E *99 3 
XVI. Observations on Naphthaline, a peculiar substance re- 
sembling a concrete essential oil , which is apparently produced 
during the decomposition of coal tar, by exposure to a red heat. 
By J. Kidd, M. D. Professor of Chemistry, Oxford. Com- 
municated by W. H. Wollaston, M. D. F. R. S. 
Read March 8, 1821. 
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 cy- 
linders open at both extremities, and successively decreasing 
in diameter, so as to be included one within another. In 
* Thomson’s Annals of Philosophy, January, 1820, page 74; and Mr. Brande’s 
Quarterly Journal, January, 1820, page 287. 
