Sulfur sticks

Sulfur sticks are tools used in industrial ammonia refrigeration systems to detect minor ammonia leaks. A sulfur stick is made from a wick which contains particles of sulfur. The sulfur stick is lit and smolders, and the color of the sulfur smoke is used to find the leak. When there is no ammonia present, the smoke is colorless, but the combination of sulfur and ammonia vapors produce a white fog.