The density of monomeric vinyl acetate has been determined over a range of temperature. The parachor and Ramsay and Shield's constant have been obtained for the monomer and some liquid polymers. On the assumption that a liquid polymer may be considered as a solution of a dimer in the monomer, parachors were calculated from the mixture law.If Staudinger's formula be assumed for the dimer the calculated and observed parachors agree to within 1%.