water power was not sufficient for both, but they should have been nearer together and on the same level. The institution of a separate fine separation-house by the side of a coarse crushing-house for the treatment of the fine stuff coming from the coarse drums is open to criticism, but is most probably a necessary arrangement, although considerable advantage might have resulted from having all the fine sizing apparatus under the same roof.

The water for the works is brought by a water-ditch, as indicated on the plan. It is not constant in amount during the different parts of the year, and the establishment is arranged so as to use it both for concentration purposes and for power. Being equipped with ample steam-power as well, the water-power can be at any time supplemented or replaced in seasons when all the water may be needed for dressing operations. The manner in which the water is used over and over again in passing through the works is of considerable interest, and quite according to the economic methods of the Hartz. After being used on each step it goes into a series of clearing-tanks under the floor or outside of the building, and, being thus partially cleared, descends to the next building, to be used again. In its downward course it goes through several series of revolving screens, spitzkasten, jigs of all classes, stamp batteries, labyrinths, buddles, and tables. It also drives four turbines, and one overshot wheel, and only finds rest when it reaches the large series of slime pits, in which it deposits its slimes before being allowed to leave the works. The details of its use in the works will be more fully treated in speaking of the details of the different buildings.

The power for the works is, as has been noted, partially steampower and partially water-power, arranged to supplement one another when necessary. By reference to the plan the points where the power is applied will be readily seen. At the top of the slope, b, is a small Corliss engine for hoisting from the shaft, d, and for giving power to the rock-breakers and sorting-drums in the building, h. In the building (1) is a turbine with 18 feet head, for giving power to the coarse drums in (1) and the fine drums in (2). In the coarse crushing-house (6) are two turbines of 18 feet head, which may, at will, supplement the power of the turbine in (1). In the middle and fine crushinghouse (8) is a turbine of 78 feet head, which gives power to the buildings (7), (8), and (9), and can supplement the power in (6). The Corliss engine (14) of 100 horse-power gives power to the second coarse crushing-house (6), and supplements the power in (7), (8), and (9), and in case of lack of water can be relied on entirely for power

in the whole flight of buildings (1), (2), (6), (7), (8), and (9). The 150 horse-power Corliss engine in the stamping-house (11) drives the stamps, jigs, buddles, and tables in that house, and also two pumps. The two Corliss engines (14) and (11) get their steam from the boiler-house (12), to which coal is elevated by the steam slope (13). Up the same slope are brought the material for dumping, arising from the buildings (7), (8), and (9). Finally, the jigs, buddles, and tables in the auxiliary washing-house (10) are driven by an overshot water-wheel, 13 feet in diameter, placed at one end of the building.

ores.

THE METHOD OF DRESSING.

The works have been equipped for handling the ordinary Clausthal These consist of low grade argentiferous galena somewhat finely disseminated in a gangue of cale spar and baryta, and more or less intimately associated with chalcopyrite, pyrite, marcasite, and zinc blende. The equipment is calculated for the reception of about onehalf of the ore as mine smalls of the size of 64mm and under, and the remaining ore of larger size. This is about the usual proportion. The only preparation the ore receives in the mines is its separation by ragging hammers from absolutely barren gangue, wall rock, etc. It was formerly separated below ground into rough classes, which were kept distinct, but this is no longer found necessary. For the sake of greater clearness, the course of the dressing, which is somewhat complicated, will be given unmixed with details of apparatus or results. In connection with this description, the skeleton on Plate IX, has been carefully prepared and is believed to be correct. On its arrival from the shafts, or by tramway, the ore enters the second story of the rock-breaker house, and is dumped from the cars on a bar grate, the bars of which are 64mm apart. By this grate the ore is divided into two first classes or sizes-above and below 64mm. All under 64 in size passes through the grate into a revolving screen below, and is screened wet. The ore remaining on the grate, or above 64mm, is pushed down a slight incline to the jaws of a Blake crusher, by which it is broken to 64mm and under, and falls into a revolving screen similar to that in which the smalls from the grate are screened, but the screening is done dry. By the screens the grate smalls and the breaker smalls are divided into similar sizes-all below 32mm, which passes through the mesh, and all above 32mm or between 64 or 32mm, which passes out at the end of the drum. The ore above 32mm from the grate screen and the breaker screen is kept distinct, and each class is picked in a special picking-house provided

mm

for it. In this hand-picking no pure galena is obtained. The following are the products of the picking :

1. Stamp ore, in which the galena is

finely disseminated.

4. Iron pyrites.

5. Marcusite.

2. Crushing ore, which contains the 6. Zinc blende. galena in coarse particles.

3. Copper pyrites.

7. Poor rock and gangue.

Of these classes, Nos. 1 and 2 are the objects of dressing together with the smaller size under 32mm previously obtained. The copper pyrites are sold to the copper works at Altenau. The iron pyrites and marcasite are sold to the sulphuric acid works in the same place, and the zinc blende is sold in open market. The ore from the sortingdrums below 32mm in size descends to the coarse sizing-drums in the coarse separation-house on the 4th step of the works. In this building it is sized wet into eight divisions. Of these, the largest size is between 32mm and 17.78mm, or in other words above 17.78mm, and goes to a third picking on the same level, from which the same products are obtained as in the other two picking-houses. The other sizes from the coarse drums are

17.78 - 13.34mm - 10mm
7.5mm-5.62mm-4.22mm

These six sizes, together with the same sizes from the coarse crushinghouse in which the crushing ore from the picking-houses is crushed and sized, are the material for coarse jigging. In addition to these sizes, the sizing-drums in both the coarse separation and coarse crushing-houses furnish an eighth size. All the ore below 4.22mm or between 4.22mm and 1mm goes through the last screen of each set and is caught in a zinc funnel, the turbid water containing ore below 1mm in size, flowing off to the spitzkasten, as will be noted. This deposit in the zinc funnels between 4.22mm and 1mm is drawn off to fine sizing-drums of which there is a small auxiliary set especially for the handling of the small amount coming from the coarse separation-drums. From the fine sizing-drums the following classes are obtained:

4.22mm-3.16mm 2.37mm 1.78m. 1.33mm 1mm and in material below 1mm which is caught in a funnel below the last screen. The same fine sizes, 4.22mm-1mm, come also from another source-the middle and fine crushing-house, where the middle products from the coarse jigging are crushed and sized. All these sizes from 4.221mm are the material for the fine jigging. The sands below 1 settling in the spitzkasten after coarse separation are drawn off to

the auxiliary washing-house. The sands below 1mm settling in the funnels below the fine sizing-drums are first jigged and then drawn off to the auxiliary washing-house. Fine jigging furnishes middle products, which, although containingmineral, need further reduction before it can be obtained. These middle products from fine jigging, and the most finely picked or stamp ore from all three picking-houses, are handled in the stamp-house. From the screens of the stamp batteries the thin pulp is first led through a classification apparatus of a number of boxes of increasing size, in which the sands deposit, and are drawn off at the bottom. The water flowing from the top of the last classfication box is led through a set of Rittinger spitzkasten for the deposition of the slimes. The sands from the classification apparatus are jigged on neighboring sand jigs, and the jigged product is either rejigged or sent to the buddles below. The turbid water from each set of jigs belonging to one classification apparatus goes into an adjoining labyrinth of 25"-30" circulation in which slimes are deposited, and then to the clearing tanks outside. Theslimes from the Rittinger spitzkasten are discharged through a rising pipe upon the upper one of two overlapping buddles on which a pure schlich is obtained, and an enriched band, which is retreated on the lower buddle. Finally the middle product from the sand jigs is treated on non-continuous tables, and the slimes from the labyrinth and slime-pits are from time to time removed and treated either on the buddles or the tables. The auxiliary washing-house alone remains to be spoken of. To this building come the slimes from the spitzkasten attached to the coarse separation and coarse crushing-house, and also the jigged slime from the fine sizing-drums in the fine separation, and middle and fine crushing-houses. These are dressed in the auxiliary washinghouse by the same combination of apparatus and operations as we have detailed as being used for the pulp coming from the stamp batteries. The buddles alone are different in this building, as instead of consisting of a pair of convex buddles on different shafts and overlapping, they consist of a concave and convex buddle one above the other on the first shaft, and a lower convex buddle on a second shaft overlapped as before.

The salient points of this method of dressing may be noted as follows: No mineral is obtained from hand-picking; sizing and jigging are carried out to the extreme limit; all the mineral obtained comes from the jigs, buddles, and tables. The extent to which sand jigs are used is almost unprecedented, and they handle finer material than has hitherto been handled on them in the Hartz. The whole

of the method for coarse material is admirable, but it is perhaps a question if a more extensive use of tables might not be of advantage in handling the sands and slimes instead of the sand jigs and buddles. It seems probable that the method of handling the pulps from the stamps is not a final one. As regards the coarsest products from the coarse screens, viz., over 17.78mm, two courses are open for its treatment (1) either to submit it to hand-picking, or (2) to send it at once to the coarse rolls. The first plan seems the best, and they have adopted it. An economy of labor might have been attained by letting it fall directly from the drum on continuous belt pickingtables, as the amount is comparatively small.

THE DRESSING MACHINERY.

The apparatus with which the establishment is equipped now demands our attention. This may for convenience be classified under three heads: I. Machinery for reducing the size of the ore. II. Apparatus for sizing and classifying the ore so reduced. III. The jigs; and IV. Other concentrating apparatus.

1. Machinery for reducing the size of the ore.-This consists of three classes of machinery-rock-breakers, rolls and stamps.

The rock-breakers are the Hanover variation of Blake's machine so much favored in Germany. They are six in number, with a capacity 5-7 tons per hour each when crushing the large ore to 64mm. Their breaking capacity therefore exceeds that demanded by the amount of ore coming to them.

The Crushing Rolls.-These are all of similar construction, and consist of a cast-iron shaft with a conical seat, on which the crushingface, which has been trued both inside and outside, is secured by a screw at the ends. On account of the large consumption of crushing surfaces in the works, careful comparative experiments have been made with faces of cast iron, chilled iron, Bessemer steel, crucible steel, and hammered cast steel. The results of these experiments seem to warrant their present preference for crucible steel as best meeting the two requirements of durability and medium cost. The pillowblocks in which one of the rolls moves are movable, with indiarubber buffers pressing against them. On the prolongation of the axes of the rolls are toothed wheels, working in one another. The power is laid on by a pulley driving intermediate gearing. The construction of these rolls is in no way peculiar. There are three sets of coarse rolls in the works, with room for a fourth set if it is at any time needed. These coarse rolls are 760mm in diameter,