Carius halogen method

The Carius halogen method in analytical chemistry is a method for the quantitative determination of halogens in chemical substances.

In this technique a chemical substance is oxidized with fuming nitric acid under pressure (in a sealed glass tube) in the presence of silver nitrate at a maximum operating temperature of 230 °C. This process forms an insoluble silver halide which precipitates when diluted with water and can be filtrated and weighted.

This chemical test works equally well for the determination of sulfur but without addition of silver nitrate. The sulfuric acid intermediate formed after reaction of sulfur with nitric acid forms insoluble barium sulfate on addition of barium chloride.