Having now described the principal varieties of stove grates or fire-places in their most improved forms, (including air stoves, which will be found under the article Aiti), we shall dose this part of the subject by a few observations on the proper construction of fire-places in general, in order that the reader may understand the defects that may exist in his own, and know how to apply the remedy. In open fires the bars should not be larger than is necessary for strength, as they obstruct the radiation of heat, and prevent the egress of air, which is requisite for making the fire burn clear. To attain a clear fire, Mr. Tredgold justly says, that the sides of the burning fuel should be at least half surrounded with slow conductors of heat, otherwise the heat developed will pass off so quickly by conduction, that the fuel will burn dead, and that heat which ought to be radiated will be expended in warming the walls, &c. behind the fire. Iron is a very rapid conductor of heat, and therefore it should be used as sparingly as possible. Fire brick, a slow conductor, is employed with much advantage for the backs and ends of grates by a few manufacturers, but iron mongers in general seem to think it more desirable to use iron than to economize fuel, or to work on sound principles. But when a fire-place, made of slow conducting materials, is large and filled with fuel, as soon as the fire becomes bright the heat is extremely intense and scorching ; when the fire is in this state it is often too powerful for the room, though perhaps barely sufficient when the combustion is less perfect. This may be remedied by any method which enables us to expose a greater surface of hot matter with the same bulk of fuel, and at a lower degree of heat. Some time ago "fire balls," (spheres made of baked clay,) were used with this object ; but their inconvenience, when not judiciously attended to, brought them into disrepute. An improved substitute for them has been suggested by Mr. Tredgold, when the fire is of greater length than 18 inches ; that of building a projection from the back of the grate (and of the same depth) to within three inches of the front bars. This projection should be of good fire brick, and built firmly in with the other part of the back. Thus is left a space for a sufficient body of fire on each side and the surface is increased without adding to the mass of burning fuel. The combustion of the fuel in an open grate should not be faster than is necessary to produce a clear fire. To guard against the loss of heat by the warm air of the room ascending the chimney, two partial remedies have been adopted—that of lowering the mantel, and contracting the throat of the chimney ; but the first of these remedies impairs the ventilation of the room, and the second, causing a rapid draught, increases the consumption of fuel. For some rules in duly proportioning the flues, see the article Cullman'. A grate should offer as little obstruction as possible to the radiation of heat, and therefore the usual mass of metal below the front bars, called a fret, is objec tionable; and the sectional form of bars should be that of a wedge, with the extremity rounded off, which part should be inside, or next to the fuel, as it is advantageous to have as little metal as possible in contact with the fuel. There is, however, no objection to the employment of metallic covinga, as reflectors of heat, when separated by a slow conductor from the metal of the rate ; and instead of these being blackened, as they are usually in the common Rumford stoves, they should he bright or polished surfaces, and preferably of brass to the other common metals. The angle best suited for the covings is 45° with the front line of the grate. The height of the grate from the floor is an object of some importance ; if it be placed too low, the heat is expended almost wholly on the hearth, and the fire-place seems buried within the fender ; if it be placed too high, a person's face is scorched, while too small a portion of heat is given to the floor to render a room comfortable ; but a high mantel has the advantage of producing a more effectual ventilation. Mr. Tredgold con sidered that the top bar of stoves ought not to be less than 20 inches from the floor, and never exceed 2 feet ; and when the lower part of the fire is not buried in a mass of metal work, there will be an abundant supply of heat thrown upon the floor from the greater height. The space between the top bar and the mantel will require to be proportioned to the size of the room and the height of the chimney, and in ordinary cases may be about 15 or 16 inches. With respect to the proportion of grates to different sized rooms, Mr. Tredgold
has, from observation, deduced the following rule :—Let the length of the front of the grate be made one inch for each foot in length of the room, and the depth of the front be half an inch for each foot in breadth of the room. If the length of the room be such as requires the grate to be longer than 24 feet, two fire-places will be necessary ; and in that case the same proportions may be adopted, divided into two grates, unless the room be very wide, when a greater length should be given, and less depth, so as to preserve an equivalent area. For various information connected with this subject, see the articles VENTILATION, COMBUSTION, AIR, FURNACES, &C.
Welles's Patent Peripurixt.—This is a small portable cooking stove, and is very ingeniously contrived. The patentee states in his prospectus of it, that " it boils water, prepares coffee and chocolate in a very supenor manner, boils eggs, cooks a beef-steak or a slice of ham, all in less than ten minutes. For dinner, it will prepare soup, steam vegetables, and cook fish, chops, or steaks, at the same time; and for these one farthing's worth of fuel is sufficient." Fig. 1 is an external view, and Fig. 2 is a vertical section ; a is a small cone of cast iron, having at the bottom a grating, on which is put the fuel (charcoal), broken into small pieces; below this is a small chamber b, perforated at its sides for the admission of air, and containing a small pan to receive the ashes, and also to light the charcoal by a piece of paper ; the vessel c contains water, which entirely surrounds the cone; the next vessel e above is intended to be used as a steamer; it has in its centre a frustrum of a cone, the lower edges of which descend below the bottom of the vessels, and fit upon the cone beneath, so as to carry up the flue to the chamber above, which has open perforated sides, whence the vapours produced by the combustion escape. On the top of the cone there is a valve for enlarging or diminishing the aperture, having a horizontal rod fixed to it, which passes to the outside of the vessel, as shown. The vessel over this, f, is, we suppose, a stew-pan, or something of the kind; it is heated by the hot air and direct influence of the fire; above this pan is placed in a cavity of the cover a small pot for warming small quantities of liquid. There are several appendages or vessels for peculiar purposes, such as the boiling of eggs, &c. which fit one over another in a similar manner to those described. The apparatus is proposed to be used on the breakfast or dining-table, to be taken in a carriage, in a boat, or carried by pedestrians.
Tozer's Patent Calefaetor. — This is another ingeniously contrived little cooking stove, and is intended to meet many of the wants of a small family, especially in the summer season, when the smallest quantity of artificial heat is desirable. The diagram in the next page is explanatory of it construction and arrangement when applied to roasting and steaming ; some of the parts in the drawing are slightly varied from their real positions, for the purpose of elucidation by a single figure. a is the steam boiler, which has a large ellip tical opening down the centre for depositing a variety of culinary vessels therein ; b an aperture for charging the boiler with water; c a stop-cock for drawing off the water as may be required, but placed high in the boiler to admit a draught of air to the grating e, on which the charcoal is burned ;—the grating is, strictly speaking, a strong iron plate, perforated all over for the free admission of air through the boles ; f is termed the 044111 pan, which is o cast iron dish, suspended about half 'way down the elliptical opening ; g a sheet-iron cover ; Is a pipe conveying the steam from the boiler a to the steamers i and j, which separate in the middle, and allow of one or both being used at a time ; each of these steamers may be subdivided into distinct compartments; k, a sliding damper for enlarging or contracting the air passage d, so as to increase or diminish the combustion of the fuel, as may best suit the peculiar culinary process. When the apparatus is not required for roasting, but for boiling, or making soup or broth, the oven pan is to be removed, and in its place the required vessels (all of which are made to fit) are deposited. In some cases the patentee adopts two half-kettles instead of one. A current of heated air is constantly kept up, entering at the grating at bottom, and passing out at the grating above, where the heat is reverberated against the top and sides of the cover, prior to its escape through a small central aperture in the latter.