THE following polyphosphines of formula (C6H5P)n have been reported in the literature: (A) m.p. 149°-150° (refs. 1-9) (B) m.p. 190° (refs. 2 and 3); (C) m.p. 252°-256° (ref. 3); (D) m.p. 260°-285° (ref. 8). Compounds C and D are insoluble in organic solvents and have, presumably, a polymeric structure. The molecular weights of A and B in solution have not been established definitely. Several isopiestic, ebullioscopic and cryoscopic methods have been used by various workers and the following identities have been proposed. A = B = I2; A = I, B = II3; A = B = II8; A = II4,5,9. Recently it has also been shown8 that compounds A and B are tetraphenyl-cyclo-tetraphosphines (II) which differ in both the dissolved and solid states and are stereoconformers.