Q. _Why is a pot, which is full to OVERFLOWING (while the water is boiling HOT), NOTHING LIKE FULL, when it has been taken off the fire for a short time?_ A. When the water was _swelled by boiling heat_, it filled the pot even to overflowing; but as soon as the water is _condensed by cold_, it _contracts_ again, and occupies a much less space. Q. _Why does the water of a KETTLE run out of the SPOUT when it BOILS?_ A. Because the steam cannot escape _so fast as it is formed_, and (being _confined in the kettle_) _presses on the water with great power_, and forces it out of the spout. Q. _How can the PRESSURE of STEAM on the SURFACE of the water, FORCE the water through the KETTLE-SPOUT?_ A. In the same manner as _the pressure of air_ on the _mercury of a barometer_, forces the _quicksilver up the glass tube_. Q. _What causes the RATTLING NOISE so often made by the LID of a saucepan or boiler?_ A. The steam (seeking to escape) _forces up the lid_ of the boiler, and the _weight_ of the lid causes it to _fall back again_: this being done _frequently_, produces a rattling noise. Q. _If the steam COULD NOT LIFT UP THE LID of the boiler, how would it escape?_ A. If the lid fitted so tightly, that the steam could not raise it up, the boiler would _burst into fragments_, and the consequences might be fatal. Q. _When steam pours out from the spout of a kettle, the STREAM begins apparently HALF AN INCH off the SPOUT; why does it not begin CLOSE to the spout?_ A. Steam is really _invisible_; and the half-inch (between the spout and the "_stream of mist_") is the _real steam_, before it has been condensed by air. Q. _Why is not ALL the stream INVISIBLE, as well as that half-inch?_ A. As the steam _comes in contact with the colder air_, the invisible particles (being _condensed_), roll one into another, and look like a thick mist. Q. _What BECOMES OF the STEAM? for it soon vanishes._ A. After it is condensed into mist, it is _dissolved by the air_, and dispersed abroad as _invisible vapour_. Q. _And what BECOMES of the INVISIBLE VAPOUR?_ A. Being _lighter than air_, it _ascends_ to the upper regions, where (being again _condensed_) it contributes to form _clouds_. Q. _Why does a METAL SPOON, left in a saucepan, RETARD the process of BOILING?_ A. The metal spoon (being an excellent _conductor_) _carries off the heat from the water_; and (as heat is carried off by the spoon) the water takes a longer time to boil. Q. _Why will a POT (filled with water) NEVER BOIL, when immersed in ANOTHER vessel full of water also?_ A. Because water can _never be heated above the boiling point_: all the heat absorbed by the water after it _boils_, is employed in _converting the water into steam_. Q. _How does the conversion of water into steam prevent the INNER POT from BOILING?_