Ccxli. the Physico-chemical Behaviour of Lecithin

THE work described in this paper is a continuation of that commenced by H. I. Price and Lewis [1929] and extended by Jones and Lewis [1932]. The former measured, by means of a dynamic method, the surface tension of aqueous dispersions of pure lecithin as a function of PH. It was found that a maximum value of the surface tension occurred at PH 2-6 (approx.) in close agreement with the value of the isoelectric point (PH 2.7) found by Fugii [1923-24] from distribution measurements'. The surface tension falls to a very marked minimum on either side of the maximum referred to. Jones and Lewis investigated the effect of the presence of pure cholesterol in the lecithin dispersion. It was found, using the same surface tension method as H. I. Price and Lewis [1929], that the addition of cholesterol, whilst leaving the general capillary behaviour of lecithin as a function of PH unchanged, nevertheless introduces modifications of the surface tension values. The most important modification is a shift in the position of the maximum in the surface tensionPH curve from PH 2-6 to PH 4. This appears to indicate a corresponding shift in the position of the isoelectric point. But, as pointed out by H. I. Price and Lewis the evidence is not sufficient to make this certain. It is with this point, in the main, that the present work on the electrophoresis of lecithin-cholesterol mixtures deals.