Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 2, 1802).djvu/380

348&#93; S48J FU R. that have ' ,f '' a granted to specula- tive individuals - — Thechlei objects in building', ami arranging a fur- nace, are : 1. To confine the heat as much as possible to the matter which is to be operated upon. Hence the fire is usually limited to a cavity formed with that intention, and which is provided with a door for supplying it with fuel, as likewise with a grate for supporting it, and permitting the air to pass through, as well as the ashes to drop down into what is called the ash-pit. — Thus, the heat is restrained so as to exhaust its force on the subject inclosed. 2. To prevent such heat from bein; dissipated; which design is effected by simply shutting the door of the furnace, and placing the matter to be acted upon, in such a direction as to receive the whole force of the fire, in its pas- sage up the chimney. 3. To produce an intense heat with the smallest possible quantity of fuel. Hence the throat, or tun- nel of ihe chimney, is occasionally contraetedbya slidingplale: which, when shut closely, prevents the passage of any smoke or ai ; and, on drawing it out in a greater Or less degree, leaves a vent propor- tionally large or small. Thus, a large quantity of fuel may be put in the furnace at one time, that will be. slowly consumed, and con- sequently require less attention, than those furnaces which are des- titute of this improvement. Where oo gr< at degree of h< at ;.-. required, the sliding plate may be o! cast- iron ; in some cases, bow evei < k iil Ik more n rvici I this contrivance is inapplicable to such furnaces as consume large FUR quantities of fuel, and especially where metals are to be melted. 4. To arrange the whole, so that the degree of heat maybe regulated at pleasure ;. which intention is ef- ■ i 1 by admitting only a certain portion of air to pass through the fuel. For this purpose, the late Dr. Black recommended to fill the upper part of the furnace fre- quently with small portions of soot, so that by closing the door of the ask-kole, and perforating it with a certain number of holes corres- ponding to each other other, a sufv ficient controul may be obtained over the fire. When the. heat is to be increased, all the passages should be opened, and the height of the vent extended ; by which means the column of rarefied air will be enlarged, at the same time its pas- sage through the fuel promoted, and consequently also the heat of the furnace rendered more intense. In Jv.nc, 1/S5, a patent was granted to Mr. Jvmes Watt, of Birmingham, for his newly-improv- ed method of constructing furnaces or fire-places for heating, boiling, or evaporating water, or other liquids; and also for heating and melting metals, or smelting ores ; by which greater effects are produced from t efuel, and the smoke is in a great measure prevented or con-* suraed. The patentee effects these different objects, by closing every passage to t e chimney or flues, excepting those left in the inter- stices of the fuel ; by placing fresh fuel above or nearer to die external air, than that which is alnady con- verted Into coke or charcoal; and by constructing the fire-places so that the flame must piss down- wards, or laterally, or horizontally, through V..c burning fuel j and from