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it may bo filled througli the funnel. Air which collects at this highest point may also
he lot off by opening the cock, after having previously stopped the open ends of the
siphon, and ponring in as much water as will supply the place of tho air, after which the
cock is to be sliiit. 2144. ^ T h e c irc u la tio n o f h ot iva te r in hermeticalhj scaled tubes is the invention ot
A M Perkins, Esq,, the son of the celebrated American engineer. This plan will be
readily understood by tho diagram ( fig . 637.) ; in wliich a 6 is a coil of wrought-iron
tubes, about an inch in diameter, by
one of which tubes (c) the hot water
ascends and circulates, and by an- j 1 _ 637
other (d ) it returns to be again
heated. The fire is made in the
centre of the coil at e ; not in direct
contact with the tubes, but separated
from them by brickwork, over which
the heat and smoke pass, and circulate
638
in the flue which contains tlie
coil. The fuel is put in from above,
and the ashes ai-e taken out below.
As water is practically an incompressible
fluid, it is evident that if
the hermetically sealed pipes were
completely filled with it, and heated,
they wonld burst; but, to provide
against this, after the pipes are filled
as high as g, there is what is called
an expansion tube ( / ) added, which allows of the expansion of the water in the form
of high-pressure steam. The advantages of this mode of heating ai*e its economy and
neatness; but its disadvantages arc,
the danger of accidents by the bursting
of pipes containing water so intensely
heated, the unpleasant smell
frequently perceived from the pipes,
their inequality of temperature, and
the rapidity with which they cool
when the fire slackens. (See E nc yc.
o f D om estic E conom y, p. 85.)
2145. B u rh id g e a nd H e a h fs conic
a l ribbed boiler, with Sylvester’s
patent fire-doors, is now considered
one of the best methods of heating
hy hot water. The boiler is round,
with a double set of supply and rc-
tiu*n pipes, as shown in fig . 638.; and
it is hollow in the centre, as shown in
the section ( fig . 639.); so that the
flame from the furnace not only goes
up each side of the boiler, but up the
middle, and thus the water is kept
so continually hot, that the circulation,
as indicated by the course of
the aiTows, is extremely rapid. Sylvester’s
patent fire-doors are very
superior to the ordinary hinged doors
used for furnaces, as tliey are fixed
in an iron frame, and slide backwards
and forwards on rollers. It
is obvious that doors of this kind,
which can be easily opened and
closed by pushing them with the
shovel used for putting on the coal,
are much less liable to go out of
repair than the old doors, which were
hung on hinges, and fastened with
a hasp, and were ever in danger of
being broken or strained by being
opened with the shovel.
Su b se c t. 9. H e a tin g by ihe C irc u la tio n o f H o t A ir .
2146. I t has long heen a desideratum in hothouse culture to combine heating with ventilation,
or, in other words, to produce an agitation of -«'arm air in plant-houses, in imitation
of tiie natural movement of the wind in the open air. The principal difficulty in
effecting this has been to find a means of warming the air before it is admitted into the
house ; as though ventilation or a cuiTcnt of air tlirough a plant-house is easily obtained
by opening the sashes at the lowest part in front, and at the highest pai-t of the roof, the
air admitted being that of the atmosphere is necessarily colder than that of the house ;
and of course, if not warmed, it will produce a chilling eficct upon the plants.
2147. The fir s t attempt to heat hotliouses hy hot air appears to have been made by
Dr Anderson as early as 1802, in a greenhouse attached to his house at Isleworth ;
and a patent was taken out for a nearly similar plan the following year by Mr. Stewart.
Neither plan, however, answered ; in the one case, from the air admitted into tlie house
hcincr too dry for the plants, and in the other, from a deficiency of heat. Some years
aftenvards, the hothouses of Messrs. Strutt, at Belper and Derby, were heated by a current
of hot air wanned by a cockle stove, and returned to be reheated by the stove after it
had been chüled in the house. By this plan, which is a very complete one, fresh atmospheric
air can be admitted when necessary, and heated before it is allowed to enter
the house : the heated air is also made to pass over water, and thus becoming surcharged
with moisture, it is free from the defects experienced in the first modes of heating by
hot air. In 1825, the large conservatory at the Grange was heated by hot air produced by
one of Mr. Sylvester’s cockle stoves in combination with steam, a plan which answered
very well, but was expensive; in 1840, the late Mr. Penn, an engineer at Lewisham,
invented ’a mode of heating by hot air in combination with hot-water pipes ; and in
18-11 the Polmaise system was invented. As the last two systems havB occasioned considerable
discussion, and have been compared with each other, though they ai-e, in fact,
essentially different, we shall describe both of them somewhat in detail.
2148. M r . P e n n’s system. According to this plan, the air in the house was heated
by hot-ivater pipes ; and there was a drain under the house fitted with a grating, through
which the air when cooled was intended to bo conveyed, so as to be reheated by the
pipes as sliown in fig . 640., in which a represents the hot-water pipes; d, the dram; b,
the opening through which the air heated hy the pipes was to enter the house ; and c,
the grating thi-ough which the air when cooled was to descend to the dram. The house
was furnished with a back shed, which had a double roof to retain the heat; and there
was a border, sho\vn at/, used for forcing sea-kale, rhubarb, &c. Where the house was
large, there were several drains, bnt care was taken in forming them, that they should
open to the pipes, not directly under the upright tubes, but in the space between them,
as sliowm in fiq . 641., in which g g are the drains ; h, the situation of the gi-atmgs over
them; i, the situation of the tubes; and k, the hot-water pipes. The object of tins
an-angement was, to allow the an from the drains to pass a short distance along the
hoc-water pipes, so as to he reheated before it ascended to enter by the openings b. » hen
it appeai-ed desirable to change the air of the house, this was not done by opening the
sashes in the usual way, but by taldng the stoppers out of two openings into the back
drain which contained the hot-water pipes, one at each end, and communieatmg with
the open air These openings were so small, that eacli might be filled up with a brick,
and made air-tight by a little clay. It ought to be observed, that the wooden tubes by
which the hot air ascended were all made perfectly air-tight; and those in the sheds,
being of rough boards rudely joined, had the joints covered with strong paper pasted or
glued on.
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