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as steep an inclination as possible, to the bottom of the boiler. The supply cistern (e) must be so placed that its bottom is not lower than the highest point of the pipes. The top of the steamvalve (v) should be level with the top of the supply cistern. Just below the valve, on the steam-pipe, may be fixed a small cock (k), connected with a pipe laid into the house, by which, whenever the water boils, the house may be steamed. In small apparatus this will happen pretty frequently, but in large houses, in order to insure this advantage, a stopcock or sluice should be placed on the flow-pipe (f), by which, the circulation being intercepted, the water in the boiler may at any time be raised to the boiling point in a few minutes.

Fig. 27. represents a contrivance which is not liable to any of the defects of stopcocks, which impedes the circulation less than any except large sluices, and which is comparatively unexpensive. The hollow plug g (fig. 27.) is fitted with a valve, perfectly watertight. This valve is opened and shut by the handle sliding through a stuffing-box in the end of the plug. By closing it the gardener may at any time cause the water in the boiler to boil, when, by opening the cock k, he admits as much steam to the house as may be desired. A small pewter pipe } in. diameter is sufficiently large to conduct steam into the house, and its flexibility renders it very convenient. Where this arrangement is adopted, the supply cistern must be larger than is otherwise necessary, and should contain 10, or 12 gallons. The steam-pipe, also, should be placed on the top of the boiler, and be of sufficient diameter to allow the water and steam to separate, that the former may not be blown out through the pipe along with the steam; and the valve should be loaded with a few ounces of lead.

Fig. 28. exhibits the apparatus, with the addition of a reservoir; this in small pits is very desirable, and I have always

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employed it in my own. The letters indicate the same objects as in fig. 26., except m the reservoir, which may be formed of thin copper in the form of a cylinder, and should be packed in a wooden or brick case, in sand or sawdust, which supports its shape, protects it from accident, and prevents the heat from escaping. All the communication pipes in this case may be of lead, and fitted with union joints, which render the fitting exceedingly easy. In my apparatus a lead pipe of 14 in. diameter supplies 40 ft. of radiating surface, and my reservoir contains about four times as much as my pipes. Reservoirs may be made of iron, but, though rather less expensive, they are so heavy and unwieldy that they could hardly be used; and the expense of attaching the pipes would greatly exceed the cost of copper. I have a 72-gallon reservoir, a cylinder 4 ft. long by 2 ft. in diameter, which cost complete, with two 14-inch union joints, 51. 5s.

The foregoing directions will, I believe, enable any intelligent gardener to plan and put up an apparatus for himself.

It remains that I should say something respecting fuel: any sort except wood and caking coal may be employed. The best of all is anthracite or Welsh coal, but a little coke is necessary to light it ; the next best is coke; and next to this, cinders. I arrange them thus, in the order of their strength; but for ordinary purposes nothing is better than cinders, - nay, even coke breeze, or small refuse coke, the value of which is next to nothing, may be burnt in these furnaces, but in that case they require 8 or 10 feet of chimney. Where it is required to produce strong heat rapidly, coke must be employed; but it is not a good fuel to maintain heat, as it allows too much draught, and burns away. Welsh coal has not this fault, and is a very durable fuel, peculiarly well suited to these boilers. When the fire is first lighted it should be allowed to burn brisk and clear, till the fuel in the bottom is well ignited; it may then be filled up to the

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throat of the furnace, when it will last through the night. In filling, care, of course, must be taken that the fuel is not so small and dusty as to stop the draught. Where cinders are used they should be well sifted. The proper management of these boilers may be best secured by explaining the principle upon which they are constructed. As fuel cannot be consumed without air, if a furnace be constructed of considerable depth, and filled with fuel, and air be admitted only at the bottom, that fuel alone is consumed which lies immediately on the bars, and first receives the draught of air. The fuel above, provided it transmits the air, becomes red-hot, or nearly so, but does not consume until that below it is destroyed. In this manner, one of these conical furnaces being lighted and filled with fuel, that portion in the upper part of the furnace which cannot burn absorbs the heat of the burning fuel below, and radiates or transmits it 'to the water on every side. So perfect is this absorption of heat, that for several hours after the furnace has been filled up with cinders, though there may be a fierce fire below, little or no heat escapes by the chimney, the whole being taken up by the surrounding water. The economy, therefore, of fuel in such an apparatus is very great; and it is also evident that excess of draught must be carefully guarded against, so much only being allowed as will consume the fuel steadily, which is easily learned by experience. The necessity, also, of keeping the aperture in front close, so that air enters the furnace only through the ash-pit, is hence evident. The water, it will be observed, is in close and immediate contact with the red-hot fuel on all sides, no black smoking coals intervening, as in most kinds of boilers; hence the great power in proportion to their size.

Economy of fuel is not, however, the sole or principal advantage of these boilers; their great recommendation is the long duration of steady heat which they insure without attendance. When properly managed, they may be depended upon for maintaining heat 12 hours untouched. This to many amateurs, who do not command the services of a resident gardener, is invaluable. In the next place, they are applicable to houses and pits on the smallest possible scale; a three-light pit may be kept at a temperature as uniform as that of the largest hot-house, without any trouble by night. It was for a purpose of this kind that I was originally led to devise them, and I have for three years past cultivated Orchideæ in a small house not 12 ft. square in this manner. My gardener does not live on the premises; and the temperature, as ascertained by a double self-registering thermometer, rarely varies 5° during the night.

It is to be observed, that, as the quantity of heat produced depends upon the quantity of fuel consumed, each boiler must contain, at one charge, fuel sufficient to supply the pipes to

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which it is attached with heat for twelve hours ; it is, therefore,
necessary that the size of the boilers be proportioned to the
work they have to do. They are cast in the following sizes,
which have been found most generally useful :

10-inch furnace, working 40 ft. to 60 ft. 4-inch pipe.
13-inch do. do. 60 ft. to 120 ft. do.
15-inch do. do. 120 ft. to 200 st. do.

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Where the quantity of pipe exceeds the above amount, two boilers have hitherto been employed ; but there is no reason why an 18-inch should not be cast, if a sufficient demand arose for them: boilers of this size have been found very effective in copper; and a 21-inch, cast in iron for Mr. Wilmot of Isleworth, worked exceedingly well. The numbers affixed to the boilers above are such as they will work properly and efficiently at all times. I am aware that some of the above dimensions have been found to do a good deal more work than is here allotted to them ; but this has only been by increasing the draught, and producing more intense combustion, a great deal of heat at the same time escaping by the chimney. When thus employed, the peculiar advantages of these boilers are lost ; fuel is burnt to waste, and consumed so rapidly that they do not maintain their heat as long as is desirable. Duration of heat and economy of fuel I consider

I paramount objects.

The only case in which stronger draught may be allowed is where the fire works into a flue in the house: but the objection of the rapid consumption of fuel is not thus removed ; nor can I generally recommend this arrangement, though sometimes convenient.

When the 10-inch boiler is employed to small quantities of pipe, it must be fitted with a reservoir, as in fig. 28. In this manner it may be made to work as low as 15 or 20 feet of 4-inch pipe.

4-inch pipe is taken as a standard, because each foot of it contains about one square foot of radiating surface. Of 3-inch, one third more, and of 2-inch, double the quantity, may be considered as the equivalents of the above amounts.

Before quitting the subject, I ought to observe that these boilers are so constructed that they can be cleaned out; and, if necessary, they can be taken to pieces, to remove any calcareous deposit which may in time take place in them. It is, however, particularly desirable, in these, as in all hot-water apparatus, that nothing but pure rain or pond water should be employed. Where the boilers are employed for steaming, this precaution is particularly important, otherwise calcareous incrustation must take place. To prevent leaves, dirt, &c., getting down the pipe of the supply cistern, it should be guarded by a double cap of

pierced zinc; one movable, that the gardener may cleanse it if clogged, and the other fixed.

The advantages of these conical boilers are no longer matter of speculation or experiment. My own, and several others constructed under my instructions, have been in use between three

, and four years. Of the iron ones very many have been erected in the course of the last eighteen months, and are highly approved ; although few of them possess all the advantages which experience has since combined in the form now described. They are peculiarly adapted for those purposes where perpetual heat is required, for plant stoves, pineries, and forcing-frames; also for small propagating-houses, or preserving-pits. To pits in general, from their small size, and from the small expense incurred in setting them, a recommendation not heretofore noticed, they are peculiarly applicable, and have been extensively applied. That employed in the half-hardy pit in the Horticultural Society's Garden, at Chiswick, is a fair specimen of their application, though that boiler is capable of doing considerably more work than is now allotted to it.*

Sevenoaks, February 7. 1840.

*

ART. XIII. Description of a Forcing-Pit heated by hot Water.

By John Rogers, Jun. The cultivation of melons, cucumbers, and pines by steam, instead of by dung or tan, has long been successfully practised in those establishments, which are of sufficient magnitude to admit of the introduction of steam apparatus. But steam-boilers exist in comparatively few gardens, and in many places where they were formerly employed they have given place to the more economical and commodious contrivance of hot water. It has become, therefore, an important consideration, to devise the best mode of employing this last agent to supply at once top and bottom heat, combined with that degree of moisture requisite in early forcing; and, as yet, such a contrivance seems to be a desideratum in horticulture.

The annexed sketches are the plan and section of a pit, by which it is proposed to attain these objects in the most efficient and economical manner, and at the same time to secure certain other effects which may by some persons be deemed of con

* I annex, according to your request, the prices of the conical boilers, with which Mr. Shewin has furnished me: - 10-inch, 41. 10s.; 13-inch, 61. ; 15-inch, 71. 10s. The fittings, comprising doors, dampers, &c., all things, in short, peculiar to the apparatus as above described, vary from about 17. 58. to 17. 15s., according to the size, and the articles required. The appendages for steaming the house are not included in the above.

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