化学教材中有相当数量的演示实验,由于受到反应器皿容量的限制,只有前几排的少数学生才能观察到实验现象。对于比较细微的化学变化,如少量沉淀的生成,微量气体的放出,颜色的微弱变化等就更难以观察。这类演示实验,如果巧妙地使用投影仪,往往会收到意想不到的效果。 There are a large number of demonstration experiments in chemistry textbooks. Due to the limited capacity of reaction vessels, only a few students in the first few rows can observe experimental phenomena. For more subtle chemical changes, such as the formation of a small amount of precipitation, the release of trace gases, the faint changes in color, etc. are more difficult to observe. This kind of demonstration experiment, if used skillfully to use the projector, often receives the unexpected result.