Reverberatory smelting is essentially a British process, developed in Wales, as already explained, owing to a plentiful supply of good furnace coal yielding a long flame, and also of good refractory material. Many Swansea workmen were, in the early days of American development, and are still, employed in charge of such copper furnaces, and it is largely due to British technical skill and to American genius for organisation and development that reverberatory smelting in the large furnaces at modern works has become so very successful. =The Principles of Modern Practice.=—Success in modern reverberatory work has been due to the recognition of the fact, that with the maintenance of constant high temperature on large masses of material, thorough fusion and separation of the products can be very efficiently conducted. =The Requirements for Successful Reverberatory Work.=—Since the action in the furnace is performed mainly by the effects of heat, it is necessary that— A. The melting should be as rapid as possible. B. The losses of heat during melting should be reduced to a minimum. The temperature required for the formation of slag and for obtaining a thorough fluidity of the materials is from 1,400° to 1,600° C., and the methods of achieving the proper conditions can best be stated as the avoiding of all circumstances likely to cool the furnace or to interfere with the melting down of the charge. A. To ensure rapidity of melting, it is essential that a very large quantity of coal shall be burned as rapidly as possible. This requires— i. A large grate area. ii. A good draft. iii. The firing and grating to be conducted so as to interfere as little as possible with the regularity and degree of heating. In localities where a supply of suitable coal is not available, other methods of heating, such as the use of oil or gaseous fuel, are necessary. B. To prevent heat losses as much as possible, it is necessary— i. To avoid leakages of cold air into the furnace. ii. To prevent radiation of heat through walls and roof. iii. To prevent the hearth from being cooled by the withdrawal of heated charges and the substitution of fresh and cold ones. iv. To utilise the heat of the already melted charge for the heating up of the fresh ore. v. To avoid as much as possible, waste of heat by the escaping gases. A. FOR RAPIDITY OF MELTING. A. i.—_Enlarged Grate Area._—In the older methods of working, there was a general tendency to employ a furnace of standard size, and improvements in the economy of the process were in the direction of reducing the fuel bill as much as possible for the given size of furnace. This was effected by keeping the grate area fairly small.