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INDUSTRIAL AND ENGISEERISG CHEhIISTRI-
observed data. Traces of naphthenes may often influence the physical constants of an assumed 100 per cent paraffin mixture to a remarkably discouraging extent. The authors have convinced themselves of the fallacy of the ‘(identification by physical constants’’ in a number of cases, with both their own and outside samples. Khereas phy4cal constants may definitely identify compounds of substantially different physical properties in simple mixtures, they are not characteristic enough for mixtures of compounds with similar properties.
Analysis of Fractions of Known Composition The results of the qualitative and approximately quantitative analysis of synthetic mixtures, unknown to the analyst, are given in Table I. The effect of concentration of a high-scattering (2,2,4trimethylpentane) in a low-scattering hydrocarbon (n-heptane) and the regular increase in line intensity can be seen in Figure 4, illustrating the spectra of some of the mixtures listed in Table I.
Analysis of Unknown Fractions The following hexanes, heptanes, and octanes haye been identified to date in the products of catalytic alkylation of isobutane or isopentane with, respectively, ethylene, propylene, and the butylenes. HEXASES. 2,3-Dimethylbutane, 2-methylpentane, and 3methylpentane HEPTANES.2,3-Dimethglpentane, 2-niethylhexane, 2,4-dimethvlDentane. 2.2-dimethvl~entane.and 2.2.3trim&L?;lbutane OCTANES. 2,3-Dimethylhexane, 2,5-dimeth>lhexane, 2,2,4-trimethylpentane, 2,2,3-trimethylpentane, and 2,3,4trimethylpentane “
I
I n the case of hexanes the Raman results lvere found to be in perfect agreement with chemical identification by means of bromo and nitro derivatives (10). Typical examples of analyses of different cuts, obtained by alkylation of a specified paraffin and olefin, are given in Table 11. The catalysts arid temperatures used are also indicated.
Accelerated Sublimation A . J . BAILEY, University of W-ashington, Seattle, Wash.
F
EW methods of purifying organic compounds are more
troublesome t’han the sublimation of a large quantity of material by means of a funnel and watch glass. Instead of this, a simple combination of common apparatus mag be used, which raises the rate of sublimation until it compares with the usual rate of distillation, without inconvenience or elaborate equipment. The sublimation is aided by passing in cool air, which condenses and removes the solid, and deposits i t in another part of the system. Use of this principle is not n e r , but the equipment previously recommended is so elaborate and rare that none of the scientific supply houses lists it. The system includes a flask with a side tube sealed t o the bulb or lower part of the neck, and a plain distilling head with a reduced end. The material to be sublimed is placed in the flask, the dist,illing head with a plug of cotton in the upper end is attached, and the assembly is mounted at about a 45’ angle as shown in the photograph. I n practice, a 60-cm. (24-inch) distilling head is used and the cotton plug is pushed down below the side tube. The flask is then heated to the usual sublimation tem-
VOL. 12, NO. 4
The theoretical discussion of these identifications from the standpoint of the alkylation reaction will be reserved for a joint publication of A. V. Grosse with H. Pines and V. N. Ipatieff.
Literature Cited (1) Birch. R . F., Dunstan, -1. E., Fidler, F. h.,Pim, E’. B., and Tait, T . , J . Inst. Petroleum Tech., 24,303-20 (1938). ( 2 ) Birckenbach and Goubeau, Ber., 65,1140 (1932). (3) Bruun, J. H . , ISD. ESG. CHEJI.,Anal. E d . , 8,224 (1930). (4) Bruun, J. H., and Faulconer, W. B. M., Ibid., 9, 192 (1937). (5) Crigler, J . Am. Chem. Sac., 54,4207 (1932). (6) Egloff, Gusrav, ”Physical Constants of Hydrocarbons. Vol. I. Paraffins, Olefins, Acetylenes, and Other Aliphatic Hydrocarbons”, American Chemical Society Monograph X o . 78, New 1-ork, Reinhold Publishing Corp., 1939. ( 7 ) Goubeau, 2. anal. Chem., 105,161 (1936). (81 Grosse. A . V.. Re.finer Sutural Gasoline .Jffr., 18, S o . 4. 149 (1939). (9) Grosse, A. V., and Egloff, Gustav, Vniversal Oil Products Co., Booklet 219 (1938). (10) Grosse, A. V., and Ipatieff, V. S . , “-klkylation of Paraffins with Olefins. Identification of Paraffins Formed”, papers presented before Petroleum Division, American Chemical Society, Rochester meeting, pp. 1-12, 1937. (11) Grosse. A. I-.,and Ipatieff, V. N.,J . Am. Chem. Soc., 57, 2415 (1935). Grosse, A . V., Morrell, J. C., and hlattox, W ,J.. ISD. ESG. CHEX.,32,528-31 (1940). Ipatieff, I-.N., and Grosse, .1.V., Ihid., 28,461 (1936). Ipatieff, V. S . ,and Grosse, A. V., J . A m . Chem. Soc., 57, 1616 (1935). Ipatieff, V. N., and Grosse, A. V., J . Gen. Chem. (U.S . S. R.), 6 , 423 (1936). Ipatieff. V. K., Grosse, A. V., Pines, H., and Komarewsky, V. I., J . Am. Chem. S’oc., 58,913 (1936). Kohlrausch and Koppl. 2. p h y s . Chem., B26, 209 (1934). Kohlrausch, Kopper, and Seka, Xonatsh., 61,397 (1932). Rlair, B . J.,and Schicktanz, S . T., IND.E N G .CHEM.,28, 1450 (1936). R a n k and Bordner, J . Chem. Phys., 3, 248 (1935:. Rosenbaum. E . J., Grosse, A . V., and Jacobson, H. F., J . Am. Chem. Soc.. 61,689 (1939). Zelinsky, N.. Ber., 44,3121 (1911). PRESENTED in p a r t before t h e Division of P e t r o l e u m C h e m i s t r y a t t h e 9 4 t h a n d 9 6 t h l l e e t i n s s of t h e .Irnerican Chemica! Society, Rochester, N. Y ., a n d Milwaukee, K i s . C o n t r i b u t i o n from t h e Research Laboratories of t h e r n i v e r s a l Oil P r o d u c t s C o m p a n y a n d t h e George H e r b e r t Jones Chemical L a b o r a t o r ? of the LTniversity of Chicago.
APRIL 15, 1940
ANALYTICAL EDITION
perature and a stream of air passed in, either bv pressure 011 the flask side tube or by suction at the upper end of the distilling head, The cool air condenses the solid and carries it to the distilling head, where it is filtered off by the cotton plug. Beta-naphthol, which has a vapor pressure of approximately 3 mm. a t its melt,ing point (122' C.), in this device sublimed a t a rate of almost 1 gram per minute. The temperature was maintained above the melting point, but enough cool
195
air was admitted to keep the deposited solid from melting. The beta-nap]lthol TTas deposited in pure colldition easily dislodged from the tube. Compared with ordinary sublimation or atmospheric or vacuum distillation, with the splattering and solidification in the condenser tube and the neck and sides of the flask, the method is more rapid and convenient, achieves purity, and avoids complicated apparatus and troublesome operation.
Quantitative Spectrochemical Analysis by Measurement of Relative Intensities E. K . JaYCOX AND A. E. RUEHLE Bell Telephone Laboratories, Inc., New York, 3.Y.
-4method is described which combines flexibility of application with the improved precision resulting from modern methods of photometry. Applications have been made to samples i n which the main component is lead, aluminum, iron, copper, nickel, and the alkaline earth oxides, respectively, with an average precision of 50 to 100 parts per thousand of element determined.
use a given line pair only a t or near the concentration of test, element giving equal intensity for bobh lines (method of homologous pair?) or else one must correct for any deviations from the straight-line port,ion of the characteri-t' 5 ic curve through a calibration of each plate. The equal density method is n-idely used abroad (1, 4, I O ) , while the practice of plate calibration has gained in favor with American
T
HE rapid extension of the application of the spectro-
graph to chemical analysis in recent years may be traced to improved methods of reproducing excitation conditions and improved methods of photomet'ry. I n earlier work the condensed spark betv-een elect'rodes made from the sample itself was the principal met,hod of excitation used. The main draxbacks of this method are relatively lon- spectral sensitivity and uncertainty in exciting representative portions of samples and standards. Both of these difficulties were circumvented by Sitchie ( 6 ) x h o used arc excitat'ion of dried solutions. S o t only are most metals more sensitive in the arc, but i t is much more convenient to make up reliable synthetic standards in solution form. Sitchie's met'hod is widely used today, hut its precision is limited by t'he inherent lack of reproducibilit,y of the arc, which is subject to "wandering" and current fluctuations. Sitchie and Standen ( 7 ) applied Gerlach's (4) internal standard method in an attempt to eliminate the effect of such variations. This particular application involves two assumptions: (1) that any variability in the arc nil1 affect the excitation of the test element and the reference element in exactly the same manner; ( 2 ) that, the difference in densities of two lines on the plate is proportional to the logarit,hm of the ratio of the intensities of these lines in the source. Experience indicates that the first assumption is reasonahly justifiable in many cases. I n some cases, however, a change in conditions will materially change the relative intensities of a pair of lines. For this reason the internal standard method must not be applied indiscriminately, but the fundamental assumption must be justified in each case. The second assumption is also a potential source of t,rouble, since it holds only for the straight-line portion of the characteristic curre of the plate. For this reason one must either
LOGl
R E L A T I V E E X P O S U R E (E= It)
FIGURE 1. TYPICAL C4LIBRATIOX A N D J T O R K I S G TINISLEAD
C U R V E S FOR
