The quantitative analysis technique of dihydrate and hemihydrate gypsum in cement was studied by thermogravimetry. DTG peaks attributed to the dehydration of dihydrate and hemihydrate gypsum were sufficiently separated by using the lidded sample cell with a micro-hole less than about 30μm in diameter. So the quantitative analysis became easily possible. The reasons of these phenomena were that the water pressure in the cell became higher caused by the dehydration of calcium sulfates and so the equilibrium of the dehydration shifted to higher temperature zone. The minimum limit of quantitative analysis of this technique was about 0.2% for dihydrate gypsum. The precision of this technique was not influenced by the type and fineness of calcium sulfates.
