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LINING   AND   DRYING   OF   FURNACES.                   4>
constant friction of the stock, so that better service is found by sacrificing" the heat qualities to those best calculated to withstand friction for stack linings.
In laying bricks, a thin grouting of the best fire-clay, without mixture of sand, is used. The clay is mixed of such consistency that a brick, if dipped into it, would, upon being lifted out, have a coating of about one-eighth of an inch adhere to it. To make a bed of clay for the brick to be laid in, a dipper is used to pour the clay upon the surface of the last course, laid to a thickness of about one-fourth of an inch. The bricks are then slid on soft clay up to each other so as to imbed themselves firmly, and closely force the clay between all joints, after which a hammer is used to crowd the joints still more closely together or bed the bricks more firmly. In order to obtain a true circle when lining the hearth, bosh, and stack of a furnace, a plumb bob-line is dropped from the top to obtain a center for a '' spindle '' with a c' sweep '' attached, which is to be carried up as the work progresses, just as a loam moulder would build a large cylinder mould. The time usually occupied in lining such a furnace as shown in Fig. 10, employing four masons and twelve helpers, is about thirty days. The work of lining a furnace is considered a specialty, and the leading men in such work are carefully selected from those having the .greatest experience in this line, as any faulty construction can easily result in a very short run of a furnace, thus causing a great expense in cc blowing out " to remedy the evil.
Space for expansion of fire-brick, as illustrated at K, Fig. 6, and both sides of Fig. 10, page 49, is a practice now followed in lining furnaces. This spaceare               jf|V