PURPOSE: To recover expensive germanium from a glass composition contg. germanium dioxide in a high yield by reducing the composition to convert the germanium dioxide into volatile lower oxide and by volatilizing and separating the oxide.

CONSTITUTION: A glass composition contg. germanium dioxide is mixed with carbon powder and put in a heating furnace heated to ≥500°C. By feeding an inert gas into the furnace or evacuating the furnace, volatile matter volatilized at the high temp. part is discharged. The volatile matter is composed chiefly of germanium monoxide, hydrochloric acid and chlorine, and by capturing the discharged matter with a cooling trap, the germanium monoxide is recovered. Hydrogen may be used as a reducing agent in place of carbon.