Ciiap. XX.

WARMING AND LIGHTING.

1225

of an agreeable temperature of 60°, there must be a surface of steam-pipe, or othersteam-vessel, heated to 200°, about a foot square for every 6 feet of glass, as much forevery 120 feet of wall, roof, or ceiling, and also for every 6 cubic feet of hot air escapingper minute, as ventilation: an ordinary sized window permits about 80 cube feet of airto pass through it in a minute, and there should be 3 feet of air per minute allowed for therespiration of each person in the room. According to Dr. Arnott’s view the quantity ofsteam pipe for a room 16 feet square and 12 feet high, with 2 double windows, each 7feet by 3, and with ventilation by them at the rate of 16 cubic feet per minute, wouldrequire 20 superficial feet, or 20 feet cf pipe 4 inches in diameter, or a box 18 inchessquare and 2 feet high. A surface when heated, and exposed to colder air, gives out heatwith a rapidity nearly in proportion to the excess of its temperature above that of thesurrounding air, less than half the heat being given out by radiation, and more than halfby the contact of the air: a foot of pipe of 200° external temperature in the air of aroom at 60°, the difference being 140°, gives out nearly seven times as much heat in aminute as when its temperature falls to 80°, reducing the excess to 20°, or a seventh ofwhat it was. The quantity of heat which changes the temperature of a cubic foot of waterproduces the same effect on 2850 cubic feet of atmospheric air.

Hot-water Apparatus for warming manufactories or large buildings, &c., which keeps upa circulation of hot water through iron pipes, the hot water having a tendency to rise, andas it cools to descend.

In France the hydraulic calorifere was thus described some years ago: the boiler was saidto resemble the human heart, and the pipes which carried out and brought back the water,the veins and arteries. In the early application of this method, the fireplace was made inthe middle of a large boiler, and from the top issued an ascending pipe, which mounted toa large cistern filled with water, from the bottom of which was another pipe that took thecold water into the bottom of the boiler. The rarefaction produced by the heat in the as-cending pipe caused the cold water to descend from the pressure exercised upon it, andthus a regular circulation was maintained.

Ilot-water apparatus is now made in a variety of forms: the most simple are those whereone pipe, of 2 or 3 inches diameter, is made to surround a small room, or where two ormore of such pipes are made use of. There are other arrangements where a number ofsmall tubes are preferred; but in all the water is made to circulate through them uponthe same principle : one of its earliest applications in England was, perhaps, at Bromley,in Kent, where the Marquis of Chabannes, in 1816, warmed the conservatory for SirSamuel Scott, Bart, though it has been asserted that Mr. Watt warmed buildings in thismanner as early as 1784.

M. Bonnemain, of Paris , who was decidedly the inventor, about 1777, had a calorifere,by which hot water circulated, and a regulator being attached to it, he could maintain soequable a temperature that he was enabled to hatch eggs, and produce a great manychickens; the variation being scarcely ever more than half a degree of Reaumur’s thermo-meter. The regulator made use of depended on the unequal dilatation of different metals:a rod of iron, screwed to another of brass, was enclosed within a tube of lead, termi-nating at its upper end in a ring of brass : the leaden tube was plunged into the watercontained in the calorifere, by the side of one of the circulating tubes; the dilatation oflead being greater than that of iron, at an equal degree of temperature, and the rod beingalso enclosed within the tube, it was heated much less than the tube; when the temper-ature was raised to the degree required, the lengthening of the tube brought the ringinto contact with a claw, at the short end of the bent lever, and when the slightest increaseof heat further lengthened the tube, the ring raised the claw of the lever, and allowed theother to descend : by this contrivance a wire was made to open or shut a valve, throughwhich air was admitted to the fire, and the combustion either increased or lessened.

Various improvements have been made in the mode of warming by hot water: at first thepipes were cylindrical, and laid horizontally, but it being found that its motion was acceleratedwhen placed in the two legs of a siphon, they are now laid in an inclined position, and flat

SECTION SHOWING PIPES.

Fig.1923,