The extinguishment of the candle flame in the well-known candle-and-cylinder experiment has been erroneously viewed as caused by the complete consumption of oxygen, for many reasons. To address this misconception scientifically, a series of experiments are carried out to illustrate the phenomenon from a new point of view. Limewater [Ca(OH)₂] placed at different heights in a container was used to qualitatively describe the distribution of CO₂ in an enclosed cylinder with one or two burning candles. Temperature sensors, CO₂ sensors, and oxygen (O₂) sensors were employed to visually and quantitatively compare the content of CO₂ at different heights within the container. The resulting temperature curves show that the heat from combustion rose first and then descended soon afterward. Chemical and sensor detection of CO₂ in the highest two quadrants of the container indicated that the hot CO₂ gas rose initially and accumulated there in the highest part of the container. Then, the hot CO₂ gas descended gradually and created a CO₂ atmosphere surrounding the flame. As a result, the flame was extinguished by the buildup of CO₂ and depletion of oxygen in the gas in the vicinity of the flame. The change of oxygen concentration showed that there was a mixing process between the remaining air and the hot CO₂. These results indicate that the extinguishment of the flame does not mean that the oxygen in the container was completely consumed. Knowing this helps students understand that the density of CO₂ depends on its temperature.

中文翻译：

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CO ₂浓度和热量的变化说明了烛形和筒形实验中火焰被熄灭的原因

由于许多原因，人们已经错误地认为在众所周知的烛缸实验中熄灭烛火是由于氧气的完全消耗引起的。为了科学地解决这一误解，我们进行了一系列实验，从新的角度说明了这一现象。使用放置在容器中不同高度的柠檬水[Ca（OH）₂ ]定性地描述在带有一两个燃烧蜡烛的密闭圆筒中CO ₂的分布。使用温度传感器，CO ₂传感器和氧气（O ₂）传感器来视觉和定量比较CO ₂的含量在容器内的不同高度。所得的温度曲线表明，燃烧产生的热量先上升，然后很快下降。化学和传感器检测CO的₂在容器的最高两个象限表明热CO ₂气体最初上升和容器中的最高的部分积累在那里。然后，热的CO ₂气体逐渐下降并在火焰周围形成CO ₂气氛。结果，由于火焰附近的气体中CO ₂的积累和氧气的耗尽，火焰被熄灭。氧气浓度的变化表明，剩余空气与热CO ₂之间存在混合过程。这些结果表明，火焰的熄灭并不意味着容器中的氧气已被完全消耗掉。知道这一点有助于学生理解CO ₂的密度取决于其温度。