To avoid the necessity of so large a surface, and such a mass of water as is required at the low-temperature the water attains in the pipes of this kind of apparatus, Mr. Perkins introduced the high-pressure system. In this the pipe is made comparatively small, but very strong, and is formed into an endless circuit cut off from the atmosphere. The water is heated by making a number of coils of the pipe itself pass through the furnace; and as the whole circuit forms a shut vessel, as it were, the temperature may be raised to 300° and upward, according to the ,strength of the pipes. This high tem perature causes a rapid circulation. In filling the tube with water care is taken to expel all the air; and at the top of the system there is an expansion of the tube, equal to 15 or 20 per cent of the capacity of the whole, which is left empty both of water and air, to allow for the expansion. of the water when heated. The arrangement of the pipe may be various: the plan gene ally followed is to place a considerable coil of it within a pedestal or bunker, with open trellis-work in front, in a convenient part of the room. It may also be made to wind round the room, behind the skirting-boarfl, which, being perforated with holes, will allow of the entrance of the warmed air.
The hot-water apparatus has been fitted up by Messrs Perkins & Heath in various public buildings, warehouses, and gentlemen's houses; and, while sufficiently effective for the desired end, it has been proved to be attended with as few drawbacks as any regulated mode of beating whatever. But there is a great obstacle to its general adop tion in its expensiveness. The temperature also becomes at times so high as to cause a disagreeable odor. Another objection is its liability to burst; though, from the tubes being of malleable iron, such an accident causes more inconvenience than serious danger.
Conservation of art of warming embraces not only the production and distribution of heat, but the construction of apartments with a view to prevent its. escape. The way to effect this—setting aside in the meantime the necessity of renewing the air—is, in the first place, to make the walls, floor, windows, doors, etc., as impervious to air as possible, to prevent the heat from being carried off by currents; and in the next place, to make them bad conductors of beat. For this last purpose, the walls ought to be sufficiently thick, and, if possible, built of non-conducting materials, Solid iron would make a cold wall; wood, a warm one; and in this respect brick or porous stone is preferable to hard stone. But the chief element in a warm wall is that it be double, which every wall in effect is when it is lined by a coating of plaster, kept apart from the wall itself by the laths. The plate of confined air between the two is the most effectual barrier to the passage of heat outward that could be contrived. By making iron walls double or cellular, with a lining of plaster, they might be rendered as warm as wished. Windows are a great source of cold, not merely by admitting cold air, but by allowing the heat to pass by conduction through the thin glass. The air of the room that touches the window is robbed of its warmth, and is constantly descending in a cold stream toward the floor. There is thus a cold influence felt from a window,
however close it is. This is partly arrested by window-blinds, shutters, and curtains, which cheek the flow of the air, and retard its carrying power. But a far more effect ual plan is to have double windows: either two frames, or double panes in the same frame. The loss of heat by a double window is said to be only one-fourth of that by a single. Double windows are considered essential in countries where the winters are rigorous.
By carrying those principles far enough, we might succeed in well-nigh imprisoning the beat, and thus produce a house of ideal perfection, so far as mere temperature is concerned. But for the habitation of living beings another condition, seemingly antagonistic to the former, is no less requisite—" air as free as that on amountain-top. ' 39 WarOp I lig.
In general practice the two hostile conditions are not so much sought to be as compromised ; and then, as usual, neither object is well attained. Circulation.
of air is got accidentally, through the imperfections of structure in our rooms—througlr -the) chinks and bad fittings of the windows, doors, floors, and the uneconomical fashion or' our fire-places. Were houses much better constructed than they are, the inmates would in many cases be suffocated outright, as they often partially are with the degree of per fection we have already attained. Neither the airing of our houses, nor the art of building them solid and warm, can advance to perfection until the former be no longer left to chance, but be in every case secured by special apparatus capable of direct con fro!. We now proceed to consider how this is sought to be attained; confining ourselves still to the leading principles, and only noticing a few of the specific plans that have been put in practice.
VENTILATION.—The necessity of constantly renewing the air wherever living beings are breathing, arises chiefly from the effects produced upon air in the lungs (see RESPI RATION). The average quantity of carbonic acid in expired air or breath is found to be 4.3 per cent by. measure. Now this gas, when taken into the lungs, is a poison, and tends to arrest the vital processes. Like other poisons, however, it can be rendered harmless by dilution. The small proportion naturally iu the atmosphere is per fectly innocuous, and may be considerably increased without sensible effect. But it is decidedly prejudicial to breathe fora long time air containing 1 measure in 100 of carbonic acid; and it is considered desirable that the proportion should never exceed 1 in 500. We may assume, then, what is near the truth, that 20 cubic ft. of air pass through the lungs of a man in an hour. To reduce the poison of this to 1 per cent, at which point it is barely respirable, it requires to mingle with as much fresh air as will make a mixture of nearly 100 cubic feet; and to make the dilution at all safe, it must be carried five times as far. In other words, the respiration of one human being vitiates hourly about 500 cubic ft. of air.