I have procured for the information of American metallurgists descriptions and drawings of the furnace and detailed statements of its working. In respect of economy it surpasses all furnaces with which I am acquainted. The extraordinarily favorable results shown by the following statements are partly due to the favorable circumstances at Clausthal, particularly in the facility with which suitable mixtures of different ores for smelting can be obtained, and the excellent fluxes (copper-slags from the Lower Hartz, and matte-slags and roasted mattes from the works themselves) which are available to the smelter. Since, however, the Raschette furnace, under the same conditions at the same place, loses more lead than the Kast, and has a shorter and more troublesome campaign, it is evident that the Kast possesses an intrinsic superiority.

The particulars of construction are best seen in the accompanying drawings. I have only to add, in explanation, that the previous existence of the large concentration-chambers at the Clausthal works compelled the choice of a certain size, which could not be increased. By the working results of the furnace it has been proved that these chambers are not absolutely necessary, the amount of dust caught in them being exceedingly small.

For the construction of a furnace with four tuyeres and two condensation-chambers, as given in the drawings, the following materials are used in Clausthal:

98 cubic feet of sandstone for a sole-stone.

763 cubic feet of dressed-sandstone blocks for the outer walls and pillars.

23,000 pieces of common brick.

200 pieces of chamotte brick.

845 cubic feet of rubble-stones for foundation.

216 hectoliters* of a mixture of common lime and plaster. 36 hectoliters of "leather-lime," (leder-kalk.)

32 hectoliters of clay.

20 cubic feet of fire-proof sand.

The following materials are of cast iron:

8 plates above the entrance to the side-tuyeres, at 5 cwt. 1 plate above the entrance to the back-tuyeres, at 63 cwt. 1 plate above the entrance to the charging-door, at 7 cwt. 3 plates around the fore-hearth, weighing 8 cwt.

4 water-tuyeres, weighing 42 cwt.

The conducting-pipes for the blast and wind stacks weigh about 36 cwt. Besides the above, iron rods and rails, or other heavy bar-iron, are required to bind the furnace and condensation-chambers. The plans followed for this purpose are various. That adopted in Clausthal is sufficiently shown in the drawings.

As far as the iron-work above enumerated is concerned a great saving can of course be effected in places far from founderies by substituting brick arches for the plates intended to support the masonry above, and for the cast-iron conducting-pipes sheet-iron ones can be made to answer. A large saving in the original cost of a furnace is made by omitting the condensation-chambers, which, as I said before, are not absolutely necessary, although it is desirable to have them.

The ores smelted at Clausthal are crushed massive ores, and the dressed ores from the Burgstaedter, Rosenhoefer, and Zellerfelder dis

tricts. Keeping in view their different gangue and varying contents of lead and silver, they are so mixed in quantities of 1,000 cwt. dry weight, that the average contents in the mixture are: of lead, 58 to 60 per cent., and of silver, 0.1 per cent.; while at the same time the gangues are so proportioned as to furnish an easily fusible slag. Such a quantity of 1,000 cwt. is divided into 20 "charges," at 50 cwt. A "charge" is mixed with 25 cwt. of roasted matte from the first smelting, 40 cwt. of copper-slags from the Lower Hartz, 20 cwt. of matte-slag from the Clausthal works, and 16 cwt. of slag from the first smelting. The last two items vary somewhat, according to whether heavier or lighter gangue is preponderating in the ore.

This charge is smelted in both the Kast and the Raschette furnaces. In the latter, however, 10 additional cwt. of slag from the first smelting is sometimes mixed with the charge.

As seen in the drawings, the Kast furnace is 20 feet high, has a diameter of 3 feet at the tuyeres, and of 5 feet at the top. There are four water-tuyeres, two being in the back wall and one on each side. The distance from tuyere to tuyere is 21 inches, with the exception of the two nearest the front, which are 42 inches apart. It is, however, proposed to put a fifth tuyére into the front wall. The diameter of the nozzles is 12 inches, the pressure of the blast 10 to 12 lines quicksilver. The average results of a month's working, reduced to 100 cwt. of ore, which consumed 51 cwt. of coke, were:

59 cwt. of lead, containing 14 to 15 quints* of silver per cwt.

78 cwt. of lead-matte, containing 2 to 3 quints of silver per cwt. and 7 to 10 per cent. of lead.

Slags with 0.08 quint silver and 0.4 per cent. of lead.

The quantity smelted in twenty-four hours was 63 cwt. of ore, or 190.65 cwt. of charge, equal to about 9.5 tons. One pound of coke carries 6 pounds of charge. The charge is spread over the whole surface of the furnace.

There is hardly ever any trouble in a campaign, the latter being invariably very long, in fact much longer than campaigns have heretofore been made in lead-smelting. There are no accretions, very little dust, and the proportion of fuel used is very small. The yield of the lead is invariably as high as the assay with black flux and iron made of the ore, and is reported to exceed it sometimes.

If I should suggest any improvement at all in the construction of the Kast furnace, in its application to the smelting of western ores, I would propose to straighten out the corners in the inside of the furnace on both sides of the breast. The object of this is simply to make the parts of the furnace immediately behind these corners more easily accessible for the bar and rabble, as in these places, if anywhere, accretions are most likely to occur. It is not to be expected that accretions can be avoided as easily with our western, undressed ores, as with the clean ores of the Hartz.

* 1 quint 5 grammes=77.165 grains.

CHAPTER XI.

·ECONOMICAL RESULTS IN THE TREATMENT OF GOLD AND SILVER ORES BY FUSION.

This chapter was written, at my request, by John A. Church, E. M., of New York City, a metallurgist of much intelligence, to whom I am obliged for the permission to insert here what I think is a very useful and suggestive essay. He desires to make acknowledgment for the information contained in the paper to Dr. Leo Turner, formerly director of the works described, and now at Brixlegg in the Tyrol.

At a time when the treatment of gold and silver ores by fusion, in opposition to the mill-process, is attracting so much attention in this country, it may be useful to consider what is done in a well-conducted foreign works. For this purpose I will ask the reader to accompany me to Lend, in Austria, a small but thoroughly organized establishment. It is situated in the Salzburg Alps, and receives its ore from mines at Rauris and Boeckstein. The former, lying 8,200 feet above the sea, is said to be the highest mine in Europe, some of its openings being made in glacier ice. It was worked by the ancients, who have left the contracted and tortuous workings peculiar to them.

The ore differs in no way, unless in extreme poverty, from countless mines in the West. It consists of gneiss, quartz, and clay-slate, containing the sulphurets of iron, copper, lead, zinc, and antimony, besides arsenical pyrites, gold, and silver. The gold is found in two conditions, free gold and gold alloyed with silver. This alloy for the year 1866 was composed, on the average, of 15.33_gold and 84.67 silver, which gives a specific gravity of 11.28. Mercury has a specific gravity of 13.6, and as the amalgamation of gold by the Austrian method is looked upon as a proceeding entirely mechanical, the separation being effected solely by the superior gravity of gold over mercury, this alloy, which is lighter than mercury, cannot be amalgamated.* Such is the lesson of long practice, the free or fine gold being extracted from a part of the ore, at least, by amalgamation, while the tailings are smelted to obtain the alloy. The following table will show the proportion of fine to alloyed gold, and also exhibit the extreme poverty of the ore. To the Rauris and Boeckstein ores I have added those from Zell in the same part of the Alps. The ore from this place is not now worked, the point of poverty having apparently been reached at which the auriferous rock ceases to be an ore.