WARMING. 



practised ; and the object of late has been, not so 

 much to do it away, as to improve it. 



Grates. One improvement consists in diminish- 

 ing the quantity of metal in immediate contact 

 with the fuel, and forming the back and sides of 

 the grate of fire-bricks. For the reason given 

 above, this renders the combustion more com- 

 plete and the yield of heat greater. 



Another point deserving attention is the shape 

 given to the chimney-mouth, or recess above the 

 grate. When the sides are square with the back, 

 none of the heat falling on them is given out again 

 into the room. With a view, therefore, to throw 

 out the heat better, the sides, or covings, as they 

 are called, are inclined to the back at an angle of 

 about 130; and sometimes they are made curved 

 and of polished metal, in order that they may 

 reflect the heat without absorbing it. It is ques- 

 tionable, however, if simple brick slabs, placed at 

 the proper angle, do not throw out more heat than 

 the most splendid polished metal plates. 



Much also depends upon the shape of the fire- 

 box, or grate, itself. To see the importance of 

 this, it is necessary to attend carefully to the 

 exact way in which an open fire heats a room. 

 It does so almost entirely by the rays of heat 

 that it throws out ; and these rays do not warm 

 the air directly ; they pass through it like light 

 through glass, just as the hottest rays of the sun 

 pass through the upper atmosphere, leaving it 

 cold enough to freeze mercury. It is only when 

 the rays of the fire fall on the floor, furniture, and 

 walls of the room, that they give out their heat ; 

 and it is by coming in contact with these solid 

 heated bodies that the air is gradually warmed. 

 We may thus see the necessity of having a fire 

 lighted and burning brightly for a considerable 

 time before the hour when the apartment is 

 expected to be comfortable. 



The law that radiant heat neither affects nor is 

 affected by the surrounding air, also explains the 

 fact that an apartment may feel very cold though 

 the air in it be at high summer heat. A church 

 or other massive stone building in frosty weather 

 may be filled with heated air, and yet retain its 

 chilling effect for many hours. The warmth of 

 the living body is lost in two ways : the film of 

 colder air that touches it receives part of its heat 

 by conduction, and rising up makes room for 

 another film to do the same ; a moderately heated 

 body, in cooling, is robbed of about half its heat 

 in this way. The other half is given off in rays, 

 which pass through the air and impinge upon the 

 objects around. These objects are radiating back 

 heat in return ; but their temperature being low, 

 the return is small, and the warmer body is 

 colder by the difference. Hence we are chilled 

 by a cold wall or a cold window without touch- 

 ing it, and though the air between us and it 

 may be at 70. To return to the shape of the 

 grate. 



The chief object is to present as large a surface 

 as possible of glowing fire to the front. With this 

 view, the grate is made long and deep, in propor- 

 tion to its width from front to back. This prin- 

 ciple, however, is carried too far in many grates ; 

 the stratum of fuel is too thin to burn perfectly. 

 The bottoms of grates should be solid, instead 

 of consisting of bars ; this, which is the usual 

 construction, causes an excessive draught and a 

 waste of fuel. The error may be corrected in an 



existing grate by placing over the bars a piece of 

 sheet-iron cut to. fit. 



The practice recently come into vogue of plac- 

 ing grates almost on a level with the floor is a 

 mistake. The floor and the feet of the inmates 

 do not thus receive their due share of the radiant 

 heat. 



The chimney-throat, instead of a gulf drawing 

 in a constant wide current of the warm air of the 

 room, and causing draughts from windows and 

 doors towards the fireplace, should just be suffi- 

 cient to admit the burnt gases and smoke that 

 come directly from the fire, and no more. This 

 is the object of the movable plate in what are 

 called register-grates. 



It would be endless to attempt to enumerate 

 the various forms of grate constructed, with more 

 or less success, on the above principles. We shall 

 content ourselves with a notice of the smokeless 

 grate invented by Dr Arnott, to whom the subject 

 of warming apartments is more indebted than to 

 any individual since the days of Count Rumford. 

 It comes nearer to the idea of perfection in an 

 open fireplace than any previous contrivance. Its 

 peculiar advantages will be understood from the 

 following description and diagram : 



Arnotfs Smokeless Grate. ab, ef, represent the 

 front bars of a grate in a chimney of the usual 

 construction, rswu. The grate has no bottom, 



\f 



Fig. I. 



and below it is an iron box, open only at top, into 

 which the charge of coal for the day from twenty 

 to thirty pounds is put Any kind of coke or 

 coal may be used. To light the fire, the usual 

 quantity of wood is laid on the surface of the fresh 

 coal at ef, and a thickness of three or four inches 

 of cinders or coked coal, left from the fire of the 

 preceding day, is laid over all. ' The wood being 

 then lighted, very rapidly ignites the cinder above, 

 and at the same time the pitchy vapour from the 

 fresh coal below rises through the wood-flame 

 and cinders, and becomes heated sufficiently itself 



483 



