CHAPTER IV.

SMOKE.

Q. _Why does SMOKE ASCEND the chimney?_

A. As the air of the room passes over the fire, it becomes _heated_; and (being thus made _lighter_,) ascends the chimney, carrying the smoke with it.

Q. _What is SMOKE?_

A. Small particles of carbon, separated by combustion from the fuel, but not _consumed_.

Q. _Why do SMOKE and steam CURL, as they ascend?_

A. Because they are moved in a _right line_, and then _pushed on all sides_; and this forces them into a _circular_ motion.

Q. _What are BLACKS?_

A. When the hot air of the chimney has been cooled by the _external_ air, it can no longer _buoy up_ the solid smoke; so it falls to the earth in condensed flakes, called "blacks."

Q. _Why are there NO BLACKS in the smoke of a RAILWAY engine?_

A. The smoke of a railway engine consists chiefly of _watery vapour_, which dissolves in air, as sugar does in water; but the smoke of a common chimney consists of small fragments of _unburnt fuel_.

Q. _Why does a "COPPER HOLE" DRAW up more fiercely than an OPEN stove?_

A. As the air, which supplies the copper hole, must pass _through the furnace_, it becomes exceedingly _heated_, and rushes up the chimney with great violence.

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

A. Air rushing 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 passes_, 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 _passes 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 _quantity 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 pass 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_.

Q. _Why will a_ ROOM SMOKE, _if there be_ TWO FIRES _in it?_

A. Because the _fiercer_ fire will exhaust the most air; and draw from the _smaller_ one, to supply its demand.

Q. _Why will a chimney_ SMOKE _if there be a_ FIRE _in_ TWO ROOMS _communicating with each other?_

A. Whenever the _door_ between the two rooms _is opened_, air will rush from the chimney of the _inferior_ fire, to supply the _other_; and _both_ rooms will be filled with smoke.

Q. _What is the_ REMEDY _in this case?_

A. Let a tube be carried from the hearth of each stove, into the external air; and then _each_ fire will be so _well_ supplied, that neither will need to borrow from the other.

Q. _Why do VESTRY CHIMNEYS so often SMOKE?_

A. Because the wind (striking against the steeple) _is reflected back_; and tumbles down the vestry chimney, forcing the smoke _into the room_.

Q. _WHAT WINDS make vestry chimneys smoke?_

A. Those from the north-east or south-east; according to the position of the vestry.

Q. _Why will the EASTERN winds make VESTRIES SMOKE, more than those from the west?_

A. Because they _strike against the steeple_, and _bound back_ to the vestry chimney: but _western_ winds cannot rebound over the roof of a church.

(N. B. The _steeple_ of a church is always due _west_, and the _other_ end of the church due _east_; if, therefore, a _western_ wind rebound, it would rebound to the _west_, or _away from the church_, and not towards it.)

Q. _Why does a HOUSE in a VALLEY very often SMOKE?_

A. Because the wind (striking against the surrounding hills) _rebounds back again upon the chimney_, and destroys its draught.

Q. _What is the common REMEDY in both these cases?_

A. To fix a _cowl_ on the chimney top, to turn like a weather-cock, and present its back to the wind.

Q. _Why will not a COWL always PREVENT a chimney SMOKING?_

A. If the wind be _strong_, it will keep the _opening_ of the cowl _towards the steeple or hill_; and then the reflected wind will _blow into the cowl_, and _down the chimney_.

Q. _As a cowl is such a poor remedy, can any OTHER be devised?_

A. If the chimney flue can be carried _higher_ than the steeple or hills, no wind can enter the flue.

Q. _Why cannot the wind enter a chimney flue, if it be carried up HIGHER than the steeple or hills?_

A. Because the reflected wind would strike against the _sides_ of the chimney-flue, and not pass over the _opening_ at all.

Q. _In what OTHER cases will a CHIMNEY SMOKE?_

A. If both door and chimney be placed on _the same side of a room_, the chimney will often smoke.

Q. _Why will a CHIMNEY SMOKE, if the DOOR and STOVE are both on the SAME SIDE?_

A. Because when the door is opened, a current of air will _blow into the chimney-place_, and drive the smoke into the room.

Q. _What REMEDY can be applied to this evil?_

A. The door must be set _opposite_ to the chimney, or nearly so; and then the draught from the door _will blow the smoke up the chimney_, and not into the room.

Q. _Why will a CHIMNEY SMOKE if it NEEDS SWEEPING?_

A. Because the obstruction in the chimney (presented by the loose soot, to the free passage of the smoke) _delays its current_, and prevents the draught.

Q. _Why will a CHIMNEY SMOKE, if OUT OF REPAIR?_

A. 1st--Because the _loose mortar and bricks_ obstruct the smoke: and

2ndly--The _cold air_ (oozing through the chinks) _chills the air in the chimney_, and prevents its ascent.

Q. _Why will an ARNOTT'S STOVE SMOKE, if the joints of the flue do not fit air-tight?_

A. Because the _cold air_ (which gets through the joints) _chills the air in the flue_, and prevents its ascent.

Q. _Why does an old fashioned FARM CHIMNEY-PLACE so often smoke?_

A. Because the opening is so _very large_, that much of the air which goes up the chimney, _has never passed near the fire_; and this cold air mixing with the other, so _reduces its temperature_, that it ascends very slowly, and the draught is destroyed.

Q. _Why does a chimney smoke, if the DRAUGHT be SLACK?_

A. Because, unless the current of air up the chimney be very powerful, it cannot _buoy the smoke up_ through the flue.

Q. _If the opening of a chimney be TOO LARGE, what REMEDY can be applied?_

A. The chimney-place must be contracted.

Q. _Why will CONTRACTING the chimney-place PREVENT its SMOKING?_

A. As the air will then pass _nearer the fire_, it will be _more heated_, and fly up the chimney _much faster_.

Q. _Why do almost all CHIMNEYS SMOKE in GUSTY weather?_

A. The gust (blowing the air _away_ from the top of the chimney) _removes_ (for a time) _all resistance to the smoke_: but when the wind _lulls_ again, the _resistance of the air suddenly returns_--the _draught_ is _checked_--and a puff of smoke rushes into the room.

Q. _What is the use of a CHIMNEY-POT?_

A. When the opening of a chimney is _large_, the top must be contracted by a chimney-pot, in order to increase the draught.

Q. _How does a CHIMNEY-POT INCREASE the DRAUGHT of a chimney?_

A. As the _same quantity_ of hot air has to escape _through a much smaller opening_, it must pass through more quickly.

Q. _Why do tin BLOWERS help to get a fire up?_

A. Because they compel the air to go _through_ the fire, and not _over_ it; therefore the fire is well supplied with oxygen, and the draught greatly increased.

Q. _Why does a tin BLOWER INCREASE the DRAUGHT?_

A. As all the air which enters the chimney has to pass _through_ the fire, it is much hotter, and ascends the chimney very fast; and the faster the air _flies up the chimney_, the faster it rushes _towards the fire_ also.

Q. _Why does a parlour often SMELL disagreeably of SOOT in SUMMER-TIME?_

A. The air in the _chimney_ (being _colder_ than the air in the _parlour_) _descends into the room_, and leaves a disagreeable smell of soot behind.

Q. _Why are the CEILINGS of PUBLIC OFFICES so BLACK and filthy?_

A. The heated air ascending, carries the dust and fine soot to the ceiling; where the hot _air_ escapes through the plaster, and _leaves the soot and dust_ behind.

Q. _Why are SOME parts of the ceiling BLACKER and more filthy than others?_

A. As the air cannot penetrate the thick _joists_ of the ceiling, _it passes by those parts_, and deposits its soot and dust on those which are more penetrable.

Q. _What is CHARCOAL?_

A. Wood which has been exposed to a red heat, till it has been deprived of all its gases and volatile parts.

Q. _Why is a CHARCOAL FIRE hotter than a wood fire?_

A. Because so large a quantity of _water_ has been abstracted from the fuel, by the red heat to which it has been already exposed.

Q. _Why does charcoal REMOVE the TAINT of meat?_

A. Because it absorbs all odoriferous effluvia, whether they arise from putrefying animal or vegetable matter.

Q. _Why is WATER PURIFIED by being filtered through charcoal?_

A. Charcoal absorbs the _impurities_ of the water, and removes all disagreeable tastes and smells, whether they arise from animal or vegetable matter.

Q. _Why are water and wine CASKS CHARRED inside?_

A. _Charring_ the inside of the cask reduces it to a _kind of charcoal_; and charcoal (by absorbing animal and vegetable impurities) keeps the liquor sweet and good.

Q. _Why does a piece of BURNT BREAD, steeped in impure WATER, make it fit to drink?_

A. The surface of the bread is reduced to _charcoal_ by being burnt; and the charcoal surface of the bread _abstracts all the impurities of the water_, and makes it palatable.

Q. _Why should the TOAST and WATER, placed by the side of the sick, be made of BURNT BREAD?_

A. The surface of the bread being _reduced to charcoal_ by being burnt, prevents the water from being affected by the impurities of the sick room.

Q. _Why are TIMBERS, which are to be exposed to damp, CHARRED?_

A. _Charcoal undergoes no change_ by exposure to air and water; therefore timber will resist weather _much longer_, after it has been charred.