The kettle is provided with a conical cover furnished with doors, which can be opened for manipulating the contents, and a wide iron pipe proceeds from the summit of the cover to convey the steam and fume, which consist of lead and foreign metals, to a flue which leads to a series of capacious chambers in which the solid matter is deposited, and from which the final volatile matters pass away by another flue to the chimney of the works. The matter deposited in the chambers is smelted with litharge in a reverberatory furnace. The process is thus described by Norman Cookson, whose firm are working it on the Tyne.

Instead of using a row of pots, as in the old process, there are two only; of which the lower is placed at such a height that the bottom of it is 12 to 15 in. above the floor level, while the upper is placed at a sufficiently high level to enable the lead to be run out of it into the lower pot. The capacity of the lower pot, which in those most recently erected is 36 tons, should not be less than double that of - the upper one. Bound each pot is placed a platform, on which the workmen, of which there are two only to each apparatus, stand when skimming, slicing, and charging the pots. The upper pot is open at the top, but the lower one has a cover, with hinged doors; and from the top of the cover a funnel is carried to a set of condensers. At a convenient distance from the two pots is placed a steam or hydraulic crane, so arranged that it can plumb each pot, and also the large moulds, which are placed at either side of the lower pot.

The mode of working is as follows: - The silver - lead is charged into the upper pot by means of the crane. When melted, the dross is removed, and the lead is run into the lower or working pot, among the crystals remaining from a previous operation. When the whole charge is thoroughly melted, it is again drossed; and in order to keep the lead in a thoroughly uniform condition, and prevent it from setting solid on the top and the outside, a jet of steam is introduced from the pipe. To enable this steam to rise regularly in the working pot, a disc plate is placed above the nozzle, which acts as a baffle - plate; and uniform distribution of the steam is the result. To quicken the formation of crystals, and thus hasten the operation, small jets of water are allowed to play on the surface of the lead. This, it might be thought, would make the lead set hard on the surface; but the violent action of the steam acts in the roost effectual manner in causing the regular formation of crystals. Owing to the ebullition caused by this action of the steam, small quantities of lead are forced up, and set on the upper edges and cover of the pot.

From time to time the valve controlling the thin streams of water playing on the top of the charge is closed, and the workman, opening the doors of the cover in rotation, breaks off this solidified lead, which falls among the rest of the charge, and instantly becomes uniformly mixed with it. Very little practice enables an ordinary workman to judge when § of the contents of the big pot are in crystals, and 1/3 liquid; and when he sees this to be the case, instead of ladling out the crystals ladleful by ladleful, as in the old Pattinson process, he taps out the liquid lead by means of 2 pipes, controlled by valves, the crystals being retained in the pot by means of perforated plates. The liquid lead is run into large cone - shaped moulds on either side of the pot; and a wrought - iron ring being cast into the blocks thus formed, they are readily lifted, when sot by the crane. To give some idea of the rapidity of the process, it may be mentioned that, from the time the lead is melted and fit to work in the big pot, to the time that it is crystallized and ready for tapping, is in the case of a 36 - ton pot from 35 to 45 minutes; and the time required for tapping the liquid lead into the larger moulds is about 8 minutes, before the lead begins to crystallize, the upper pot is charged with lead of half the richness of that in the lower pot.

Thus, when the liquid lead has been tapped out of the lower pot, it is replaced by a similar amount of lead of the same richness as the remaining crystals, by simply tapping the upper or melting pot, and allowing the contents to run among the crystals. The same operation is repeated from time to time, until the crystals are so poor in silver that they are fit to be melted, and run into pigs for market. The large blocks of partially - worked lead are placed by the crane in a semicircle round it, and pass successively through the subsequent operations.

The process has other great advantages in addition to that of saving labour. In the first place, after taking into account the fuel used for supplying the crane power, and the steam for crystallizing, it still shows a great economy in fuel. In the case of Cook - son's firm, they find that, as compared with the Pattinson process, as formerly carried out by them, they only use 1/3 of the amount of coal, though of a slightly better quality. Another most important advantage is that the steam, in addition to its mechanical effect, produces an effect of a chemical nature. Almost all silver - leads, as received, contain impurities, such as copper, arsenic, iron, and antimony. In the Pattinson process, these extraneous metals had to be removed by calcination before the lead could be used in the separating department. But it is found that in the Rozan or steam process these extraneous metals, if they exist in moderate quantities (as is usually the case in English, Spanish, and other leads of similar quality), are readily oxidized by the steam; and that their presence in the desilverizing apparatus, instead of being a disadvantage, is a positive advantage, since, where a small quantity of antimony or copper exists, it has the effect of lessening the oxidation of the lead.

A small quantity of lead and other oxides is carried mechanically from the lower pot by the steam and other gases, which escape from it after having done their work; but these are conducted by the funnel on the top of the pot cover to condensers, where the metals are practically all recovered. Those oxides are found to contain a very large quantity of antimony and copper, and in colour are nearly black, instead of the yellow proper to pure ead oxide.