Parachor

parachor [′par·ə‚kȯr]

(physics)

The molecular weight of a liquid times the fourth root of its surface tension, divided by the difference between the density of the liquid and the density of the vapor in equilibrium with it; essentially constant over wide ranges of temperature.

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Parachor 

the quantity that may reflect certain physical properties of substances, especially nonassociated organic liquids. The parachor was first proposed by the British scientist S. Sugden in 1924. It is calculated according to the formula P = Mσ^¼/(ρ₁ — ρ₂), where M is the molecular mass of the substance, σ is the surface tension, and ρ₁ and ρ₂ are the densities of the liquid and saturated vapor, respectively.

The parachor is an additive quantity; that is, a compound’s net parachor is the algebraic sum of the parachors of the compound’s constituent parts—individual atoms, atomic groups, or interatomic bonds. The quantities that are associated with the subunits of a compound can be obtained from handbooks. The parachor provides an approximate value for the surface tension of a liquid and is also one of the parameters used to determine the structure of organic compounds.

REFERENCES

Bretsznajder, S. Svoistva gazov i zhidkostei. Moscow-Leningrad, 1966. (Translated from Polish.)
Fizicheskie metody organicheskoi khimii, vol. 1. Edited by A. Weissberger. Moscow, 1950. Page 215. (Translated from English.)