ABSTRACT

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Mellon Institute and are tike average results of a number of tests on each type of material. For convenience in calculating heat losses for various mean temperature conditions, the conductivity of a few of these insulations is given in Figure 3. The thickness of insulation required to prevent sweating on the above air duct for any of the insulations whose conductivities are included will be found to be directly proportional to conductivities of the insulations chosen and the insulation used in calculating the table . . In conclusion, the author wishes to express his thanks to R. W. Ortmiller who determined the conductivities of the various insulations. Literature Cited(1) Griffith and Davis, Natl. Phys. Lab., Special Kept. 9 (1922).(2) Heilman, R, H.t Trans. Am. Soc. Meek. EngrsFuels Steam Power, 51, 257 (1929).(3) HotteL H. C" Ibid., 53(19b), 265 (1931).

Substantially all of the chemical and physical evidence concerning the nature of rubber is consistent with the chemical formula (C5H8)x, and this is the generally accepted formula for “rubber hydrocarbon.” An examination of the evidence discloses, however, that the above formula is not the only one which is consistent with this evidence. The difficulty of establishing beyond question the chemical composition of rubber hydrocarbon has been due largely to the lack of efficient physical methods for fractionating the hydrocarbon, of proving that the final fractions are one-component systems, and of chemically identifying these fractions. If, as seems not improbable, rubber hydrocarbon is a mixture of closely related hydrocarbons not all of which can be represented by the formula (C5H8)x, no single method of fractionation can be relied upon to separate this mixture into its constituents. The only methods heretofore available for this purpose have been those based upon extraction with different liquids and fractional precipitation. One of the most powerful methods for fractionating a mixture of hydrocarbons is systematic crystallization, and the purpose of this investigation was to develop a technic for applying this method to rubber.

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