ISO 2222:1972

The specified method is applicable when the required limit is not greater than 0,1 % and not less than 0,001 %. If the required limit lies outside that range, the mass of the test portion should be changed. The principle ot the test consists in comparison of the turbidity obtained by the addition of barium chloride solution to a solution of the sample, in the presence of hydrochloric acid, with that similarly produced from a sulphate solution of known concentration.