初三化学实验１－１空气中氧气含量测定按课文和图示进行往往失败。主要因是钟罩内空气体积相对庞大难以快冷却，红磷燃烧后体积膨胀的剩余组分水面不能上升到预先测定的１／５体积标处。为此，笔者对该实验进行了重新设使实验准确省时，成功率可达１００％，也除了红磷点燃时 The third chemical experiment 1-1 Determination of oxygen content in air often fails in texts and diagrams. The main reason is that the air volume in the bell jar is relatively large and it is difficult to quickly cool. The remaining component water that has volume expansion after combustion of red phosphorus cannot rise to the 1/5 volume standard that is determined in advance. For this reason, the author reset the experiment so that the experiment is accurate and time-saving, the success rate can reach 100%, and in addition to the red phosphorus ignition