Estimation of Halogens -- Carius Method

Halogens are estimated by a variant of the same Carius method used for sulphur: a known mass of the organic compound is heated, sealed in a Carius tube, together with BOTH fuming nitric acid AND silver nitrate. As before, the carbon, hydrogen and any sulphur present are oxidised away (to CO2, H2O and SO2 respectively), while this time the halogen present combines directly with the added silver nitrate to precipitate as the corresponding silver halide (AgCl, AgBr or AgI).

Practically: the weighed sample, fuming nitric acid and silver nitrate are sealed together inside a Carius tube, which is placed in a protective iron tube and heated for roughly five hours at 530-540 K. After cooling, a small vent hole releases any built-up gas pressure, the tube is then broken open, and the resulting silver-halide precipitate is filtered off, washed, dried and weighed. …