Q. _Does HEAT EXPAND the AIR?_ A. Yes; if a bladder (partially filled with air) be tied up at the neck, and _laid before the fire_, the air will _swell_ till the bladder _bursts_. Q. _Why will the AIR SWELL, if the bladder be laid before the fire?_ A. Because the heat of the fire _gets between the particles of air_, and drives them _further apart from each other_; which causes the bladder to expand. Q. _Why do unslit CHESTNUTS CRACK with a loud noise, when ROASTED?_ A. Chestnuts contain a great deal of air, which is expanded by the heat of the fire; and, as the thick rind prevents the air from escaping, it violently _bursts through, slitting the rind_, and making a great noise. Q. _What occasions the loud CRACK or report which we hear?_ A. 1st--The _sudden bursting of the rind_ makes a report, in the same way as a piece of _wood_ or _glass_ would do, if _snapped in two_: and 2ndly--The _escape of hot air_ from the chestnut makes a report also, in the same way as _gunpowder_, when it escapes from a _gun_. Q. _Why does the sudden BURSTING of the rind, or SNAPPING of a piece of wood, make a REPORT?_ A. As the attraction of the parts is suddenly overcome, _a violent jerk_ is given to the air; this jerk produces _rapid undulations_ in the air, which (striking upon the ear) give the brain the sensation of _sound_. Q. _Why does the ESCAPE OF AIR from the chestnut, or the EXPLOSION of GUNPOWDER, produce a REPORT?_ A. Because a quantity of air (suddenly let loose) _pushes against the air around_, in order to make _room for itself_; and as the _air of the chestnut_ slaps against the _air of the room_, a _report_ is made, (as when I _slap_ a book or table). Q. _If a CHESTNUT be SLIT, it will NOT CRACK; why is this?_ A. Because the _heated air_ of the chestnut can _freely escape_ through the _slit in the rind_. Q. _Why does an APPLE spit and SPURT about, when roasted?_ A. An apple contains a vast quantity of _air_, which (being expanded by the heat of the fire) _bursts through the peel_, carrying the juice of the apple along with it. Q. _Does an APPLE contain MORE AIR, in proportion, than a CHESTNUT?_ A. Yes, much more. There is as much condensed air in a common apple, as would fill a space 48 _times as big as the apple itself_. Q. _Where is all this quantity of AIR stowed in the APPLE?_ A. The _inside_ of an apple is _made up of little cells_ (like a _honey-comb_), each of which contains a portion of the air. Q. _When an APPLE is ROASTED, why is one part made SOFT, while all the rest remains hard?_ A. When an apple is roasted, the air in the _cells next to the fire_ is expanded and flies out; the _cells are broken_, and their juices _mixed together_; so the apple _collapses_ (from loss of air and juice), and feels _soft_ in those parts. Q. _What is meant by the "apple COLLAPSING?"_ A. The _plumpness_ gives way, and the apple becomes _flabby_ and _shrivelled_.