(average area approximates 2'/2 square feet) 

 to accommodate at least a frying pan and a 

 coffee pot. The area may be increased, as 

 hereafter explained, if more cooking surface is 

 required. 



The size of the firebox is to some extent de- 

 termined by the amount of surface wliich is 

 desired for cooking purposes. In the larger 

 unit, the dimensions will approximate the 

 following: Height 8 to 10 inches, length 20 to 

 30 inches, and width 12 to 18 inches. The height 

 is normally from 8 to 10 inches, inasmuch as 

 the best cooking fire comes from the glowing 

 coals rather than from a high flaming fire. 



In order to procure increased cooking and 

 warming surface and at the same time preserve 

 the minimum dimensions of the firebox, a type 

 of design may be adopted as shown on plate 

 XIII, figure 3. The open area between the 

 firebox and the flue virtually becomes a part 

 of the flue, although it is covered with a sohd 

 plate, the surface of which is sufficiently hot 

 for cooking. 



The open end of the firebox should face the 

 prevailing wind. The shape of the firebox is 

 normally rectangular. Sides splayed to the 

 front are of some advantage in the case of a 

 warming fire; but they add to the difficulty of 

 procuring and installing the grates, plates, and 



linin g. 



In all stoves and fireplaces the firebox should 

 be so constructed that there is a sUght slope 

 from the back of the hearth to the front of the 

 hearth, in order that any water which accumu- 

 lates on the hearth will immediately drain out 

 of the firebox. 



Because of the fact that the ordinary kind of 

 stone available for camp stoves and fireplaces 

 is not resistant to sudden extremes of heat and 

 cold without undue damage, the best practice 

 is to Hne the firebox with fire-clay brick in order 

 to protect the stonework against direct exposure 

 to these extremes. In some instances, a lining 

 of 10-gage sheet iron, made to conform to the 

 measurements of the proposed firebox, and 

 with a grating attached, is used in place of fire- 

 brick. These combined grates and sheet-iron 

 sides can be manufactured at smaU cost, and 

 where the cost of procuring fire brick is ab- 

 normal, this type of Hning is a practical answer 

 to the problem of protecting the stone-masonry 



sides against injury from direct exposure to 

 the fire. 



Sometimes it has seemed desirable to con- 

 struct a precast firebox of reinforced concrete, 

 so that the firebox may be set into a space sur- 

 rounded by stone masonry walls which forms 

 the sheU of the camp stove. The theory being 

 that if the firebox is damaged by heat it can 

 be removed easily and replaced by another 

 firebox. This procedure does not seem to be a 

 logical procedure for the reason that a firebox 

 of a much more permanent character can be 

 constructed of fire-clay brick as a permanent 

 part of a camp stove. Concrete thus exposed to 

 intense heat will undoubtedly suffer definite 

 damage in a very short time. 



Ordinary brick is sometimes used for hning 

 some of the simpler types of fireplaces which 

 are not intensively used and which are not 

 doused with water. This type of construction is 

 not recommended. In locahties where lava 

 rock may be procured easily, the lava rock 

 hning is equally as acceptable as fire-clay 

 brick. Ordinary brick will shatter and disinte- 

 grate if subjected to extreme and sudden 

 changes in temperature caused by water 

 dousing. 



Fire-clay brick (sometimes called fire brick) 

 is mode from fire clay by what is known as a 

 dry pressing process. In this process, 4 or 5 

 percent of water by volume is added to the dry 

 fire clay which, when thus moistened, seems 

 hardly damp. The thoroughly mixed fire clay 

 is then formed into bricks under a pressure 

 estimated to approximate 4,000 to 5,000 

 pounds per square inch. 



Fire clay, from which hre-clay brick is made 

 is dehned by the American Society for Testing 

 Materials as a "sedimentary clay of low flux 

 content, and consisting essentially of hydro- 

 silicate of alumina." There are at least six or 

 eight distinct kinds of fire clay, having different 

 properties with respect to chemical composition. 



The standard size of fire-clay brick is 9 by 

 4'j by 2': inches. There are four classes of fire- 

 clay brick, classified according to heat resist- 

 ance. The class commonly known as third 

 quahty fire-clay brick, or correctly designated 

 as moderate-heat-duty brick (according to the 

 standard definition), is generally used for hning 

 fireboxes and hearths in camp stoves and hre- 



13 



