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IAYDCSTRIALB S D ENGINEERING CHEMISTRY
capacity, we find that as the oxygen content is decreased the lower limit of inflammability rises very fast, as shown in Figures 3 and 4. The data here presented offer an opportunity to test the law of mixtures of LeChatelier, who stated that a mixture of any two limit mixtures (both upper or b o t h l o w e r ) will itself be a limit mixture. This law has been found to hold for most substances although certain exceptions h a v e b e e n obs e r ~ e d .With ~ the a1co h 01-a ce tone mixtures in air this law holds to within the experimental Per cent oxygen in gas before addition of solvent error. Figure &Explosion Limit of Methanol in The effect of the C O 2 - a and N1-01Mixtures a n t i k n o c k compounds, lead tetraethyl and diethyl selenide, was tested by mixing up to 1 per cent of the compounds with the acetone. N o change in the lower limit of inflammation was noted. The writers’ results in air are compared with certain others in the literature in Table I. Most of the results give narrower limits than those of this 9
Vol. 17, NO. 6
paper. The writers believe this is because narrower tubes and less positive methods of ignition were used. The low results of Wheeler and Whitaker for acetone were criticized by White on the ground that the analysis of the vapor mixture was . faulty. Table I Lower limit Per cent 2.9 2.6 2.16 2.88 3.65 2.6 6.0 7.2 7.06 6.1
Upper limit Per cent
... ...
INVESTIGATOR Acetone
9.7 12.40 8.92 10.4
Mefhnnol LeChatelier and Boudouardlo Kubierschkyll 36.5(at 60’ C.) Whites This paper
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16
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Summary
1-The limits of inflammability of acetone and methanol have been determined in mixtures of oxygen and nitrogen, and of oxygen and carbon dioxide. 2-The law of mixtures of LeChatelier has been found to hold for the mixtures studied. 3-Lead tetraethyl and diethyl selenide have no effect on the lower limit mixture of acetone. Compt. rend., 136, 1510 (1898). Z . angew. Chem., 14, 129 (1901). 11 J . Chcm. SOC.(London), 111, 267 (191i). 13 Ibid., 116, 1462 (1919). 1 4 Z . Elekfrochem., SO, 29 (1924). 10
11
White, J . Chem. SOC.(London), 131, 2561 (1922).
The Seed Hairs of the Milkweed’ By A. W. Schorger C. F. BVRGQSS LABORATORIES, MADISON, U’IS.
OTTON appears to be unique among seed hairs and other vegetable fibers in its freedom from incrusting materials. The seed hairs of the milkweed are, like those of cotton, unicellular and almost colorless, but differ in being lignified. On account of their luster they are classified with the vegetable silks, but brittleness and slight felting properties have prevented them from becoming of more than minor importance in the textile industry. Aside from the observation that the fibers are “somewhat lignified,”2 no information on their chemical composition appears to be available. I n fact, the fibers are as highly lignified as those of hardwoods and furthqr resemble them in having a high pentosan content. Since the fibers have only a yellowish tinge, it may be assumed that lignin in nature is colorless or only slightly colored. Most lignified tissues are highly colored through the infiltration of extraneous substances. Digestion of the milkweed fibers with 2 per cent ammonia in the cold gives a greenish yellow extract, but their yellowish tinge is accentuated rather than decreased by the treatment. The fibers of the species (Ascelpias ~yriaca)~ examined were collected in October. Their composition is shown in the following table: Received April 25, 1925 Matthews, “The Textile Fibers,” 1934, p. 668. 8 The writer wishes t o express his thanks to C. E. Allen for the identiBcation. 1 2
Lignin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pentosans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Per cent
........
22.18 34.55 1.05
Soluble in alcohol ........ Soluble in ether.. ................................. Ash ..............................................
4.28 1.36 0.97
Lignin was determined with 72 per cent sulfuric acid.‘ On adding the acid the fibers became a dark green. The residual dark brown lignin became yellowish on chlorination and gave the characteristic lignin color reaction with sodium sulfite solution. Cellulose was determined by chlorination in the usual way. At the point where the lignin disappeared the cellulose became gelatinous and was very difficult to wash. I n this respect it differs from wood cellulose. Carbohydrates were determined as follows: The raw fibers were extracted with 2 per cent ammonia, then boiled gently with 2 per cent sulfuric acid for 2 to 4 hours. The sirup, obtained in the usual way, gave a positive test for xylose, typical crystals of cadmium bromoxylonate being readily obtained. The residue from the above hydrolysis was hydrolyzed with 72 per cent sulfuric acid. The resulting sirup gave glucosazone, m. p. 203” C. Careful examination of the sirups gave negative results for arabinose, mannose, and galactose. 4
Mahood and Cable, THISJOURNAL, 14, 933 (1922).
