The density p of N(p-ti-heptyloxy benzylidene) p-n-butyl aniline (HYBBA) is measured as a function oftemperature from the isotropic liquid to the smectic-G phase. The compound is tetramorphic exhibiting three smectic phases s,, s,-, s,., and a nematic phase. The density changes across the phase transformations and the calculated thermal expansion coefficient confirm the order of the S,-Sc, S,-Nand N-Itransitions as first-order, with Sc-S, transition as weakly first or second-order. The first-order S,-N phase transformation in this compound, which is weakly polar, is in agreement with McMillan's theoretical predictions, and is different from other polar compounds.