A Guide To The Scientific Knowledge Of Things Familiar Part 14

Q. _What produces the ROARING noise made by a COPPER-HOLE fire?_

A. Air rus.h.i.+ng rapidly through the crevices of the _iron door_, and up the _chimney flue_.

Q. _Why is the ROAR LESS, if the copper-hole DOOR be thrown OPEN?_

A. Because _fresh_ air gets access to the fire _more easily_; and as the air is not so intensely heated, its motion is not so _violent_.

Q. _Why do some CHIMNEYS SMOKE?_

A. If fresh air is not admitted into a room, _as fast as it is consumed by the fire_, a current of air _will rush down the chimney_ to _supply the deficiency_, and bring the smoke along with it.

Q. _What prevents air being supplied, as fast as it is consumed by the fire?_

A. Leather and curtains round the doors; sand-bags at the threshhold and on the window-frames; and other contrivances to keep out the draught.

Q. _Why is it needful for cold fresh air to be so constantly supplied?_

A. If water be taken with a pail out of a river, _other_ water will rush towards the hole, as soon as the pail is lifted out; and if air be taken from a room, (as it is, when some of it goes up the chimney) _other air_ will rush towards the void to fill it up.

Q. _Why will it come down the chimney?_

A. Because if doors and windows are all made _air-tight_, it can get to the room in no _other_ way.

Q. _What is the best REMEDY in such a case?_

A. The _speediest_ remedy is to open the door or window: but by far the _best_ remedy is to carry a small tube from the hearth into the external air.

Q. _Why is that the BEST remedy?_

A. Because the fire will be plentifully supplied with air by the tube; the doors and windows may all remain air-tight; and we may enjoy a warm fireside, without the inconvenience of draughts and cold feet.

Q. _Why is a CHIMNEY raised so high above the ROOF?_

A. If it were not so, it would smoke; as all funnels do which are too short.

Q. _What is meant by the funnel, or flue of a chimney?_

A. That part of a chimney through which _the smoke pa.s.ses_, is called the funnel, or flue.

Q. _Why does a CHIMNEY SMOKE, if the funnel be very short?_

A. Because the _draught_ of a short flue _is too slack_ to carry the smoke up the chimney.

Q. _Why is the DRAUGHT of a SHORT FLUE more SLACK that that of a long one?_

A. For many reasons. 1st--_The fire is always dull and sluggish_ if the chimney be too short.

2ndly--The smoke rolls _out_ of the chimney, before it has acquired its _full velocity_.

3rdly--The wind, rain, and air, have more influence over a _short_ funnel, than over a _long_ one.

Q. _Why is the FIRE always DULL and sluggish if the CHIMNEY-FLUE be very SHORT?_

A. Because the draught is so bad: and as the rarefied air _pa.s.ses up the chimney very tardily_, _fresh air_ flows as tardily _towards the fire_, to supply it with _oxygen_.

Q. _On what does the INTENSITY of fire depend?_

A. The _intensity_ of fire is always in proportion to the _quant.i.ty of oxygen_ with which it is supplied.

Q. _Why does not SMOKE acquire its full VELOCITY in a SHORT funnel?_

A. Because the _higher_ smoke ascends in a flue, (provided it be clear and hot) the _faster_ it goes; (as a stone falls faster and faster the lower it descends): if, therefore, a _funnel be very short_, the smoke never acquires its full velocity.

Q. _Does the DRAUGHT of a chimney depend on the SPEED of the SMOKE through the flue?_

A. Yes. The more quickly _hot_ air flies _up the chimney_, the more quickly _cold_ air will rush _towards the fire_ to supply the place; and, therefore, the _longer the flue_, the _greater the draught_.

Q. _Why is the DRAUGHT of a LONG FLUE greater than that of a short one?_

A. Because the _higher_ smoke ascends, the _faster_ it goes; (as a stone falls faster and faster, the nearer it approaches to the earth): if, therefore, a funnel be _long_, the smoke acquires great _velocity_, and the _draught_ is great.

Q. _If a CHIMNEY be TOO SHORT, and cannot be lengthened, what is the best REMEDY to prevent smoking?_

A. To _contract the opening of the chimney_ contiguous to the stove.

Q. _Why will a_ SMALLER OPENING _against the stove_ PREVENT _the_ SMOKING?

A. As all the air (which enters the chimney) _must pa.s.s near the fire_, it will become _greatly heated_, and _rise rapidly_ through the funnel; and this _increase of heat_ will compensate for the _shortness of the flue_.