TEEATMENT OF THE COMSTOCK OEES. 225 



flat-bottomed and made either with or without a steam-chamber. When the 

 latter is desired the false bottom is cast separately, with a rim an inch deep, 

 and is then bolted to the main pan-bottom, thus forming the chamber. There 

 are no standards or legs for the pan to stand upon, the bottom being a square- 

 cornered plate of iron, projecting beyond the pan-rim, and it may be bolted 

 directly to the timbers on which it is to rest. The bottom, with its central 

 hollow cone, may be cast in one piece with the pan-rim, or, instead of the 

 latter, a simple flange may be cast, corresponding in size with the rim, to 

 which flange the rim, which may then be either a cast piece or made of sheets 

 of iron riveted together, is bolted. 



An improvement has lately been made to save the wear of the rim or 

 side of the pan and prolong its usefulness, by placing in the bottom of the 

 pan a false rim or circular facing for the pan-side, about nine inches deep. 

 This is cast in segments and made to correspond in form to the rim of the 

 pan. When fixed in place it saves the pan-rim from wear in that part which 

 would otherwise suflfer the greatest degree of friction, just as the shoes and 

 dies protect the pan-bottom and muUer-plate. When worn thin by the 

 friction of the pulp the plates may be removed and new ones substituted for 

 them. The driving shaft or spindle, c, passes up from below through the 

 central hollow cone, h, but its point of support is usually independent of the 

 pan, resting, in such case, in a step-box, 7^, which is fixed on a timber below. 

 Some, however, prefer to have hangers bolted to the bottom of the pan 

 and furnishing the support for the driving shaft, so that, if the foundations 

 of the pan settle, the relative position of the several parts is more readily 

 maintained. 



The step-box is cast in one piece, with a bearing for the end of the shaft 

 on which the vertical miter-wheel and pulley of the common driving gear are 

 fixed. 



The driver or hub, E, which is secured to the vertical shaft, is in two 

 parts, an upper and lower. The upper is fixed to the shaft by two strong 

 feathers or sliding keys, k. The base of the upper driver is cast with lugs, or 

 projections, which fit into corresponding recesses in the top of the lower driver, 

 by which means the latter is supported and set in motion. Above the upper 

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