Short description
The nitrogen monoxide and nitrogen dioxide present in a defined sample volume of the gas to be investigated are quantitatively oxidized to nitric acid by a hydrogen peroxide solution acidified with sulphuric acid. The method described covers all nitrogen oxides with the exception of nitrous oxide.*Subsequent conversion with sodium salicylate in a concentrated sulphuric acid medium produces nitrosalicylic acid. The addition of Rochelle salt in a solution of caustic soda produces a yellow anion of nitrosalicylic acid whose concentration is determined photometrically. The total concentration of the nitrogen oxides in the sample of gas is stated in terms of nitrogen dioxide.