635
V O L U M E 25, N O . 4, A P R I L 1 9 5 3 0.2 ml. of serum and can measure the fluorescence of bile acids in 0.1 aliquot of this ~ e r m volume. ACKNOWLEDGMENT
The authors are indebted to Roger H. Machinist for the preparation of a,7-hydroxycholesterol, and to Ralph Heimer for his suggestions in fluorometric analysis. LITERATURE CITED
(1) Baker, H. W., Anderson, C. E., and MoCluer, R. H., Pmc. Soe. Ezptl. B i d . Meed., 76,218 (1951). ( 2 ) BermtrBm, S., and Wintersteiner. O., J . Bid. Chem.. 143, 503 119421.
(3) Glover, M., Glover, J.. m d Morton, R. A,, Biochem. J . , 51, 1 (1952). (4) Hardepger, E.,Ruaicka, L., and Tegmann, E., Helu. Chim. Acta, 26,2205 (1943). (5) Minibeck, H.,Biochem. 2.. 297, 29 (1938). (6) Moore, P. R., and Bsumen. C. A, 6. Bid. Chem., 195, 615 (1952).
Rosenheirn, 0.. and Callow. R. K., Biochem. I . , 25,74 (1931). Sehoenheimer. R., and Speny, W. M., J. B i d Chem., 106, 745 (1934). Sobel, A. E.,Goodman, J., and Blm, M., ANAL.CHEM.,23, 516 (1951). Sobel, A. E.,and Mayer, A. M., J . Bid. Chem., 157, 255 (1945). Sobel, A. E., Mayer, A. M., and Kramer, B.. Ind. Ew. Cham., 17,160 (1945). Sobel, A. E., Owades. P. S.. and Owades, J. L., J . Am. Chem. Soe., 71,1487 (1949). Sebel, A. E., and Snow,S. D., I . B i d . Chem., 171, 617 (1947). Waddell, J., Ibid., 105,711 (1934). Windma. A,, and Bock,F.. 2. phwiol. Chem., 24596 (1937). . . Winkert. J. W..B. S. thesis. Polvtechnic Institute of Brooklvn. 1951. (17) Wintersteiner. C (1940). R e c ~ i v s ofor review O o i o ~ e rz,. 18s~. aooeprea ~ & n u & wz, isos. n e sented belore the Division of Biological Chemistry at the 122nd Meeting of the AMERICANCHBMICAG SOOIET?, Atlantio City, N. J. R u d y sided by B grant lrom Carl Marks.
The Ultimate Anialysis of Decaborane E. L. SIIVIUIY>, fi. W . DALIS, AND H. A. LIEBHAFSKY Research Laboratory, General Electric Co., Scheneetady, N. Y . formula of decahurane. a t best difficult to establish be1 came of the large number of hydrogen atoms per molecule, has rested largely on Stock and Pohland's original analyses (S), THE
which were of limited precision because of the small amount of material available to them. Although the work of Kasper, Lucht, and Harker on determination of the crystal structure ( 1 ) has recently corroborated the formula, BmH,,, as convincingly as is possible by present x-ray diffraction methods, i t is nevertheless desirable to improve the earlier analytical data. I n principle, the permeability of palladium to hydrogen can be utilized to separate the elements formed in the pyrolysis of decaborane.
Figure 1.
calculations was the average of the first two successive weighings which differed from each other by less than 40 micrograms. To achieve this degree of reproducibility n i t h palladium it was neoessary to establish, by tests on empty tubing, a definite schedule for the heating and n-eighing operations.) About 250 mg. of solid deoaborane (purified by high vacuum, room temperature sublimation) were added, and the tube was attached to thevacuum manifold (Figure 2, stopcock 2) by means of a short length of rubber tubing. After evacuation the rubber tubing was pinched shut, the palladium tube was sealed in the hydraulic press, and the capsule was weighed. The sample weight, corrected to vacuum by estimating the volume of the capsule, was then obtained by difference. A picture of the capsule is shown in Figure 1.
Sealed Palladium Capsule
Preliminary experiments showed that deoaborane in sealed palladium capsules could be oompletely decompasedby heating without producing pressures high enough to rupture the capsule. Consequently, when a weighed sample of decaborane is thus heated under proper experimental conditions, the weight lost is that of the hydrogen in the sample, and the weight of boron can be obtained by difference. EXPERIMENTAL
F'igure 2. Apparatus for Pyrolysis of Deoaborane
The capsules were prepared from 4-inoh lengths of palladium tubing of 0 125 inch inside diameter, with a wall thickness of 0.025 inch. If the metal were cleansed of any oxide layer by heating in vacuo a t 900' C., a vacuum-tight weld could be made, without changing the weight of metal, by pinching shut the end of the tube in a vise mounted an an hydraulic press under a pressure of 5WO pounds per square inch. After one end had been welded, the tube was again heated in vacuo a t 900" C. to constant weight. (The weight used in
The palladium capsule, resting In 8. Flintex (aluminum silicate) boat, wm placed in a Vycor tube (12 inches long, hy 0.5-inch inside diameter) attached to a'vacuum manifold by means of a 14/35 standard taper joint and surrounded by an electric furnace, as shown schematically in Figure 2. The system wm evacuated through stopcock 1, which was closed before the furnace was turned on. The progress of the pyrolysis was followed by observing the rise of pressure accompanying the rise
.
.
_.
.. .
...
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A N A L Y T I C A L CHEMISTRY
in temperature. The last traces of hydrogen were removed, and constancy of weight was attained, by continuous pumping for 2 to 3 hours a t 900" C. That complete removal of hydrogen was achieved by this procedure Fas shown by the fact that the residue from one determination yielded less than 0.001% by n-eight of hydrogen when subjected to vacuum fusion a t 1700" C. RESULTS
Seven runs were performed with the purified decaborane. Two n-ere unsuccessful because the weld sealing the tube burst open before pyrolysis was complete. I n Table I are shown the data for the remaining five runs. The mean of the five atomic ratios of hydrogen to boron is 1.400 with a standard deviation, sm, of 0.002, the standard deviation, s, of the individual runs being 0.004.
Sm =
Table I. Decaborane 232.37 226.29 258.62 239.31 223,42
S
-
l/n
= 0.0°20
Ultimate Analysis of Decaborane Wt. in hIg. Hydrogen 26.73 26.20 29.81 27.64 25.73
Boron 205.64 200,09 228.81 211.67 197.70 Mean (i)=
Atomic Ratio. H/B 1.395 1.406
1.398
1.402
1.397 1.400
4-hour period a t 200' to 210' C., and overnight heating a t 300' C. led to 63% pyrolysis. The considerable amount of decomposition noted in these experiments a t 200" C. is in contrast to Stock's report ( 2 ) that on heating for 48 hours a t 200" C. in an evacuated sealed tube the decomposition still remained very slight. The more rapid decomposition noted in this investigation may have been due either to the rapid removal of hydrogen from thepyrolysis zone (which would imply reversible steps in the decomposition) or to catalytic activity on the part of the palladium. NATURE OF THE PYROLYSIS RESIDUE
In all of the runs there was some evidence of alloying between the boron and the palladium. Shiny patches appeared on the outer surface of some of the capsules, and the palladium, after prolonged heating. became very brittle. In all cases the residue remaining after the pyrolysis consisted of large (0.5 to 1.0 mm.), hard, shiny black granules, many of them imbedded in the wall of the tube. X-ray diffraction patterns of two of the residue8 showed only a few diffuse rings, indicating an amorphous material. The palladium contents of residues 1 and 3 (Table I ) were 4.9 and 4.5 weight per cent, respectively, or approximately one atom of palladium per 200 atoms of boron. The density of residue from the fifth sample was 2.38 grams per ml. ACKNOWLEDGMENT
The authors express their appreciation to A. E. Xewkirk for the sample of purified decaborane, to TV. R. Grams for his cooperation in developing the cold welding procedure, to Miss M. J. Ferguson for the weighings, to R. S.McDonald for the vacuum fusion, and to Mrs. B. Decker for the x-ray diffraction work. LITERATURE CITED
The mean (a), 1,400, corresponds exactly to the formula B,,H,,, and sm is comparable to the level of accuracy (one part per thousand) to 1% hich the atomic weight of boron is reported. In all of the runs hydrogen evolution did not become noticeable until a temperature of about 200" C. had been reached, a t which point a rapid pressure increase was observed. In one experiment 29% of the total hydrogen was evolved during a
(1) Kasper, J.
S.,Lucht, C. M.,and Harker, D., Acta C ~ u s t .3, , 436
(1950). (2) Stock, A,, "Hydrides of Boron and Silicon," p. 83, Ithaca, S . Y . ,
Cornel1 University Press, 1933. (3) Stock, A , , and Pohland, E., Ber. deut. chem. Ges., 62B, 90 (1929). RECEIVED for review Kovember 17, 1952. Accepted December 12, 1952. Presented before the Division of Physical and Inorganic Chemistry at the SOCIETY, Atlantic City, X. J. 122nd Meeting of the - ~ M E R X C CHEsfIcAx. AX
Determination of 1,Z-Propylene Glycol in Ethylene Glycol Mixtures CHARLES B. JORDAN AND VIRGIL 0. HATCH Paint and Chemical Laboratory, Aberdeen Proving Ground, Md. preparations of ethylene glycol, appreciable Ipresent. amounts of 1,Ppropylene glycol and other glycols are often The procedure described in this paper is applicable to ?\'
cOM?ZERCIAL
the determination of l,2-propylene glycol in ethylene glycol mixtures. I t is a quantitative chemical method utilizing standard laboratory equipment. It is based on the formation of iodoform from 1,2-propylene glvcol and the subsequent quantitative determination of iodoform volumetrically. -4nalyses of samples of knoa n composition varying in lj2-propy1ene glycol content from 1 to 100% showed it to be a reliable and accurate procedure. When used in conjunction with other analyses, this procedure is applicable to the analysis of permanent-type antifreeze solutions. Commonly used inhibitors or inorganic impurities do not interfere. It is also applicable to aqueous solutions of glycols without any modifications. Most of the previous work involved the periodate splitting of vicinal glycols (3, 6, 9 ) ) with subsequent determination, by one method or another, of the acetaldehyde or formaldehyde formed by the splitting. Reinke and Luce (12) determined the acetaldehyde in the presence of the formaldehyde by the reaction of the
latter with a slight excess of glycine and reaction of the acetaldehyde with sodium bisulfite. The reaction of some of the acetaldehyde with glycine limits the accuracy of their method. Warshowsky and Elving (14) and Cannon and Jackson (1) used a polarographic analysis of the aldehydes. Mitchell (11) used an optical crystallographic method for measuring the aldehydes. Other analytical methods involving the use of the Beckman spectrophotometer ( 2 ) and the infrared spectrophotometer have been investigated with varying results. All analytical instrumentation methods Tvere more complicated and gave greater errors than the proposed method. The qualitative iodoform reaction was considered applicable to the problem. This method had, a t an early date, been used in the gravimetric determination of acetone in methanol ( 7 ) and ethyl alcohol in water (8). Messinger (IO)and later Houghton ( 5 ) refined the procedure and used it in acetone determinations. Hatcher and Mueller (4)used the procedure to determine acetaldehyde. However, when these applications were used in the analysis of 1,2-propylene glycol in ethylene glycol mixtures, low and inconsistent results were obtained.
