Smokes: Part I.—A study of their behaviour and a method of determining the number of particles they contain

Abstract

Theoretically, at least, systems of solid particles of ultra-microscopic size suspended in a gaseous medium, should show many resemblances to those analogous systems in which the dispersion medium is a liquid. It might be expected that the well-known characteristics of colloidal matter, such as coagulation, peptisation, protective action, gel formation, etc., would have their counterpart in the simpler gaseous systems. Should this prove to be the case much information should accrue from a study of these aerosols in which many complicating factors are absent. Now although the movement of individual particles (not necessarily of ultra-microscopic size), suspended in gases, has been investigated very carefully, and the study has led to experimental and theoretical results of the greatest importance, for instance, the measurement of the unit electronic charge (de Broglie (1), Ehrenhaft (2), Millikan (3)), little attention has been paid to the question of the stability of gaseous systems and the changes they undergo, and no attempt has been made to compare the properties of solid colloidal suspensions in the gaseous and liquid states. From this point of view, dusts, fumes, smokes, and clouds are colloidal systems possessing varying degrees of stability, dispersion, and concentration, which sometimes flocculate or precipitate rapidly, sometimes remain highly disperse for long periods of time, and correspond to the many types of liquid systems which vary from coarse suspensions to fine-textured sols.