_The Apparatus for Roasting_ depends to some extent on the class of material to be dealt with, which may be in the form of either (_a_) lump ores, or (_b_) fine ores. (=a=) =Roasting of Lump Ores.=—In modern copper-smelting work, the practice of roasting lump ores is practically obsolete. The conditions under which its use might still be justified are those associated with newer mining districts, where rapid concentration of heavy sulphide ore into matte is required, before the time is ripe for smelting the material pyritically, and where further, it is desired to employ the blast furnace for the smelting operations under these circumstances. The advantages possessed by the method are— (1) No preliminary crushing is required. (2) The product is largely in the form of lumps, and hence immediately suitable for blast-furnace work. (3) The plant and appliances required are simple. The two methods employed are—(A) open-air roasting, (B) roasting in kilns. A. _Open-air Roasting of Lump Ores._—This method is conducted in heaps or stalls, and the features just considered apply particularly to this branch of roasting practice. The modern tendency is to avoid heap-roasting altogether, and it is only conducted when the conditions are exceptional. Amongst the many grave objections to open-air roasting are— (_a_) It is very slow, since a long period of time is required for the oxidising effect to penetrate through massive lumps of ore. (_b_) A large amount of capital is tied up in the material at the roast-yards. (_c_) The losses occasioned by wind and rain are very considerable. (_d_) It is difficult to use up a large quantity of fines in the roast-heaps. (_e_) Difficulties arise owing to damage by the fume, and from interference by litigation. There is one special instance of a modern smelter making a great success of heap-roasting—namely, at Rio Tinto—but the circumstances are peculiar, as the roasting is followed by leaching operations of the immense ore heaps _in situ_. This branch of roasting need not be considered at length, and the older standard text-books give full descriptions of the various methods employed. The following particulars are important, however, when under exceptional circumstances such work has to be undertaken:—