second tube of 7-mm. diameter, 10 inches long, also sealed a t one end. The air is displaced from this jacket by purging with helium, and the tube attached to a vacuum pump. After evacuating to about 1 mm. of Hg, the jacket is sealed at a point about 4 inches from the closed end. The entire assembly is then placed in a heating mortar, set to the desired temperature, and left there for the desired period of time (15 minutes a t 400' C. in our experiments). After cooling, the jacket is scratched with a file and placed in a short section of rubber tubing which forms a bypass in the helium inlet line of the chromatograph. The helium stream is then directed through the bypass until it is purged of air, as indicated by the detector of the chromatograph, after which the glass jacket is broken in the rubber tubing and the chromatogram of the gases and volatile light ends obtained. Figure 1 is a diagram of the arrangement of the component parts. I n our experiment.. polyethylene, polypropylene, and copolymers of the t w o wcre run. The chromatogram was obtained on a 6-foot column of didecyl phthalate on firebrick a t 70" C., using a Perkin-Elmer Model 154B Chromatograph. As a n example, the chromatogram obtained from polypropylene showed six distinct peaks corresponding to hydrocarbons ranging from methane to isomers of pentane and pentene. The reproducibility of the relative heights of the peaks was approximately 1%, based on replicate analyses (two sets of triplicates and five duplicate runs on different samples of polyolefins).
Rubber Tubing
e
Sample Jacket
ir
f i -
Chromatographic Column
Figure 1.
Arrangement of component parts
The pyrolyzate produced in the pyrolysis of these materials consisted of a gaseous and liquid phase. Only the gas phase enters the column and the distribution of those gases containing five carbon atoms and less were used for characterization. The question arose concerning absorption of the gases by the rubber tubing. To check this point, the rubber tubing was replaced with a 6-inch length of copper tubing of 3/s-inch 0.d. and equipped with metal fittings. The glass sample tube was broken by squeezing the copper tubing with a pair of pliers. There was no detectable difference in the gas distribution; thus the more convenient rubber tubing was used for this work. However, for other applications in which gases are produced which are absorbed by rubber, the copper tubing must be used. The metal tubing would also be useful if there was interest in the heavier pyrolytic components because
it may be heated for volatilization purposes. We believe this technique is simpler than the distillation procedure described above and less liable to error due to loss of volatile components in transferring to the chromatograph. We feel that this technique is superior to the hot wire technique in that time and temperature are accurately controlled, the sample is uniformly heated, and the procedure permits the use of nonvolatile catalysts as an aid to pyrolytic degradation. LITERATURE CITED
(1) dehgelis, G., Ippoliti, P., Spina, N., Racerca sci. 28,1444 (1958). (2) Janak, J., Nature 185,684 (1960). (3) Radell, E. A,, Strutz, H. C., ANAL. CREM.31,1890(1959). (4) Strassburger, J., Brauer, G. M., Trson, M., Forziati, A. F., Zbid., 32, 454 (1960).
An Improved Siwoloboff Micro Boiling Point Method Clarence Karr, Jr. and Edward E. Childers, Low-Temperature Tar Laboratory, Bureau of Mines, U. S. Department of the Interior, Morgantown, W. Va.
w
characterizing the components of low-temperature coal tars the Bureau of Mines has had to use micro boiling point determinations for small samples. An old and widely used technique was first described by Siwoloboff (11). The Bureau of Mines has devised a considerably improved method. Apparatus. The boiling point apparatus, shown schematically in Figure 1, was designed for radiant heating, with minimum heat loss and with optimum conditions for viewing the onset of boiling. High-boiling compounds can be analyzed as readily as lower boiling compounds. Bath oils a t high temperatures tend to smoke and, in particular, tend to darken or become turbid so that, eventually, microsamples cannot be observed properly. HILE
Aluminum foil, B1, was wrapped firmly around a 16 X 150 mm. test tube, A , until it fitted tightly into a 25 X 150 111111. test tube, C, leaving approximately 23 mm. between the bottoms of the tubes. Nichrome wire, D (No. 30), was wrapped around tube C, with a spacing between wire turns of approximately 5 mm. for the lower one third of the tube, increasing to about 8 mm. for the upper two thirds. The Nichrome wire was held in place with adhesive-type glass tape, and both the tube and wire were covered with firmly wound asbestos ribbon, E. Aluminum foil, Bz, next was wrapped around the apparatus to a thickness of about 5 mm., followed by 6 mm. of glass wool, F, and an outside covering of glass tape, H . A 5 X 10 mm. viewing slit was cut, and this opening was sealed with a glass viewing window, G, of the same
dimensions. The aluminum foil provided a reflecting surface for infrared radiation. The removable portion of the apparatus, shown to the right of Figure 1, consisted of a 5 X 40 mm. sample tube, J, containing an inverted 2 X 40 mm. capillary tube, K , held firmly to two glass rods, 11,IZ ( 5 X 210 mm., 5 X 190 mm.), by fine wire, LI, L z . These small tubes were made by sealmg off one end of tubing of the proper size. An iron-constantan thermocouple was inserted into the channel formed by the sample tube and the two glass rods. This removable portion was inserted into tube A so the open end of the capillary tube K could be seen through the viewing window G. The open space a t the top of tube A was filled with glass wool, packed tightly around the glass rods, 11,I*. The longer glass rod 11, VOL. 33,
NO. 4,
APRIL 1961
655
was held in a thermometer clamp. For viewing the sample a small, highintensity light source was placed immediately above the glass rods. The tubes transmitted light down to the sample tube. A balance-type magnifying glass was placed in front of the viewing window. The heat input was controlled by a 11Bvolt 10-ampere variable transformer, and the millivolt output of the thermocouple was measured with a Leeds & Northrup Type K-3 potentiometer. It is believed that the construction used effectively eliminated thermal gradients in the sample region.
d A
BI
PROCEDURE A N D RESULTS
Sufficient sample material was placed in tube J to cover the opening of capillary tube K , or about 1 small drop when molten. The apparatus was heated rapidly to a point several degrees below boiling. Heat application was a t a decreasing rate as the boiling point approached. Below the boiling point, bubbles could be seen leaving the open end of the capillary tube a t widely spaced intervals. At the moment of boiling these bubbles were emitted in a continuous stream. rl. new sample tube and a new capillary tube were used for each determination.
C
D
ill! 1-1 Figure 1. A.
Test tube, 1 6 X 1 5 0 mm.
61, ei. Aluminum foil C. Test tube, 2 5 X 150 mm. D. E.
F.
Nichrome wire, No. 30 Asbestos ribbon Glass wool
Table I.
No. of Determmations 11 1
3 2 4 4 9
1 1
4 4 4 4 3 4 4 2 3 6
4 4 4 2 2
656
Boiling point apparatus G.
Glass viewing window, 5 X 10 mm.
H. Glass t a p e Glass rods (11, 5 X 2 1 0 mm., I:, 5 />, I*. J. Sample tube, 5 X 40 mm. K. Capillary tube, 2 X 40 mm. L1, Lz. Fine wire
X 190
mm.1
Boiling Points by Improved Siwoloboff Method Compared with Literature Values
Compound
p a g e B.P., C./Av. Mm.
1,2-Dimethyl-4-ethylbenzene 188.73/738.7 1-Methyl-3-tert-butylbenzene 187.8/737.9 1,2,3,5-Tetramethylbenzene 197.52/744.16 1,2-Diisopropylbenzene 203.93/740.6 1,4Diisopropylbenaene 209.28/741.90 1,3,5-Triethylbeneene 215.79/743.7 1,4-Di-terl-butylbenzene 235.17/733.2 2-Methylnaphthalene 239.5/741 1-Ethylnaphthalene 257.15/740.2 1,2-Dimethylnaphthalene 269.40/744.9 1,5-Dimethylnaphthalene 268.32/731.58 1,6-Dimethylnaphthalene 264.45/744.2 1,7-Dimethylnaphthalene 261.73/740.8 2,3-Dimethylnaphthalene 267.78/739.1 2,6-Dimethylnaphthalene 260.92/741 2,7-Dimethylnaphthalene 261.68/740.4 1,3,7-Trimethylnaphthalene 280.65/743.2 2,3,5-Trimethylnaphthalene 287.93/743.96 2,3,&Trimethylnaphthalene 287.36/725.1 Biphenyl 254.01/744.15 3-Methylbi henyl 270.53/730.9 3,3’-DimetfylbiphenyI 285.24/741.4 Phenylcyclohexane 238.53/733.1 2a,3,4,5-Tetrahydroacenaphthene 250.46/734
ANALYTICAL CHEMISTRY
Ljterature B.P., C./760 Mm. 189.48 ( 1 ) 189.26 ( 1 ) 198.00 ( 1 ) 203.75 (8) 208.9 (1) 215.4 (9) 236.5 (9) 241.0 (6) 258.67 (1) 268 (1) 269.1 (6) 264 ( 4 ) 263 ( 1 )
Maximum Deyiation, C. 10.51 f0.75 f0.73 f0.21 10.25 f O .49
% if] 280 ( 1 )
288.0 (6) 288.1 (6) 255.0 (1) 270 (10) 286 (7) 238/759 (3)
10.45 f0.42 10.13 f0.20 1 0 .07 10.51 1 0 . 19 f0.14 f O .58 10.97 A0 .35 1 0 .54 f O .25 f O .24
249.5/719 (6)
1 0 .13
ZSS (jj
The boiling point determinations for 24 aromatic hydrocarbons are presented in Table I as an example of the results obtained by the Bureau with this apparatus. These samples were the best specimens available, such as American Petroleum Institute standard samples, Repetitive determinations on new samples of the same compound were generally well within 0.5” C. of the average value and the average value usually deviated less than 1” C. from the literature value, taking into consideration the pressure differences. LITERATURE CITED
(1) American Petroleum Institute Re-
search Project 44, “Selected Values of Properties of Hydrocarbons and Related Compounds,” Carnegie Institute of Technology, Pittsburgh, Pa. (2) Boedtker, E., Bull. SOC. chim. France [3] 31,965 (1904). (31 Case. F. H.. J. Am. Chem. SOC.56, 715 (1934). (4) Coal Tar Research Association, “Coal Tar Data Book,” Gomersal, near Leeds, England (1953). (5) Gesellschaft fur Teervermertung mbH, “GfT-Aromaten,” Duisburg-Meiderich, Germany. (6) Lebeau, P., Picon, X, Compt. rend. 159,70 (1914). (7) Mayer, F., Freitag, K., Ber. 54, 347 (1921). (8) Melpolder, F. W., Woodbridge, J. E., Headington, C. E., J . Am. Chem. SOC. 70, 935 (1948). (9) Norris, J. F., Ingraham, J. N., Zbid., 62,1298 (1940). (10) Perrier, G., Bull. SOC. chim. France 131 7, 180 (1892). (11) Siwoloboff, A., Ber. 19,795 (1886). \ - I
