Within the past dozen years skilled investigators in several laboratories have achieved considerable success in detecting distinct crystalline modifications of both pure and mixed sodium soaps. Some measure of the resulting clarification of knowledge pertaining to soap crystals is general acceptance of the Thiessen and Stauff alpha sodium stearate as a hemihydrate with monoclinic crystal symmetry established by Buerger and his coworkers. Unfortunately, however, such wide agreement does not extend over proposals for at least nine other crystalline phases said to exist at room temperature and atmospheric pressure. This present investigation had been undertaken with the hope not of solving the multitudinous problems pertaining to soap structures, but more simply of demonstrating the possibilities for applying refined techniques of water vapor sorption and desorption in conjunction with x-ray diffraction measurements to these problems.