On its arrival at the reduction works the ore is taken direct to the stamp mill.  At the Huanchaca works there are sixty-five heads of stamps, each head weighing about 500 lb., with five heads in each battery, and crushing about 50 cwt. per head per twenty-four hours.  The ore is stamped dry, without water, requiring no coffers; this is a decided advantage as regards first cost, owing to the great weight of the coffers, from 2 to 3 tons—­a very heavy item when the cost of transport from Europe at about 50_l_. per ton is considered.  As fast as the ore is stamped, it is shoveled out by hand, and thrown upon inclined sieves of forty holes per lineal inch; the stuff which will not pass through the mesh is returned to the stamps.

Dry stamping may be said to be almost a necessity in dealing with these rich silver ores, as with the employment of water there is a great loss of silver, owing to the finer particles being carried away in suspension, and thus getting mixed with the slimes, from which it is exceedingly difficult to recover them, especially in those remote regions where the cost of maintaining large ore-dressing establishments is very heavy.  Dry stamping, however, presents many serious drawbacks, some of which could probably be eliminated if they received proper attention.  For instance, the very fine dust, which rises in a dense cloud during the operation of stamping, not only settles down on all parts of the machinery, interfering with its proper working, so that some part of the battery is nearly always stopped for repairs, but is also the cause of serious inconvenience to the workmen.  At the Huanchaca mines, owing to the presence of galena or sulphide of lead in the ores, this fine dust is of such an injurious character as not unfrequently to cause the death of the workmen; as a precautionary measure they are accustomed to stuff cotton wool into their nostrils.  This, however, is only a partial preventive; and the men find the best method of overcoming the evil effect is to return to their homes at intervals of a few weeks, their places being taken by others for the same periods.  In dry stamping there is also a considerable loss of silver in the fine particles of rich ore which are carried away as dust and irrevocably lost.  To prevent this loss, the writer proposed while at Huanchaca that a chamber should be constructed, into which all the fine dust might be exhausted or blown by a powerful fan or ventilator.

Roasting.—­From the stamps the stamped ore is taken in small ore cars to the roasting furnaces, which are double bedded in design, one hearth being built immediately above the other.  This type of furnace has proved, after various trials, to be that best suited for the treatment of the Bolivian silver ores, and is stated to have been found the most economical as regards consumption of fuel, and to give the least trouble in labor.

At the Huanchaca mines these furnaces cost about 100_l_. each, and are capable of roasting from 2 to 21/2 tons of ore in twenty-four hours, the quantity and cost of the fuel consumed being as follows: