The concrete for the base of an 80ft. chimney-stack should be formed of good Portland cement and ballast, or stone chippings, in proportion by measure of 1 cement to 2 sand or fine chippings, and 5 large gravel or broken stone. A block of concrete, 13 ft. square by 5 ft. deep, would require about 130 bushels of Portland cement. The materials for the concrete should be mixed dry, about half a cubic yard at a time, and then thoroughly re-mixed while being watered through a rose, so as to moisten the whole without washing out any cement. It should then be wheeled to the trench and tipped in, spread level, and gently beaten on top to consolidate it. Often the building commences directly the concrete is all laid, but it will be better to leave it for a week to harden. Any part projecting above ground should be supported by boards until well set.