请问这一步实验描述怎么操作呢?

The corresponding sulfone (0.1 mmol) was dissolved in 0.4 mL of CH2Cl2 and added to a solution of magnesium (10 equiv, previously flame-dried under a stream of argon) in 1 mL of MeOH under argon atmosphere. After complete consumption, 10 equiv more of magnesium was added.
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怎么用火焰干燥镁呀？看不懂，望大牛回答，谢谢！