Q. _Why does WATER SIMMER before it boils?_ A. The particles of water _near the bottom of the kettle_ (being formed into _steam_ sooner than the rest) _shoot upwards_; but are _condensed_ again (as they rise) _by the colder water_, and produce what is called "simmering." Q. _What is meant by SIMMERING?_ A. A gentle tremor or _undulation_ on the surface of the water. When water _simmers_, the bubbles _collapse beneath the surface_, and the steam is condensed to _water again_: but when water _boils_, the bubbles _rise to the surface_, and _steam is thrown off_. Q. _Why does a KETTLE SING when the water simmers?_ A. Because the _air_ (entangled in the water) escapes by _fits and starts_ through the _spout of the kettle_; which makes a noise like a wind instrument, when it is blown into. Q. _Why does NOT a kettle SING, when the water BOILS?_ A. As _all_ the water is _boiling hot_, the steam meets with no _impediment_, but freely escapes in a continuous stream. Q. _When does a kettle sing most?_ A. When it is set on a _hob_ to boil. Q. _Why does a kettle SING MORE when it is set on the SIDE of a fire, than when it is set in the MIDST of the fire?_ A. When the kettle is set on the _hob_ to boil, the heat is applied very _partially: one side is hotter than the other_, and therefore the steam is more _entangled_. Q. _Why does a KETTLE sing, when the boiling water begins to COOL again?_ A. Because the _upper_ surface cools _first_; and the steam (still rising from the lower parts of the kettle) is _again entangled_, and escapes fitfully. Q. _Why does BOILING WATER SWELL?_ A. Water (like air) _expands by heat_. The heat of the fire drives the particles of water _further apart from each other_; and (as they are not _packed so closely together_) they take up _more room_; or (in other words) the water _swells_. Q. _What is meant when it is said, "that HEAT drives the PARTICLES of water further APART from each other."_ A. Water is composed of little globules, like very small grains of sand; the heat _drives_ these particles _away from each other_; and (as they then require more _room_) the water _swells_. Q. _Why does BOILING WATER BUBBLE?_ A. Water contains _air_; and (as the water is heated) _the air is driven out_, and raises a _bubble_ in that part of the water which resists its escape. Q. _Why does a KETTLE sometimes BOIL OVER?_ A. Liquids _expand very much by heat_; if, therefore, a kettle be _filled with cold water_, some of it must _run over_ as soon as it is _expanded by heat_. Q. _But I have seen a KETTLE BOIL OVER, although it has not been filled FULL of WATER; how do you account for THAT?_ A. If a fire be _very fierce_, the air is expelled so _rapidly_, that the _bubbles are very numerous_; and (towering one above the other) _reach the top of the kettle, and fall over_.