Jan.] the HOT-HOUSE. 93 
with a separate range of flues; in either case you may form them 
wholly on the outside, or part outside and part running through 
the wall. 
This furnace is to be made large or small according to the kind 
of fuel intended to be used, and the number of returns of the flues 
inside; for when there are but few returns, a greater quantity of fire 
will be necessary to keep a sufficient heat. If the returns are fre- 
quent, and wood is to be the fuel, the furnace is to be made only 
three feet deep, to receive wood two and a half feet long or better; 
but if the flues run only once round with no returns, the depth must 
be five feet to receive four feet wood, especially if the house be 
large; in either case the furnace is to be made eighteen inches 
wide at bottom, the sides sloping outward to the height of twenty 
inches, where it is to be twenty-two inches wide, covered from thence 
by an arch, the top of which is to be two feet from the grate, which 
is to be made of iron bars, and one half of the depth of the furnace; 
the brick for the furnace should be laid in good well-worked brick 
clay (not in mortar), which, when burned by the fire, will cement 
so as to become a solid mass; this must have an iron barred grate 
one-half of the depth of the furnace, as before observed, the re- 
mainder of the depth to be made solid with brick, having an ash- 
hole underneath, with a close-shutting door to it. The furnace must 
also have an iron door placed in an iron frame, which door must be 
furnished near the lower part with another small door, for the 
admission of air to the fires, both having latches, so as to shut close 
occasionally; observing that this door is not to be wider than what 
is necessary for the admission of the firewood. Having both your 
ash-hole and furnace thus provided with close shutting doors, you 
may manage your fires to great advantage, by closing them up 
occasionally from too great a current of air, especially when burned 
clear, which would carry oft" the heat through the flues tOo rapidly. 
If you intend to burn stone coal, the furnace need not be so large, 
but the grate must run the whole depth. 
Having finished the furnace, proceed to carry up the walls, ob- 
serving particularly to leave a scarcement a foot wide in both end 
walls, immediately opposite where the back wall flues are to be 
erected, from the level of the lowest flue to the top of the highest, 
by which means you can open the ends of the flues and clean them 
when necessary, either by running in scrapers on the ends of long 
poles, or hauling any kind of small brush wood through them, by 
means of a line, from one end to the other; these scarcements may 
either be made up with brick from time to time, or with sashes and 
shutters, which will be more convenient. Whenever there arc 
returned flues, one above the other, similar contrivances will be 
found useful; but where there is only one running flue, a top tile 
may be taken off at convenient distances, by which means it can 
be cleaned. 
When the walls are finished, then begin to erect the flues along 
the inside walls; but, as before mentioned, it would be advisable to 
have them detached therefrom two or three inches, that, by being 
thus apart, the whole heat may arise from both sides of the said 
