in a method of preparing sodium monosulfide by means of reacting sodium and sulfur under protective gas , the entire sodium determined for reaction is placed in a receiver in a first stage , preheated to temperatures of 100 °- 150 ° c ., sulfur is gradually added in the required amount of the material in the receiver under intensive mixing , whereby the temperature of the reaction mixture is maintained at 120 °- 250 ° c ., and in a second stage the formed initial product is allowed to react under continuation of the mixing at 250 °- 480 ° c ., until a na 2 s content of at least 95 % by weight has been attained .