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利用压缩空气引火仪和附带的硝化棉,表演压缩空气做功,使气体内能增加的实验是很方便的。但是,很多学校没有硝化棉,自己配制又很麻烦,用教科书上说的“浸有乙醚的一小块棉花”做实验往往也不成功。因为这“一小块”太笼统了,不知这一小块到底小列什么程度,为此我们对压燃点火可燃物的选择及发火条件进行了充分的研究。我们的实验结果是,凡是常见的可燃物都可用来做这个实验。例如,固体可燃物有棉花、纸片、火柴头、火柴杆、塑料、蜡、头发等;液体可燃物有乙醚、酒精、汽油、柴油、煤油等,以及浸有各种可燃液体的棉花。实验成功的条件是投入筒内的可燃物的量必需极少。例如,桃花只取几根棉丝;火柴头只取一点粉末;火柴杆只刮比针尖大的一点木屑;乙醚、汽油、酒精等只是用棉球在筒底蘸一下即可,只有往筒内投入极少量的可燃物,才不致于严重降低空气被绝热压缩后产生的高温(可达500℃～600℃),以保证压缩后空气的温度超过可燃物的燃点,从而使可燃物立即燃烧,并发出火光。
It is convenient to use the compressed air pilot instrument and the attached nitrocellulose to perform compressed air work to increase the internal energy of the gas. However, many schools do not have nitrocellulose, and they are very cumbersome to formulate. It is often unsuccessful to use textbooks to describe “a small piece of cotton impregnated with ether”. Because this “small piece” is too general, I do not know to what extent this small piece is listed in the end. For this reason, we have conducted a full study of the selection of ignition and ignition combustibles and the firing conditions. Our experimental result is that all common combustibles can be used for this experiment. For example, solid combustibles include cotton, paper, match heads, match sticks, plastics, waxes, and hair; liquid combustibles include ether, alcohol, gasoline, diesel, kerosene, and the like, and cotton impregnated with various flammable liquids. The success of the experiment was based on the fact that the amount of combustibles in the input cylinder must be minimal. For example, Peach only takes a few cotton yarns; the match head only takes a little powder; the matchstick scrapes only a little more than the tip of the needle; ether, gasoline, alcohol, etc. just use a cotton ball to dip at the bottom of the cylinder, only inside the cylinder. Injecting a very small amount of combustibles will not seriously reduce the high temperature (up to 500°C~600°C) of the air after it is adiabatically compressed, so as to ensure that the compressed air temperature exceeds the ignition point of the flammables, so that combustibles will immediately burn. And fire light.