The Works of Benjamin Franklin, Volume 2. Бенджамин Франклин

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      XXX. AN ACCOUNT OF THE NEW-INVENTED PENNSYLVANIAN FIRE-PLACES ^{Ref. 022};

      wherein

      their construction and manner of operation is particularly explained; their advantages above every other method of warming rooms demonstrated; and all objections that have been raised against the use of them answered and obviated. with directions for putting them up, and for using them to the best advantage. and a copper-plate in which the several parts of the machine are exactly laid down, from a scale of equal parts.

      PHILADELPHIA;

      printed and sold by b. franklin, 1744.

      In these northern colonies the inhabitants keep fires to sit by generally seven months in the year; that is, from the beginning of October to the end of April, and, in some winters, near eight months, by taking in part of September and May.

      Wood, our common fuel, which within these hundred years might be had at any man’s door, must now be fetched near one hundred miles to some towns, and makes a very considerable article in the expense of families.

      As therefore so much of the comfort and conveniency of our lives, for so great a part of the year, depends on the article of fire; since fuel is become so expensive, and, as the country is more cleared and settled, will of course grow scarcer and dearer, any new proposal for saving the wood, and for lessening the charge and augmenting the benefit of fire, by some particular method of making and managing it, may at least be thought worth consideration.

      The new fire-places are a late invention to that purpose, of which this paper is intended to give a particular account.

      That the reader may the better judge, whether this method of managing fire has any advantage over those heretofore in use, it may be proper to consider both the old and new methods, separately and particularly, and afterwards make the comparison.

      In order to do this it is necessary to understand well some few of the properties of air and fire, viz.:

      1. Air is rarefied by heat, and condensed by cold; that is, the same quantity of air takes up more space when warm than when cold. This may be shown by several very easy experiments. Take any clear glass bottle (a Florence flask stript of the straw is best), place it before the fire, and, as the air within is warmed and rarefied, part of it will be driven out of the bottle; turn it up, place its mouth in a vessel of water, and remove it from the fire; then, as the air within cools and contracts, you will see the water rise in the neck of the bottle, supplying the place of just so much air as was driven out. Hold a large hot coal near the side of the bottle, and, as the air within feels the heat, it will again distend and force out the water. Or, fill a bladder not quite full of air, tie the neck tight, and lay it before a fire as near as may be without scorching the bladder; as the air within heats, you will perceive it to swell and fill the bladder, till it becomes tight, as if full blown; remove it to a cool place, and you will see it fall gradually, till it becomes as lank as at first.

      2. Air rarefied and distended by heat is specifically ^{Ref. 023} lighter than it was before, and will rise in other air of greater density. As wood, oil, or any other matter specifically lighter than water, if placed at the bottom of a vessel of water, will rise till it comes to the top, so rarefied air will rise in common air, till it either comes to air of equal weight or is by cold reduced to its former density.

      A fire, then, being made in any chimney, the air over the fire is rarefied by the heat, becomes lighter, and therefore immediately rises in the funnel, and goes out; the other air in the room (flowing towards the chimney) supplies its place, is rarefied in its turn, and rises likewise; the place of the air thus carried out of the room is supplied by fresh air coming in through doors and windows, or, if they be shut, through every crevice with violence, as may be seen by holding a candle to a key-hole. If the room be so tight as that all the crevices together will not supply so much air as is continually carried off, then, in a little time, the current up the funnel must flag, and the smoke, being no longer driven up, must come into the room.

      1. Fire (that is, common fire) throws out light, heat, and smoke (or fume). The two first move in right lines, and with great swiftness; the latter is but just separated from the fuel, and then moves only as it is carried by the stream of rarefied air, and without a continual accession and recession of air to carry off the smoky fumes, they would remain crowded about the fire and stifle it.

      2. Heat may be separated from the smoke, as well as from the light, by means of a plate of iron, which will suffer heat to pass through it without the others.

      3. Fire sends out its rays of heat, as well as rays of light, equally every way; but the greatest sensible heat is over the fire, where there is, besides the rays of heat shot upwards, a continual rising stream of hot air, heated by the rays shot round on every side.

      These things being understood, we proceed to consider the fire-places heretofore in use, viz.:

      1. The large open fire-places used in the days of our fathers, and still generally in the country, and in kitchens.

      2. The newer-fashioned fire-places, with low breasts and narrow hearths.

      3. Fire-places with hollow backs, hearths and jambs of iron (described by M. Gauger in his tract entitled La Méchanique de Feu), for warming the air as it comes into the room.

      4. The Holland stoves, with iron doors opening into the room.

      5. The German stoves, СКАЧАТЬ