Cool, add ca 200 ml H2O, cool 25 Celsius, add 25 ml of the sulfide or thiosulfate solution, and mix to precipitate Hg. Add few Zn granules to prevent bumping, tilt flask, and add layer of NaOH without agitation. (For each 10 ml H2SO4 used, or its equivalent in diluted H2SO4, add 15 g solid NaOH or enough solution to make contents strongly alkaline.) (Thiosulfate or sulfide solution may be mixed with NaOH solution before addition to flask.) Immediately connect flask to distilling bulb on condenser, and, with tip of condenser immersed in standard acid and 5-7 drops indicator in receiver, rotate flask to mix contents thoroughly: then heat until all NH3 has distilled (more than 150 ml distillate). Remove receiver, wash tip of condenser, and titrate excess standard acid in distillate with standard NaOH solution. Correct for blank determination on reagents.