ISO 1897-4:1977

Phenol, o-cresol, m-cresol, p-cresol, cresylic acid and xylenols for industrial use — Methods of test — Part 4: Visual test for impurities insoluble in sodium hydroxide solution (Excluding cresylic acid and xylenols)

Simple empirical test of no great precision. The principle consists in shaking a test portion with sodium hydroxide solution under specified conditions and assessment of any insoluble matter present in suspension in the mixture by comparison either with an agreed standard turbidimetric solution or with sodium hydroxide solution. The comparison of the turbidity of the two solutions is carried out by viewing vertically and with the electric lamp equipped with a ligth blue dayligth-bulb switched on.