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ANALYTICAL EDITION
ment in the cases of water and benzene, and water and carbon tetrachloride. Unfortunately, however, the results were not consistent or reproducible, presumably because of the unusual sensitivity of water surfaces to the presence of foreign materials. As there are few pairs of immiscible liquids of practical interest that do not include water as one of the liquids, the study of this displacement test was not pursued further. It is possible, however, that in porous media other than paper
Vol. 6, No. 2
have been directed entirely t o checking the validity of the theory presented. Such a check cannot be complete, and must be supported by the mutual consistency of results obtained in further work. Assuming the theory to be sufficiently accurate to justify its use in interpreting data, i t permits the determination of relative values of penetration tension in paper and further studies may show it to be applicable to textiles and thin wood sections. The experimental procedure reauires merelv the measurement of the rate of rise of the held i n a ;esse1 c l o s e d t o i r e v e n t evaporation. B y plotting the observed liquid height, h, against time, t, the rate of rise, dhldt, may be evaluated Eraphi-
portional to y. q (the ratio of penetration tension to viscosity), the slope being a function of.thc distribution of pore sizes in the medium. Yalues of the viicosity of the liquid 0 0.01 0.02 0.03 0.04 0.05 niultiplied by the slope of the plot of FIGURE6. PIIOTOWCROGRIPIIS OF PAPEH USED is TESTS dh, dt versus h give, therefore, relative values of penetration teiision for liquids results would be olnained of sufficient constancy to make the tested with a given mediuin. Comparison of the values of displacement test a useful method of determiniug adhesion penetration tension for a single liquid and several different tension. The theory for such cases may be readily developed mydia can be made only when it i.5 ki1on.n that the media are along the lines indicated. identical in pore structure or in the distribution of pore sizes, or when tests can be macle with a reference liquid which is SIX\l.\RY known to have a zero contact angle with all the media to be The theory presented above for capillary penetration into tested. While the method of analysis given applies primarily to fibrous materials is an extension of that developed by Washburn for uniform capillaries. It has been shown that this fibrous materials in which the rate of rise may be observed simpleracase may be conveniently studied in terms of the directly, i t may be used to interpret data on the rate of penerelation between rate of penetration and the reciprocal of tration into porous systems for which only the rate of weight the distance penetrated, and that in this way both the radius increase by penetration is known, provided the mean crossof the capillary and the penetration tension may be computed sectional area of pore space is known, so that the linear rate of from the test data. The method is of value in that the penetration can be calculated. measurement is made under dynamic conditions. LITERATURE CITED It has been shown that the treatment for penetration into a (1) Bartell, F. E., and Osterhof, H. J., IND.ENQ.CHEM.,19, 1277 porous medium is similar to that for a uniform capillary, save (1927). that consideration must be given to the fact that the variation (2) Bosanquet, C. H., Phil. Mag., [6], 45, 525 (1921). in pore size causes the resistance to viscous flow of each (3) Haller, W., Kolloid-Z., 54, 9 (1931). “Handbook of Chemistry and Physics,” 16th channel to be similar to that of a number of capillaries in (4) Hodgman-Lange, ed., Chemical Rubber Publishing Co., 1931. series. The final expression therefore involves quantities (5) McLean, D. A , , and Kohman, G. T., paper to be published in whose values depend on the distribution of pore sizes. The EZectricaZ Engineering. ENG.CHEM.,21, 1237 (1929). general character of these quantities has been indicated b y (6) McMillan, E. L., IND. H. J., and Bartell, F. E., J . Phys. Chem., 34, 1399 evaluating them for the case of a uniform distribution of pore (7) Osterhof, (1930). sizes. (8) Shewhart, W. A., “Economic Control of Quality of Manufactured Data have been presented on the penetration of six organic Product,” Van Nostrand, 1931. fluids into strips of filter paper. It has been shown t h a t these (9) Washburn, E. W., Phys. Rev., 17, 273 (1921). data agree with the theory in character. These experiments RECEIVED September 2, 1933.
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FIRE-HAZARD TESTSWITH CIGARETS.Tests have been conducted in the fire-resistance section of the Bureau of Standards t o determine the fire hazard of discarded lighted cigarets. The efficacy of certain modifications, such as slow-burning paper and the application of tips over one end, was also investigated. The burning cigarets were placed on representative specimens of grass and forest floor materials. Under the conditions of the test, with the most favorable drafts and with relative humidities in the range 25 to 50 per cent, fires were caused on the average by 9 out of 10 lighted halflength untipped fast-burning cigarets discarded on grass, forest litter, or duff. The percentage of cases resulting in fires in-
creased somewhat with decrease in relative humidity. The fire hazard of the slow-burning cigaret was much lower than for the fast-burning type. In the former the glow will not progress appreciably after the cigaret is discarded, while the latter will continue t o glow until fully consumed. The fire hazard of discarded lighted cigarets can be decreased by applying tips of cigaret paper. In tests with half-length fastburning cigarets having tips 1 inch long of paper similar to that used on this type of cigaret, 4 fires occurred on the average for every 10 trials. With tips of the same length made of the paper used on slow-burning cigarets, the occurrence of fire in the exposed materials was reduced t o 1 out of 4 trials.
