Numerous varieties of the close stove, bearing more or less on the above construction, have been brought forward since the publication of Dr. Arnott's first book on this subject in 1838. Each professes to possess some peculiar merit ; but all present these features in common : that the air-bole, by which the combustion is fed, is very small, and capable of adjustment; that there is a body of air to be warmed, external to the grate or fire-box itself, but confined within an outer case; that the consumption of fuel is much smaller than in any variety of open fire-places; and that the flue for carrying off the smoke and gases is small in diameter, and capable of being carried in any direction. In one variety, called the Vesta stove, there is a very ingenious arrangement whereby the ashes can be raked from the grate into an ash-receiver, and new fuel thrown into the grate, without any dust rising into the room, or any air entering the stove except through the customary air-vent. In the different forms of kitchen-ranges the open fire-place is combined with what may be deemed a close stove ; for the oven and hot-closet are representatives of the heated space within the outer case of a close stove. The stoves often employed in shops, balls, &c., are adjusted not so much for the economising of fuel as for the consumption of their own smoke.
Gas-Stoves.—In addition to the use of gas for lighting, described in its proper place, gas is now extensively employed for heating, by means of stoves of various kinds. The stoves are mostly cylindrical in form, with openings at the top and bottom. At the lower end, a few inches above the flour, is a ring-burner pierced with numerous minute jet holes. The top has frequently a sliding valve or damper to regulate the heat. The details vary greatly in different kinds. Edwards's gas stove has bulbous-shaped burners of fire-resisting clay, pierced with numerous small boles. Air enters through a lower row of holes and mixes with the gas. The bulb becomes gradually covered with a thin yellow flame. Several such bulbs are combined in various ways, and arranged to form cooking and heating stoves. One form of this stove, the so-called 41 Imapyre, consists mainly of small cylinders of pipe-clay. Each cylinder is from two to four inches long, and perforated with holes Lth of an inch in diameter. One end of the cylinder is fixed upon a gas-burner; the gas, being turned on, mixes with the atmo spheric air in the cylinder ; the little jets which penetrate the minute holes are ignited, the cylinder becomes red-hot, and presents the appearance of a solid red flame. By placing many such cylinders within another of larger size a very intense heat may be produced, applicable to manufacturing purposes.
Whatever form a gas-stove may present, its assumed advantages are: a comparative freedom from dust and dirt; a saving of time and labour; facility for adjusting the temperature of a room ; and economy in cost and maintenance. The disadvantages are alleged to be : a ditiusion of aqueous vapour, nitrogen, and carbonic acid gas ; these ought to be carried off by a chimney or flue, which however is seldom provided for gas-stoves. Moreover, all the bad gases are given off near the floor (in gas-stoves, though not in gas-lights), so as to mix with the whole of the air in the room ; and any defect in the burning of any one of the numerous small jets leads to the production of an offensive odour. To
lessen these evils, it has been recommended that the stove should have two or three concentric cylinders; that the heated air should be allowed to circulate between them ; that there should be no opening at the top; that a flue of two inches diameter should be placed at about mid-height, to carry off vapour, dust, and deleterious gases ; that there should.be an increased amount of metallic and reflecting surfaces to receive the heat; that only the radiative, not the ascensive, heat should be allowed to combine with the air of the room ; that the size of the stove ought to bear some well-ascertained proportion to the size of the room ; that care should be taken not to overheat the stove, for fear of producing an empyreumatic odour ; and that the gas-jets should never exceed three-quarters of an inch in height. If the flue be long enough to allow the stove to stand near the middle of the room, nearly all the heat will be rendered practically available. In a well-arranged gas stove seven-eighths of all the heat may be economised. A more equable heat can be maintained by such a stove than by any mode of using coal or coke, on account of-the jet-holes remaining constantly of the same size. So far as regards safety, the flue of a gas-stove is not so likely to be highly heated as that of other stoves. Whether such a flue could be made conformable to the decorations or furniture of a room, instead of being an eyesore is a question worthy the attention of architects and upholsterers. In relation to economical use, it has been calculated that a gas-stove will boil one gallon of water by the expenditure of gas to the value of one farthing; while a pennyworth of gas will bake three quartem loaves or six pounds of meat. On this subject, the application of gas to cooking, See COOKING APPARATUS.
Warming by Heated Air.—In all the arrangements yet described, the stove or fire-place is in the room which is to be warmed, and its beating effects are calculated with respect to that room alone. A notable advance, carried to a great extent in the present day, is to have the fire in an outer or lower apartment, and to carry the heated air from thence in a pipe to the apartment to be heated. The Chinese have been beforehand with us in this matter. In the better class of Chinese houses there are hollow flues extending beneath the floors, and con nected with a fire-place constructed either against the exterior wall of the apartment to be heated, or else in an inferior room adjoining. The flues are perforated with numerous holes, through which they give out the heated air and smoke to the whole of the under side of the flooring. This flooring consists of flat tiles or flag-stones nicely imbedded in cement, so as to prevent the escape of the smoke or heated air from the flues beneath into the room. After circulating beneath the tiled floor, the smoke escapes by a chimney into the open air. In this arrangement it is obvious that the apartment is warmed by the con duction of caloric from the warm tiled floor to the air of the room ; and as this conduction proceeds slowly, the tiles retain heat enough to warm the room many hours after the fire has been extinguished.