This bottom is now put in also in a manner different to the older practice, and excellent results have accrued from the change. The old method of constructing sand bottoms consisted of putting in the beds of sand, layer by layer, and thoroughly fritting each one before the addition of the next: in modern practice, it is found that proper consolidation is not attained with beds of the enormous area now employed, when the bottom is constructed in such layers. The present method of working the reverberatory furnace is not to drop the charge on to the sand hearth at all, but into the deep pool of matte, and the sand-hearth is regarded more as a convenient foundation for the support of this liquid working-bed, on account of its constituting a cheap non-conducting and fire-proof material which is unaffected by the materials resting upon it. It was found, however, on commencing this matte-pool practice, that the older method of putting in the bottom in successive sand layers was not suitable for this work; after a little wear, the beds became raised in layers, this being especially the case if any holes happened to be eaten through in places. Moreover, the large weight of matte tended to find its way down between the layers and raise them up bodily, or else it worked down at the edges of the hearth and side walls, and either broke out underneath the former or through the latter. When it was ascertained that liquid matte itself had no corrosive action on the siliceous hearth if the latter be kept constantly covered, and that the causes of breakouts were principally due to mechanical weaknesses, it required only improvements in design and construction in order to avoid them. This is now attained by constructing the bed in a compact and perfectly massive form, and is best accomplished by putting in the whole layer of 26 inches of sand at once, and firing as hard as it is possible for the brickwork to stand. The method has met with exceptional success in practice, rigid and impervious hearths are obtained; it being found that less than 1 inch has worn off the bed after two years’ working. [Illustration: Fig. 28.—Sectional Plan and Elevation of Reverberatory Furnace at Anaconda.] =Large Reverberatory Furnaces: Details of Construction.=—The large furnaces at Anaconda were the first of the modern type to be constructed, they have met with enormous success in practice and constitute the standard form. Similar furnaces are now in operation or under construction at many of the large modern camps, and are of similar design and construction. The _hearth_ is 102 to 116 feet long by 19 feet wide. _Grate_, 16 feet by 8 feet = 128 square feet grate area. Ratio of hearth to grate area is 16 : 1.