The furnace for making the gas consists of two divisions. The first a deep square chamber where the fuel is distilled, is about 2 feet square, and 8 deep, and at the bottom has a blast pipe by which air is blown in. The top of this chamber, or gas generator as it is called, is covered by an iron box with a sliding top and bottom, by which fuel is introduced without allowing any escape of gas. Sinding's original generator was more complicated, having the blast pipe high up, and the lower part of the generator smaller than the upper, in order to make the fire burn downwards. This apparatus was for wood; for coal the simpler arrangement first given is used. The generator communicates with the second chamber by a short horizontal canal in the upper part of the generator, and in this air is mixed with the gas in regulated quantities, by means of a blast pipe with stopcocks.

The second chamber, which contains the mundic, is nearly a cube, about 8 feet each way, the roof being slightly arched. This chamber has openings in the bottom by which the gas formed passes off to the precipitation chambers. These openings are covered by a brick roof to keep the mundic from filling them. There are also openings at the two sides of this chamber for drawing out the spent mundic, and one in the end for charging fresh sulphide. This furnace is worked as follows:-The generator is filled with fuel and lighted. The blast coming in at the bottom supports combustion, and the carbonic acid formed is reduced in passing up through the column of fuel. The fresh fuel on the top is distilled by the hot gases passing through it, and gives off hydrocarbon gases. The gas that passes off from the generator is a mixture of carbonic oxide and hydrocarbon gases. On meeting with the blast in the canal, a portion of the gas is burnt, and it is essential that only a part of it should be consumed, the object being to get sufficient heat to distil sulphur from the mundic, but at the same time to leave sufficient gas unburnt to form sulphuretted hydrogen. By regulating the blasts in the generator and canal, the mundic chamber is filled with a sheet of flame so smoky as to give little or no light; by this means the mundic is heated to low redness, sulphur distils off, and the smell soon indicates that sulphuretted hydrogen is present in large quantities. A ton of mundic should give about 5 cwts. of sulphuretted hydrogen gas. The mundic used in the furnace may be that from which the copper is obtained, since it is not wasted in the manufacture of the gas, but rather prepared for the process of roasting. The precipitation of copper is conducted in an air-tight wooden chamber divided into compartments, so that the gas which enters at one end must pass in a zigzag direction through the whole chamber. The top is formed by a tank, into which the

solution of copper is pumped. The bottom of this tank is pierced with small holes, by which the solution trickles through the gas, and there becomes blackened and thickened by precipitated sulphide. The solution now runs out at the bottom, and is again pumped up, and so on until the precipitation is complete. It is then run off into pits, where it settles, the clear liquor is let off, and the precipitate dried. This is run down in a furnace, and gives a regulus yielding 70 per cent. of copper, and from which fine copper can be made in one operation. The solution usually contains iron, and consequently should not be much exposed to the air previous to precipitation, as the iron salt becomes peroxidised, and much gas is wasted in reducing it to the state of protoxide.

This process has been in successful operation for some five years near Fulda, in Norway, and yields a handsome profit. It was experimentally tried, last winter, in Wicklow; but, owing to the sulphur in the ore being as valuable as the associated copper, the process was not found to answer, since by it the whole of the sulphur of the ore is removed. If tried on the same ore, after leaving the vitriol works where the sulphur has been burnt off, it might, probably, yield a more favourable result. The advantages claimed for this process over ordinary precipitation by iron are, first, that it is cheaper; secondly, that the precipitate is richer. The precipitate obtained by Sinding's process contains 60 per cent. of copper, and is not contaminated by iron.

PARKES' PROCESS FOR DESILVERIZING LEAD.

This invention is founded on the property possessed by zinc of uniting with the silver contained in argentiferous lead, and, when fused together, forming with it an alloy which is readily skimmed off from the surface of the metallic bath. Messrs. Neville and Co., who employ this process of desilverization in their works at Llanelly, conduct the various operations as follows :

The lead treated contains but little silver, usually not more than from 10 to 15 ounces per ton, and is frequently that reduced from litharge obtained by the cupellation of rich lead, of about 250 ounces per ton produce.

From 6 to 7 tons of the lead are first melted in a large cast iron pot, close to which is a smaller one for fusing the zinc. The melted lead is then skimmed, and a sample taken for assay.

When the zinc has melted it is added to the lead, in the proportion of from 1 to 2 s. to each ounce of silver contained in the lead operated on, and the alloy is well stirred for from 1 to 2 hours. The fire is subsequently withdrawn, and the metal

allowed to rest until a scum forms on the top, which, when it has reached a certain thickness, is removed in the same manner as the crystals of lead in Pattinson's process.

After a time, when a crust no longer forms, the lead is ladled into a gutter, which conducts it to a reverberatory furnace, the bottom of which is of cast iron, where it is kept at a low red heat for some hours to give any traces of zinc, which still remain in combination with it, the opportunity of evaporating or becoming oxidised. A scum thus forms on the top of the lead, which is removed from time to time, and is added to the other matters taken to the liquation retorts. When the lead has been sufficiently purified, it is tapped into a large iron pot, and agitated for from 1 to 2 hours with green wood, as is usual in the case of tin smelting. The quality of the lead thus obtained is said to be exceedingly good, and the extraction of nearly the whole of the silver is effected. The scum from the pots invariably contains a considerable quantity of lead, which is separated by putting it into an iron retort, placed in a sloping position. As soon as this becomes heated, the greater portion of the lead runs out into a mould placed for that purpose, carrying along with it silver to the amount of 1,000 ounces per ton, and is at once cupelled. The portion which remains in the retort is subsequently heated with small coal, in clay pots, and the zinc distilled from it in the ordinary way.

The residue, after distillation, contains about 600 ounces of silver per ton, together with lead, copper, arsenic, and nickel, if these metals were originally present, since zinc has the property of combining with these bodies and separating them from lead. Messrs. Neville and Co. first tried distillation in clay retorts, but have since given it up, as the oxide of lead was found to destroy them. The quantity of zinc recovered by distillation is said to be about half that originally employed.

The further treatment of the alloy of zinc and silver consists in melting it with lead, and as soon as a sufficient quantity of this alloy has been obtained, the cupellation of the rich lead produced. The great advantage of this method is stated to consist in the concentration of the silver in a very small quantity of lead, by means of few operations. The loss on the lead is said to be per cent.

1

At the Llanelly works, Pattinson's process was formerly employed; but they have now entirely given up this mode of treatment, finding the new method, from its simplicity and accuracy more advantageous.

LINZ PROCESS.

At Linz on the Rhine, and some other localities in Germany, the poorer sulphides of copper, containing from 1 to 5 per cent. of that metal, are treated by the following process:

:

The ores coming directly from the mine, and without any preliminary dressing, are first roasted in a double-soled furnace, and then taken to a series of tanks sunk in the ground and lined with basalt. These tanks are also provided with a double bottom, likewise formed of basalt, so arranged as to make a sort of permeable diaphragm, and on this is placed the roasted ore, taking care that the coarser fragments are charged first, whilst the finer particles are laid upon them.

The cavity thus formed between the bottom of the tank and the diaphragm or false bottom, is connected, by means of proper flues, with a series of oblong retorts, through each of which a current of air is made to pass from a ventilator or a pair of large bellows, set in motion by steam or water power.

In order to use this apparatus, a quantity of ore is roasted in the reverberatory furnace, and subsequently placed in the tanks, taking care that the first layer shall be in a coarser state of division than those which succeed it.

The retorts, which are formed of fire-tiles and about 6 inches in height by 1 foot in width and 6 feet in length, are now brought to a red heat, charged with blende and the blast applied.

The sulphurous acid thus formed is forced by the draught through the flues, where it becomes mixed with nitrous fumes, obtained from a mixture of nitrate of soda and sulphuric acid, and ultimately passes into the chambers beneath the diaphragms on which are laid the roasted ores, which must be previously damped by the addition of a little water, of which a small quantity is also placed in the bottoms of the tanks. The sulphuric acid thus generated attacks the oxide of copper formed during the preliminary roasting, giving rise to the production of sulphate of copper, which percolates through the basaltic diaphragm into the reservoir beneath.

The liquors which thus accumulate are from time to time distributed over the surface of the ore, and the operation repeated until the greater portion of the copper has been extracted, when, by shifting the damper, the gases are conducted into another tank similarly arranged. The liquors from the first basin are now pumped into the second, and the operation continued until the ores which it contains have ceased to be acted on by the acid. When sufficiently saturated, the liquors are drawn off into convenient troughs and the copper precipitated by means of scrap iron. The

sulpbate of iron thus formed is subsequently crystallised out and packed into casks for sale.

On removing the attacked ores from the tank, the finer or upper portions are thrown away as entirely exhausted, nearly the whole of the copper having been removed from them, whilst the coarser fragments are crushed and re-roasted, and finally form the upper stratum in a subsequent operation.

It has been found that, by operating in this way, ores yielding only 1 per cent. of copper may be treated with considerable advantage, since the sulphate of iron produced, and the increased value of the roasted blende, are alone sufficient to cover the expenses of the operation.

By this process 3 cwts. of coal are said to be required to roast one ton of ore, whilst the same quantity of blende is roasted by an expenditure of 4 cwts. of fuel.

TREATMENT OF COPPER ORES BY HYDROCHLORIC

ACID.

At a short distance from the village of Twista, in the Waldeck, several considerable bands of sandstone, more or less impregnated with green carbonate of copper, have been long known to exist. Although varying considerably in its produce, this ore, on an average, yields 2 per cent. of copper, and was formerly raised and smelted in large quantities; but this method of treatment not having apparently produced satisfactory results, the operations were ultimately abandoned.

The insoluble nature of the granular quartzitic gangue with which the copper is associated, suggested, some two years since, to Mr. Rodius, of the Linz Metallurgic Works, the possibility of treating these ores by means of hydrochloric acid, and a large establishment for this purpose has ultimately been the result.

These works consist of a crushing mill, for the reduction of the cuperous sandstone to a small size, sixteen dissolving tubs, and a considerable number of tanks and reservoirs for the reception of the copper liquors and the precipitation of the metal by means of scrap iron. Each of the sixteen dissolving tubs is 13 feet in diameter and 4 feet in depth, and furnished with a large wooden revolving agitator, set in motion by a run of overhead shafting in connection with a powerful water-wheel. This arrangement admits of the daily treatment of 20 tons of ore, and the consequent production of from 7 to 8 cwts. of copper. Each operation is completed in 24 hours, the liquor being removed from the tanks to the precipitating trough by the aid of wooden pumps. The ore is stoped and brought into the works at 4s. per ton.