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Why are the distillation flasks used in vacuum distillation made with a curved neck? The purpose of giving the vacuum distillation flasks used in vacuum distillation procedures for determining boiling points a curved neck is to prevent the liquid that splashes out when the distillate boils over or forms foam from being forced together with the steam into the side tubes. It has the effects of soothing, moderating, harmonizing, and breaking up foam. Reduced-pressure distillation can be performed without introducing air to achieve good reproducibility of the measurement results. The purpose of making a standard Kjeldahl flask with two necks is also to prevent the distillate from surging and splashing, thus avoiding its entry into the distillate. On the side of the bottle’s straight neck, a very thin capillary can be inserted, all the way to the bottom of the bottle. Allow tiny air bubbles to continuously enter the distillate, so that the gas phase is not formed delayedly, thereby preventing overheating and splashing. The other neck of the bottle branches off from the straight neck; its upper part runs parallel to the straight neck and is used to insert a thermometer for measuring the distillation temperature, and it also has a branch pipe for the escaping distillate. The bend at its lower part serves to prevent splashing liquid from escaping. The entire diameter of this neck tube should be uniform, and it should not narrow at the weld point with the straight neck; otherwise, oil leakage will occur.