The number of compounds of phosphorus hitherto examined refractometrically is small, the only investigator of an homologous series of such substances being Kowalewski (1). The present work has been undertaken with a view to extension of our knowledge in this field, particularly with respect to types of compounds and their number.The first to determine the atomic refractivity of phosphorus was Haagen (2), who from measurements on phosphorus trichloride with C light, deduced the value 14.93, in terms of the Gladstone-Dale (3) formula. For the Fraunhofer lines A and H, Gladstone (4) gave the values 18.3 and 21.3, respectively, for the atomic refractivity of fused phosphorus. Zecchini (5) calculated the atomic refractivity of phosphorus in terms both of the Gladstone-Dale and of the Lorenz-Lorentz (6) formulas in eight of its liquid compounds. He found that the value of the Lorenz-Lorentz atomic re-
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