| http://www.w3.org/ns/prov#value | - In this embodiment, an inert gas-supply device (not shown) for introducing an inert gas such as N.sub.2 or He is connected to the gas port17a of the upper cylindrical part 17.When such a drawing furnace is used for drawing an optical fiber, an inert gas 20 such as N.sub.2 or He is introduced into the furnace core chamber through the gas port 17a of the upper cylindrical part 17 using the inert gas
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