对初中物理课本第二册p.79“水在低压下沸腾”的演示实验装置,笔者认为,它至少有两个不可忽视的缺点:第一,它只可演示“压强减小,沸点降低”,至于课本上说“相反,如果增加压强,液体的沸点就要升高”是无法直接明确演示的;第二,它易让学生产生“沸腾不需要吸热”的错误认识(因演示中没有对水加热,水也确实未从外界吸热)。笔者对这个实验作了改进,装置如图所示,现将演示方法简述如下。先不接上抽气筒,在瓶中装上适量的冷水,对水加热,当加热到80℃左右时,水并未沸腾,再接上抽气筒,抽出瓶中的部分气体,减小压强,可以立即看到瓶中的水沸腾起来,而且从温度计上可直接读出沸腾时的温度只有80℃左右,甚至更低。并能定性演示出,抽出的气体越多(这可以抽气的次数、速度上体现),即压强越小,水就能在更低的温度下沸腾。这便说明“压强减小,沸点 For the demo experimental device of p.79 “Boiling water under low pressure” in junior high school physics textbook second book, the author believes that it has at least two non-negligible disadvantages: First, it can only demonstrate “lower pressure and lower boiling point”. As for textbooks, “Conversely, if the pressure is increased, the boiling point of the liquid must increase” cannot be explicitly demonstrated. Second, it is easy for students to get a false impression that “boiling does not require heat absorption” (because there is no When water is heated, water does not absorb heat from the outside. The author has made improvements to this experiment. The installation is shown in the figure. The demonstration method is briefly described below. Do not connect the pumping tube first. Put a proper amount of cold water in the bottle. Heat the water. When it is heated to about 80°C, the water does not boil. Then connect the pump to the pump to withdraw some of the gas from the bottle, reducing the pressure. The water in the bottle can be immediately seen boiling, and the temperature at which boiling can be directly read from the thermometer is only about 80°C or even lower. And it can be qualitatively demonstrated that the more gas is drawn out (this can be reflected in the number of times and speed of the pumping), that is, the lower the pressure, the water can boil at a lower temperature. This shows that "the pressure is reduced, the boiling point