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that no air or smoke may pass up it, without going under the false back. Then from side to side of your hollow, against the marks you made with chalk, raise a tight partition, brick-on-edge, to separate the air from the smoke, bevelling away to half an inch the brick that comes just under the air-hole, that the air may have a free passage up into the air-box. Lastly, close the hearth over that part of the hollow that is between the false back and the place of the bottom plate, coming about half an inch under the plate, which piece of hollow hearth may be supported by a bit or two of old iron hoop; then is your chimney fitted to receive the fire-place.
To set it, lay first a little bed of mortar all round the edges of the hollow, and over the top of the partition ; then lay down your bottom plate in its place (with the rods in it) and tread it till it lies firm. Then put a little fine mortar (made of loam and lime, with a little hair,) into its joints, and set in your back plate, leaning it for the present against the false back; then set in your air-box, with a little mortar in its joints; then put in the two sides, closing them up against the air-box, with mortar in their grooves, and fixing at the same time your register; then bring up your back to its place, with mortar in its grooves, and that will bind the sides together. Then put in your front plate, placing it as far back in the groove as you can, to leave room for the sliding plate; then lay on your top plate, with mortar in its grooves also, screwing the whole firmly together by means of the rods. The capital letters, A, B, D, E, &c. in the annexed cut [Plate VI.], show the corresponding parts of the several plates. Lastly, the joints being pointed all round on the outside, the fire-place is fit for use.
first fire in it, perhaps, if the
chimney be thoroughly cold, it may not draw, the work too being all cold and damp. In such case, put first a few shovels of hot coals in the fire-place, then lift up the chimney sweeper's trap-door, and putting in a sheet or two of flaming paper, shut it again, which will set the chimney a drawing immediately, and, when once it is filled with a column of warm air, it will draw strongly and continually.
The drying of the mortar and work by the first fire may smell unpleasantly, but that will soon be over.
In some shallow chimneys, to make more room for the false back and its flue, four inches or more of the chimney-back may be picked away.
Let the room be made as tight as conveniently it may be; so will the outer air, that must come in to supply the room and draft of the fire, be all obliged to enter through the passage under the bottom plate, and up through the air-box, by which means it will not come cold to your backs, but be warmed as it comes in, and mixed with the warm air round the fire-place, before it spreads into the room.
But, as a great quantity of cold air, in extreme cold weather, especially, will presently enter a room if the door be carelessly left open, it is good to have some contrivance to shut it, either by means of screw hinges, a spring, or a pulley.
When the pointing in the joints is all dry and hard, get some powder of black lead (broken bits of black lead crucibles from the silversmiths, pounded fine, will do), and mixing it with a little rum and water, lay it on, when the plates are warm, with a hard brush, over the top and front plates, part of the side and bottom plates, and over all the pointing; and, as it dries, rub it to a gloss with the same brush, so the joints will not be discerned, but it will look all of a piece, and shine like
new iron. And, the false back being plastered and whitewashed, and the hearth reddened, the whole will make a pretty appearance. Before the black lead is laid on, it would not be amiss to wash the plates with strong lie and a brush, or soap and water, to cleanse them from any spots of grease or filth that may be on them. If any grease should afterwards come on them, a little wet ashes will get it out.
If it be well set up, and in a tolerably good chimney, smoke will draw in from as far as the fore part of the bottom plate, as you may try by a bit of burning paper.
People are at first apt to make their rooms too warm, not imagining how little a fire will be sufficient. When the plates are no hotter than that one may just bear the hand on them, the room will generally be as warm as you desire it.*
* When this pamphlet was first printed, a copy of it was sent by Mr Cadwallader Colden to the celebrated Gronovius, with a letter from which the following is an extract.
"I send with this a curious and new invention for warming a room with a small fire, and more effectually than can be done by a large fire, in the common method, and is free of the inconveniences which attend the Dutch and German stoves, because by this contrivance there is a continual supply of fresh warm air. It may be particularly useful to you and Dr. Linnæus, by preserving your health while it keeps you warm at your studies. It is the invention of Mr. Benjamin Franklin of Philadelphia, the printer of it, a very ingenious man."
To this passage Gronovius replied as follows, in a letter dated at Leyden, July 9th, 1745.
"I am very much obliged to you for Mr. Franklin's book, which I don't doubt the next letter shall bring to you translated into Dutch.' — EDItor,
I received your favor of the 20th past, with your medical piece enclosed, the reading of which gave me a great deal of pleasure. I showed it to our friend Mr. Bartram, who carried it home, and, as he since tells me, is taking a copy of it. His keeping of it for that end has prevented my showing it to any other gentleman as you desired, and hitherto prevented my writing to you upon it, as I intended. But, lest you should conclude me the very worst correspondent in the world, I shall delay no longer giving you some thoughts, that occurred to me in reading of it, choosing rather to be blamed for not writing to the purpose, than for not writing at all.
I am extremely pleased with your doctrine of the absorbent vessels intermixed with the perspiratory ducts, both on the external and internal superficies of the body. After I had read Sanctorius, I imagined a constant stream of the perspirable matter issuing at every pore in the skin. But then I was puzzled to account for the effects of mercurial unctions for the strangury, sometimes occasioned by an outward application of the flies, and the like; since whatever virtue or quality might be in a medicine laid upon the skin, if it would enter the body, it must go against wind and tide, as one may say. Dr. Hales helped me a little, when he informed me, in his Vegetable Statics, that the body is not always in a perspirable, but sometimes in an imbibing state, as he expresses it, and will at times actually grow heavier
by being exposed to moist air. But this did not quite remove my difficulty; since, as these fits of imbibing did not appear to be regular or frequent, a blistering plaster might lie on the body a week, or a mercurial unguent be used a month, to no purpose, if the body should so long continue in a perspirable state. Your doctrine, which was quite new to me, makes all easy; since the body may perspire and absorb at the same time, through the different ducts destined to those different ends.
I must own, however, that I have one objection to the explanation you give of the operation of these absorbents. That they should communicate with the veins, and the perspirants with the arteries only, seems natural enough; but, as all fluids by the hydrostatical law pass equally in all directions, I question whether the mere direction of one of those minute vessels, where it joins with a vein or artery, with or against the stream of blood in the larger vessel, would be sufficient to produce such contrary effects as perspiring and absorbing. If it would, both perspirants and absorbents might proceed from the arteries only, or from the veins only, or from both indifferently; as, by the figure in the margin, whether the vessel a b is an artery or a vein, if the stream moves from a to b, the minute
communicating vessel c shall be a perspirant, and d an absorbent; and the contrary, if it moves from b to a. Yet I cannot say I am certain the mere direction of the vessels will have no effect; I only suspect it, and am making a little machine to try an experiment with, for satisfaction.
It is a siphon made of two large joints of Carolina