224 
THE COTTAGE GAEDENEB AND COUNTEY GENTLEMAN, Janttaby 15, 1861. 
bounding the furnace would themselves get so hot inside as to be 
continually radiating heat to the pipes instead of cooling them. 
Keeping this in view, I have some doubts if the mass of pipes 
forming the grating and summndings arc such an advantage, as 
to counteract the extra expense they ocoasion, as more heat will 
be obtained from the fuel, in proportion as it is placed directly 
on materials of slow conducting properties. 
Fig. 2i. 
Fig. 21 is one of Ormson’s tubular boilers; and Jig. 22 one 
of Skinner’s boilers, both of these boilers being identical in 
principle with Weeks’. The only difference being, that each 
tube of Weeks’ is fitted separately, and 
Ormson’s is all cast in one piece. Both 
plans have their advantages and disadvant¬ 
ages. The first may be more easily in¬ 
jured, but as easily repaired. The second is 
less likely to have a faulty piece, but when 
faulty can scarcely be mended. Amongst 
all these boilers which I have either worked 
or seen at work, I would not despise any 
of them when well set and managed and 
kept clean, the latter being of importance, 
particularly in the simple but useful saddle¬ 
backs. 
A dispute has obtained as to whether in 
such cases as saddle-backs, wrought iron 
or cast iron is best. I have no preferences. 
Cast iron generally lasts longest when 
but they are apt to crack almost at first 
even when well proved. If there 
Fig. 
MR. SKINNER’S BOILER. 
thoroughly seasoned; 
from no assignable cause, 
should be a little the matter with a wrought-iron boiler it is easily 
remedied, 
I have wrought the commonest boilers that must have been in 
use more than thirty years. I have known some crack a few days 
after being in use, and some quite worn out in less than ten 
years. The large one-boiler system for large establishments is by 
far the most economical, both for labour and fuel; but I could 
scarcely sleep sound at night with one boiler for a town of hot¬ 
houses. A second boiler should be set ready to act in case of 
accident. The extra expense would be a small per centage on 
security. Most large establishments are securing this desirable 
object. 
All that has yet been done to test the efficiency of different 
boilers, is to my mind unsatisfactory. What little I have 
attempted myself would lead me to the conclusion that theory 
did not quite agree with practice. The only conclusion I have 
arrived at is, that the simplest boiler is the best, and when we 1 
set and well managed will act well. All our improvements have 
proceeded on the principle of exposing a large surface to a small 
amount of water. Of course, under these circumstances, when 
the fire is out, the water will suddenly cool. The same rule 
applies to pipes. When we want a quick, sudden heat, two, 
two and a half, and three-inch pipes will be best. When we 
want a regular, continuous heat, pipes four inches in diameter 
will be more suitable. 
The following table from the Cottage Gardeners' Dictionary } 
taken, I presume, from Hood’s excellent work on heating, will 
give an idea of the extent of surface of boiler exposed to the fire 
to heat a certain number of feet of pipe. 
Surface of Boiler exposed to fire. 
4-in. pipe. 
3-in. pipe. 
2-in. pipe. 
34 Square feet will heat. 
200 
300 
400 
M )» .. 
300 
400 
600 
400 
533 
800 
83 ,, i> . 
500 
666 
1000 
12 
700 
933 
1400 
1 * >» » . 
1000 
1333 
2000 
For higher temperatures we would rather increase the surface, 
and especially for small houses, as the fire burns less thoroughly 
in a very small furnace than a larger one. Mr. Hood also gives 
tables and formulas, showing the number of feet of piping 
necessary to heat one and a half cubic feet of air for each square 
foot of glass, according to the heat required, and the external 
temperature, but for practical purposes it will be sufficient to 
state, that for all lean-to houses, dividing the cubic feet of air 
inside by 30, will give the number of four-inch pipe sufficient to 
heat the house to 60°, unless in extraordinary weather. Divid¬ 
ing the cubic feet of air by 20, will show the length of piping to 
keep up a heat of 70° to 75°, and when from 75° and up¬ 
wards, the cubic feet of air must be divided by 18. Span-roofed 
houses must have more piping in proportion. The large Con¬ 
servatory at Chatsworth lias been kept to 60° in very severe 
weather, with one foot of four-inch piping to every thirty cubic 
feet of air, although it is glass all round. But for a span-house 
not a third or a fourth of the height, more piping would be re¬ 
quired in proportion, as the great body of enclosed air in such a 
large house prevents the house, as a whole, from being suddenly 
cooled. The smaller the house, the more quickly is it acted 
upon, either by heat or cold. 
The size of the furnace will be regulated by the size of the 
boiler, but where continuous heat is wanted, and the cylinder 
and conical form are not adopted, the furnace should have more 
space at the end and at the back, as well as sides, besides that 
occupied by the fire-bars. Unlike a common flue, the fore heat 
should be kept about the boiler by lessening the outlet as men¬ 
tioned by blocking with a firelump the outlet below a saddle 
boiler. In all other forms the outlet from the fireplace should 
be small, and a good damper placed in the chimney as near the 
boiler as convenient. The economy in working will depend on 
the regulation of the damper and the ash-pit door. As previously 
remarked, a small jet of air introduced over the fire, or better 
still, in front of it, will answer the combustion of most of the 
smoke, &e. 
In trying to estimate the power of boilers, regard must be 
had to the fuel used. Cinders and breese from coke-ovens have 
more clinkers and less heat than good coal. Good coke with a 
little small coal is, perhaps, the best for all kinds of boilers. 
Coke varies in price according to its heating power. We are not 
able to give the heating powers of different coals, but some are 
specified in the Cottage Gardeners' Dictionary. Thus if the 
heating power of Scotch Cannel coal be . 199 
Lancashire, Wigan, will be . 196 
Yorkshire Cannel . 188 
Newcastle, Wallsend . pgg 
Gloucestershire, Forestof Dean. 108 
Welsh, common, very low indeed. 
It is also calculated that about 3 l-10th lb. of the best coal 
will be necessary <0 raise eight gallons of water from 50° to 
boiling-point. The same weight of good dry wood will be 
necessary to effect the same object, and if the wood is wet, it 
will require half as much more weight and more time. Hence, 
lb. of dry charcoal will be as effective in heating. In this 
neighbourhood we can get good Silkstones at from 22s. to 23s. 
per ton, and Derbj Cobbles at 14s., but when carefully used the 
first are not only best but cheapest. With common stoking there 
is not apt to be so much waste with the latter. E. Fish, 
THE VABIEGATED AEABIS. 
I A3I glad to see that public attention is directed to this 
useful variegated plant, and having grown it some years I can 
confirm all that has been said in its favour, excepting its perfect 
hardihood, and that I by no means deny ; but having occasion 
in former years to remove the plants from the quarters they 
