2070. The Russian manner of heating dwelling-houses is adopted in these hothouses; that is, instead of keeping up a fire all the time that heat is required, a brisk fire is made at first, and the combustibles are burnt rapidly, in order to preserve the embers produced as long as possible, and to have a magazine of heat accumulated in a body which is a bad conductor, in order that it may be communicated slowly and by degrees to the surrounding air. To obtain this result, a great current of air must be established for the rapid combustion of the wood; and when the wood is entirely reduced to embers, this current must be stopped by closely shutting up all the openings. The stoves of dwelling-houses that are well constructed are rarely heated more than once a day, unless in the case of a very severe cold; as a house once heated to a temperature of from 14ï¿½ to 16ï¿½ Reaum. (64ï¿½ to 68ï¿½ Fahr.) retains the heat for twenty-four hours. Hothouses, on account of the great extent of the glazing which they contain, cannot retain this temperature so long; and it is necessary, generally, to heat them every twelve hours, especially when the stoves are not very large, which they cannot be without danger to the plants. The hothouse stoves with their flues are constructed in the following manner: ï¿½ Upon a sufficiently solid foundation, flags are placed horizontally over all the space which the breadth of the flues (which can either be single or double) is intended to occupy. Bricks are then placed at certain distances, to form feet for the flues to rest upon; and these flues ought to be surrounded on every side with a chamber of air, communicating directly, or by means of vent holes, with that of the hothouse. Upon these feet is placed a second range of flags, which flags form the immediate base for the flues; and on these is put another range of bricks flatwise. The lateral walls of the flues are also constructed of bricks placed flatwise, which gives them a thickness of 5.25 in. or 5.33 in. (English), and makes the interior aperture of the flue 10.5 in. wide and 14 in. deep. The interior surface is slightly coated with loam, and it is covered on the top by bricks placed flatwise; the flues are afterwards covered with an additional layer of bricks or flags, so as to form a larger mass of non-conducting material, for the retention of heat. The fines, when thus arranged, serve as paths in the hothouses, and will also form a very suitable place for forcing vegetables. In the old hothouses, the bricks were laid in loam or clay; but lately calcareous cement has been introduced, which is found to make the flues last much longer. The stove itself is not placed upon brick feet; but is separated from the ash-pit by a grating of iron bars. The upper surface of this grating ought to be at least 7 in. lower than the bottom of the flue. The fireplace widens towards the interior, where it ought not to be less than 26 in. in breadth; and it is desirable to have cast-iron pipes communicating between the interior of the fuel chamber and the external air, in order, when necessary, to augment the activity of the fire by admitting an additional current of air. The lateral walls are 8 or 9 inches thick, and the top of the fireplace is vaulted, and is at least 5 in. thick; it ought to be made of firebricks, which it would be always advantageous to use in the construction of all stoves, although they cost triple the price of the others. At the place where the flues enter the upright chimney, an aperture is made by which the soot can be removed; and in the chimney itself another is made, in which is placed the sort of valve called a damper, which serves to close the chimney when the wood is reduced to embers, A little iron frame, with a door hung upon hinges, is fixed on the exterior of the aperture of the chimney top; and is worked from within the house by an iron rod: it is shut and opened with the damper, and co-operates with it, in retaining heat in the flue. At St. Petersburgh, they reckon, generally, that a hothouse from 10 to 20 feet high requires a fireplace for every 3 or 4 yards in length, and an orangery one for every 4 or 5 yards. The stoves are heated sometimes in the interior of the hothouses, and sometimes from the passages behind. The best manner is to make niches for them in the hothouses; which may be shut by the means of panels sliding in grooves in the side walls; so that, if the stove smoke, the smoke may be easily excluded from the house. The outlets in the chimneys ought also to be made in these niches. The fuel which is preferred in Russia above all others is the wood of the birch tree, as it produces more solid embers, which preserve the heat longer than any other white wood. When the stoves are to be heated, the covers of the chimneys are first lifted up, and the damper drawn out; then wood is placed in the fireplace, till it is filled to the height of 2 ft., and a strong current of air is introduced until all the wood is reduced to embers. When the blue flame of the inflammable gas has disappeared, the doors of the stove and ash-pit are shut, the dampers are pushed in, and the covers of the apertures of the chimney-tops are let down. In the middle of winter the stoves are generally heated at one or two o'clock in the morning. It is necessary that the highest temperature of the flues should coincide with the time when the greatest degree of cold is expected in the external air; but experience is the best guide on this subject. Heating by steam is not generally practised in Russia: wherever it is used, it is a modification of the old English method; and the houses are heated by the steam itself, instead of being heated only by the hot surface of metallic tubes, in which the steam is circulated.