ABSTRACT

In the opening remarks of his 1869 Bakerian lecture Andrews quoted from an earlier communication in 1863 (which was published in the 3rd edition of Miller's Chemical Physics, p. 328). In it he said:

This phenomenon, subsequently termed critical opalescence, attracted the attention of a number of experimentalists in the late nineteenth and early twentieth centuries. Avenarius (1874) described the experimental results in great detail noting striking changes of colour and the onset of turbidity in carbon disulfide, ether, carbon dichloride and acetone. Altschul (1893), Wesendonck (1894), Travers and Usher (1906) and Young (1906) investigated the phenomenon more precisely, although none of them refers to the observations of Andrews or Avenarius. It is indeed striking to observe a colourless transparent fluid suddenly becoming opaque and changing colour in a narrow band of temperatures around Tc. As the temperature is lowered, the fluid splits into colourless liquid and gas with a meniscus separating them. In addition to the fluids mentioned by Avenarius, the phenomenon was observed for sulfur dioxide, pentane, isopentane, hexane and octane, so that it could reasonably be regarded as universal. Doubts were expressed as to whether the simple van der Waals theory was capable of accounting for the observations.