in water byproducts: H2S; addn. of aq. (NH4)2S soln. to ground S; slow addn. of NaCN soln. (half amt.); heating to 90°C; addn. of the rest;; expelling H2S by CO2; concentrating by heating to 135°C; cooling down; crystn. of Na2CO3; concentrating filtrate by heating to 145-150°C;;
