The Amateur's Greenhouse and Conservatory/Chapter 2
CHAPTER II.
HEATING THE PLANT HOUSE.
The heating of plant-houses presents a difficulty proportioned to their size in an inverse geometrical ratio. To put the case in another way, it may be said, that the larger the house or group of houses to be heated the more easily may the desired end be accomplished, but the smaller the house the more difficult the task. In the preceding chapter it is remarked that the atmosphere of a small house is quickly influenced by changes of external temperature; and here it may be added that it is equally soon affected by the action of any kind of heating apparatus. Hence, the amateur who finds his plants hard frozen may light a fire to save their lives, and actually roast them to death in an hour or two, through indiscreet management. Nevertheless, the amateur who has but one small house need not be discouraged by this statement, for it is a part of the ostensible purpose of this book to render aid in this extreme but not uncommon case, as well as in the broader subject of heating in general.
It is of the utmost importance that the mode of heating should be thought of when a plant-house is designed in the first instance, because heat is generated and diffused, in accordance with fixed laws, to which all our arrangements must conform. Thus, if we build a house in a low, swampy position it will be found a difficult matter to give it the benefit of artificial heat by any means whatever, because as heat ascends from the level at which it is produced, it follows that the heat generator or furnace must be placed at a lower level than the house itself, and, in the case of a house in a swamp, the only place for the furnace will be in the water. This is another extreme case for which, so far as the laws of nature permit, we shall endeavour to provide; and it is cited simply for the purpose of impressing the amateur plant-grower with the necessity of considering the subject of heating coincidently with the construction of the houses.
The Flue System.—The simplest method of heating is by means of a furnace and brick flue. Every skilled bricklayer knows how to heat a house by this method, but it is well that those who have to pay and take the consequences should know something about it also. It is necessary, in the first place, to provide a sufficiently capacious stoke-hole at the end of the house, or, in the case of a lean-to, behind the back wall. This must be sunk below the level, and there must be a decided rise from the fire to the flue, to enable the draught to overcome the check which the heat encounters in taking the horizontal course of the flue. The simplest arrangement in the case of a lean-to is to take the flue along the front of the house, rising slightly all the way, and terminating in a chimney at the other end. In the case of a span-roofed house it will be desirable to take the flue round the house, rising gently all the way, and terminating in a chimney over the furnace. It will be understood that the necessity of a continuous rise of the flue renders it desirable to place the furnace low enough in the first instance. It is desirable to detach the flue at every point from the floor of the house by means of piers, to allow of a circulation of air around the whole exterior of the flue, and promote a consequent equable distribution of the heat. A small flue of four-inch or six-inch drain-pipes, well cemented at the joints, may suffice for a small house, but what we should consider a good flue would be two feet high and one foot wide, the sides of brickwork, and the top and bottom red foot tiles or slates. A serviceable flue, however, may be made eight inches wide and sixteen inches deep, and in any case the depth should, exceed the width, or it will not draw well. It is a good plan to plaster the flue on the outside, to prevent the escape of smoke, but this is not needed if it is well built, and it certainly does slightly check the communication of heat to the house for the first hour or so after the fire is lighted. A trough for water on the top of the flue should be provided. In some districts tiles, with sunken surfaces, may be obtained for this purpose, but a cistern of zinc or iron is everywhere obtainable. But whoever can construct a flue will find no difficulty in securing an evaporation of water from the top of it. The kind of fuel to be burned will, in some degree, determine the size and material of the flue, for the greater the production of soot, the more frequent the necessity of cleansing, and the smaller the flue in that case, the more troublesome will it be to keep it in order. In any case, however, periodical cleansing must be provided for, and for the flue of average capacity, iron soot doors answer best, or common flagstones may be employed. These should be inserted at the end of every straight line of flue; consequently, wherever the flue turns will be the place for a soot door or something equivalent thereto.
The furnace should be of brick, with double iron doors, and a damper above in the first part of the flue, and a valve in the door of the ashpit for regulating the draught. In determining the dimensions it is well to remember that a comparatively large fire burning slowly is to be preferred to a small fire with a brisk draught. But here, again, the nature of the fuel to be burnt must also be considered, for if it is of a kind that produces little smoke, the opening in front may be dispensed with. It is well, however, to provide for any kind of fuel, and especially for the consumption of the waste fuel of the household, for the cinders the servants “get rid” of will, in many places, sufrice for the preservation of a good collection of plants.
The flue system is now rarely adopted, having been in a great measure superseded by the hot water system, which will next be described. Plenty of good plant growing has been accomplished by means of flues, but they occupy much space, and are liable to crack and emit sulphureous fumes, to the sudden destruction of the plants they are intended to preserve.
The Hot-water System is so generally adopted that there are as many plans of apparatus provided for it as there are days in the year, and, as a matter of course, everybody’s boiler is the best. To a beginner in hothouse practice the variety of boilers must be extremely perplexing, but it will soon be found that they differ but little in essential particulars. In every case there is a furnace beneath a boiler or in the centre of it, and from the boiler proceed iron pipes, laid horizontally around and about the house. The heated water passes out of the top of the boiler into what is called the “flow” pipe, and having traversed the length of the house comes back to the bottom of the boiler by what is called the “return” pipe, and this motion of the water is described as the “circulation.” It is analogous to the circulation of the blood in the body—the fuel is the food, the fire is the life, the boiler is the heart, the flow pipe the aorta, and its ramifications the arteries; the return pipe is the vena cava and its ramifications the veins.
In making a selection of a boiler it is of the utmost importance to ensure greater power than will be required under ordinary circumstances, and in the case of an extensive range of houses there should be two boilers, and they should be in use alternately during periods of a month or so at a time. In case of an accident to one of them—and the best boilers will at times break down—there is another ready for use, and with all
CONICAL BOILER WITH FEEDING TOP.
(Thames Bank Iron Company.)
connections complete, so that the turning of a valve and the lighting of a fire are sufficient to save the plants from destruction. We have seen a collection of plants, valued at some thousands of pounds, destroyed through the breaking down of a boiler in a season of intense frost, and at a moment of festivity when no one was prepared for such an emergency.
The simplest form of boiler for a small house is the Upright Conical, which consists of a furnace communicating with an upright chimney through the boiler, which is an upright cylinder not necessarily of a “conical” form. This may be used without any brick setting, but is far more serviceable with setting than without it, because of the great power of brickwork to prevent waste of heat. One great advantage of this form
JONE’S TERMINAL SADDLE-BOILER
Fig. 1.—Front View when in operation.
JONE’S TERMINAL SADDLE BOILER
Fig. 2.—Sectional View showing the course of the circulation.
JONE’S TERMINAL SADDLE BOILER
Fig. 3.—Boiler detached from the brick setting.
The most generally useful boiler, whether for heating one house or a range of houses, is the Saddle, of which there are many forms, but all of them are variations of an arch or saddle, the interior of which is appropriated to the fire, while the exterior contains the water. The horizontal course of the draught moderates its force, and tends rather in the direction of slow than of fast combustion; but the saddle is not to be regarded as a “slow combustion” boiler, in the proper sense of that term; it is simply not rapid, and hence does not require frequent attention. The great power of these boilers, and the fact that—to use a gardener’s phrase—they will “burn anything,’ are their two principal merits, but it must be added that they do not require to be set any great depth below the course of the pipes, and they are remarkaby economical in respect of consumption of fuel, in consequence of slow but perfect combustion. Amongst the best forms of saddle boilers mention may properly be made of the Cannon, which is cylindrical; the Flat Saddle of the Thames Bank Iron Company; the Terminal, made by Mr. Jones, of David Street,
jones’s double L saddle-boiler.
Manchester; and the Double L, made by Messrs. Jones and Son, of 6, Bankside, London.
If a final choice is to be made amongst these, we shall vote for either of the Inst two, as they are well contrived to catch up the heat which is apt to accumulate at the end of the saddle furnace, and thus ensure a quicker circulation and greater economy of fuel than other forms of the saddle.
The most powerful and hence best adapted for extensive ranges of houses are those known as Upright Tubular boilers. If, instead of an upright water jacket enclosing the fire, as in the
week’s upright tubular boiler.
conical boiler, we provide a series of upright tubes, and allow the fire to play amongst and around them, the result will be a tremendous increase of power and a proportionate increase of the consumption of fuel. In great undertakings in the way of plant growing, whether in private or public gardens, the upright tubular is usually employed, as in emergencies it is capable of an almost instantaneous effect, while for every-day work it is valued for its great power, a tubular boiler of a given size being capable of heating to a given degree ten or twenty times the extent of pipe that any other boiler of equal size would heat to the same degree. Messrs. Weeks and. Co., of King’s Road, Chelsea, have developed the capabilities of this form of boiler to an extent which entitles them to the first place in this department of engineering. Their “One-boiler system” renders one boiler sufficient for any number of connected or separate plant houses, even though to heat them sufficiently several miles of pipes may be required; and their Duplex tubular boiler is so constructed that, in case of an accident to any part of it, that part can be instantly detached, and the heating business, instead of breaking down, as it would with any other boiler, proceeds without interruption, or, at the most, with the interruption only of the interval between the occurrence of the flaw and the operation of detaching the portion of the boiler in which it has occurred.
The most suitable boiler having been selected, the business of setting and attaching pipes is a matter of the simplest mechanism. But mistakes occur, and a few words of advice may be useful on these and other matters. Be sure that the workmen who are to set the boiler know what they have to do. It would be simply absurd for us to describe how each particular boiler is to be set, and if the manufacturer undertakes the work it will be properly done. But a second-hand boiler may be purchased, and the village smith or bricklayer have the job of setting and attaching pipes. It should be understood, then, that a decided rise of the pipes from the level of the boiler to the level of their extreme distance from it is necessary to ensure a good circulation. The rise should be gradual but continuous, and at the highest point where the flow ends and the return begins, a reed-like pipe should be inserted to promote escape of air, which might blow the whole affair to pieces if allowed to accumulate without means of egress. In a heating system of any extent there should be several air-pipes inserted. The feeding cistern should be on a level with the highest point of the extreme end of the flow-pipe or a few inches higher. It must not be lower on any account, or the water will never reach that point, and there will be no circulation. It is common in stoves where a moist boat is required to place several feed cisterns over the flow-pipe to promote evaporation. It only needs to here mention that “water will find its level” to render all these considerations as simple as A B C, and, whether or no, the recognition of this law of nature is the essence of hot-water engineering.
In the adoption of pipes, those of one or two-inch bore are adapted for small houses, and for subsidiary systems in heating parts of houses, such as propagating compartments. But the teachings of experience are all in favour of four-inch pipes for all ordinary purposes, and of two-inch or three-inch pipes for any part of a system where the heat has simply to be conveyed and not diffused, as in the intervals between houses that are heated from the same boiler. In the fitting of the pipes there is nothing so good and cheap as rings of india rubber, which are placed over the end of each length, and then driven with it into the socket. If these are of the right size and the pipes are properly forced home with the rings, &c., there is no occasion for cement or any kind of waterproof stopping. There may be a leakage here and there for a week or so, but it will cease without requiring help, and the joints will keep for a lifetime.
In setting boilers of all kinds the size of the flues must be regulated according to the fuel to be employed. If coal is to be used they should be half a size larger than would be desirable for coke, or they will be soon choked up with soot. The pipes should be laid above the level in all cases, if possible, for if they dip anywhere, as, for example, to pass under a doorway or a path, there will be great loss of heat, and it will be impossible to get up a heat quickly. Have plenty of piping, for there is no economy in a stint. In setting a saddle it is well to place it on a row of fire bricks, to afford more space for fuel. This is especially necessary when the fire has to be made up to last some time. “Driving” is a detestable practice, and should only be resorted to in emergencies. A large steady fire is far more economical as to consumption of fuel than a small fire with a quick draught, for the stronger the draught the greater the quantity of cold air from without, as well as water within, to be heated. Careful stoking is required for all tubular boilers, on account of the exposure of the tubes to the fire; hence, in a place where things are done roughly, the saddle form is to be preferred.
Gas-heating.—The heating of houses by means of gas is a modification of the hot-water system above described, and should, as far as possible, be conducted on precisely the same principles, the fuel being gas instead of wood, coal, coke, or charcoal. There are several kinds of gas apparatus in use, and there is now no difficulty in heating a plant house in an efficient manner, provided only that the proprietor is prepared to employ experienced engineers and pay the extra cost of fuel, for gas is the most expensive of materials employed for the purpose of heating, though it is the cheapest for the purpose of lighting.
The principal advantage of gas-heating is that stoking is dispensed with, and, if the pressure in the pipes is pretty constant, the apparatus may be left for many hours without attention, as the heat given off will be constant, and to a great extent determinable beforehand. It must not be concealed, however, that to manage a gas-heating apparatus requires some amount of experience, and those who would succeed must habituate themselves to observation, not only of the action of the apparatus, but of its influence on the temperature of the house at different hours and in different states of the weather. A body of flame sufficing only to keep out frost on a frosty night with a clear sky might suffice to raise the temperature of the house to 70° or 80° on a mild night with a cloudy sky, and, as a matter of course, alternations so great and sudden would seriously injure the plants the apparatus was intended to preserve. Granting, then, that the adoption of a system of gas-heating will not absolve the amateur from responsibility to attend to its management, the nest question is, what form of apparatus is the most to be desired?
The simplest form of gas-heating apparatus consists of a ring of jets burning blue, through wire-gauze, under a small vessel tilled with water, over which is placed a vertical pipe, the mouth of which expands like a hood over the whole affair, to catch and carry into the air without all the products of combustion. This has the advantage of extreme simplicity, and the disadvantage that it is slightly injurious to nearly all kinds of plants, but especially so to camellias, oranges, and other winter-flowering subjects. But for preserving bedding plants and ferns, and other quick-growing subjects, it answers very well; for, being in use only when severe frost compels the temporary employment of heat, the injury done is trifling, and the plants soon recover from it when the growing days of spring return. A merely common gas-flame is, however, not to be tolerated in a plant house, except in the way of a few small jets to afford light, and these are always allowable, the minuteness of the combustion exercising so minute an influence as to be practically of no consequence whatever.
The best form of apparatus is that which consists of boiler and circulating pipes, and it is always advisable to place the boiler in a separate apartment, even if a portion of the plant house has to be screened off by means of glass for the purpose. However careful we may be to provide ready exit for the products of combustion, a gas-flame of sufficient power to afford the amount of heat required must prove prejudicial to plants when in close proximity to them. It commonly happens, however, that the house best adapted for gas-heating occupies a position adjacent to an entrance-hall or some other 
apartment, in which the boiler can be placed for both use and ornament. It must not be forgotten either that a boiler adapted for the purpose can be placed, as well beneath as beside the conservatory to be heated, for the pipes in which the water circulates may range vertically or horizontally at discretion, provided the work is well done. In many cases a gas apparatus might be adapted to heat a bath-room and a plant house, and afford the additional convenience of management within doors, without any occasion for exposure to the night air in the winter season.
A simple and effective form of gas-stove is that known as Trotman’s. which is manufactured by Mr. Trotman, of Isleworth. The stove stands about thirty inches to the top of the lid; the diameter nine inches. The centre to within six inches of the top is hollow, so that the flame of the burner is in the centre of the water, thus economising the heat. The foul air passes away by a pipe through the water, and afterwards can be carried about the house as convenient, but must not be carried horizontally, or there will be a likelihood of a back draught. The pipe produces a considerable amount of heat, and is no more objectionable than a common flue, hence it may be used to heat the back wall, or run under a stage. The heat from the stove itself is the same as any other hot-water apparatus. The lid is perforated, and the moisture thus obtained will counteract the dry heat from the pipe. There is no escape of foul air whatever if properly set. Its simplicity is one great recommendation wherever gas is available, as it is the cleanest and least troublesome of any method of heating 
small greenhouses.
The subjoined sketch may be accepted as a plan which any skilled workman may carry into effect without infringing any one’s patent, or treading on anybody’s toes.
The apparatus consists of an iron or copper boiler ( a ), through which passes a hot-air funnel (g). The boiler is supplied by a small pipe from an open cistern in the house (b), entering the boiler at the bent arrow. The heat is derived from a small furnace formed of a circular hoop of iron with a bottom of wire gauze (f). The furnace is filled with lumps of pumice stone, and is supplied with a gas burner placed below the wire gauze, and the gas passes up through the pumice stone, and is there lighted. There are two distinct sources of heat, one by the flow-pipe (c), which passes round the house and returns to the boiler at d, and the other by means of the hot-air pipe (g), which is carried along under a shelf against the back wall, and then out of the house at the other end. The only precaution necessary is to prevent an accumulation of air in the boiler or pipes, and every time the gas is lighted, the stopcock at c should be opened to allow of its escape. The heat should at first be very slight, and may be increased as the circulation is established.
A—Copper Gas Boiler.
B—Wrought-iron Jacket or Cover, to prevent the too rapid escape of heated air and the fumes of the sras entering the greenhouse.
C—Ring Gss Burner.
D-Supply-cistern. This can be placed as shown, or in any convenient position.
E—Supply-pipe from Cistern to Boiler.
E— Flow-pipe, for heated water from Boiler.
G— Return Pipe.
H-Hot-air Escape Pipe
GAS-HEATING APPARATUS OF THAMES BANK IRON COMPANY.
(Boiler 10 inches high, 9 inches diameter.)
Probably the best gas-heating apparatus now before the public is that manufactured by the Thames Bank Iron Company. The apparatus consists of a boiler (a), capable of heating fifty feet of four-inch pipe; it is encased in a wrought-iron jacket, which serves the purpose of a brick setting; the iron jacket, with escape pipe (h), renders it perfectly safe to use this boiler inside the house, as it is impossible for the fumes to affect the plants. The hot air escape pipe might be carried round the house, and it would be an advantage if it terminated in one of the chimnies of the dwelling-house.
A correspondent of the ‘Floral World’ describes a gas-heating apparatus which any skilled workman could manufacture at a very small cost. He says:
“The size of my house is twelve feet by nine feet, and it stands about thirty yards distant from the cellar, in which the gas-meter is fixed. I have a three-quarter-inch iron pipe running from the meter close to the front of the house. I thought it best to have rather a large size pipe to conduct the gas, as the water will sometimes condense in pipes in the winter time; and, of course, if the pipes are of small size, there is more danger of the gas going out. I have a small sheet-iron box, about fifteen inches square, which is fixed inside the house, close to where the gaspipe comes, and proceeding from the top of the box is some two-inch stove piping, to carry away the fumes of the gas through the roof into the open air. The box is made so that there can be no escape of the fumes into the house. Inside of the box there is a small saddle-shaped copper boiler, which holds just five pints, and, proceeding from the top of the boiler, and through the top of the box or cover, is a piece of one-inch lead pipe, which is carried straight for about two feet, and then bent down and attached to a one-inch iron pipe which runs round the house, and which returns again through the box into the boiler at the bottom. Under the boiler is fixed a small Bunsen burner gas stove (which any gasfitter will supply). To prevent the fumes of the gas getting into the house, I have a small door in front of the iron box, so that I can light it from the outside. The cistern is fixed just at the bend of the flow-pipe, the furthest point from the boiler, with a tap to turn the water on or off, although I always leave it on; and at the same point I have a bit of thin composition piping fixed in the iron pipe, and carried out into the open air as a kind of safety-valve. A small tap, which is fixed in the pipe at the highest point just over the boiler, must be turned on before the gas is lit, to allow the air to escape out of the pipes, or the water will not circulate. I have nearly seventy feet of piping, and, after the gas has been lit an hour it is nice and hot all round. The whole affair can be made and fitted by any gasfitter for a little over three pounds, and I can only say, in conclusion, that it works admirably, and the only trouble I have met with is, to see that the cistern is supplied with water about once a week, and to turn the gas on at night and off again in the morning.”
There yet remains to be noticed a few contrivances for heating which cannot be properly ranked under any of the foregoing heads. One of the most important of these, for the amateur who has but one or two houses, is Riddell’s slow combustion boiler, which consists of furnace and water jacket, constructed of iron, and needing no brick-setting, although, in common with all other boilers, it should be sheltered from the weather by means of a shed, or in one end of the plant house screened off from the rest. This is a very economical boiler, quick and powerful, and well adapted for pipes of small bore. It is manufactured by Messrs. Riddell, 155, Cheapside.
SECTIONAL VIEW OF CARTER’S APPARATUS.
Carter’s Portable Apparatus has been found economical and trustworthy for the heating of small houses. It consists of a fireplace (a) closed in front with a regulator to ashpit door to regulate the draught: b, flue pipe passing through the outer base (c), and conducted out of the house at any convenient part; d, water space round the fire and flue pipe; e, return pipe for circulating the water; f, small funnel or small cistern for supplying the water.
The general dimensions are as follows:—Fire-box, twelve inches by sixteen inches; outside pipe, six inches diameter, inside flue pipe, three inches diameter, which leaves a space of one and a half inch for water.
The cost will vary according to size and length of house, &c. The sketch represents a twenty-feet house, with apparatus eighteen feet long. The cost of one of the dimensions given will be about £5, made of strong galvanized iron.
The advantages of this arrangement is the portability, with the economy of fuel and equal distribution of heat along the front of the house.
In a large or extensive range of houses the pipes can be carried in any direction, as any other hot-water applications, and two or more fireplaces can be attached with the fireplace outside the building, or inside with an air pipe from without to supply air to the fire if found injurious by taking it from the inside of the house.
The manufacturer is Mr. J. J. Carter, Peak Hill, Sydenham.
The Thermostat-Thermosiphon, introduced to public notice by our friend M. Sisley, of Lyons, may be considered as an ingenious modification of Riddell's slow combustion stove, and, like it, is simply placed where it is to stand, and requires no brick-setting. It is a peculiarly safe apparatus, the fuel and flames being on all sides in contact with iron, which cannot become excessively heated, because that is in contact with water. Hence, this apparatus is well adapted to place in an entrance-hall for heating the adjoining apartments, and perhaps a greenhouse or conservatory not far removed. M. Sisley, in describing it to us, says:
“By stirring it once in the morning and once at night, we could, by burning good coke, set light to the fire on the 1st of October, and keep it burning to the 1st of May, at an expenditure of from 16 to 24 kilogrammes of coke every twenty-four hours.
“The apparatus could be placed in the same locality—that is to say, in the plant house—destined to be heated, and its 
INTERIOR OF A GREENHOUSE WITH CARTER’S APPARATUS IN ACTION.
radiating heat rendered useful. But, according to our idea a glass-house well constructed ought to be preceded by a lobby,
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Thermostat-thermosiphon. (Section.) A. Firegrate. B. Vent-holes, through which the smoke passes to go out at D. C. The bars. D. Opening for allowing the escape of gas in combustion. E. Openings serving to excite the draft when the apparatus is lighted. E. The chimney.
(Front Elevation.) At the foot, the ashpan; above the door of the fireplace; above, on the left, the two pipes for the circulation of the water, that above for the flow, that below for the return.
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or workshop, which gardeners call a ‘tambour;’ we shall always advise to place the apparatus in the place which precedes the house, and content ourselves with the pipes for heating the house or houses, because the same apparatus is capable of heating several during the severe cold. The smallest apparatus could easily heat 100 mètres of pipes. Some dissatisfied minds object that this apparatus does not contain sufficient water about the fireplace, because, up to the present time, they have seen enormous boilers, and they think it is the size that gives power. Experiment has demonstrated that a huge quantity of water about the firegrate is useless, and that with a less volume of water a circulation is better kept up, because the difference in temperature is greatest between the point of departure and the extremity of the pipes. What do we require, then, to obtain a good result? That the water in the pipes obtains as quickly as possible the temperature required, and preserves it for the longest possible time. The Thermostat-Thermosiphon realises these conditions.”
Lastly, we are bound to mention Musgrave’s Slow Combustion Stove, which is a stove simply, and not a boiler. It merits mention, because it is the only thing of its kind we would, without fear, place inside a plant house. It must be understood that we do not recommend either the introduction of a gas-flame or a fire of any kind into the same enclosure with any kind of plants, but it is our business to provide for a variety of circumstances, and it is with pleasure we are enabled to testify, from observation and experience, that Musgrave’s stove is the least harmful amongst many contrivances recommended for placing inside a plant house, and at the same time easily managed, economical, and efficient, as a diffuser of heat. It is manufactured by Messrs. Musgrave Brothers, High Street, Belfast, and the prices range from 90s. upwards, according to size. For a house of one hundred to two or three hundred square feet of surface or more, this stove may be employed with safety, and in the case of a large house two or three stoves of small size would be more useful than a single large one. A 90s. stove will suffice for a house measuring twenty-five or thirty feet by eight or ten feet wide, but for any smaller sized house it is not suitable at all. The small upright charcoal stoves that are often used to protect miniature greenhouses are better than nothing if carefully managed, and that is all that can be safely said about them.
Mr. Rothney submits, for the amusement of those readers of this work who are inclined to speculations in engineering, the subjoined plan of a self-acting Thermostat. The description is as follows:
The expansive effects of heat on liquids is well known. Water when heated expands in the following ratio:—At 40° it is at its greatest density; at 65° it increases 1700 part; at 100°, 1139 part; at 140°, 155 part; at 180°, 132 part; at 212°, 123 part. This being the case, we have a power which can be applied for regulating the temperature in hothouses, by causing the hot water in the pipes to remain at or not increase above a certain temperature desired, also at the same time storing up
ROTHNEY’S SELF-ACTING THERMOSTAT.
in a tank or otherwise any extra amount of heat which may be carelessly applied in the furnace.
Let b represent a common boiler, having a feed cistern (c); let e and f be the ordinary flow and return pipes for heating the greenhouse, under the floor of which is placed the rainwater tank (h). All this will be seen to consist of what is found in an ordinary greenhouse only. The rest can be added to any common house and heating apparatus, and consists of a layer or coil of pipes (i) in the bottom of the tank, and communicating with the return pipe and boiler at k; while from the other end of this coil is fixed the pipe (l) terminating in a cistern (m), the bottom of which is on the same level as that of the feed cistern (c). An upright pipe (n), with a sliding tube (o), marked with degrees, is attached to the flowpipe (e), and also enters the aforementioned cistern (m). The tube (o) regulates the whole affair, according to its position; e. g. if this tube be raised one inch above the level of the water in the cistern and return-pipe (m) no circulation can take place through the coil unless the water be heated some 40°. If the orifice of the tube (l) be ten feet above the bottom of the boiler, and that of the tube (o) ten feet one inch, the circulation will commence only through the coil when the temperature of the water in the pipes exceeds 100° (the ordinary circulation will at all times proceed through the pipes in the greenhouse). If the temperature of the water be required to be 180°, the sliding tube would have to be raised about four inches above m; this is reckoning the water there to be about 40°; and it will be seen that these calculations are based on the table given at the beginning, and that no deduction is made for the water becoming slightly heated in the return-pipe (m); this being done for clearness. I find this is easily got over by the graduating of the tube (o) accordingly (the cistern (m) ought to be kept cold by a stream of air). The reader will see that no water can circulate only in the ordinary manner, unless the heat of the same exceed what is required; in that case it will, instead of flowing only through the pipes in the greenhouse, leave them and flow through the coil in the cold-water tank, and entering the boiler almost as cold as that in the tank, and continue to circulate through these until it becomes sufficiently cold to again flow through the pipes in the greenhouse.
In small greenhouses a very large fire may be made up under the boiler at night without any danger, but rather the reverse, as any extra heat so applied will only heat the water in the cistern slightly, and which will be given off when the fire is gone out, thereby giving an equal temperature through this excess, while softening the water there and making it fit for watering purposes.
WIRE POT FOR FERNS AND LYCOPODIUMS.