volatilization of the sulphur, arsenic, and antimony, for the space of an hour; but as soon as only sulphurous acid was formed, and the heat by this procedure had attained its highest degree, the blowing was discontinued and the product taken out.  This consisted of a dross, or, rather, of the collected pieces of ore themselves, which, on account of the flinty contents of the stones composing the funnel, were transformed by the decomposition of the sulphurous metal into a porous mass, and which could not be converted into dross nor form combinations with silicious acid, being deficient in the base as well as in the requisite heat; and also of a very impure “stone,” of from four to five kilograms weight, and containing from fifty to sixty per cent of copper.

[The copper “stone".] Several of these “stones” were melted down together for the space of about fifteen hours, in a powerful fire; and by this means a great portion of the three volatile substances above named was again evolved; after which they placed them, now heated red-hot, in an upright position, but so as to be in contact with the draught; the coals, however, being at the sides of the furnace.  After blowing for an hour or half-an-hour, they thus obtained, as residuum, a silicate of iron with antimony and traces of arsenic, a “stone” containing from seventy to seventy-five per cent of copper, which they took off in very thin strips, at the same time using refrigerating vessels; and at the bottom of the hollow there remained, according as the mass was more or less freed from sulphur, a larger or smaller quantity (always, however, impure) of black copper.

[Purifying the product.] The purified stones obtained by this second process were again made red-hot by placing them between rows of wood, in order that they might not melt into one another before the fire had freed them from impurities.

The black copper obtained from the second operation, and the stones which were re-melted at the same time, were then subjected to a third process in the same furnace (narrowed by quarry stones and provided with a crucible); which produced a residuum of silicious iron and black copper, which was poured out into clay moulds, and in this shape came into commerce.  This black copper contained from ninety-two to ninety-four per cent of copper, and was tinged by a carbonaceous compound of the same metal known by its yellow color, and the oxide on the surface arising from the slow cooling, which will occur notwithstanding every precaution; and the surface so exposed to oxidation they beat with green twigs.  When the copper, which had been thus extracted with so much skill and patience by the Igorots, was to be employed in the manufacture of kettles, pipes, and other domestic articles, or for ornament, it was submitted to another process of purification, which differed from the preceding only in one particular, that the quantity of coals was diminished and the air-draught increased according as the process of smelting drew near to its termination, which involved the removal of the carbonaceous compound by oxidation.  Santos found, by repeated experiment, that even from ores of the mean standard of twenty per cent, only from eight to ten per cent of black copper was extracted by the third operation; so that between eight to twelve per cent still remained in the residuum or porous quartz of the operation.