By adopting a simple notion of the volume of a molecule it has been possible to produce an empirical correction factor for the Stokes equation to enable one to apply it to molecules down to two angstroms in radius.

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. Can. J. Chem. 53,2965Chem. 53, (1975. The partial molal volumes ii of nonpolar organic molecules (i.e. those having more than three aliphatic carbon atoms per polar hydroxyl, ether, amine, amide, or urea group) in water at 25 "Care given by their van der Waals volumes v, plus the additional empty volume provided by an enclosing shell 0.53 A thick. An equation relates fi to v,. More polar compounds (i.e. those having fewer than two or three aliphatic carbon atoms per polar group) have ii smaller than calculated by the equation; the shrinkage in fi from that computed is linearly related to th'e fraction of the total surface area of the molecule occupied by the polar group. JOHN T. EDWARD et PATRICK G. FARRELL. Can. J. Chem. 53,2965Chem. 53, (1975. Les volumes molaires partiels ii de compos6s organiques non-polaires (i.e. ceux contenant plus que trois atomes de carbone aliphatique pour chaque groupement hydroxyle, ether, amine, amide ou urk) dans l'eau a 25 "C sont Cgaux a leurs volumes van der Waals v, avec l'increment du volume vide donne par une enveloppe d'une epaisseur de 0.53 A. La relation entre fi et v, est contenue dans une equation. Les composes plus polaires (ayant moins d'atomes de carbone aliphatique) ont ii plus petit; la diminution fractionnelle en fiest li& ala proportion de la surface molkulaire occupke par le groupement polaire.

The partial molar volumes of a number of ethers, ketones, esters and alcohols in water at 25.0"C have been determined and related to their van der Waals volumes by one of two equations, depending on whether the molecules are spherical or cylindrical in shape. Allowance has been made for the void volume associated with each molecule and the results imply that calculated volumes must be reduced by a constant amount for each carbonyl or hydroxyl group present, owing to hydrogen bonding to water. No such reduction in the calculated volume is required for the oxygen atom of an ether. It is shown for diols that the amount of void volume per additional -C&-group remains constant for straight-chain compounds (ix., cylinders), whereas for spherical molecules the amount of void volume decreases with increase in the number of carbon atoms, as predicted.

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