1956 年 1956 巻 22 号 p. 1175-1178
When plaster of Paris is mixed with water in order to make a plaster mold, there takes place a phenomenon so called “segregation of water” in the mold. This phenomenon is one of the causes of the change of dimension of plaster mold. So called “Segregation” is caused by the excess water during setting of plaster. It can be explained exactly by means of measuring the water content, the micro-photo graph, and the thermal expansion of different parts of a mold. We have studied how to prevent the phenomenon and obtained some effective results.