LAYING OUT THE DESIGN OF WORKS. 41 



and tear against wages, and must be decided by local 

 conditions. 



A common defect in the small works is the provision of 

 one chimney for the whole of the settings, and that too 

 lofty, too large in section, and square inside. There may 

 be good reason for carrying the products of combustion up 

 to 50 or 60 feet above ground level when they proceed from 

 twenty or more furnaces, and the surrounding district is 

 fully populated. But for one to three beds, and with 

 ploughed fields on three sides, this does not apply. 

 For many years it was supposed that a long chimney gave 

 a better draught, but it is now known that the " pull " of a 

 chimney is more a matter of proper sectional shape and 

 area, as compared with the work to be done, than of length. 

 But a chimney is not made of elastic material, and if the 

 section is right for July it is not large enough for December. 

 If three furnaces are under weigh at Christmas, and only one 

 at Midsummer, the chimney must be too large at one time or 

 too small at another. Taking up or letting down one bed 

 upsets the working of the others, and some waste of coal 

 takes place until a satisfactory adjustment suited to the new 

 conditions is arrived at. At the heaviest season of the 

 year, just when the full working is needed, it is found that 

 the pull is not equal on each bed, and the one farthest 

 away, or otherwise least favourably situated, will not heat 

 properly. A crack or accumulation of dust in the chimney 

 upsets the whole of the settings, and cannot be repaired or 

 cleared without interference with the daily routine. 



Thirty feet or so in height, sufficient to clear the ridge of 

 the retort house roof, and an area of 100 to 120 square 

 inches for each bed in use, is quite sufficient. If soundly 

 built, lined with fire-brick to the top, so as to keep in the 

 heat, and round in section, such a chimney will give a pull 



