An electrophotometric method has been worked out for the determination of magnesium in cast iron using titan yellow as indicator.Briefly,the method consists of dissolving the sample in dilute sulphuric acid,separating iron and other metals such as copper and nickel by electrolysis with mercury cathode and precipitating manganese from ammoniacal solution with ammonium persulfate.Ammoniwn salt,silica,and traces of alumina.ase thenremoved.Finally,the prepared titan yellow reagent is added to the solutionand the magnesium content determined from the electrophotometric reading.The time required for each determination is approXimately 5 hours.