you have the benefit of its heat, whereas in common chimneys a great
part goes away in smoke which you see as it rises, but it affords
you no rays of warmth. One may obtain some notion of the quantity of
fuel thus wasted in smoke, by reflecting on the quantity of soot that
a few weeks firing will lodge against the sides of the chimney, and
yet this is formed only of those particles of the column of smoke
that happen to touch the sides in its ascent. How much more must have
passed off in the air? And we know that this soot is still fuel;
for it will burn and flame as such, and when hard caked together is
indeed very like and almost as solid as the coal it proceeds from.
The destruction of your fuel goes on nearly in the same quantity
whether in smoke or in flame: but there is no comparison in the
difference of heat given. Observe when fresh coals are first put on
your fire, what a body of smoke arises. This smoke is for a long
time too cold to take flame. If you then plunge a burning candle
into it, the candle instead of inflaming the smoke will instantly be
itself extinguished. Smoke must have a certain degree of heat to be
inflammable. As soon as it has acquired that degree, the approach of
a candle will inflame the whole body, and you will be very sensible
of the difference of the heat it gives. A still easier experiment
may be made with the candle itself. Hold your hand near the side of
its flame, and observe the heat it gives; then blow it out, the hand
remaining in the same place, and observe what heat may be given by
the smoke that rises from the still burning snuff. You will find it
very little. And yet that smoke has in it the substance of so much
flame, and will instantly produce it, if you hold another candle
above it so as to kindle it. Now the smoke from the fresh coals laid
on this stove, instead of ascending and leaving the fire while too
cold to burn, being obliged to descend through the burning coals,
receives among them that degree of heat which converts it into flame,
and the heat of that flame is communicated to the air of the room, as
above explained.
4. The flame from the fresh coals laid on in this stove, descending
through the coals already ignited, preserves them long from
consuming, and continues them in the state of red coals as long as
the flame continues that surrounds them, by which means the fires
made in this stove are of much longer duration than in any other,
and fewer coals are therefore necessary for a day. This is a very
material advantage indeed. That flame should be a kind of pickle, to
preserve burning coals from consuming, may seem a paradox to many,
and very unlikely to be true, as it appeared to me the first time
I observed the fact. I must therefore relate the circumstances,
and shall mention an easy experiment, by which my reader may be in
possession of every thing necessary to the understanding of it. In
the first trial I made of this kind of stove, which was constructed
of thin plate iron, I had instead of the vase a kind of inverted
pyramid like a mill-hopper; and fearing at first that the small
grate contained in it might be clogged by cinders, and the passage
of the flame sometimes obstructed, I ordered a little door near the
grate, by means of which I might on occasion clear it: though after
the stove was made, and before I tried it, I began to think this
precaution superfluous, from an imagination, that the flame being
contracted in the narrow part where the grate was placed, would be
more powerful in consuming what it should there meet with, and that
any cinders between or near the bars would be presently destroyed
and the passage opened. After the stove was fixed and in action, I
had a pleasure now and then in opening that door a little, to see
through the crevice how the flame descended among the red coals,
and observing once a single coal lodged on the bars in the middle
of the focus, a fancy took me to observe by my watch in how short a
time it would be consumed. I looked at it long without perceiving
it to be at all diminished, which surprised me greatly. At length
it occurred to me, that I and many others had seen the same thing
thousands of times, in the conservation of the red coal formed in
the snuff of a burning candle, which while envelloped in flame, and
thereby prevented from the contact of passing air, is long continued
and augments instead of diminishing, so that we are often obliged
to remove it by the snuffers, or bend it out of the flame into the
air, where it consumes presently to ashes. I then supposed, that to
consume a body by fire, passing air was necessary to receive and
carry off the separated particles of the body: and that the air
passing in the flame of my stove, and in the flame of a candle,
being already saturated with such particles, could not receive more,
and therefore left the coal undiminished as long as the outward air
was prevented from coming to it by the surrounding flame, which
kept it in a situation somewhat like that of charcoal in a well
luted crucible, which, though long kept in a strong fire, comes out
unconsumed.
An easy experiment will satisfy any one of this conserving power of
flame envelloping red coal. Take a small stick of deal or other wood
the size of a goose quill, and hold it horizontally and steadily in
the flame of the candle above the wick, without touching it, but in
the body of the flame. The wood will first be inflamed, and burn
beyond the edge of the flame of the candle, perhaps a quarter of an
inch. When the flame of the wood goes out, it will leave a red coal
at the end of the stick, part of which will be in the flame of the
candle and part out in the air. In a minute or two you will perceive
the coal in the air diminish gradually, so as to form a neck; while
the part in the flame continues of its first size, and at length the
neck being quite consumed it drops off; and by rolling it between
your fingers when extinguished you will find it still a solid coal.
However, as one cannot be always putting on fresh fuel in this stove
to furnish a continual flame as is done in a candle, the air in the
intervals of time gets at the red coals and consumes them. Yet the
conservation while it lasted, so much delayed the consumption of the
coals, that two fires, one made in the morning, and the other in the
afternoon, each made by only a hatfull of coals, were sufficient to
keep my writing room, about sixteen feet square and ten high, warm a
whole day. The fire kindled at seven in the morning would burn till
noon; and all the iron of the machine with the walls of the niche
being thereby heated, the room kept warm till evening, when another
smaller fire kindled kept it warm till midnight.
Instead of the sliding plate E, which shuts the front of the box C,
I sometimes used another which had a pane of glass, or, which is
better, of Muscovy talc, that the flame might be seen descending
from the bottom of the vase and passing in a column through the box
C, into the cavities of the bottom plate, like water falling from a
funnel, admirable to such as are not acquainted with the nature of
the machine, and in itself a pleasing spectacle.
Every utensil, however properly contrived to serve its purpose,
requires some practice before it can be used adroitly. Put into the
hands of a man for the first time a gimblet or a hammer (very simple
instruments) and tell him the use of them, he shall neither bore a
hole or drive a nail with the dexterity and success of another who
has been accustomed to handle them. The beginner therefore in the
use of this machine will do well not to be discouraged with little
accidents that may arise at first from his want of experience.
Being somewhat complex, it requires as already said a variety of
attentions; habit will render them unnecessary. And the studious man
who is much in his chamber, and has a pleasure in managing his own
fire, will soon find this a machine most comfortable and delightful.
To others who leave their fires to the care of ignorant servants, I
do not recommend it. They will with difficulty acquire the knowledge
necessary, and will make frequent blunders that will fill your
room with smoke. It is therefore by no means fit for common use in
families. It may be adviseable to begin with the flaming kind of
stone coal, which is large, and, not caking together, is not so apt
to clog the grate. After some experience, any kind of coal may be
used, and with this advantage, that no smell, even from the most
sulphurous kind can come into your room, the current of air being
constantly into the vase, where too that smell is all consumed.
The vase form was chosen as being elegant in itself, and very
proper for burning of coals: where wood is the usual fuel, and
must be burned in pieces of some length, a long square chest may
be substituted, in which A is the cover opening by a hinge behind,
B the grate, C the hearth-box with its divisions as in the other,
D the plan of the chest, E the long narrow grate. (Plate, Figure
17.) This I have not tried, but the vase machine was completed in
1771, and used by me in London three winters, and one afterwards in
America, much to my satisfaction; and I have not yet thought of any
improvement it may be capable of, though such may occur to others.
For common use, while in France, I have contrived another grate
for coals, which has in part the same property of burning the smoke
and preserving the red coals longer by the flame, though not so
completely as in the vase, yet sufficiently to be very useful, which
I shall now describe as follows.
A, is a round grate, one foot (French) in diameter, and eight inches
deep between the bars and the back; (Plate, Figure 18.) the sides
and back of plate iron; the sides having holes of half an inch
diameter distant three or four inches from each other, to let in air
for enlivening the fire. The back without holes. The sides do not
meet at top nor at bottom by eight inches: that square is filled by
grates of small bars crossing front to back to let in air below,
and let out the smoke or flame above. The three middle bars of the
front grate are fixed, the upper and lower may be taken out and put
in at pleasure, when hot, with a pair of pincers. This round grate
turns upon, an axis, supported by the crotchet B, the stem of which
is an inverted conical tube five inches deep, which comes on as many
inches upon a pin that fits it, and which is fixed upright in cast
iron plate D, that lies upon the hearth; in the middle of the top and
bottom grates are fixed small upright pieces E E about an inch high,
which as the whole is turned on its axis stop it when the grate is
perpendicular. Figure 19 is another view of the same machine.
In making the first fire in a morning with this grate, there is
nothing particular to be observed. It is made as in other grates,
the coals being put in above, after taking out the upper bar, and
replacing it when they are in. The round figure of the fire when
thoroughly kindled is agreeable, it represents the great giver of
warmth to our system. As it burns down and leaves a vacancy above,
which you would fill with fresh coals, the upper bar is to be taken
out, and afterwards replaced. The fresh coals, while the grate
continues in the same position, will throw up as usual a body of
thick smoke. But every one accustomed to coal fires in common grates
must have observed, that pieces of fresh coal stuck in below among
the red coals have their smoke so heated as that it becomes flame
as fast as it is produced, which flame rises among the coals and
enlivens the appearance of the fire. Here then is the use of this
swivel grate. By a push with your tongs or poker, you turn it on
its pin till it faces the back of the chimney, then turn it over on
its axis gently till it again faces the room, whereby all the fresh
coals will be found under the live coals, and the greater part of the
smoke arising from the fresh coals will in its passage through the
live ones be heated so as to be converted into flame: whence you have
much more heat from them, and your red coals are longer preserved
from consuming. I conceive this construction, though not so complete
a consumer of all the smoke as the vase, yet to be fitter for common
use, and very advantageous. It gives too a full sight of the fire,
always a pleasing object, which we have not in the other. It may
with a touch be turned more or less from any one of the company that
desires to have less of its heat, or presented full to one just come
out of the cold. And supported in a horizontal position, a tea-kettle
may be boiled on it.
The author's description of his Pensylvania fireplace, first
published in 1744, having fallen into the hands of workmen in Europe,
who did not, it seems, well comprehend the principles of that
machine, it was much disfigured in their imitations of it; and one
of its main intentions, that of admitting a sufficient quantity of
fresh air warmed in entering through the air-box, nearly defeated,
by a pretended improvement, in lessening its passages to make more
room for coals in a grate. On pretence of such improvements, they
obtained patents for the invention, and for a while made great profit
by the sale, till the public became sensible of that defect, in the
expected operation. If the same thing should be attempted with this
vase stove, it will be well for the buyer to examine thoroughly
such pretended improvements, lest, being the mere productions of
ignorance, they diminish or defeat the advantages of the machine, and
produce inconvenience and disappointment.
The method of burning smoke, by obliging it to descend through hot
coals, may be of great use in heating the walls of a hot-house. In
the common way, the horizontal passages or flues that are made to go
and return in those walls, lose a great deal of their effect when
they come to be foul with soot; for a thick blanket-like lining of
soot prevents much of the hot air from touching and heating the brick
work in its passage, so that more fire must be made as the flue grows
fouler: but by burning the smoke they are kept always clean. The same
method may also be of great advantage to those businesses in which
large coppers or caldrons are to be heated.
_Written at Sea, 1785._
FOOTNOTE:
[60] From the Transactions of the American Philosophical Society, in
which it was read January 28, 1786. _Editor._
TO MISS STEPHENSON.
_Method of Contracting Chimneys. Modesty in Disputation._
_Craven-Street, Saturday Evening, past 10._
The question you ask me is a very sensible one, and I shall be
glad if I can give you a satisfactory answer. There are two ways
of contracting a chimney; one, by contracting the opening _before_
the fire; the other, by contracting the funnel _above_ the fire.
If the funnel above the fire is left open in its full dimensions,
and the opening before the fire is contracted; then the coals, I
imagine, will burn faster, because more air is directed through the
fire, and in a stronger stream; that air which before passed over
it, and on each side of it, now passing _through_ it. This is seen
in narrow stove chimneys, when a sacheverell or blower is used,
which still more contracts the narrow opening.--But if the funnel
only _above_ the fire is contracted, then, as a less stream of air
is passing up the chimney, less must pass through the fire, and
consequently it should seem that the consuming of the coals would
rather be checked than augmented by such contraction. And this will
also be the case, when both the opening _before_ the fire, and the
funnel _above_ the fire are contracted, provided the funnel above
the fire is more contracted in proportion than the opening before
the fire.--So you see I think you had the best of the argument; and
as you notwithstanding gave it up in complaisance to the company, I
think you had also the best of the dispute. There are few, though
convinced, that know how to give up, even an error, they have been
once engaged in maintaining; there is therefore the more merit in
dropping a contest where one thinks one's self right; it is at least
respectful to those we converse with. And indeed all our knowledge
is so imperfect, and we are from a thousand causes so perpetually
subject to mistake and error, that positiveness can scarce ever
become even the most knowing; and modesty in advancing any opinion,
however plain and true we may suppose it, is always decent, and
generally more likely to procure assent. Pope's rule
To speak, though sure, with seeming diffidence,
is therefore a good one; and if I had ever seen in your conversation
the least deviation from it, I should earnestly recommend it to your
observation.
I am, &c.
B. FRANKLIN.
TO MICHAEL HILLEGRAS ESQ.
_Respecting covering Houses with Copper.[61]_
_London, March 17, 1770._
DEAR SIR,
I received your favour of November 25, and have made enquiries, as
you desired, concerning the copper covering of houses. It has been
used here in a few instances only, and the practice does not seem to
gain ground. The copper is about the thickness of a common playing
card, and though a dearer metal than lead, I am told, that, as less
weight serves, on account of its being so much thinner, and as
slighter woodwork in the roof is sufficient to support it, the roof
is not dearer on the whole, than one covered with lead. It is said,
that hail and rain make a disagreeable drumming noise on copper; but
this I suppose is rather fancy; for the plates being fastened on
the rafters, must, in a great measure, deaden such sound. The first
cost, whatever it is, will be all, as a copper covering must last for
ages; and when the house decays, the plates will still have intrinsic
worth. In Russia, I am informed many houses are covered with plates
of iron tinned, such as our tin pots and other vases are made of,
laid on over the edges of one another like tiles; and which, it is
said, last very long, the tin preserving the iron from much decay by
rusting. In France and the Low Countries, I have seen many spouts or
pipes for conveying the water down from the roofs of houses, made of
the same kind of tin plates soldered together; and they seem to stand
very well.
With sincere regard, I am,
Yours, &c.
B. FRANKLIN.
FOOTNOTE:
[61] The two following letters, and the accompanying paper, appeared
in several periodical publications, both English and American, many
years before the death of Franklin, which is sufficient to give them
authenticity. _Editor._
TO SAMUEL RHOADS, ESQ.
_On the same Subject._
_London, June 26, 1770._
DEAR FRIEND,
It is a long time since I had the pleasure of hearing from you
directly. Mrs. Franklin has indeed now and then acquainted me of your
welfare, which I am always glad to hear of. It is, I fear, partly,
if not altogether, my fault, that our correspondence has not been
regularly continued. One thing I am sure of, that it has been from no
want of regard on either side, but rather from too much business, and
avocations of various kinds, and my having little of importance to
communicate.
One of our good citizens, Mr. Hillegras, anxious for the future
safety of our town, wrote to me some time since, desiring I would
enquire concerning the covering of our houses here with copper. I
sent him the best information I could then obtain, but have since
received the inclosed from an ingenious friend, who is what they call
here a civil engineer. I should be glad you would peruse it, think of
the matter a little and give me your sentiments of it. When you have
done with the paper, please to give it to Mr. Hillegras. I am told
by Lord Despencer, who has covered a long piazza, or gallery, with
copper, that the expence is charged in this account too high, for his
cost but one shilling and ten-pence per foot, all charges included.
I suppose his copper must have been thinner. And, indeed, it is so
strong a metal, that I think it may well be used very thin.
It appears to me of great importance, to build our dwelling houses,
if we can, in a manner more secure from danger by fire. We scarcely
ever hear of fire in Paris. When I was there I took particular notice
of the construction of their houses, and I did not see how one of
them could well be burnt, the roofs are slate or tile, the walls are
stone, the walls generally lined with stucco or plaster, instead of
wainscot, the floors of stucco, or of six square tiles painted brown,
or of flag stone, or of marble; if any floors were of wood, it was of
oak wood, which is not so inflammable as pine. Carpets prevent the
coldness of stone or brick floors offending the feet in winter, and
the noise of treading on such floors, overhead, is less inconvenient
than on boards. The stairs too, at Paris, are either stone or brick,
with only a wooden edge or corner for the step; so that on the whole,
though the Parisians commonly burn wood in their chimneys, a more
dangerous kind of fuel than that used here, yet their houses escape
extremely well, as there is little in a room that can be consumed
by fire except the furniture: whereas in London, perhaps scarcely a
year passes in which half a million of property and many lives are
not lost by this destructive element. Of late, indeed, they begin
here to leave off wainscoting their rooms, and instead of it cover
the walls with stucco, often formed into pannels like wainscot,
which being painted, is very strong and warm. Stone staircases too,
with iron rails, grow more and more into fashion here: but stone
steps cannot, in some circumstances, be fixed; and there, methinks,
oak is safer than pine; and I assure you, that in many genteel
houses here, both old and new, the stairs and floors are oak, and
look extremely well. Perhaps solid oak for the steps would be still
safer than boards; and two steps might be cut diagonally out of one
piece. Excuse my talking to you on a subject with which you must
be so much better acquainted than I am. It is partly to make out a
letter, and partly in hope, that, by turning your attention to the
point, some methods of greater security in our future building may be
thought of and promoted by you, whose judgment I know has deservedly
great weight with our fellow-citizens. For though our town has not
hitherto suffered very greatly by fire, yet I am apprehensive, that
some time or other, by a concurrence of unlucky circumstances, such
as dry weather, hard frost, and high winds, a fire then happening
may suddenly spread far and wide over our cedar roofs, and do us an
immense mischief. I am,
Yours, &c.
B. FRANKLIN.
_Paper referred to in the preceding Letter._
The carpentry of the roof being formed with its proper descents,
is, in the first place, sheeted or covered with deals, nailed
horizontally upon the rafters, after the same manner as when intended
to be covered with lead. The sheets of the copper for this covering
are two feet by four, and for covering the slopes of the roof are
cast so thin, as to weigh eight or nine pounds, and for covering the
flats or gutters, ten or eleven pounds each, or about one pound, or a
pound and a quarter, to the superficial foot.
A string of strong cartridge paper (over-lapping a little at its
joints) is regularly tacked down upon the sheeting, under the copper
covering, as the work proceeds from eaves to ridge. It prevents the
jingling sound of hail or rain falling upon the roof, and answers
another purpose to be mentioned by-and-by.