.30
CHI 33.60 35.35 34.77 34.90 32.90 35.00
..
CsHt 0.08 0.11 0.08 IroCaHio 13.58 12.55 13.08
nCiiIio 41.01 42.94 38.94
CIHS 43.96 43.84 47.31
... ...
25.39 26.88 24.49
C4Ha 27.20 27.44 29.75
a Contamination of methane fraction n i t h lower boiling noncondensables was disregarded, as tlicse coinjioncnts arc not fractionally separated in Podbielniak column under normal operating conditions.
Table 11.
fractions and 9% in the small fraction (C6), the resultant error in the analysis on a total sample basis is small. However, the accuracy of the mass spectrometer for the lighter components in somt> of these cases is in the order of 1 to 2% of the total fraction. In the case of saniple 2 a considerable quantity of Cais shown in the analysis of the Cq fraction. KO CB was indicated from the distillation curve. This apparent anomaly may be due in part to the limitation of the distillation equipment and in part to the mass spectrometer analysis of the fraction. The effect of distillation rate on the amount of contamination shows no definite trend, and it is indicated that the highest rate (100 cc. per minute) may be used on gases without any appreciable loss in accuracy. In general, the effect of these contaminants on the
Effect of Distillation Rate on Purity of Heart Cut (Sample 1) of Heart C u t Fraction (A1.S. Analysis) CHI CzH4
Mole C I fraction
R a t e Dist.. Cc./LIin. 25
a
100.00 100.00 100.00 99.96 100.00 99.96 100.00
25
00 50 50 100 100 Cz fraction 25 25 50 20 00
100 100
C3 fraction
25 25 50 50 50 100 100
4
Mole
... ... ...
, . . . . ...
...
0.01 0.01
...
...
0.04
, . I
0.04
C2Hd 33.91 44.39 41.80 47.09 40.49 46.13 44.57
CzHe 65.70 55,39 57.42 52.01 58.79 53.20 54.91
C3Hs 0.27
C3H8 0.02
0.68 0.75 0.57 0.36 0.40
...
&Ha
C2H6
C3Ha 65.58 74.86 72.48 83.89 83.83 76.33 72.93
CaHs TotalCa 34.36 0.06 ... 25.14 26.26 0.74 15.56 0.25 15.56 0.49 23.53 ... 25.93 0.52
,
,.
0.30 0.12 0.14 0.43
... ... 0.52 ... ... ...
0.19
Sample Basis-
CZH4
CHI 0.10 0.22 0.10 0.15 0.15 0.17 0.12
. . ...
r0C o n t a m i ~ l a n t
__Total
...
...
. . ..
,
0.15
...
CHI 0.01 0.02 0.01 0.01 0.02 0.02 0.01
0.06 0.06 0.06 0.03 0.04
CzHi
C2H6
...
...
... ,..
0.05 0.02 0.02 0.07
C3H6
0.03
...
,..
CaHs 0.00
... .. ...
O.'Ol
...
TotalC~ 0.01
...
0.11
... ... ...
0.15 0.04 0.08
0.03
0.09
...
Contamination of methane fraction with lower boiling noncondensables was disregarded, as, these components are not fractionally separated i n Podbielniak column under normal operating condltlons.
V O L U M E 21, N O . 10, O C T O B E R 1 9 4 9 further analyses of each fraction by present chemical or spectroscopic methods would be approximately the same or less than the amounts of contaminant shown. Determination of Purity of Heart Cut. In order t o determine t'he purity of the fractions a t the several distillation rates, heart cut samples were taken of each fraction after about 50 cc. of gas had been taken overhead and before the next cut point was reached. This ensured dctermination of the purity of the fraction without regard to contamination due to error in cut point. These fractions were analyzed by mass spectrometer, and the results are shown in Table I1 (Sample 1). KO trend in contamination of the heart cuts may be seen \Tith increase of distillation rate, and the quantities of contaminant in each case are small. In both studies, precision of total fractiori analysis and purity of heart cut, it wiis neccssary to place the column under total reflux for several minutes while changing receivers to acccmmodate the indicitted fractions. Although this was not desirable in a study of the effect of distillation rates, it was necessary because of the nature of the apparatu3 employed. DETERMINATION OF OPTIMUM CUT POINTS
1199
Table 111. Analysis of Cut Point Fractions" Cut
Point
(Sample 1) Fraction
Tempeyture Range, C.
Mole % of Fraction ( X S .Analysis) CH4
FIRSTDISTILLATION C3H4 CzHs
Mole % of Total Sample C H ~
czm
............................................................
c1-c*
1 2 3 4
-104 to -104 - 1 0 4 t o -104 - 1 0 4 t o -104 - 104 to - 104
35.21 4.91 0.69
...
CzH4
c2-c1
1
2 3 4
-88 to -52
1 2 3 4
C,-Cob
1 2
3 4
0.09 0.01
. ,. ...
C3H5
0.16 0.25 0.26 0.27 CZHB
C3HB
...................................................................... -52 to -49 -49 t o -49 -49 t o -48
0.79 0.57
CJFIS (-a-Ci
61.02 0.78 91.60 0.81 96.21 0.49 99.79 ... CzHe CaHs S o M.S. analysis
-40 t o -14
9.19
.................
64.61 33.21 13.99 82.91 S o b1.S. analysis
CaHs 73.69
Iso-CiHm 15.80
..............
1.27 2.03
CIHS 1.32
0.10 0.20
0.17 0.04
...
C3Ha 0.02
.......
-12 - 1 2 t o -12 -12 to -12
...
CaHs Iso-C4Hlo C4Ha 0.20 0.04 ,,,
..............
2.83 22.89 69.53 4.70 0.06 0.19 0.01 0.01 2.81 7.25 85.48 4.46 0.05 0.23 1.03 2.51 90.81 5.65 ... 0.25 0.02 n-CiHla n-CaHs I S O - C ~ H I ?CSHIO n-CaHs Iso-CslIli Ca&o -15 to -A0 4.53 89.06 3.78 2.27 0.08 .., , , , -10to -a 3.49 82.16 8.94 4.19 0.08 0.01 , ."..........'.'.....6"74.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.04 9.68 0.06 0.01 0.01 -3to +I 4.29 + I to A 4 0.97 43.14 41.34 13.22 0.04 0.04 0.01 -14to
SECOXDDISTILLATIOX CI-C,
CZYC3
c3-c4
1
2
-150to -14Jto
8 4
-11:
CzHs
to -104 -104 t o -104
-58
-3Oto
2 3 4
- 5 8 t n -50 -5Oto - % 8 - - 8 t o -+8
CZHI
CzH4 0.38 1.37
46.49 3.70 CzH4 1.97
52.35 95.69 CzHa 79.42
0.30 C3Hs 16.69
CzHs 0.60
0.i4' 0.26 CzHs 0.21
0.70 0.42 0.09 C3Hs 0.74 0.90
73.87 19.64 4.01 C3Hs 97.54 89.52
23.60 77.59 93.75 Iso-CaHio 1.40 9.19
0.60 1.31 1.45 CaH5 0.12 0.39
0.20 0.06 0.05 0.21 0.01 0.25 CaHs Iso-C~Hlo 0.26 . ,. 0.24 0.02
... 0.27 0.10 0.27 ............................................... -I45 -115
1
1 2
CHI
CHI 99.41 98.39
0.13 0.01
C3Ho 0.04
................................................................
--12 t o -30 - 3 0 t o -18
..............................................................
-188 t o -13 64.56 33.13 2.11 0.17 0.10 3 I n this study, the distillation was - 13 to - 12 4 15.71 80.45 3.36 0.04 0.23 allowed to proceed a t a predetermined n-CaHlo n-C4Ha Iso-CSHH CbHlo n-CaHs I s o - C ~ H ICaHla ? rate (25 cc. per minute) until the temC4-Csb 1 - 2 0 t o --I 0.73 64.91 24.68 7.70 3.06 0.02 0.01 ................................................................... perature of the gas taken overhead from -'?to -2 1.33 43.96 41.38 13.07 0.04 0.04 0.01 2 + 2 to +4 0.10 28.79 53.23 15.59 0.03 0.05 0.01 3 the distilling column began t o rise above 4 + 4 to + 4 0.15 22.19 59.30 16.76 0.02 0.06 0.01 the boiling point of the highest boiling a Horizontal dotted lines indicate nearest approximation t o normal cut point. component in the fraction. At this point * Distillation column pressure 300 mm. absolute. the overhead gas line \vas switched to a manifold containing 15-cc. capacity r e ceivers filled with mercury, " , and the mercury was slowly disp1:tced by the effluent gas. Employing fractions was recorded and the gas analyzed by mass spectrometer. As each of the distillations reported in this paper emthis procedure, it was possible to segregate fractions without placing the distillation column under total reflux a t any critical ployed approximately 5000 cc. of gas, these specially collected fractions represent'ed only a few tenths of 1% of the total gas. point in the distillation. The boiling range of each of these small The results of the analyses of these fractions are given in Table 111. I t was necessary t o c o l l ~ c tequal quantities of Table 11. (Cont'd) each of the small fractions in order to accumulate ( S a m d e 1) sufficient amounts for mass spectrometer analysis. Mole r0of Heart C u t Fractlon hlole % Contaminant Accordingly, none of the boiling ranges shown in R a t e Dist., ~ . . _ (h1.S._ Analysis) Total Sample Basis __________ Table I11 corresponds exactly to the normal cut Ca fraction Cr./R.lln. CaHs C4H8 n-C4Hlo I s o - C ~ H ~ O C3Hs points. However, horizontal dotted lines indicate 25 N o L1.S. analysis 25 0.53 39.38 10.46 49.63 0 07 for each fraction the point that most nearly ap50 ... 38.34 7.53 54.13 50 ... 32.66 1.51 65.83 proximates the normal cut point. Values for the 37.94 5.38 66.68 50 ... lighter component falling below this line indicate 100 ,.. 45.16 9.68 45.16 100 ... 45.91 9.39 44.70 the amount of "carry-over" of this component into the next fraction and values of the heavier coniCb fraction CiHe n-CaHiz ISO-CLHLZCaHia ponents above this line indicate the amount of con25 KO 11.53. analysis N O R1.S. analysis 25 ... ... tamination of the previous fraction with the heavier 0.83 50 6.87 46.61 45.69 ... 0.02 ... 3.65 1.24 50 76.66 17.80 0.65 0.05 0.00 fraction. In each case, this amount is small when 5.44 50 1.95 69.69 22.15 0.77 0.10 0.01 determined on the total sample basis. Although it 2.95 2.11 100 68.71 25.88 0.35 0.06 0.01 2.35 100 3.66 61.21 32.06 0.72 0.05 0.02 has generally been considered that the first fraction a See opposite page for footnote t o table analysis would be low and the last fraction high by the same amount, owing to holdup of the column
1200
ANALYTICAL CHEMISTRY
atb well as the lines beyond the point at which the temperature is
LITERATURE CITED
measured, only a very slight trend in this direction is shown by the results in Table 111. -4s the fractions analyzed represent only a few tenths of 1% of the total sample, the results shown in Tahlr IT1 should he accurate on a total sample hasis.
(1) Office of Rubber Reserve (RFC), “Butadiene Laboratory Manual,” Method L.M. 2.1.51.1. Butadiene Analytical Committee, 1941. (2) Podbielniak Manual, “Hyd-Robot Instructions,” Podbielnisk, h c . , Chicago, Ill. ( 3 ) Podbielniak, TT. J., IND.ESG.CHEM.,. ~ - A L .ED., 13, 639 (1941). (4) Starr, C. E., Jr., Anderson, J. S., arid Davidson, V. &I., A s . 1 ~ . CHEM.,19,409 (1947). (5) Washburn, H. T,,Wiley, H. F,,arid Rock Y. >I., Ihid., 15, 541 (1943 1.
CONCLUSIONS
The results obtained show that distillatioil r:itCs as high :IS 100 (T. per minute may be employed with accuracy equal to that attained at the slower rates prescribed in the literature. Cut points between fractions could be raked somewhat over those previously 1 ) 1 ~ e s ( ~ iwith h ~ d a n d t i n g very slight incrt:asc in nccur:rcy.
HECEIY~:U >larch 15, 1948. Presented before the Bouthwe\t Regional Neeting, AXERICAS CHE\rIc.+L SOCIETI.Houston. Tex., December 12 anrl 13. 1947.
Water-Soluble Polycarboxylic Acids from Oxidation of Bituminous Coal Determination of Molecular Weights NATHAN BERMAN’
AND 13. C. IIOWiARD Coal Research Laboratory, Carnegie Institute of Technology, Pittsburgh, Pa.
The application of modifications of the MenziesWright molecular weight apparatus to the determination of the molecular weights of the watersoluble pol) carboxy acids formed by oxidation of coal is described. Acetone and methyl ethyl ketone were used as solvents and benzoic, salicylic, phthalic, and mellitic acids as standard solutes. For solutes that obey Raoult’s law there is a linear relation between the rise in the differential thermometer and the millimoles of solute present, if a constant volume of solvent is added to the apparatus and a constant
C
OKTROLLED oxidation of suspensions of bituminous coal in aqueous alkali by oxygen gas, a t elevated temperatures and pressures, results in a mixture of water-soluble carboxylic acids in yields as high as 60% bj- weight of the coal ( 1 ) . Simple aliphatic acids, acetic and oxalic, are formed in small amounts, but aromatic polycarhox acids predominate. Benzene di-, tri-! tvtra-, and pentacarbos) c acids have been isolated and there i.5 evidence of the presence in significant amounts of : i d s of more complex nucleus than the benzene ring. Because the acids differ both as to nuclear size and number of functional groups per molecule (equivalent weight) it is necessary, in foIlou.ing the effects of process variables and fractionation procedures, to have available rapid methods for determination of both equivalent and molecular weights. Determination of the former presents no difficulty, inasmuch as we are dealing lvith strong water-soluble arids, the equivalent weights of ti-hich arc’ readily determined by the usual titrimetric procedures. For the molecular weight determinations the Menzies-Wright apparatus ( 5 , 6 ) as modified in this laboratory and by Hanson and Bowman (P) has been found satisfactory from the standpoint of convenience, speed, and reproducibility. Data on four known solutes-benzoic, phthalic, salicylic, and mellitic acids-as well as on samples of the mixed aromatic acids recovtlrcd from the 1
I’meent addre..,
V n i v e r a i t y of California, Beverly Hills, Calif.
energj input to the boiler maintained. This constant relating the rise in the water therniorneter and molar concentration combines the classical ebullioscopic constant and the coefficient o f the water thermometer, and greatl) simplifies calculations. This constant is affected bj changes in barometric pressure, about 1.670 for each 10 mm., and detiations from Kaoult’s law are shown by departure from linearit) at higher concentrations. No such deviations greater than experimental error were obserted with these solutes in the ketonic solvents used.
oxidation of coal, are presented. Acetone and methyl ethyl I+ tone were used as solvents. A simple method for estahlishing thc constant for calculation of the results is described. REAGENTS AND APPARATUS
The acetone and the benzoic and salicyclic acids \yere ~Ialliiickiodt analytical reagent grade. The acetone \vas used without further purification. The phthalic acid (Eastman) was crystallized once from water. The mellitic acid was prepared by osid:ition of carbon black; the crude acid was precipitated as the ammonium salt and the free acid recovered by electrolysis of :in aqueous solution of the salt. The equivalent weight, by titration with 0.1 S alkali using phenolphthalein indicator, was found to hr 57.3: theoretical, 57.0. All the acids were dried 2 houw :it 110”C. before being used. The methyl ethyl ketone was ii commercial product fractioii:itetl through an 8-plate column, packed ivith O.125-inch stainless s t w l helices, a t a 20 to 1 reflux ratio. The cut used boiled bet\vc.cvi 78.5” and 78.8” C. (uncorrected). Two modifications of the apparatus were employed. The f k - t was the original type of 1Ienzies-\Vright apparatus without V N C uum jacket and with a removable Cottrell pump, modified fol. electric heating by the introduction of a helical coil of S o . IS Sichrome wire. The external diameter of the helix was such :I> t o allow the mouth of the Cottrell pump to pass over it and [ h e ends were brazed to 2-mni. tungsten leads sealed through thr glass. The total resistance of heater and leads was about 0.8 o h ~ n and the electrical energy for heating was supplied through H smull transformer. The second mot1ific:itinn \vas a recent model of t h e
