Before the improved methods of warming factories came into use, Mr. Strutt, of Derby, devised a form of stove which, under various modifications, was called the " cockle stove," the " Derby stove," and the " Belper stove," for warming his cotton-factories. In these stoves the fire was contained in an iron receptacle, shaped sometimes cylin drically, sometimes rectangularly; and at a certain distance from it, encompassing it on every aide, was a brick casing or envelope, so that a body of air existed between it and the fire-box. The fire-box had three openings to the exterior, one to introduce the fuel, one for an ash.pit and air-vent, and one for a chimney ; the exterior envelope had two openings, wholly distinct from the others, one to carry off heated air to the various rooms of the factory, and another to admit a renewed supply of fresh air. Dr. Fyfe describes an arrangement adopted in a church, which may perhaps be taken as a fair example of a numerous class of instances. The body of the church is warmed by two stoves about four feet high, made of cast-metal, and shaped nearly like a bell. A square ash-pit, about a foot high, rests on four balls, and supports a fire-box or furnace. Concentric with this fire-place is an outer case; space between the two containing the air which is to be warmed. The usual adjustments are provided for the introduc tion of fuel and of air to feed it, for the exit of smoke, for the entrance of fresh air to the air-chamber, and for the exit of the heated air to perform its wonted office. The air-tubes, communicating with the air-chamber of the stove, are conveyed along the lower edge of the gallery of the church; and small branch pipes opening from them at regular intervals give out a stream of hot air which mingles with the cold air of the building. The fires are lighted early on the Sunday morning. From this time till the congregation assembles the fires are constantly supplied with fuel, and a supply of heat is thus kept up sufficient to warm the whole interior of the church during the time of divine service. A stove such as this is likely to give a tainted and offensive character to the air, like the common German stoves, unless a rapid current be kept up. Hence a change has been occasionally intro duced, by having the outer casing made of brickwork, instead of metal, and by making its dimensions much larger, an arrangement which beats the outer case less intensely, and provides a larger body of air heated to a lower temperature.
Very numerous varieties of the hot-air apparatus have been brought into use ; but the principle on which they all act can readily be under stood. When the nave and dome of St. Paul's cathedral were recently titled up for Sunday evening services during the winter, six stoves, constructed on a plan devised by Mr. Goldsworthy Gurney, were placed in the crypt. Gratings admitted the heated air from these stoves into the body of the cathedral. The vitiated air escaped by openings at the top of the dome. Each stove was a cylinder, with radiating wings all round. It stood in a vessel of water. The hotter the stove, the more the water evaporated, so as to keep the air in a proper hygro. metric state. The steam generated from this water also carried off the heat from the iron quickly, and thus aided in warming the building.
Warming by Steam.— The employment of steam-boilers in large esta blishments where steam-engines are worked, is one of the circumstances which have led to the very extensive adoption of the method of warm ing by steam. A marked difference is observable in the principle of this method, as compared with that of hot-air warming. The heated agent, that is, the steam, is not permitted to mingle with the air of the room which is to be warmed, but acts through the medium of the metallic tube which confines it, and which it raises to a temperature sufficient to warm the room, without imparting a burnt quality to the air.
Time general arrangements of a steam-heating apparatus, as suggested by Mr. Scott Rumen, are somewhat as follows :—At a convenient part of the building, and as low as possible, there is to be placed a close steam-boiler of the ordinary construction. From this boiler a small steam-pipe is to be carried to the part of the building which is to be warmed. This small pipe should be pretty thick, and carefully rolled round with a bandage of flannel to the thickness of a quarter of an inch, and the boiler should be wholly covered with bricks and plastered over to keep in the heat. This smaller steam-pip e should have an area of one square Inch for every six gallons of water that the boiler can boil off in an hour. Pipes of a larger size are to be laid round the room above the floor ; or under the floor, if apertures be left to allow a free circulation of warmed air to enter the room. Into these larger pipes the steam is to be conducted, and in them the steam will be con densed into water, giving out its heat to the colder air of the room which is in contact with the outside of these pipes. Small leaden or tin pipes must be provided, for the purpose of bringing back this condensed water into the boiler, for which movement a gentle slope is given to the pipes. The water thus returned, being again heated in the boiler and converted into steam, is again made to ascend and give out its calorie to the room which is to be warmed.
The efficacy of this mode of heating depends on the great capacity for heat which steam possesses, a capacity equal to 1000°, that is, a pound of water at will absorb a thousand degrees of heat in becoming a pound of steam. Steam will thus communicate as much heat as a mass of red-hot iron; and it will have this advantage over the iron, that it can carry this heat to a distance without a similar loss, because the hest, being latent, will not be given out until it arrive at its destination and become condensed, when the whole of its 1000° will be usefully applied.
Tredgold, Mr. Scott Russell, Dr. Arnott, and other writers on this subject have given the results of their calculations as to the quantity of steam and steam-pip thus required. Dr. Arnott, after taking into account the loss of heat through the thin glass of windows, through the thick walls of buildings, and through various openings and crevices, arrives at the following result :—In a winter day, with the external temperature at 10' below freezing, to maintain in an ordinary apart ment the agreeable and healthful temperature of 60°, there must be of surface of steam.pipe, or other steam-vessel, heated to 200° (which is the average surtace temperature of vessels filled with steam of 212"), about one foot square for every six feet of singlo.glass window of usual thickuess ; as much for every 120 feet of wall, roof, and ceiling of ordinary material and thickness; and as much for every six cubic feet of hot air escaping per minute as ventilation, and replaced by cold air. A window with the usual accuracy of fitting is held to allow about 8 feet of air to pass by it in a minute; and there should be for ventila tion at least 3 feet of air a minute for each person in the room. According to this view, the quantity of steam.pipe or vessel needed, under the temperatures supposed, for a room 16 feet square by 12 feet high, with two windows, each 7 feet by 3 feet, and with ventilation by them or otherwise at the rate of 16 cubic feet per minute, would be— that is 20 feet of pipe 4 inches in diameter, or any other vessel having the same extent of surface.