Part 4

We do not propose, in our present work, to enter upon the investigation and discussion of the various theories of heat, light, color, radiation, &c., which properly belong to scientific treatises on these subjects. We intend to give only practical examples and results, from an extensive professional experience, with numerous designs and plans of buildings, most of which are now in successful operation, with the expectation that this volume will contribute not only to the general information of our horticulturists, and of gentlemen who are establishing themselves in the country, but also to create and encourage a taste for this kind of culture of exotic and delicate fruits, as well as the exquisite but tender gems of the floral world. When we find that we can command, at comparatively small cost of money and attention, the beautiful and luscious fruits of southern and tropical climes--their rarest and choicest flowers--the most delicious grapes, the finest peaches, nectarines, and apricots, the fig, and the pineapple, if we will; and that we can command these in abundance, to load and adorn our tables daily, the time cannot be distant when horticultural buildings, of various descriptions, will be found on all our country places or attached to our city homes.

POSITION OF HOUSES.

For lean-to or single-roofed structures used as forcing-houses for grapes or other fruits or plants, a southern aspect is generally preferred. Our own preference would be a position facing South-East, on account of the advantage gained from the morning sun, which is so favorable to the health and growth of all descriptions of plants. Although an hour or two of the evening sun might be lost to a building in this position, yet the rays are then comparatively feeble, and this loss would be much more than compensated by the more genial morning light.

Cold Graperies, with span roofs, and glazed at both ends, are better placed North and South,--that is, with the ends facing these points,--as nearly as a due regard to the positions of other buildings in the vicinity, and the general symmetry and apportionment of the grounds will permit. Each side of the roof will thus receive an equal amount of sun-light. For span-roofed Green-houses the rule is not so arbitrary, the glass not being lined with foliage, as in the case of graperies, the diffusion of light would not be materially obstructed. Under some circumstances, Green-houses may be placed east and west, as when a portion of the house is to be devoted to the purposes of propagation. The north side can thus be advantageously used, being less exposed to the sun's rays. Many plants requiring partial shade, would find there, also, the most favorable conditions for their cultivation.

Green-houses or Conservatories attached to dwellings, will answer in almost any position that convenience may require, or the taste suggest, as they are generally not so much intended for the growth of plants as for their display when in bloom. The sun should shine upon them, however, at least half the day. When they are intended for the growth of plants, then the more sun-light they can have the better.

FORMS OF HOUSES.

Until within a few years past, the straight-pitched roof, both single and double, has been used almost exclusively in the construction of glass houses. That there is an advantage in this form over some others, on the score of expense, and because there is less skill required in the builder, we admit, but there the advantage ends. The superiority of the curvilinear form is now beginning to be very generally acknowledged, on account of its being more graceful and pleasing to the eye, and because of its superior adaptability to the growth of plants. When to the curved roof is added the further improvement of circular ends, as illustrated in some of the designs furnished in this work, we have secured forms of houses that will admit double the light of the old-fashioned, heavy sliding sash structures which were built twenty-five years ago. Happily these old glass houses are fast falling into decay, and but few new ones are erected on their model.

Curvilinear roofs possess advantages over those of a straight pitch which may be briefly summed up as follows:

1. A larger run of roof for a given width of house, and consequently, more and better diffusion of light.

2. A greater power of reflecting the sun's rays, because of the constantly varying angle at which they strike the glass.

3. A greater amount of head room within the building, without the necessity of high parapet walls, or perpendicular sides.

4. Greater strength of the roof, enabling it to resist pressure from accumulated snows, without the necessity of supporting columns under the rafters, which are indispensible under a straight roof of considerable span, to prevent its settling down, and the opening of joints in glass and wood work, admitting the cold air from without.

A good proportion for a grapery or conservatory, is twenty feet in width by fifty feet in length. We think the width should never be much less where the roof is of double pitch. Single pitched houses should not exceed sixteen feet in width.

Mistakes are frequently made in the erection of structures for the growth of plants which, notwithstanding all the skill and art of experienced gardeners, render it impossible to arrive at satisfactory results. One of the most common of these is the excessive height of the roof. Men of experience in the construction and use of glass houses, have satisfied themselves that the lowest elevation which the uses and purposes of the building will admit, is the best. The difference in temperature between the floor and roof of a house twenty feet in height, will vary from ten to fifteen degrees. It is obviously desirable that there should be as little difference as possible in the temperature of the air on the ground, among the lower parts of the plants, and in the upper regions of the house. The nearer we can approach an equilibrium, the better success will attend our efforts. Nurserymen generally, and sometimes other cultivators, understand this, and they build their plant houses with roofs of low pitch, affording scarcely room to stand upright within them. Their plants are thus brought near the glass, and they grow stocky and firm, presenting quite a different appearance from the attenuated specimens frequently met with in private establishments.

HEATING.

The proper heating of Horticultural buildings being an important feature in their general management, and an essential condition of their success, we shall consider the subject at some length, availing ourselves of the practical experience of others, as well as of the knowledge we have acquired in our own experiments and practice.

Hot air stoves have been so generally condemned and discarded as a means of heating glass structures, that we shall not discuss their faults or merits, but confine ourselves to heating by flues, steam, and hot water in pipes and tanks.

FLUES.--Flues have been generally used in heating for many years, and although the method is rude, imperfect and unsatisfactory, they possess certain advantages on the score of economy, which will prevent their total supercedure until some equally cheap and effective method shall be found, to take their place. It cannot be questioned that houses of moderate extent can be heated at much less expense for the original cost of apparatus by the flue system than by any other now before the public. Flues have the advantage over steam or hot water in their power to generate heat and supply it to the green or hot house in a very short space of time, and with this apparatus, the fires may be allowed to go out on mild and bright days in winter, with the certainty that heat can be easily and quickly commanded at nightfall. Steam cannot be generated quickly, and the hot water apparatus requires considerable time to get into full operation, with the usual amount of fuel.

Among the serious objections to the use of flues, is the unequal distribution of heat throughout the house; the parts near the furnace being overheated, while at the chimney it is scarcely warm. This difficulty can be partially obviated by the use of materials in the construction of the flues, of different thicknesses,--being made thick and heavy at the furnace, and gradually becoming thinner and lighter as it extends towards the chimney. Again, flues generally require more fuel than a hot water apparatus, and moreover, they are unsightly in an ornamental house, and with the best care in their construction and management, they do not give entirely satisfactory results.

Earthenware drain-pipe is frequently employed for flues, and when care is taken to prevent their cracking by the excessive heat near the furnace, they answer the purpose very well. When properly secured at their joints they prevent the escape of gaseous matter more perfectly than brick flues.

Flues should be elevated a few inches above the floor, and supported by bricks, to allow all the radiating surface to act upon the atmosphere of the house, and should have, in order to secure sufficient draft, a gradual rise through their whole length from the furnace to the entrance into the chimney.

The furnace should be built inside the house at one end, with the fire and ash-pit doors opening into a shed outside, to prevent any escape of gas into the house while replenishing the fire. It will be necessary to place the furnace low enough to allow a proper rise to the flue. If the flue be made to rise immediately from the furnace about one foot, it may then be carried fifty feet, with a rise of not more than six inches, and the draft will then be sufficient.

The dimensions of the flue may vary from 8 to 12 inches in width, and from 12 to 18 inches in height, according to the space required to be heated. The usual mode of construction, when bricks are used, is to lay them crosswise and flat for the bottom and top, and to set them edgewise for the sides. Tiles for the bottom and covering are an improvement upon bricks: being thinner, the heat passes through them more readily, while they still retain the heat sufficiently to equalize the temperature. Tiles used for the top covering are sometimes made with circular depressions for holding water for evaporation.

STEAM.--The employment of steam for heating green houses, graperies, &c., is almost entirely superceded by the hot water method. It will, therefore, be necessary only to allude briefly to this part of our subject. It occasionally happens that a conservatory attached to a dwelling is heated by the same steam apparatus employed to heat the latter, but we believe that a person who should advocate, at the present day, the general adoption of steam as a means of heating horticultural structures, would be regarded as belonging to a generation which has now passed away.

Steam travels through pipes with great rapidity, and parting with its heat rapidly, it becomes quickly condensed, unless the boiler is of large capacity and capable of furnishing a full supply. It is, at best, an unsatisfactory mode of heating plant houses, for if from any cause the water in the boiler is reduced below the boiling point, the steam in the pipes is instantly condensed, and with it all heat, except that remaining in the iron of the pipes, and the condensed steam, is withdrawn.

Hood, an English author on heating, quoted by McIntosh in his valuable work the "Book of the Garden," thus compares the merits of steam and hot water. "The weight of steam at the temperature of 212° compared with the weight of water at 212°, is about as 1 to 1694, so that a pipe that is filled with water at 212°, contains 1694 times as much matter as one of equal size filled with steam. If the source of heat be withdrawn from the steam pipes, the temperature will soon fall below 212° and the steam immediately in contact with the pipes will condense: but in condensing, the steam parts with its latent heat and this heat in passing from the latent to the sensible state, will again raise the temperature of pipes. But as soon as they are a second time cooled down below 212° a further portion of steam will condense, and a further quantity of latent heat will pass into the state of heat of temperature, and so on until the whole quantity of latent heat has been abstracted and the whole of the steam condensed, in which state it will possess just as much heating power as a similar bulk of water at the like temperature; that is, the same as a quantity of water occupying 1-1694th part of the space that the steam originally did.

By experiments made by the above authority, it has been proved that a given bulk of steam will lose as much of its heat in one minute as the same bulk of hot water would in three hours and three quarters. And further admitting that the heat of cast iron is nearly the same as that of water, if two pipes of the the same calibre and thickness be filled, the one with water and the other with steam each at 212° of temperature, the former will contain 4.68 times as much heat as the latter; therefore if the steam pipe cools down to 60° in one hour, the water pipe will take four hours and a half to cool down to the same point. In a hot water apparatus we have in addition to the above, the heat from the water in the boiler, and of the heated material in and about the furnace, which continues to give out heat for a long time after the fire is totally extinguished; whereas in a steam apparatus, under the same circumstances we have no source of heat except the pipes by which it is conveyed--giving an advantage in favor of hot water over steam as regards its power of heating hot houses, and maintaining heat after the fire ceased to burn, in nearly the proportion of 1 to 7--that is, hot water will circulate from six to eight times longer than steam under the above circumstances."

TANKS.--This mode of heating horticultural buildings has been used in England for some years, and has, of late, obtained considerable popularity in this country; mainly, however, for the purpose of obtaining bottom heat. The tank method is more steady and reliable in its operations in this respect, than heating by flues or pipes, but even its most strenuous advocates must admit that for atmospheric heat hot water pipes or flues must be employed in some shape or other, where the tanks are covered with earth or sand beds for propagating purposes. With slate or metallic covering they are sometimes used solely for atmospheric heat, and are found to answer well. But if tanks are constructed of substantial and enduring materials, they possess little if any advantage, on the score of expense, over hot water pipes, while they occupy much more room and are unsightly objects in a well ordered green-house.