LAYING OUT THE DESIGN OF WORKS. 43 



affecting or interfering with the other settings. A con- 

 venient arrangement when the flue outlet is on the top of 

 the setting is to run up a dwarf chimney, 14 inches square 

 inside, for a height of 4 or 5 feet. This should preferably 

 be placed over the division wall, rather than immediately on 

 the crown of the arch. On the top of the chimney is an iron 

 base-plale, carrying a length of 12 or 15 feet of wrought- 

 iron tube. Tubing of a suitable diameter is now made in 

 the solid, and it need not be carried higher than sufficient 

 to clear the ridge of the retort house roof. The damper 

 can be controlled by a rod and lever on the front of the 

 setting. This arrangement admits of covering and closing 

 the top of the chimney, which is the only really effective 

 way of checking excessive draught, either for banking up or 

 for Sunday stoppage, and is useful as a protection from the 

 weather when the bed is not in use. There is always a 

 leakage of air when the bottom dampers are supposed to 

 be closed, and the generator arch, or furnace arch, suffers 

 as a consequence. A large waste of fuel and proportionate 

 shortening of the life of the setting has been known to 

 result from neglect in this respect, and the introduction of 

 the top valve has proved a satisfaction and economy all 

 round, reducing fuel consumption and labour and pro- 

 longing the life of the setting. The valve consists simply of 

 a disc a little larger than the top of the chimney, carried 

 on a vertical spindle attached to the side of the tube by 

 guiding eyes at suitable intervals, and supported at the 

 bottom by the iron base-plate. A lever handle is fixed to 

 the lower part of the spindle, at right angles to the disc, 

 and by giving it a half circle turn the disc can be placed 

 square over the mouth of the chimney, or turned quite clear 

 of it, as may be required. 

 A common mistake in the small retort house is an excess 



