454 WARMING AND VENTILATION represents the ventilating capacity of the chim- ney. Gen. Morin says that a common chim- ney removes in an hour, on an average, an amount of air which equals five times the capa- city of the room it is intended to warm, which is " sufficient in rooms of the usual size to se- cure a ventilation of over 1,000 ft. of cubic air an hour for each person, supposing there be more than one for every 10 sq. ft. of floor room." Yet it is from the air below the level of the mantel, the purest in the apartment, that the fire is supplied, the vitiated air above being only withdrawn as it cools and descends. There is also very imperfect diffusion, as the air that is drawn in under the doors and through minute openings streams along the floor to the fireplace, chilling the feet in its way. The changes which of late have been effected in the construction of the fireplace to save heat, the contracting of its dimensions and the lowering of the chimney piece, have been unfavorable to ventilation. The double fireplace is an ad- mirable arrangement both for heating and ven- tilation. A fireplace of soapstone or other material is sot up within another, leaving a vacant space between them into which cold air is admitted from without, warmed, and thrown into the room through an opening or register above. Fireplaces upon this principle, with hollow backs for warming air to be admit- ted into the apartment, and with hearths and jambs of iron, were constructed by Cardinal rolignac as early as 1713. The latest improve- ment of this kind is the fireplace or stove de- vised by Capt. Douglas Galton of the English army, for use in the barracks. The grates or open stoves, of different sizes, are set in chim- ney openings to suit the capacities of the rooms. They give the advantage of an open fire with very complete combustion, and the greatest amount of radiant and reflected heat. The smoke flue is an iron tube set in the chimney and surrounded by air space. On the back of the stove broad iron flanges are cast, so as to present the largest possible heating surface, and these project backward into the air cham- ber. If the fireplace is built in an external wall, there is an inlet for fresh air from with- out immediately behind it ; but if in an inner wall, a channel of perforated bricks or gra- tings is laid and passes beneath the flooring or behind the skirting. The fresh air from without, heated in this chamber, enters the room by a louvred opening near the ceiling, or by two such openings, one on either side of the chimney breast. The same principle has been applied to kitchen ranges and stoves in halls; and a cheap cottage grate upon this principle has been devised by Penfold, consist- ing of well burnt fire clay instead of iron. Dr. Franklin described the early Holland stoves as plain iron boxes with a flue or pipe proceed- ing from the top, and a small iron door open- ing into the room. He also mentions the old German stove as an iron box with one side open, which was set outside of the room, the stove itself projecting through the partition. Smoke and fuel in the apartment were thus avoided, but at the expense of ventilation. The Franklin stove, invented in 1746, was a great step in advance of the older forms, and has been thus described : " It was a rectangu- lar box of cast-iron plates, open in front ex- cept near the top, with a sliding shutter by which the whole might be closed entirely or in part, either for safety or for increasing the draught. The hearth projected in front, and was cast with double ledges to receive the edges of the upright plates, and also with a number of holes, viz. : one in the front part with a regulating valve for admitting air to the fire from an air flue beneath when the shutter was down ; one behind the first upright plate in the back, for discharging the air brought under the hearth from without into a narrow rectangular air box that was as long as tho width of the stove, and as high excepting the space for the smoke flue over its top ; and lastly three holes near the extreme back edge for the smoke, after it had passed over the air box and descended behind it, to enter tho flue leading into the base of the chimney. The air box at its sides was furnished with holes through which the heated air was admitted into the room, and a succession of shelves one above another was provided in this box, reaching not quite across, by which tho circu- lation of tho air was extended and it was long- er exposed to the heated surfaces before pass- ing out into the room. The back plate of the stove, heated by the descending smoko flue, imparted heat to the air between it and the chimney, the stove standing a little out from the wall. A register of sheet iron was intro- duced in the descending flue, which could be closed wholly or in part, and check the fire to any desired extent. Thus this stove embodied the principles of the modern air-tight stoves, and the directions Dr. Franklin gave for using it are just as applicable to these." Stoves in the United States are of great diversity of forms, of oast iron, sheet iron, and sometimes of soapstone ; while iron stoves, especially for burning coal, are commonly lined with fire brick, which not only increases their durabil- ity, but prevents the metal from being over- heated. They heat by radiation in all direc- tions from their surfaces ; they also heat the air which, rising into the upper part of the room, is diffused by circulation. Where a room is light, with no loss of heat by outflow- ing air, and the smoko escapes into tho chim- ney at the temperature of the room, the stove becomes the perfection of economy in heating. Air-tight stoves admit the air in small regula- ted quantities, so as to produce a slow combus- tion; but this smothered burning is not eco- nomical. The desirable points in stoves are self-acting contrivances to regulate the draught, accurate fitting of the parts, enclosure of the fire space with slow conductors, and the bring- ing of all the heated products of combustion in
