为什么水扑灭了大火。
我经常困惑,写在T e·b·詹姆斯he Tradesman, to answer for myself why water extinguishes fire. A great many people say it is because the water and its steam so envelop the burning material as to exclude the oxygen, and thus the fire must stop. This seems to be an inefficient if not an entirely erroneous reason. My reason is this: We know that nothing will burn (i. c., unite with the evolution of heat and light) unless and until it has been raised to a given temperature. Thus : Sodium burns at ordinary temperature—about sixty degrees, if dry—the gas of ordinary kerosene at about 170 degrees or less, and soon. Why do we tip a piece of stick with sulphur and then with phosphorus to make matches? Because, while wood must have quite a high temperature, phosphorus will burn at a comparatively low temperature—so low that the heat developed by slight friction will ignite it. The phosphorus makes heat enough to ignite the sulphur, but not enough to start the wood. But I will ask another question : Wood ashes are white. Why is the remaining end of the match and often most of it black in color ? Is it not because carbon being black, and the wood being composed of carbon and compound substances, which are very inflammable, the latter burn, but do not generate enough heat to oxidize the former. This seems to me the reason for the carbon remaining. Thus premising and showing that carbon, which forms the bulk of wood (as well as of paper, cotton, etc.) requires to be very hot before It will unite with the oxygen, we may consider the water for a moment.
也许最清楚的观点的最简单方法是采用一个共同的插图。每个人都知道，如果一个人在加热的炉子上放一块水，他必须等待很长时间才能变热，或者温度为212摄氏度。在水中，后者将更早达到212度。为什么是这样？这是因为水占据了大量的热量，但温度计不是索引。现在，如果达到212度后，他将它们从汞中脱离，将更快地达到周围空气的温度。现在，假设我们希望将所有的水烧开，以蒸发它 - 在这种情况下，请记住，从水到蒸汽中，温度也不会升高，甚至没有任何一部分，也不会立即蒸发。通过稍微提高温度吗？我们都知道他不能。大火具有一定程度的热量，但是水壶必须保持很长时间，而水则逐渐逐渐消失。 Why so? Because the water, in becoming steam, must take into itself a large amount of heat not shown by the themometer and as the heat can be added only gradually, the formation of steam is slow. Now, in the large amount of heat which water can take up, and the fact that ordinary inflammables must be raised to a high temperature in order to burn, we have the cause of water putting out fire. Put a burning match into a very small drop «f water and it is extinguished, because of the very large amount of heat taken from the match in reducing the water to steam which renders the temperature of the match too far below 212 degrees, or at least that far, if there is water enough, and so the carbon and its compounds forming the wood will no longer unite with the oxygen of the air. For the same reason a hot iron thrust into the water is cooled, and water sprinkled on the floor cools the air, the heat of evaporation in the latter case coming from the air itself, thus cooling it. Now, if we could find a fluid very plentiful, which requires more heat than water to make it boil, evidently we could put large fires out much more readily.
