116 
THE DICTIONARY OF GARDENING, 
Heating—continued. 
generated by the combustion of fuel inside a boiler, heat 
may be conveyed, by water or air, to a considerable dis- 
tance ; the more remote it is, the less will be the amount 
that reaches the further extremity. Heated air or water 
becomes lighter than when cold, and naturally ascends in 
consequence. Either may be conducted in an upward 
incline, or in a perpendicular or horizontal direction, but 
not readily downwards, on account of the disposition of 
all heated substances to ascend. ‘This transmission of 
heat in pipes containing water is usually termed circula- 
tion, and the arrangement of the pipes throughout, to 
allow an unimpeded circulation, is one of the main prin- 
ciples of Heating, but is not sufficiently recognised in 
many instances. ‘The boiler must be placed below the 
level of any point the heat from it is intended to reach, 
the upper, or flow pipe, being connected on the top. The 
return pipe, by which the cold water enters, should be 
rendered free from the action of the fire by connecting 
it near the base—at the front preferably—-and on both 
sides, if this is convenient. Dips in the pipes at any 
point should be specially avoided, as they frequently im- 
pede free cireulation—generally more so when extra heat 
is applied. Houses erected for various purposes may have 
their quantity of pipes in proportion to the heat re- 
quired, and still be in connection with the same mains 
conducting heat to others having much higher tempera- 
tures. ‘There are no special rules applicable, in all cases, 
as to how many pipes a certain house will require, so 
much depending on stoking, and upon the amount of 
heat that may be available. It is best to provide for 
emergencies, in the first place, by insuring a sufficiency 
of piping, and inserting valves in the flow and return 
pipes, for regulating the admission of heat. In the 
arrangement of a Heating apparatus, an important 
part should be taken by the gardener in charge, as, 
although the workmen employed may understand the 
principles on which the success of their work depends, 
they do not similarly understand the requirements of 
plants. A proper system must be adopted where there 
are several houses to be heated and kept at different 
temperatures, by one or more boilers set and connected 
together. Main flow and return pipes should be fixed, 
with a gradual rise, at a point below all others in con- 
nection, and near the central part of the distance the 
heat is intended to reath, so that branches may be taken 
on either side. All houses or pits intended for Heating 
separutely, and irrespective of the one adjoining, should be 
provided with check valves near the junction with the main 
pipes. As heat always rises most rapidly to the highest 
points, it should be arranged that these are in the houses 
required at the highest temperatures. Pipes 4in. in 
diameter are those most largely used for top heat; 
others, only 3in., are well adapted for beds or for small 
» In houses specially devoted to plants requiring 
a somewhat dry atmosphere in winter — Pelargoniums, 
for instance—an extra 2in. pipe is sometimes fixed along 
the lower part of the rafters for drying the air, this 
being generally attended with excellent results in the 
production of large, clean flowers, free from damp. 
 _ Boilers. Of these, there are numerous forms in use. 
Some are composed of one or two series of cast-iron 
pipes placed in an upright or horizontal direction, and 
exposed to the action of the fire. Others are made 
of welded or wrought iron, and as they can be pur- 
chased in such a variety of sizes, and invariably answer 
well, their use 1s somewhat extensive. The more simple a 
boiler is in construction, and the greater surface it ex- 
poses to the direct action of fire used, the better. Tubu- 
lar boilers frequently become choked with fuel amongst 
the pipes or tubes, and, if this is not prevented, a great 
loss of heat is sustained. Boilers having complicated 
arrangements of any sort are seldom so effective as 
those of a simple form, the divisions between the 
Heating—continued. 
parts in the furnace soon becoming choked with soot. 
The requisite size of boiler depends on its approximate 
Heating power, the length of pipes connected, and the 
amount of heat required. It is advisable to make pro- 
vision, in the first place, by fixing a Heating power con- 
siderably higher than that absolutely necessary. A great 
deal depends on the sort of fuel used, the rapidity of 
draught, and the manner of stoking. The plain Saddle 
Boiler is well known as being one of the oldest types, 
but, when properly set, still amongst the most efficient. 
There are various modifications of it, which claim various 
advantages, such as economising fuel, heat, &c. One 
of the most useful and efficient forms is the Flue and 
ic 
Fic, 172. FLUE AND TERMINAL END SADDLE BOILER, 
a, Flow Pipe; b, b, Return Pipes; c, Flue. 
Terminal End Saddle (see Fig. 172). It is a wrought 
welded boiler, made in sizes varying in length from 
2ft. to 5ft., heights and transverse inside measure- 
ments being in proportion. The approximate Heating 
power of one of these boilers, 2ft. long, is given as 500ft. 
of 4in. piping; 3ft. long as 800ft.; and 5ft. long as 2000ft. ; 
the unequal proportion, in results corresponding with 
length, being accounted for by the enlargement of all 
parts, and the variation in height and width. The flue 
extends nearly to the back, and through it the whole of 
the heat must pass from the fire. Sometimes, another 
flue is formed with bricks on the outside surface, as with 
the ordinary Saddle; at others, the whole is covered with 
an arch without any division. As the full surface of the 
boiler on both sides is exposed to heat, nearly the fullest 
possible amount is absorbed before reaching the chimney. 
The Gold Medal Boiler (see Fig. 173), so named from that 
award being conferred on it after a working competition at 
the Birmingham’ Exhibition in 1872, is of wrought iron, 
and virtually a flued Saddle with a terminal end, the flue 
being in the form of three chambers instead of one, 
Fic. 173. THE GOLD MEDAL BOILER. 
as in that previously noticed. This boiler maintains & 
high position, and a large number are in use. Various 
sizes are made, ranging from 2ft. to 6ft. long, and pro- 
portionately large in all parts. The approximate Heating 
power of one 2ft. long, is 500ft.; that of 4ft., 1700ft.; and 
that of 6ft, in length, 3500ft.—all of 4in. piping. 
