The idea of arsenic in the substance alluded to, is perfectly erroneous, and has originated in an ignorance of the nature of the ores of these mines. It is the sulphuret of lead, and not the arseniate. That there is a small portion of silver and antimony in combination with the ore, is probable; but they too are mineralized by sulphur. Reflecting on this, I became convinced of the popular error, and, to ascertain the point, made the following experiments:
A. I took a lump of the sublimated matter, freed from adhering impurities, and reduced it to the state of a fine powder by pulverizing in an agate mortar, and trituration. Of this I mixed six parts with four of pulverized borax, and a little charcoal, and submitted it to the intense heat of a small chemical furnace. On removing the crucible, I found a button of metallic lead in the bottom, weighing nearly four.
B. Dissolved a quantity of the powdered sublimate in nitric acid; it effected a ready solution, with violent effervescence. Poured on liquid carbonate of potash until no more precipitate fell. I then collected the precipitate, and washed away the superfluous alkali by clear water, and dried it in the shade. The result was a very fine, and a very white powder, of considerable weight. This was a carbonate of lead (white lead). With a quantity of the white lead thus made, I mixed linseed oil, and painted a board. The color was of the most delicate white, and it gave a good body. On inspecting this board several months afterwards, I found the color inclining a little to yellowish. But perhaps it stands as well as any white lead would, prepared from litharge, by solution in nitric or acetic acids, and precipitation by carbonated alkali.
C. Mixed eight parts of sublimate with twelve of muriate of soda, and fused in a crucible, with a tight cover, in a high heat. Result, a yellow, hard, heavy, vitrified mass, resembling muriate of soda and lead.
M'Kain's Mine is situated on a small stream called Dry creek, running into Big river not far from its junction with the Maramec. The mine is worthy of remark only on account of a body of steel-grained lead-ore found there. This ore is found to yield less lead in smelting than the common broad-grained ore, and, as may be inferred from its texture, contains silver.
So little has been done, of late years, in mining in the rock, that the character of the veins must be judged of from limited facts. But there can be no question, from what is known, that the true scene of mining operations is the rock.
Along the west banks of the Mississippi, and also in some of the interior valleys, we observe that the metal-bearing limestone rests on crystalline sandstone. Both preserve a horizontal position, and both are deposited, at the distance of about seventy miles south of Potosi, upon pre-existing formations of sienitic granite, embracing hornblende rock; some of the latter of which is porphyritic.
These primitive formations mark the geography of the country at the sources of the St. Francis. They form alpine peaks, through which the river forces its way. Mine à La Motte is within two miles east of this tract. These peaks have been raised to their present position without disturbing the horizontality of the limestones and sandstones. Hence the conclusion of their prior elevation.
At a still further southern point, and before reaching the banks of the St. Francis at Bettis's ferry, the horizontal rocks again appear. But, in this instance, sienitic and granitic boulders are scattered over the southern series of the calcareous strata, showing, with equal clearness, that the geological era of the boulder stratum was posterior to the deposition of the horizontal strata, and that the force which scattered the boulder stratum was from the north.