We all know that in this case the water cools down by degrees. The water gives out its heat. Now, it is evident that while on the fire, the water had absorbed heat; and that it gave out that heat on being put in a colder place. But what will become of the water if it is allowed to continue to absorb heat? What becomes of a pot of water, if, on beginning to boil, it is not taken off the fire? Does such water continue to absorb heat? Observation shows that this is not the case. Put a thermometer into boiling water; it will immediately rise to 212 degrees; let it remain there ever so long, it will not rise a degree higher. But during that time there was a brisk fire; it is evident, therefore, that heat was continually passing into the water. Where, then, is this heat? It has not remained in the water, or else the thermometer would have continued to rise. It must be, then, that it has passed away with the burning hot steam which has been constantly rising and floating about in the room. Moreover, it is well known that water, when allowed to continue to boil, decreases in quantity. Our housewives call this "_boiling down_." In truth, however, the water boils _up_; for, if you notice carefully, a part of the water, while boiling, is changed into steam, which may be seen rising from the pot and ascending in the air. The question naturally arises now, where is the heat that the boiling water has been continually absorbing? It has not remained in the water, or the thermometer would have continued to rise. The answer is now evident: the heat has risen with the steam, and with it floats about in the air; or, in other words, the heat has been absorbed by the steam; or, which is the same, the heat has become latent in the steam. Therefore we are correct in saying, _it takes heat to change water into steam_. We know now where the heat has gone; it has become latent in the steam. The next question might be: Can this latent heat become free again? Certainly it can; and many a good housewife has convinced herself of it very often, though perhaps she did not philosophize about it. When touching unawares the spout of the tea-kettle with her hand she felt as though her hand was wet, and scalded besides. Whence did this come? The hand was wetted by the steam, which, on coming in contact with the hand, changed to water again, but in the same moment, also, the steam gave up its heat to the hand by scalding it. Steam, therefore, when changing into water, gives its latent heat up again; or, the latent heat becomes free. This phenomenon, which may be witnessed in every kitchen, happens in nature on a larger scale; by what powerful effects it is accompanied, we propose to show in the next chapter. CHAPTER VIII. LATENT HEAT PRODUCES COLD; FREE HEAT, WARMTH.