Considerable misapprehension seems to have prevailed concerning the quality of the ores of ldria. Some authors have affirmed, that it contains 50 per cent. of metal at an average, and that portions afford even 80 per cent. But the mean produce of 9908 tons was only 8616 per cent. by exact observation. Virgin mercury, as we have seen in the preceding list of combinations, exists in various situa tians, elaborated exclusively by the hand of nature. It appears in pure globules, and has been known to issne in a slender stream from some narrow fissure in the rocks. A miner is said to have collected 36 pounds of mercury in this manner in six hours. The quantity of virgin mercury procured annually is very unequal. When Dr. Pope visited the mines in 1663, it amounted to 11,862 pounds, which nearly doubled the product of 1661, and somewhat exceeds the statement of Keysler and Jars, at 100 quintals, or 10,000 lib. Probably it is more rare at present. A small portion is always presented in a leathern purse to foreigners of distinction who inspect the mines.
The ores being separated, according to their quality, by the miners, arc drawn up in strong square boxes, each capa ble of containing 700 or 800 lib. by means of a hydraulic wheel put in motion by the water of a canal led from the Idrixa. All are then conveyed to the lavatories, or wash ing rooms, where they undergo a new assorting, and the richer kinds are set apart by themselves. The object of washing is to disengage all the earth which contains no mercury ; and for this purpose seven wire sieves are first employed, and the result then transferred to another set of very expert workmen. Sieves suspended in a cistern, and while immersed, kept in constant motion, are now used, that the heaviest particles may fall to the bottom ; and great care is taken to preserve those of a red colour, as they con tain cinnabar. After these two levigations the ores are pounded, and again carried to the lavatories, to undergo a third on inclined planes. From the lavatories they are conveyed to furnaces, to be subjected to distillation ; but, before being exposed to the action of the fire, the whole are rigorously assayed, in order to anticipate what product may reasonably be expected. As there are two kinds of ore, one in large pieces, and the other in powder, there is a furnace for each. The furnace destined to receive the first has two fire-places and four chambers or ovens, which communicate by conduits with two rows of reser voirs, ur very high chambers of mason work, separated by intermediate walls, but mutually commtlnicating by means of alternate apertures a foot square. Of these reservoirs or condensers there are twenty-eight. The second furnace,
appropriated for burning the ores in powder, has six fur naces and twenty-four chambers, instead of twenty-eight. The area in both is inclined to facilitate the flowing of the mercury, and a conduit common to the whole condensers brings the mercury into another great reservoir, where it is collected for use. The charge of the first furnace is 30,000 lib. of ore, that uf the second 60,000. When the fur naces are charged, all their apertures, and those of the con densing chambers, are carefully lined with clay and slacked lime. The fire is then progressively augmented during nine hours, until the earthen duds, wherein pieces of ore or the powder have been put, become red hot, and the ores burn vehemently. The whole is then allowed to cool for six days, and the mercury, completely disengaged, is col lected in the general reservoir. As the heat of the furnace, particularly of that which burns the larger pieces, is retain ed a long time, it would be difficult to collect the metal sooner. A single charge of the furnaces will frequently produce 8000 pounds of quicksilver. The mercury is taken out of the common reservoir, and packed in white sheep skin bags, which have been tanned with alum, in quantities of 25, 50, or 100 pounds. The bags are then conveyed to a magazine, where each is covered by a second skin, and packed up in casks, which are exported to the various places where they are required.
But, independent of the pure mercury thus obtained and exported from ldria, there are mercurial preparations to a very great extent of all the different kinds which are known in commerce. With the exception of Chinese vermilion, the products seem scarcely susceptible of im provement. For these purposes there is a spacious build ing, divided into three great laboratories. The first is ap propriated for amalgamation of sulphur and mercury, which is then converted to cinnabar ; the second is consecrated to the preparation of vermilion, wherein eight mills are employed in grinding the cinnabar ; and in the third there are twenty-two furnaces, each provided with six large iron capsules. Much accessory apparatus is used besides.
In addition, and subsidiary to the mining establishment, and that for mercurial preparations at Idria, there are se veral branches of arts and manufactures. These consist chiefly of a glass work, for providing the bottles and win dow glass ; a pottery for all the earthen ware required ; tannery for preparing the leather packages ; and a rope work which furnishes cordage. Numerous mechanics, and artizans of all descriptions, are also ready to provide the necessary apparatus for the various operations.