Specifies a spectrophotometric method for the determination of the phosphorus content of iron and steel. The method is applicable to the determination of phosphorus contents between 0.005 percent and 2.0 percent, provided that the following elements are not present in amounts greater than that specified: niobium 1 percent, tantalum 1 percent, titanium 2 percent, tungsten 11 percent, zirconium 1 percent.