" A remarkable and very valuable quality of this fire is its tenacity of life, so to speak, or its little tendency to be extinguished." Even after it sinks below the level of the box it does not go out, but continues to smolder slowly for a whole day or night, and is ready to burn up actively when the piston is raised.
Another peculiarity of the Arnott grate is the means taken to diminish the propor tion of the heat usually carried up the chimney. Of the thick column of smoke that issues from a common chimney-can, only a small fraction is true smoke or burned air; the rest consists of the warmest air of the room, which becomes mixed with the true smoke in the large space usually left between the top of the fire and the throat of the chimney. " The whole of the air so contaminated, and which may be in volume twenty, fifty, or even a hundred times greater than-that of the true smoke or burned air, is then all called smoke, and must all be allowed to ascend away from the room that none of the true smoke may remain. It is evident, then, that if a cover or hood of metal bs placed over a fire, as represented by the letters yab in the diagram—or if, which is better, the space over the fire be equally contracted by brickwork, so as to prevent the diffusion of the true smoke or the entrance of pure air from around to mix with it, except just what is necessary to burn the inflammable gases which rise with the true smoke—there will be a great economy. This is done in the new fire-place with a saving of from one third to one-half of the fuel required to maintain a desired temperature. In a room, the three dimensions of which are 15 ft., 131 ft., and 12 ft., with two large windows, the coal burned to maintain a temperature of 65° in cold winter days has been 18 lbs. for 19 hours, or less than a pound per hour."—A.rnott's Warming and Ventilation.
The hood is furnished with a throttle-valve or damper, t, having an external index showing its position, so as to give complete control over the current. The provision made for ventilation in this fire-place is considered further on.
Even in this, perhaps the most economical form of open fire yet contrived, there is still great waste of the heat actually produced by the combustion. To say nothing of what passes by ecnduction from the fire itself into the wall and is mostly lost, the quan tity carried off in combination with the hot gases, though no more air is allowed to enter than is necessary for complete combustion, is still great. It deserves being noticed that
the proportion thus carried off is greatest in the case of fu21 that burns with flame. Experiment shows that a fire of wood radiates one-quarter of its heat, the rest flying up; while the radiation from wood-charcoal is one-half of the whole heat produced. Every one has felt that a blazing fire has far less warming effect than a glowing one. Not that flame has not intense heat in it—more intense even than a glowing fire, but it gives it out only by contact and not by radiation. It thus appears that any mode of heating that depends upon direct radiation, as the open fireplace chiefly does, necessa rily involves great waste of fuel. This can be avoided only by applying the heat on a different principle, which consists in first making the fire heat certain apparatus with considerable surface, which then by radiation and contact with the air of the apartment diffuses its heat throughout it. This is the principle of the other methods of warming, which we now proceed to describe. The consideration of methods that combine the two principles will come most conveniently last.
Warming by Stoves. close stove is simply an inclosure of metal, brick, or earthen ware, which s heated by burning a fire within it, and then gives out its heat to the air by contact, and d to surrounding objects by radiation. The simplest, and, so far as mere temperature is concerned, the most effective and economical of all warming arrange ments, is what is called the Dutch stove; which is simply a hollow cylinder or other form of iron standing on the floor, close at top, and having bars near the bottom on which the fire rests. The door by which the coals are put in being kept shut, the air for combustion enters below the grate, and a pipe issuing from near the top carries the smoke into a flue in the wall. If this pipe is made long enough by giving it, if necessary, one or more bends, the heated gases from the fire may be made to give out nearly all their heat into the metal before they enter the wall; and thus the whole heat of the combustion remains in the room.