Hydrofluoric acid distillation has been applied to the determination of phosphorus and germanium in siliceous materials based on the formation of their heteropolymolybdates. Silicon and arsenic are separated by distillation from phosphorus, germanium and the remainder of the sample. The formation of colourless P2M050236-is employed to avoid the interference of phosphorus in germanium determination. Germanium is determined spectrophotometrically as its heteropolymolybdate and phosphorus gravimetrically by difference.