Specifies the treatment of a test portion with an excess of carbonate-free sodium hydoxide solution. Elimination of ammonia by boiling. Precipitation of carbon dioxide by an excess of barium chloride. Neutralization with hydrochloric acid solution using thymolphthalein as indicator. Addition of an excess of standard volumetric hydrochloric solution and back-titration with standard volumetric sodium hydroxide solution using methyl red as indicator.