June, 1925 T-\7D17LqTRIAL AAVD ENGINEERING CHEMISTRY 64 1

Effect of Nitrogen and Carbon Dioxide Dilutions on Explosion- Limits of Acetone and Methanol

and Their Mixtures'.' By H. Crouch and E. K. Carver

EASTMAN KODAK Co., ROCHESTER, N. Y.

N CONSIDERING the safety precautions in certain solvent recovery processes, it became desirable to know the explosion limits of acetone and methanol vapors in

air and the effect of changes in oxygen content on them. Al- though the literature3 contains about one hundred and fifty papers on gaseous explosions, none of these contain the re- quired information.

It has been clearly shown that the most important factors affecting the explosion limits are the mode of ignition4 and the

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Man o m e fer and Source of

Gas

Figure 1

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dimensions of the explosion vessel.6 The small varia- tions of temperature and pressure which occur in the laboratory have proved to be negligiblee6 The direc- tion in which the flame is propagated is important if the vessel is tubular. How- ever, for both theoretical and practical purposes, the ideal form of vessel would be an infinitely large cham- ber in which an actual flame is started.

The writers used a 2-liter balloon flask (Figure 1) and ignited the mixtures with a bit of nitrocotton, which in turn was ignited by a spark from a Ford induction coil. Control experiments showed that the same explosion limit was obtained for acetone in air with this vessel as with a 13-liter flask, and that so long as the nitrocotton gave a flame about 2.5 cm. (1 inch ) i n d i a m e t e r , the a m o u n t used had little effect.

The mode of filling was as follows: The flask was evacuhted to about 1 mm.

1 Received March 12, 1925, Presented before the Division of Industrial and Engineering Chem- istry a t the 69th Meeting of the American Chemical Society, Balti- more. Md.. April 6 to 10. 1925. . . .

* Communication No. 230 of the Research Laboratory of the East- man Kodak Company.

* Katz and Rosecrans, University of Illinois, Bull. 19, No. 50 (1922), give an almost complete bibliography of papers up to 1921; Berl and Fischer, Z . Eleklvochern., S O , 29 (19241, give a bibliography of eighty-nine papers.

4 Wheeler, J . Chem. SOC. (London), 137, 14 (1925). 6 White, I b i d . , 121, 1244 (1922). @ Berl and Fisher, loc. cit . , determined the temperature coefficients for

the explosion limits of most solvents. Mason and Wheeler, J . Chem. SOL. (London), llS, 45 (1918), observed the temperature and pressure coefficients of the explosion limits of methane-air mixtures.

of mercury and the required amount of oxygen was ad- mitted from a cylinder. A 0.2-cc. pipet, A , containing the required volume of acetone or other liquid was then inserted in the rubber tubing above the glass stopcock, B, and connected with the source of nitro- gen or carbon diox- ide, which was ad- mitted up to atmos- pheric pressure. ,4 few glass beads in the bottom served to mix the gases when the flask was shaken.

When the mixture was just above or just below the explo- sion limit, it was a little difficult to de- termine whether or not the flame would p r o p a g a t e itself. The phenomenon usually observed

Per cent oxygen in gas before addition of solvent Figure 2-Explosion L imi t s of Acetone and

Methanol Mixtures in Air Containing Various Percentages of Oxygen

was the enlargement of the flame of the nitrocotton up to the point a t which it filled the flask, but as this whole enlargement took place over a range of, say, 0.15 per cent for acetone a t the lower limit, the errors involved were not large.

In Figure 2 are shown curves inclosing the areas of explosi- bilitv for acetone and methanol in mixtures of oxygen and nitrogen. It will be noted that the lower limit of explosibility is hardly changed by decreasing the oxygen content- i. e., the excess oxy- gen seems to act chiefly as a diluent. This same phenom- enon has been ob- served with gases by Terres,' and a similar one by Pay- man,* who found that with methane- oxygen-n i t rogen mixtures any oxy- gen in excess of that required for com- plete combus t ion

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Per cent oxygen in gas before addition of solvent Figure 3-Explosion L imi t of Acetone in

C a - G , Nz-Oa, and COP-Nz-0, Mixtures

had almost the same effect as nitrogen in reducing the speed with which the flame would travel.

With carbon dioxide, however, because of its higher heat 7 J . Gasbel., 65, 785 (1921). * Payman, J . Chem. SOC. (London), 117, 48 (1920).

642 IAYDCSTRIAL B S D ENGINEERING CHEMISTRY Vol. 17, NO. 6

capacity, we find that as the oxygen content is decreased the lower limit of inflammability rises very fast, as shown in Fig- ures 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 ( b o t h u p p e r o r b o t h lower ) will itself be a limit mixture. This law has been found to hold for most sub- stances although certain exceptions h a v e been ob- s e r ~ e d . ~ With the a1 co h 01-a ce tone mixtures in air this law holds to within the experimental error. Per cent oxygen in gas before addition of solvent

Figure &Explosion L imi t of Methanol i n CO2-a and N1-01 Mixtures The effect of the

a n t i k n o c k com- pounds, 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 White, J . Chem. SOC. (London), 131, 2561 (1922).

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 Upper limit limit

Per cent Per cent INVESTIGATOR Acetone

2 . 9 2 . 6 2 . 1 6 2 . 8 8 3 . 6 5 2 . 6

... . . . 9 . 7

12.40 8 . 9 2

10 .4 Mefhnnol

6 . 0 . . . LeChatelier and Boudouardlo 7 . 2 16 Kubierschkyll 7.06 3 6 . 5 ( a t

60’ C.) Whites 6 . 1 . . . This paper

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.

10 Compt. rend., 136, 1510 (1898). 11 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).

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 classi- fied with the vegetable silks, but brittleness and slight felt- ing 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 ap- pears to be available. In fact, the fibers are as highly lig- nified 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 sub- stances. 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:

1 Received April 25, 1925 2 Matthews, “The Textile Fibers,” 1934, p. 668. 8 The writer wishes to express his thanks to C. E. Allen for the identi-

Bcation.

Per cent Lignin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 . 1 8 Pentosans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34.55

. . . . . . . . 1.05

Soluble in alcohol . . . . . . . . 4 . 2 8 Soluble in ether.. ................................. 1.36 Ash .............................................. 0 . 9 7

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. In 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 hy- drolyzed 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, THIS JOURNAL, 14, 933 (1922).