ISO 6839:1982

Preliminary the temperatures are determined at which solutions of known concentration change on heating from being cloudy to clear and on cooling from being clear to cloudy. Two solutions of the same concentration, one being colder and cloudy and the other being warmer and clear, are placed in a bath, controlled at a preliminary determined temperature and their appearance at temperature equilibrium is noted. The test is repeated at varying temperatures until the clear solution remains clear and cloudy solution cloudy.