This International Standard specifies an alizarin sulphonate photometric method for the determination of soluble zirconium in magnesium alloys containing zirconium as an alloying element. Rare earths, thorium and silver do not interfere. The method is applicable to alloys having zirconium contents between 0,1 and 1,0 % (m/m). The method does not apply completely to the special case of alloys containing lead and/or bismuth, for which it should be modified as described in the annex. NOTE — Hafnium which is normally present in conjunction with zirconium (up to 1 % zirconium) will be determined with zirconium.