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2110 B ro a d and deep flu e s , agreeably to the Dutch practice, have been
recommended by Stevenson {C a le d . Mem.); that of making J»'-
row and deep, agreeably to the practice in Russia, is recommondod by
Oldacro, gardener to Sir Joseph Banks ; and that of u^ng thin bricks (fig .
614.) with tliiek edges, by J. R. Gowen, Esq. (H o rt. T ra n s ., m.) In Mi.
Gowen’s flues, the section (fig . 615. a)
shows less materials than any other brick
flue, the covers (b ) and the sidc-wall
bricks (c) being quite thin, the base requisite
for building the latter on one another
i l
being obtained by the thickness of their
edges (d, e), which is equal to that of
common bricks. Glazed tiles are now
frequently used for making flues.
2111. Can-Jlues (fig . 616.),long since
used by the Dutch, embedded iu sand,
and for the last fifty years occasionally . , , n
in England, are sometimes employed. They consist of earthen pipes, straight (a ), oi
rounded at the ends for returns (b ), and joined together by cement, placed on bricks (c).
They are rapidly heated, and as soon cooled. None of the heat, however, which passes
through them, can be said to be absorbed and lost in the mass of enclosing matter, as
Knight and Sir Joseph Banks (H o rt. T ra n s .) assert to be the case with common flues.
They are only adapted for moderate fires, but, judiciously chosen, may frequently be
more suitable and profitable than commou flues; as, for example, where there arc only
slight fires wanted occasionally, or where there is a regular system of watchi^ the
fires; in which case, but not otherwise, the temperature can be regulated with sufficient
certainty. These can-flues are now very seldom met with.
2112. T h e best sort o f fin e s , after all that has been said on the subject, is, in our opinion,
the common form, huilt of thin well-bm-ned bricks neatly joined, with the bottoni
and top of tiles, and no plaster used either inside or outside. Where only one course of
a flue can be admitted, the broader it is the more heat will he given out as it proceeds,
and, as a consequence, one extremity of the space_ to be heated will be hotter than ffie
other ; a return or double coui'se of a narrow flue is, therefore, almost always preferable
to one course of a broad flue. _ . , . , • -j
2113. T he size o f fin e s is seldom less than 9 in. wide, by 14 in. or 18 in. high mside
measure, which suits a furnace for good coal, whose floor or chamber is 2 ft. long, 18 in.
wide, and 18 in. liigh. According as the object vaiics, so must the proportion both of
furnaces and flues. .
2114. Th e d irection o f flu e s , in general, is round the house, commencing always withm
a short distance of the parapet; and after making the com-se of three sides, that is, of the
end at wliich the fire enters, of the front, and of the opposite end, it rctiu-ns (in narrow
houses) near to or in the back waU, or (in -wide houses) up the middle, fonnmg a path;
and (in others) immediately over or along side of the first com-se. In all narrow houses
this last is the best mode.
2115. T he pow er o f fin e s depends so much on their construction, the kind of fuel, the
roof, mode of glazing, &c., that very little can be affii-med with any degree of certainty on
this subject: 3000 cubic feet of air is in general enough for one fire to command in stoves
or forcing-houscs; and 5000 in lean-to greenhouses. In houses exposed on all sides,
2000 cubic feet is enough in stoves, and 3000 cubic feet for greenhouses. Tlie safest
side on which to err is rather to attach too little than too much extent to each fire, as
excessive fires generally force through the flues some smoke or mephitic air; and besides
produce too much heat at that pait of the house where the flue enfyrs.
2116. D am p ers, or w/aes, are useful in flues and chimneys, both in case of accident and
also to moderate the heat, or, in case of one furnace supplying two flues, to regulate the
f smoke and heat. Eor general purposes, however, the ash-pit door is perfectly
sufficient. The damper, and furnace, and ash-pit doors ought seldom to be all shut at
the same time, as such a confinement of the hot air of the flue is apt, owing to its expansion
by increased heat from tlic hot masonry, to force some of it through the joints of
the flue into the house.
Book I.
2117. W itty ’s smoke-consuming fu rn a c e . The advantage of this furnace is, that ail
the fresh coal supplied to it is carbonised hy the heat fr-om the burning coke or carbonised
coal below ; the gas disengaged from the coal by the process of carbonisation
being also inflamed by the heat. The coal is thus, instead of being burned in a crude
state, subjected to carbonisation previously to combustion, and consequently does not
produce smoke. In fig . 617., which is a section of the fm-nace, a is the hopper, mto
which slack, or reliise coal, is put through
the door (b ) ; d is an oblong square box
the ividth of the furnace, fitted with a
screw and cross-bar, by which the pusher
or presser (c c) is moved backwards and
forwards at pleasure, in order to let the
coals down from the hopper, or to advance
them fonvard down the inclined
plane ( / / ) which is made of fine tile supported
by cross-bearing bars (g g ). The
grate (h ) swings on its centre ( i) , which
may be placed at the most convenient
angle, and supported by a brick placed in
the opening atn, which sei-ves for clearing
out the ashes and clinkers, when required
; k is the ash-pit, and I, the steps leading to it.
SuBSECT. 7. Steam B o ile rs and Tabes.
2118 Steam afford s a simple and effectual mode o f heating hothouses, and, indeed, large
bodies of air in eveiy description of chamber ; for no other fluid is found so convenient
a can-ier of heat. Steam was the first improvement on the old mode of heating by flues,
and it is still occasionally used, though it has been almost superseded by hot
water. The heat given out by vapour differs in nothing from that given out by
smoke ; though an idea to the contrary prevails among gardeners, from the cfrcrnn-
stances of some foul air escaping into the house from the flues, especially if these are
over-heated or over-watered ; and from some vapour issuing from the steam-tubes when
these are not perfectly secure at the joints. Hence flues are said to produce a burnt or
drying heat, and steam-tubes a moist or genial heat ; and in a popular sense this is correct,
for the reasons stated. It is not, however, the genial nature of steam heat which
is its chief recommendation for plant-habitations, but the equality of its distribution,
and the distance to which it may be carried. Steam can never heat the tubes, even close
to the boiler, above 212 degrees, and it will heat them to the same degree, or nearly so,
at the distance of 1000, 2000, or an indefinite number of feet. Hence results the convenience
of heating any range or assemblage of hothouses, however gi-eat, from one
boiler, and the lessened risk of over or insufficient heating at whatever distance the house
may be from the fireplace. The secondary advantages of heating by steam are, the
saving of fuel and labour, and the neatness and compactness of the whole apparatus.
Instead of a gardener having to attend to a dozen or more fires, he has only to attend to
one • instead of ashes, and coal, and unsightly objects at a dozen or more places in a garden,
they are limited to one place ; and, instead of twelve paltry chimney-tops, there is only
one which, being necessarily large and high, may be finished as a pillar, so as to have
effect as an object ; instead of twelve vomiters of smoke and flakes of soot, the smoke may
be bm-ned by using some smoke-consuming furnace. The steam-tubes occupy much
less space in the house than flues, and require no cleaning ; they may often pass nnder
paths where flues would extend too deep ; there is no danger of steam not draw ing , or
circulating freely, as is often the case with flues, and always when they are too narrow or
too wide, or do not ascend from the furnace to the chimney ; steam is impelled from the
boiler and wfil proceed with equal rapidity along small tubes or large ones, and descending
or ascending. Finally, with steam, insects will be effectually kept under in
hothouses, with the gi-eatest ease, by merely keeping the atmosphere of the house chai-ged
with vapour from the tubes for several hours at a time.
2119. T h e disadvantages o f steam as a vehicle f o r conveying heat to hothouses are lew.
On a small scale it is more expensive than the mode by flues, and more trouble is required
to attend to one boiler than to one or even two or three fiirnaces. It is also somewhat
more expensive than heating hy hot water. These ai-c all the disadvantages we know ot.
It has been stated by some that steam draws up or etiolates plants, and lessens the tl^our
of fruits ; but we are inclined to consider such effects, when attendant on plants or firaits
in houses heated by steam, as resulting from some deficiency of management in other
points of culture.