London: E. & F. N. Spon, 48, Charing Cross. Kell. Bros Lith. London.
TREVITHICK'S ROUTE ACROSS THE ISTHMUS OF COSTA-RICA.
"When I landed in June, 1822, only five or six mines had been discovered, but in January 1823, when I left the country, I cannot pretend to enumerate those in a state of progress and of promise. It is not only in the mining part of the business that the want of skill is prejudicial to the result. It is imperfectly ground, for instance, and consequently cannot be brought into that intimate contact with the quicksilver which is necessary to perfect amalgamation. The machine for grinding is very simple: a large flat stone, like a mill-stone, is made to revolve upon its fellow by an ox or mule power. The poorest people reduce it to powder by manual labour, in the same way as they grind corn preparatory to baking it into cakes. Alverado's machine promised to be a great acquisition. The grinding was facilitated by a little water; when the ore is judged to be sufficiently well ground, a portion of quicksilver is thrown in by guess, and the motion of the machine continued until the union of the metals is supposed to be complete; the whole is then removed into large wide-mouthed conical-shaped wooden vessels. In these receptacles it undergoes repeated washings, by stirring occasionally round, and afterwards communicating to the vessel a swinging or half-rotary motion, by which a quantity of the water, having the earthy particles suspended, is driven over the edges; the amalgamated mass naturally sinks to the bottom, and at last remains tolerably clean.
"The next step is the recovery of the quicksilver by distillation, after which the gold is melted in a crucible and run into ingots. The coasts are hot, and from the luxuriant vegetation that everywhere abounds, emit, as in all situations of the kind, febrile miasma in abundance when acted on by heat and moisture; but black vomit is unknown, and all the fever cases I have seen have been of the remitting and intermitting, free from character of malignancy. As the ground begins immediately to spring from the coast, and does so indeed very rapidly, a few miles takes us beyond the region of even these slight fevers, and as we continue ascending to the central table-land, a climate is encountered that may vie with any in the world for benignancy and beauty. We there meet with the fruits of the torrid zone, and near them the apple and the peach of Europe. The orange tree is in bearing the whole year. As in all situations within the tropics, it has a proper rainy season, but it is less inconvenient and disagreeable than might be expected, for it seldom rains two days in succession, and when it does, is invariably succeeded by an interval of fine weather; for the most part every day presents a few dry hours. The mines are situated on the ridges of the Cordillera, which without presenting snow-covered peaks, attain, nevertheless, considerable elevation. The clouds, constantly attracted by those high summits, render the rainy season more severe in the mining district than in the plains. The greatest inconvenience was from the snakes, which in those solitary jungles, now first invaded by man, are very numerous and many of them venomous. Provisions are cheap and excellent. In short, there is but one fault I find with the country, and it is a great one, I mean the frequency of earthquakes.
"J. M. Gerard."
Mem. in Mr. Gerard's Writing.
"Illustrations of the Map.
"Though the plans and sections explain themselves, a few observations will not be misplaced. The deep adit for the Coralillo would be 600 yards, that for Quebrada-honda 400 yards, and besides serving as drains would form admirable roads for conveying the ores into the vale where the stamps must be erected.
"The veins would be worked upward from the adits, and thus no expense would be incurred for ages to come in lifting either water, ore, or rubbish to the surface. Padre Arias Mine is an exception, requiring a powerful water-wheel, or an hydraulic pressure-engine, for which there is a fine fall of water of 135 feet. The mines in Quebrada-honda are those in which an interest has been procured. Captain Trevithick has an interest in the mine of Coralillo; the great watercourse is also his.
"It will be seen by the plan that there are 75 fathoms fall to the point where his present mill is situated, and other 75 fathoms to the junction of the rivers of Quebrada-honda and Machuca. The whole length does not amount to two miles, within which it is estimated that sufficient power may be commanded to stamp 500,000 of quintals annually. To bring it up to that pitch, the waters of Machuca must be brought to join those of Quebrada-honda at Trevithick's mill, and then 40 tons of water per minute could be delivered in the dry season."