The Density of Chlorine

Abstract

THE article on the density of chlorine, bromine, and iodine at high temperatures which appeared in NATURE, vol. xxi. p. 461, places before your readers in the clearest manner the present condition of this important question. The conclusion hinted at in the closing sentences of the article, viz. that these gases are under certain circumstances decomposed, is however scarcely, warranted. Dr. Armstrong thinks that these substances may be more liable to decomposition when in a nascent state. It is generally supposed that in this condition the atoms of a substance are separate, having as yet had no opportunity of selecting a mate for their further career; if therefore we could observe the density of a gas in the nascent state, we should find that it was only half the theoretical density. In the case of chlorine evolved from platinum chloride at a high temperature we may readily imagine the emerging atom, set in rapid movement by the great heat, to be unable at any time to join with another to form a molecule; we should thus have the nascent state maintained, if I may be allowed the expression, as long as the temperature was high enough. It is further possible that there may be a wide interval between the temperature at which chlorine gas is molecular and that at which it is entirely atomic, and that in this interval a certain proportion of the gas varying with the temperature is resolved into its atoms, the rest remaining molecular. The gas would then have a density intermediate between the theoretical density 2.45 and its half, 1.23, a density in fact corresponding with that obtained in Meyer's experiments.