ISO 4279:1977

Applicable to products having Na contents, expressed as Na2 O, of equal to or more than 0.05 % (m/m). The principle bases on fusion, at a controlled temperature, of a test portion with a mixture of lithium carbonate and boric oxide or with a mixture of lithium carbonate and lithium tetraborate in a platinum or platinum-gold alloy crucible. Extraction of the fused mass with hydeochloric acid solution. Aspiration of the solution into a flame and photometric measurement of the intensity of the radiation emitted at 589 nm.