In constructing chimney shafts for Lancashire boilers, the area of the chimney at the top is based upon the size or capacity of the boilers. Thus, area in square inches = 180a/√h = 100HP/√h = 15P/√h , where a = area of firegrate in square feet, IIP = indicated horse-power of engine, or P = quantity of coal consumed per hour in pounds. The diameter externally at the base should be 1/10 to 1/12 of the height. The latter should be o;;in. to the foot, or about 1 in 33, though this is not imperative. The brickwork should be 9in. in thickness for the top 25 ft., and increase half a brick at each 25ft. from the top. If the inside diameter at the top exceeds 4ft. 6 in., the top length should be 1 1/2 bricks thick, and each of the lower lengths consequently half a brick thicker. The foundations should be carried down to the solid; they should be spread out so as to make a good broad base, and the load on the foundation should not exceed 1 ton on the square foot. After arriving at what appears to be a solid bed, it is a good plan to sink a trial hole under the centre of the chimney some feet lower; if the ground is found to be good, the hole may be filled with concrete at 10 or 12 to 1. The base for the chimney should consist of a solid block of concrete, 6 to 1, not less than 2 1/2 ft. or 3 ft. thick; and as concrete is cheaper than brickwork, it may be carried up in concrete to the invert of the flue.