The Best-Selecting process, and the Nicholl and James process are likewise valuable and ingenious modifications of the Swansea method for special work.
In general, however, up to 1880, there had taken place but little change in principle from the older methods of smelting. The chief improvements involved a slow change in furnace size, and progress in several details in practice. The more important of these advances were—
(a) In Roasting Practice.—1865. Introduction of the mechanically driven furnace (the Brückner cylinder); not, however, adopted for copper smelting till many years afterwards. Later—Arrangements for using roaster gases for sulphuric acid manufacture.
(b) In Reverberatory Furnace Smelting.—1861. Gas firing introduced, but with very little success for copper smelting, even at the present day.
(c) In Blast-Furnace Smelting.—Several very important changes were introduced in the construction of furnaces.
1863. Elongation of the furnace.
Rachette in Germany introduced the elliptical blast furnace. (Intended first for lead smelting; rapidly adopted for copper matte smelting.)
1875. The water-jacketing of blast furnaces.
The Piltz water-jacketed furnace was likewise first employed in lead smelting, and subsequently introduced into copper smelting practice. The principle had, indeed, been utilised in certain branches of iron smelting before this date, but for non-ferrous work the idea was new.
Although the method of water-jacketing was recognised as leading to great improvement in the working of the furnace, its use was at first somewhat restricted, owing to various practical difficulties, and the ultimate great success was effected when in American practice, the plan of working the two principles of elongated furnaces and water-jacketing in conjunction, was adopted.