Igorot-mining successful.What Europeans yet appear unable to accomplish, the wild Igorots, who inhabit that trackless range of mountains, have carried on successfully for centuries, and to a proportionally larger extent; and this is the more remarkable as the metal in that district occurs only in the form of flints, which even in Europe can be made profitable only by particular management, and not without expense.
Long-established and considerable.The copper introduced into commerce by the Igorots from 1840 to 1855, partly in a raw state, partly manufactured, is estimated at three hundred piculs yearly. The extent of their excavations, and the large existing masses of slag, also indicate the activity of their operations for a long period of time.
Copper kettles attributed to Negritos.In the Ethnographical Museum at Berlin is a copper kettle made by those wild tribes. Meyer, who brought it, states that it was made by the Negritos in the interior of the island, and certainly with hammers of porphyry, as they have no iron; and that he further found, in the collection of the Captain General of the Philippines, a large shallow kettle of three and one-half feet in diameter, which had been bought for only three dollars; whence it may be inferred that, in the interior of the island, the copper occurs in large masses, and probably solid; for how could those rude, uncultivated negritos understand the art of smelting copper?
Copper-working a pre-Spanish art.The locality of these rich quarries was still unknown to the Governor, although the copper implements brought thence had, according to an official statement of his in 1833, been in use in Manila over two centuries. It is now known that the copper-smiths are not Negritos but Igorots; and there can be no question that they practiced this art, and the still more difficult one of obtaining copper from flint, for a long period perhaps previous to the arrival of the Spaniards. They may possibly have learnt them from the Chinese or Japanese. The chief engineer, Santos[13], and many others with him, are of opinion that this race is descended from the Chinese or Japanese, from whom he insists that it acquired not only its features (several travellers mention the obliquely placed eyes of the Igorots), its idols, and some of its customs, but also the art of working in copper. At all events, the fact that a wild people, living isolated in the mountains, should have made such progress in the science of smelting, is of so great interest that a description of their procedure by Santos (essentially only a repetition of an earlier account by Hernandez, in the Revista Minera, i. 112) will certainly be acceptable.
The Igorots’ Method.The present mining district acquired by the society mentioned, the Sociedad Minero-metalurgica Cantabrofilipina de Mancayan, was divided amongst the Igorots into larger or smaller parcels strictly according to the number of the population of the adjacent villages, whose boundaries were jealously watched; and the possessions of each separate village were again divided between certain families; whence it is that those mountain districts exhibit, at the present day, the appearance of a honeycomb. To obtain the ore, they made cavities, in which they lighted fires in suitable spots, for the purpose of breaking the rock into pieces by means of the elasticity of the heated water contained in the crevices, with the additional assistance of iron implements. The first breaking-up of the ore was done in the stream-work itself, and the dead heaps lay piled up on the ground, so that, in subsequent fires, the flame of the pieces of wood always reached the summit; and by reason of the quality of the rock, and the imperfection of the mode of procedure, very considerable down-falls frequently occurred. The ores were divided into rich and quartziferous; the former not being again melted, but the latter being subjected to a powerful and persistent roasting, during which, after a part of the sulphur, antimony, and arsenic had been exhaled, a kind of distillation of sulphate of copper and sulphate of iron took place, which appeared as “stone,” or in balls on the surface of the quartz, and could be easily detached.[14]
The Smelter.The furnace or smelting apparatus consisted of a round hollow in clayey gound, thirty centimeters in diameter and fifteen deep; with which was connected a conical funnel of fire-proof stone, inclined at an angle of 30°, carrying up two bamboo-canes, which were fitted into the lower ends of two notched pine-stems; in these two slips, covered all over with dry grass or feathers, moved alternately up and down, and produced the current required for the smelting.
Smelting.When the Igorots obtained black copper or native copper by blasting, they prevented loss (by oxidation) by setting up a crucible of good fire-proof clay in the form of a still; by which means it was easier for them to pour the metal into the forms which it would acquire from the same clay. The furnace being arranged, they supplied it with from eighteen to twenty kilograms of rich or roasted ore, which, according to the repeated experiments of Hernandez, contained twenty per cent of copper; and they proceeded quite scientifically, always exposing the ore at the mouth of the funnel, and consequently to the air-drafts, and placing the coals at the sides of the furnace, which consisted of loose stones piled one over another to the height of fifty centimeters. The fire having been kindled and the blowing apparatus, already described, in operation, thick clouds of white, yellow, and orange-yellow smoke were evolved from the partial 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.