XVI. Observations on naphthaline, a peculiar substance resembling a concrete essential oil, which is apparently produced during the decomposition of coal tar, by exposure to a red heat

Abstract

Although the existence, and many of the properties of the substance above-mentioned, have been already noticed in two of the Philosophical Journals of this country, there has not yet appeared, as far as I can discover, any systematic description of the mode by which it may be obtained, or of its relation to the substance from which it is produced; on which account I have been induced to offer to the Royal Society the following observations respecting these points of its history. In the experiments which led, in the present instance, to the detection of the substance in question, it was proposed to effect the decomposition of coal tar by passing its vapour through an ignited iron tube; and, in order to increase to the utmost the extent of the ignited surface, that portion of the tube which was constantly kept up to a red heat, was filled, in the first instance, with a series of hollow iron cy­linders open at both extremities, and successively decreasing in diameter, so as to be included one within another. In other instances these cylinders were removed, and their place supplied by sand, or by pieces of well burnt coke, or by pieces of brick; but it was found that the interstices between the cylinders, or between the particles of sand, &c. were so soon choaked up with carbon from the decomposition of the tar, as to be rendered absolutely impervious to the gas produced during the decomposition; so that it became necessary to pass the vapour of the tar simply through the tube itself.