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Fill an open container with nitrogen as follows:
(1) Pre-cooling with a small amount of liquid nitrogen before nitrogen filling; ② When filling nitrogen, let the evaporated nitrogen in the container be discharged smoothly; ③ Do not overfill. 4, liquid nitrogen supplement: for long-term storage, it is necessary to regularly supplement liquid nitrogen. The average molecular weight of air is 29. The molecular mass of nitrogen is 28, and if you do that as described here, you're going to cause the gas to escape and the right way to do that is to put the mouth of the bottle down.