Abstract: To facilitate a preheating operation in a vacuum degassing apparatus having a flow path of a glass melt in an uprising pipe, a vacuum degassing vessel and a downfalling pipe constituted by a refractory material. Flow of a glass melt G between a melting vessel 100 and an upstream pit 210 of a first conducting pipe structure connected to a vacuum degassing vessel 320 is shut off, and in a state where the flow of the glass melt G in a by-pass 500 for the glass melt G is shut off by a first closing means 220, a combustion gas from preheating burners 530, 540 is introduced to the by-pass 500 to preheat the flow path of the glass melt G in an uprising pipe 330, the vacuum degassing vessel 320 and a downfalling pipe 340.

Abstract: An electroerosion boring method and apparatus for machining a small hole in a workpiece at high speed using a supplemental working fluid flushing means for directing working fluid toward a peripheral edge of the inlet-side opening of the hole being machined, and a working fluid supply means for supplying the working fluid to the jet nozzle means under pressure so that the working fluid at a pressure of at least 20 kg/cm.sup.2 or more is directed from the supplemental flushing means. The supplemental high pressure flushing effectively prevents the machined chips from adhering to the peripheral edge of said hole without interfering with high-speed machining performance.