CHAPTER VI.
93. How many kinds of combustion are there?
There are three, viz., slow oxydation, when little or no light is evolved; a more rapid combination, when the heat is so great as to become luminous; and a still more energetic action, when it bursts into flame.
94. Why does phosphorous look luminous?
Because it is undergoing slow combustion.
95. Why do decayed wood, and putrifying fish, look luminous?
Because they are undergoing slow combustion. In these cases the heat and light evolved are at no one time very considerable. But the total amount of heat, and probably of light, generated through the lengthy period of this slow oxydation, amounts to exactly the same as would be evolved during the most rapid combustion of the same substances.
It is gaseous matter burning at a very high temperature.