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.