English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

It has long been known that in the immediate vicinity of the critical state, many substances exhibit a strong and characteristic opalescence. In recent years, the phenomenon has been studied by Travers and Usher in the case of carefully purified CS2, SO2, and ether, by S. Young, by F. B. Young in the case of ether, and in a quantitative manner by Kammerlingh Onnes and Keesom in the case of ethylene. An explanation of the phenomenon on thermodynamic principles as due to the accidental deviations of density arising in the substance was put forward by Smoluchowski. He obtained an expression for the mean fluctuation of density in terms of the compressibility of the substance, and later, Einstein applied Maxwell’s equations of the electromagnetic field to obtain an expression for the intensity of the light scattered in consequence of such deviations of density. He showed that the fraction α of the incident energy scattered in the substance per unit volume is 8 π 3/27 RT β ( μ 2 – 1)2 ( μ 2 + 2)2/N λ 4 (1) In this, R and N are the gas constant and Avogadro’s number per grammolecule, β is the isothermal compressibility of the substance, μ is the refractive index and λ is the wave-length of the incident light. Keesom tested this formula over a range of 2·35° above the critical point of ethylene and found good agreement except very close to the critical point.

The molecular scattering of light in vapours and in liquids and its relation to the opalescence observed in the critical state