PLANTS, WITH GLASS ROOFS. 



209 



the front, as high as the desired depth of the ash-pit, the boiler is fixed upon 

 it, and the brick- work carried up to its lower flange or rim. The side-walls 

 should then be raised, in four-inch work, level with the top of the boiler, as 

 represented in fig. 148 : a is the ash-pit, h the boiler, c the aperture in front 

 of the boiler, closed with fire-brick, e e and d d two bars, one supporting the 

 fire-brick plug, and the other fitting to the rim of the boiler to support a slate 

 which closes the front as in fig. 149 ; ff^ fig. 148, is the chamber around the 

 boiler, filled with sawdust as a non-conductor of heat ; and a layer of saw- 

 dust extends over the top of the boiler, under the slate slab g g, which is fitted 

 over the brickwork, an aperture being cut in it to allow the throat of the fur- 

 nace to pass through. 



Fig. 149 gives the same view farther completed : the front of the chamber 



is closed with a slab of slate, and on the slab 

 which covers the boiler is erected a chimney, 

 having a feeding- door, through which fuel 

 is supplied, placed in its sloping face directly 

 over the mouth of tlie furnace. This chim- 

 ney must not exceed four or five feet in 

 height, and its area must in no case exceed 

 the area of the mouth of the furnace. That 

 here represented, viz., a brick base, with a 

 piece of four-inch iron pipe about three feet 

 in length, will probably be found most con- 

 venient, unless a moveable chimney be pre- 

 ferred. This chimney should be fitted with 

 a damper just below the iron part, to give 

 greater command of the draught. The 

 aperture of the boiler, which is closed with 

 fire-brick, and the front of the ash-pit, 

 should also be closed by a door or blovrer. 

 having a regulator to admit or exclude 

 draught. A blower is preferable to a door, 

 as hinges are always liable to rust, and 

 then break or strain ; and it is important to 

 be able to close the ash-pit pretty accu- 

 rately. 



Fig. 149. Rogers's boiler set, with the chim- Fig. 150 shows the relative position of 

 ney added. the boilcr and pipes, and the mode of at- 



taching and arranging them. In the first place, the whole of the pipes 

 should, if possible, be above the boiler. One foot is sufficient, but, when con- 

 venient, the higher the better. When two or three-inch pipe is employed, 

 the pipes may rise uniformly about one inch in twenty feet, from a and 6 to 

 c; on which, being thus the highest point of the pipes, an air-cock is placed. 

 But if four-inch pipes be employed, it is better that a should be the highest 

 point, and the air -cock placed there ; and that the pipes should fall uniformly 

 one inch in twenty feet from a to c, and from c to & : indeed this is generally 

 the best arrangement, where not inconvenient. From h the return-pipe, r, 

 should descend either perpendicularly, or with as steep an inclination as pos- 

 sible, to the bottom of the boiler. The supply cistern, e, must be so placed 

 that its bottom is not lower than the highest point of the pipes. The top of 

 the steam-valve, v, should be level with the top of the supplj^ cistern. Just 



