The vein of silver that is found nearest the surface is known by the name of “crudaria.”[959] In ancient times, the excavations used to be abandoned the moment alum[960] was met with, and no further[961] search was made. Of late, however, the discovery of a vein of copper beneath alum, has withdrawn any such limits to man’s hopes. The exhalations from silver-mines are dangerous to all animals, but to dogs more particularly. The softer they are, the more beautiful gold and silver are considered. It is a matter of surprise with most persons, that lines traced[962] with silver should be black. CHAP. 32.—QUICKSILVER. There is a mineral also found in these veins of silver, which yields a humour that is always[963] liquid, and is known as “quicksilver.”[964] It acts as a poison[965] upon everything, and pierces vessels even, making its way through them by the agency of its malignant properties.[966] All substances float upon the surface of quicksilver, with the exception of gold,[967] this being the only substance that it attracts to itself.[968] Hence it is, that it is such an excellent refiner of gold; for, on being briskly shaken in an earthen vessel with gold, it rejects all the impurities that are mixed with it. When once it has thus expelled these superfluities, there is nothing to do but to separate it from the gold; to effect which, it is poured out upon skins that have been well tawed, and so, exuding through them like a sort of perspiration, it leaves the gold in a state of purity behind.[969] Hence it is, too, that when copper has to be gilded,[970] a coat of quicksilver is laid beneath the gold leaf, which it retains in its place with the greatest tenacity: in cases, however, where the leaf is single, or very thin, the presence of the quicksilver is detected by the paleness of the colour.[971] For this reason, persons, when meditating a piece of fraud, have been in the habit of substituting glair of egg for quicksilver, and then laying upon it a coat of hydrargyros, a substance of which we shall make further mention in the appropriate place.[972] Generally speaking, quicksilver has not been found in any large quantities. CHAP. 33.—STIMMI, STIBI, ALABASTRUM, LARBASIS, OR PLATYOPHTHALMON. In the same mines in which silver is found, there is also found a substance which, properly speaking, may be called a stone made of concrete froth.[973] It is white and shining, without being transparent, and has the several names of stimmi, stibi, alabastrum,[974] and larbasis. There are two kinds of it, the male and the female.[975] The latter kind is the more approved of, the male[976] stimmi being more uneven, rougher to the touch, less ponderous, not so radiant, and more gritty. The female kind, on the other hand, is bright and friable, and separates in laminæ, and not in globules.[977] CHAP. 34.—SEVEN REMEDIES DERIVED PROM STIMMI.