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2188. T o circulate w a te r in ascending and descending pipes, it is necessafy to hare a
close or covered toiler. In tins case a pipe may, at any distance from the boiler, rise to
any lieiglit, and descend again ; but it must neither rise twice, nor dip after L e m n g the
boiler, mere it is necessary to raise it, there should be an open pipe inserted at its
extremity, of a height equal to the rise. In heating hothouses, advantage may be taken
of this circumstaiiee to carry the hot water over doonvays, as in Jig. 632.
2139. T h e boilers fo ,' either o fth e abcme ,nodes o f heating may he constructed m such a
manner as to have the largest possible bottom surface exposed to the action « “ e "®-
Accordmg to Mr. Tredgold, tor burning a bushel of coals per hour, the
grate should not he less than 8, or greater than 16, square feet; and the bottom suiface
should ho four times the area of the grate, with 32 feet of side-flnc. A consideiahle advantage,
accordmg to tliat engineer, results from adopting the larger pro^rtion foi toe
grate and bottom surface, on account of the fire requinng less attention. The best mode
of rcgidating too fire is, by means of a door to the ashpit liaving a registei ; “ ™-
provctacnt which was first suggested by Dr. Black, and afterwards adopted Count
Eninforcl. One of toe most effective boilers is that adopted hy Messrs. Cottam and
Hallcn, Winsley Street, Oxford Street, London ( fig . 633.).
2140. F o r c irc u la tin g w ater below the level o f the boiler, it is necessary, in the first place,
to raise the water, as it is heated, to as great a height above tho boiler as it is propascd
to circulate it below. This may he done m any closed boiler with a tube pioecedino
fi-om its cover ; or in any boiler of a height above the fire, oqiml to toe depth below it, to
which it is intended to circulate the water. This mode will he very readily understood by
a reference to the apparatus of Mr. Weeks, explained by toe following diagram (Jig . 634 ).
In this flgm-o, a is a section of the fireplace, which, instead of having a common boilei
over it, is surrounded by cast-iron tubes. The uppermost of these tubes communicates,
hy means ofthe upright tube b, with the open vessel c ; and toe lowermost is connected,
h'i a similar manner, by means of the tube d, with one or any number of tMies undei
toe level of toe boiler at e. The uppermost of the tubes, at e, is connected by the titoe
/with the open vessel c. Now, all those tubes being so comiectcd as to admit ol watei
oo 0 a o
o 0
0 «
circulating freely tlirough them, when afire is made in a, the lieated
water ascends by its rarefaction into the open vessel c ; and its place
in the tubes round the fire is supplied by the colder water from e,
through d ; the heated water descending to supply its place from
the open vessel c, by the tube / . The limit of the depth to which
the water will circulate below, is that of the height of the open
vessel above. To produce this circulation, it is not necessary that
the water should boil; for, as every heated particle will ascend to
the open vessel c, its place must be supplied by a cold particle
from d. When the fire is lU'ged so as to raise the water in the open
vessel nearly to the boilmg point, the circulation goes on with the
greatest rapidity. The substitution of tubes round the fire for a
boiler over it, is by no means necessary for the success of this plan,
though by tubes the rapidity of the circulation is greatly increased.
Any close boiler with the tube b attached to its cover, and communicating
with an open vessel fixed at any height, such as c, having
another tube, similar to / , affixed to it, will circulate the heated
water from such vessel to a point below the bottom of the boiler,
nearly equal to the balance of atmospherical pressure, or say 30 ft.
below it. Messrs. Cottam and Hallen, and Mi-. Timothy Bramah,
have both circulated hot water on a large scale upon this principle.
2141. The c irc ula tio n o f hot w ater on the siphon p rin c ip le appears
to have been invented about the same time by Kewley and Fowler,
already mentioned ; bnt it was first exemplified by the former engineer,
in Colvill’s nursery, in 1826. Mr. Fowler took out a patent
for his mode in 1829, and some hothouses in Devonshire have since
been heated by it. Mr. Kewley’s mode has been extensively employed
in vai-ious pai-ts of the counti-y. We shall describe both.
2142. F o w le r ’s method o f c irc u la tin g hot w a ter in his thermosiphon conshts in employing
the power of the descending fluid iu the leg of a common siphon, to draw up hot
fluids in the opposite leg, “ for the purpose of causing hot fluids to flow from boiler to
boiler, or from vessel to vessel, through connecting tubes of various
lengths and forms. How tliis is done will be readily understood by
reference to the diagram shown in fig . 635. Supposing the water
of an uniform temperature in both legs of the siphon (a b), no circulation
would take place; but supposing it to cool sooner in the long
leg (a) than in the short leg (6), then the equilibrium would be destroyed,
and tlie water in the long leg (a) wonld descend, and draw
up hot water throngh the short leg (¿); and this circulation would
continue as long as the water at c was maintained at a temperature
above that of the surrounding atmosphere.” Any engineer will
easily see how this principle may be applied to the circulation of hot
water in horizontal tubes; and tliis apphcation has been made in a
very perfect manner by Mr. Kewley.
2143. K e w le y’s method o f cii'culating hot w a te r on the siphon p rin c ip le is one of the vciy
best modes wliich has yet been applied to the heating of hothouses, but as it requires
some scientific knowledge, as well as practical skill, ou the part of the mechanic who fits
it up, and as this branch of engineering is in the hands of ironmongers who know very
little of its principles, it has by no means become so general as it deserves. Mi-. Kewley’s
mode will be understood by the following diagram (fig . 636.) : a c e represent the two
legs of the siphon; the „gg
upper lee:, commencing at J
c, being that through '
wliich the heated water
ascends, and the lower leg
being that by which it returns.
The point e may
be at any distance from the boiler containing the open ends of the siphon. On the upper
part of the pipe, at e, a small orifice is connected with an air-pump, by a pipe which need
not be more than half an inch in diameter. The air-pump may be placed in any convenient
situation, and the pipe connecting it with the siphon may be bent in any direction.
The use of the air-pump is twofold: first, to exhaust the siphon, in order that it
may be filled with water ; and, secondly, to exhaust the air which always collects in the
highest part of any tube in which wator is circulated. The expense of a good air-pump,
suitable for this pm-pose, is about 2/.; but for those who think this too much, there may
be a small brass cock introduced on the upper surface of the liighest part of the pipe,
and, a fiinnel being put over it, and stoppers of any kind in the open ends of the siphon,
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