Qualities of Valency

Abstract

IN his article in Science of July 22 (see NATURE, September 15, p. 101), and in his address to Sections A and B of the British Association at Edinburgh, Dr. Irving Langmuir asks us to believe that the sodium and chlorine atoms in sodium chloride are never united by a chemical bond, i.e. that the salt is ionised in its synthesis and remains ionised under all conditions. This appears to be a denial of the existence of NaCl molecules, yet such molecules exist in the state of vapour at cir. 2000° C. Are we, then, to suppose that sodium and chlorine ions are held together at this temperature by electrostatic attraction only? Difficult to reconcile with this idea, if it is applied to salts in general, are the phenomena of aqueous solutions of some salts—mercuric salts, for example—which are attributed to imperfect ionisation and the increase of specific conductivity of imperfect electrolytes on dilution. These difficulties, if they are real, might be removed by reverting to the idea of electrons acting as binding material in compounds capable of ionisation instead of supposing that they have passed completely and irreversibly over from the positive to the negative atom and have been incorporated into the sheath of the latter. This is not to confuse electrovalency with covalency, for the essential difference between the two kinds of valency is still that electrons are transferable in the one case and not in the other.