In spite of the neutral atmosphere, however, the smelting of the roasted materials usually results in a higher concentration than would be expected from the calculation of the sulphur, copper, and iron in the charge. The reason of this is that the smelting operation results in some further elimination of the sulphur, which causes the production of a higher grade matte. This additional elimination of sulphur in the reverberatory furnace smelting of the roasted charge is due to the reactions which take place on melting, between the oxides, sulphates, and sulphides of copper, all of which exist in the products from the roasters. These reactions are expressed by the equations— Cu_{2}S + 2Cu_{2}O ➡ 6Cu + SO_{2} Cu_{2}S + CuSO_{4} ➡ 3Cu + 2SO_{2}, which indicate a further addition of copper to the matte, and a corresponding loss of sulphur. Thus a typical reverberatory charge of the following composition:— Silica, 27·2 per cent. Iron, 31·0 " Lime, 2·3 " Sulphur, 8·4 " Copper, 8·3 " should theoretically yield, on melting down, a matte running— ─┐ ┌─ ─┐ ┌─ [8]Cu (8·3) -> Cu_{2}S 10·4 │ │ Cu 8·3 │ │ Cu 30 % ├─ = ─┤ S 8·4 ├─ or ─┤ S 30 % S (8·4−2·1) -> FeS 17·6 │ │ Fe 11·3 │ │ Fe 40 % ─┘ └─ ─┘ └─ In actual practice however, the matte resulting from the reverberatory smelting of the charge had the composition— ┌─ │ Cu 45 per cent. ─┤ S 27 " │ Fe 28 " └─ the 3 per cent. loss of sulphur causing a 15 per cent. increase in the copper contents of the matte. Experience in the working of the plant enables the management to determine this important factor with fair accuracy, and thus from a knowledge of the composition of the roaster product, to regulate and control the grade of the matte produced at the reverberatories. In modern reverberatory practice, therefore, the control of the furnace products is carried out at the roasting plant, and the reverberatory furnace has simply to melt the charge and ensure good settling. _Anaconda Practice_ affords a good illustration. The foreman of the reverberatory furnaces simply charges what is sent him from the roasters, and practically nothing else is put in,[9] his duty being to smelt this mixture and to obtain from it a clean slag and fluid matte. He is not responsible for the grade of the matte, and if this is not satisfactory, some change is made in the working at the roasters. The reverberatory foreman does not learn the composition of the materials passing into his furnace until he is furnished with the daily assay reports on the following day.