1249
V O L U M E 20, N O . 1 2 , D E C E M B E R 1 9 4 8 T a b l e I.
Effect of Rates of Air Leakage on Pressure M a i n t e n a n c e a t 10 Mm. of Mercury
Rate of Air Leakage .WE./Xin.
Pressure Deviations" Mm.
Hg
0.00 0.00 0.00 0.01
0
20
40 60 80
0.02 0.03
100 120 140
0.05
0.08
0.15
160
180 0.24 a Pressure deviations were measured with a butyl phthalate gage which could be read with an accuracy of t0.01 mm. of H g .
OPERATION
The amount of mercury or butyl phthalate (about 20 ml.) used in the regulator is not critical. However, the upper level of the liquid shown by I should be several millimeters below the safety trap, e (Figure 2). The height of the liquid, h, above o will determine the maximum pressure a t which the regulator can be used. The regulator is removed from the metal housing and readily filled simply by immersing the pump arm of the regulator in the liquid to be used, and applying gentle suction to the other a r m until the desired amount of liquid is obtained. When filling with butyl phthalate, care should be taken to keep it from obstructing the side-arm constriction, c, or sluggish pressure control will result. The glass part is replaced in the housing, mhich is then clamped in a vertical position. The pressure, which is controlled by the regulator, may be measured by an ordinary mercury manometer or a more sensitive butyl phthalate gage. The regulator is connected t o the apparatus and to the pump by no! less than 15-cm. lengths of flexible rubber suction tubing in order t o allow the regulator to be tilted through a 90" angle. When the tubing is attached (using lubricant), it is twisted slightly to make a press gently against s. When the system is ready for evacuation, it is important that the stopcock on the regulator be in an open position before the exhaust pump is started. This stopcock is used for by-passing the bulk of the air around the regulator and thereby prevents excessive turbulence of the liquid within the regulator during the evacuation process. After the pressure reaches a few millimeters above the final pressure to be maintained, the stopcock is closed for the remainder of the vacuum operation. The head, h, which is the difference in pressure between the t\vo side arms on the regulator, is controlled to any desired pressure simply by tilting the regulator by means of s. The true pressure as measured by a manometer is the 'sum of h and evacuation pump pressure. The regulator can be moved with precision through any angle from a vertical position with maximum pressure to a horizontal position with zero pressure. After the vacuum operation is completed, the stopcock must be opened before air is slowly ad-
13. 2-Methylnaphthalene
T
HE compound 2-methylnaphthalene is very unusual in that it possesses almost no tendency to crystallize with plane faces. The orthopinacoid face, 100,is always present, but under no simple laboratory conditions is it possible to obtain other faces. The crystals used for the present study were prepared from fusion or by sublimation (Figure 1). There is no evidence for polymorphism in these studies.
CRYSTAL MORPHOLOGY (determined by W. McCrone). Crystal System.
Rlonoclinic.
mitted to the evacuated stystem. If this is not done, some of the liquid in the regulator may be forced through the safety trap into the system. The efficiency of the regulator in handling air leaks or evolved gases is illustrated by Table I. The table shows that this regulator, using a Cenco Hyvac pump, maintained relatively stable pressure control even when exaggerated air leaks mere intentionally allowed. The use of a larger pump showed that these deviations of pressure from 10 mm. were due to. the fact that the exaggerated rates of air leakage began to exceed the exhausting capacity of the Hyvac pump, and not to the incapacity of the regulator. The many vacuum conditions under which this new design of vacuum pressure regulator can be readily used suggest a wide field of application where sensitivity, stability, and ease of precise pressure control are essential. The absence of any moving mechanical parts during the operation of this regulator practically eliminates the possibility of fouling, loss of sensitivity, or wear. LITER4TURE CITED
Bachman, G. B., IND. ESG.CHEM.,ANAL.ED.,7, 201 (1935). Bailey, -4.J.,Ibid., 15, 283 (1943). Bruun, J. H., Ibid., 11, 628 (1939). Caldwell, M .J.. and Barham, H. N., Ibid., 14, 485 (1942). (5) Central Scientific Co., Catalog No. 94610. ESG. CHEM., h i v k r , . ED.,1, 7 (1929). (6) Cox, H. L., IND. (7) Dalin, G. A., Ibid., 15, 731 (1943). ( 8 ) Douslin, D. R., and Wells, W. S., Ibid., 16, 40 (1944). (9) Ellis, L. M., Jr., Ibid., 4, 318 (1932). (10) Emerson, R. L., and Woodward, R. B., Ibid., 9 , 347 (1937) (11) Ferguson, B., Jr., Ibid., 14, 164 (1942). (12) Ferry, C. W., Ibid., 10, 647 (1938). (13) Gilmont, R., and Othmer, D. F., I b i d . , 15, 641 (1943). (14) Huntress, E. H., and Hershberg, E. B., Ibid., 5, 144 (1933). (15) Ibid., 5 , 3 4 4 (1933). (16) Jacobs, G. T.,I b i d . , 7 , 70 (1935). (17) Lewis, F. M . , I b i d . , 13, 418 (1941). (18) Liebig, G. F., Jr.,Ibid., 6, 156 (1934). (19) Melville, H. J., J . Chem. Soc., 1931, 2509. (20) Munch. R. H., J . Chem. Education, 9, 1275 (1932.) ESG. CHEM., ASAI. ED.,12, 274 (1940). (21) Nen-man, hl. S., IXD. (22) O'Gorman, J. M., Ibid., 19, 506 (1947). (23) Palkin, S., I b i d . , 7 , 436 (1935). (24) Palkin, S., and Nelson, 0 . A , , Zbid., 6, 386 (1934). (25) Schierholtz,0. J., Ibid.. 7, 284 (1935). (26) Spadaro, J. J., et al.. Ibid.. 18, 214 (1946). I b i d . , 3, 259 (1931). (27) Sunier, A. A , and White, C. M., (28) Thelin, J. H., I b i d . , 13, 908 (1941). (29) Todd, F., U. S. Patent 2,419,042 (-1pril 15, 1947). ENG.CHEM., A N ~ LEn. . 15, 637 (1943). (30) Warner, B. R., IND. (1) (2) (3) (4)
RECEIVED September 2,1947.
Form and Habit. Rounded crystals, no definite form or habit by ordinary crystallization methods from the common organic solvents. Groth reports tablets by sublimation with the forms orthopinacoid, (100); and clinodomes (011). Interfacial Angles (P7lar). 110 A 110 = 76'28'.
Beta
lo3" l6
*
Twinning Plane. Shows plastic deformation with mechanical ttvinning. Cleavage. lOO(1). X-RAYDIFFRACTION DATA(determined bv 2). Cell Dimensions. a = 18.6A; b = 5.98; c = 7.80. Formula Weights per Cell. 4. Formula Weight. 131. Density. 1.088; -1.10 (2). "
I
ANALYTICAL CHEMISTRY
1250
Figure 1. %Methylnaphthalene (50 X) h f c . Cmstals obtained by careful maoraublimation Right. Thin crystalline film from fusion
OPTICALPROPERTIES (deterzined by W. McCrone). Refractive Indices (5893 A,; 25" C.), CL = 1.494 * 0.001, 0 = 1.640 0.004. y = 1.77 0.01. f
f
Optic Axid Angles (5893 b.; 25" C.). 2V, = 81"; 2Er =
form hrientatia& orientation. These cryst& crystals, ne& never show angles ,eit,her either growing or in mixed fusion. 2. All crystals from the melt show a centered obtuse hisectrix interference figure with isogyres just included by N . A . = 1.25; 2 H y = 108'; v > r on this view and the sign is negative. A mixed fusion with Citrgille index liquid, 1.414,oauses the crystals cryst,als t o distlppear in the position showing alpha at 2C"
-
108".
I CITED
Dispersion. v > II (on centered obtuse hisedrix figure). Optic A.xidalPlrtne. L!OO. Sign of Double Refraction. ( Acute Bisectrix. In the 100 p
uramiscne nnsrauographie." Vol. Engelmann, 1910. (2) Neuhaus, Z. R ~ i s t .101, , 177-92 (1939).
(1) CTrocn,
0,
p.
*LA,
~ieiymg.
meter Analysis SIR: The reoent article on "Mass Spectrometer Analysis" by Brown et al. [ANAL.CHEM.,20, 5 (19481 contains mme excellent work on the application of this technique to liquid samples. The d s h presented in Tablea XI a i d XI1 introduce into the literature for the first time the conclusion that 3-ethylpentane and other ethylparaffins are present in oonsiderable quantities in cracked naphthas. The data. submitted on this point should, therefore, be examined oritioally. The following data are presented in Table XI: NaBtha. B, Vol. % Naphtha A, Vol. % Fraotion No. 2 3 4 2 3 4 3-Methylhersne 6.06 1.78 2.94 4.74 3.57 1.10 3-Ethyl~enthne %-Heptane
.. .,
0.26 1.62
ii.92
.. ..
0.82-
2.26
li.78
In distillation outs of the type being analyzed here. the abundanoe ratio 01 the compounds found on analyzing successive fractions has been ioun'd to follow a regular pattern determined by boiling points. I n the case of naphtha A, for example, if 3-ethylpentane were present to the reported extent between 3-methylhenme and n-heptane in fraction 3, it would normally be found in much IcLrger amount in fraction 4, where both the adjacently boiling oompounds are increased. In the oorresponding cuts from naphtha. B a similar situation appears, and the amount of 3-ethylpentme would be expected to be roughly the same in fraotions 3 and 4. Accordingly, the total amounts of this compound in the original samples are probably much larger ,than those reported here if the No. 3 cut analyses &re reliable. or much less if the No. 4 cut analyses are correct. In previous naphtha analyses by fractional distillation, infrared, or Raman spectroscopy, it has usually been impossble to demonstrate that the ethylparaffins'me present in more than trace amounts. Specific statements hcwe been made with regard to the apparent absence of 3-ethylpentane.in the seven virgin naphthas examined by A.P.I. Project 6 (I), and the absence of the methylethylpentams in alkylates and hydropolymers (2). I n view of the data previously reported and the internalinconsistency of the present data, it Seems that 8 further study of these samples may be in order. The above situation suggests t h t a major defioiency of the method
a8 described may be the uncertainty of the qualitative analysis of thr samples. In Table XII, for example, it is not clear why 2,2.3-trimethylbutane was included in the analysis and 2,Z-dimethylpentane left out. The authors report that these compounds have very similar maas spectra, and previous data indicate that the 2.2-dimethylpentane is .a likely and 2,2,3-trimethylbutane an unlikely constituent. The vduelues reported for the trimethylpentanes in.Ta,ble XI1 and 3,3-dimethylpentane in Table XI m e also interesting in this oonneotion. It would appear that further experiments are warranted to determine whether or not these compounds are as rare in naphtha samples 88 has commonly been supposed. Hohma J. HAIL Esso Laboratories, Standard Oil Development Co., Elisabeth, N. J.
LITERATURE CITED
(1) Foruiati, A. F., Willingham. C. B., Mair. B. J.. and Rossini, F. D., J . Resewch Nail. Bur. Standards, 32,31 (1944). (2) Glasgow, A. R., Streiff. A. J., Willingham, C. B., and Rossini, F. D., Proc. Am. Petroleum Inst., 26.111. 169 (1946). SIR: It is well recognized that the ability of the mass speotrometer aoourately to resolve an isomeric mixture is largely dependent on both the nature of the mixture and the relative concentrations of individual components therein. To verify independently the presenoe of 3-ethylpenhne in naphtha BI cut 3 was analyeed by an infrared spectrometer subsequent to the receipt of Hall's communication. At the wave length 01 11.13 microns, 3-ethylpentane exhibits a unique absorption relative to other hydrooabons present in the 92' to 96O C. distillate cut. The data show positive infrared confirmation of the maas spectrometer analysis, thereby establishing beyond reasonable doubt the presence of 3-ethylpentane in the cut in question. In out 4,*however,the total volume of the sample was oonsiderably larger, with the oonoentration of heptanes present in excess of 75%. thereby rendering the
