GP-a general purpose grade,either magnesium or sodium reduced and finished by leaching or inert gas sweep,or both.EL-electrolytic produced.SL-sodium reduced and finished by leaching.ML-magnesium reduced and finished by leaching or inert gas sweep.MD-magnesium reduced and finished by disbllation.Sodium or magnesium,max0.50%.The chemical requirements for grade MD sponge have been modifine to reflect the use of stainiess steel production vessels,which are the norm for this grade of sponge.the use of stainiess steel necessarily now incorporates unavoidable chromium and nickel contaminants.these contaminants do not alter the basic property requirements of the sponge.however,it is necessary to incorporate there two unavoidable contanminants into the chemical requirements for this grade,just as the other unavoidable contaminants have been assigned maximum permissible levels.