Sankyo Kasei Co., Ltd.

Yoshio Aoyama

Kannosuke Maeda

Disclosed is a process for preparing crystals of anhydrous sodium sulfide, the process being characterized in that the process comprises the steps of heating crystals of polyhydrate of sodium sulfide under a pressure of about 500 torr or less at a temperature varying not more than .+-.about 10.degree. C. from the phase transition point between polyhydrate crystals and monohydrate crystals of sodium sulfide for about 2 hours or longer and further heating the monohydrate under atmospheric or reduced pressure at about 90.degree. to about 200.degree. C. for about 2 hours or longer.

Process for preparing crystals of anhydrous sodium sulfide

Disclosed is a process for preparing crystals of anhydrous sodium sulfide, the process being characterized in that the process comprises the steps of heating a water-containing non-crystalline sodium sulfide at a temperature of about 30.degree. to about 89.degree. C. under a pressure of about 500 torr or less for about 2 hours or longer in a first-stage heating step and further heating the sodium sulfide at a temperature of about 90.degree. to about 200.degree. C. under atmospheric pressure or reduced pressure for about 2 hours or longer in a second-stage heating step.

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Kyoto, Japan

Yoshio Aoyama