Method and apparatus for making vitreous silica of high purity including producing a melt of liquid silicon in a first chamber, mixing the liquid silicon with carbon dioxide in an upper zone of a second chamber to produce silicon monoxide, mixing the silicon monoxide with oxygen in a lower zone of the second chamber producing silicon dioxide in gaseous form, condensing the silicon dioxide on the wall of the second chamber, and withdrawing the resultant tube of vitreous silica from the lower end of the second chamber. The apparatus is lined with silica to prevent introduction of impurities. The liquid silicon is produced by mixing hydrogen and trichlorosilane.