METALS. The metals, if we except the bases of the alkalies, and earths, are distinguished by hardness and tenacity, great specific gravity, opacity. and pecu liar brilliancy, generally termed metallic lustre.
The properties of the metals have been already de scribed in the article CHEMISTRY. At the time when that article was written, they amounted to 27.
Selenium.
The sulphur procured from the pyrites of Fahlun, when employed in the preparation of sulphuric acid, was observed by Bjuggren to leave a reddish brown substance, which, by some chemists, was supposed to contain arsenic ; on which account the use of the py rites of Fahlun was discontinued. Berzelius has sub jected this brown matter to analysis, and has discover ed, that besides iron, copper, lead, zinc, tin, mercury, and arsenic, it contains a peculiar substance, possessed of metallic properties, to which he has given the name of selenium, (from selene the moon,) to recal its ana logy with tellurium, which it very much resembles.
Berzelius, in his analysis of the brown matter left after the preparation of sulphuric acid, digested it in nitro-muriatic acid Water and sulphuric acid were then added ; and the mixture was filtered, by which sulphur and sulphate of lead were separated. To a portion of the filtered fluid ammonia was added, which threw down a precipitate, which, when heated with potassium, was decomposed with ignition. This pre cipitate was partly soluble in water ; the solution ac quired a brown colour ; and, on the addition of nitric acid, deposited a reddish substance, which, when brought in contact with flame, communicated to it a blue tinge, and emitted the odour of horse raddish. This made Berzclius suppose that it contained tellu rium; but he afterwards found that it was caused by the new metal When the fluid which had yielded the precipitate on the addition of ammonia was sub jected to distillation, a yellowish liquid was collected, which contained sulphurous acid, and deposited a brown powder. A black substance was sublimed into the neck of the retort. The fluid, when boiled, de posited more of the brown powder ; and the sublimate, when washed, afforded the same matter. These were
selenium.
To procure selenium free from the other substances contained in the pyrites, Berzelius passed sulphuretted hydrogen through the fluid obtained by filtration, after the digestion of the substance in nitro-muriatic acid a By this means, an orange-coloured precipitate was produced, which was treated with nitro-muriatic acid.
b Water was added to the solution, which occasioned a copious white precipitate.
c This, when heated to redness, yielded a chrystalline sublimate, having a strong acid taste ; and when sub jected to heat with soda and borax, it left a metallic button, possessing the properties of tin. It was there fore an oxid of tin, in union with the sublimed acid, which Berzelius found was an acid of selenium d To the liquid from which the above precipitate was obtained, muriate of baryta was added, which threw down the sulphuric acid. The fluid, after fil tration, being subjected to heat, afforded a white chrys talline sublimate, and a whitish matter was left behind.
e The sublimate (d) was an acid having a metallic taste, communicated to it by mercury ; for when pre cipitated by potassa, it yielded mercury on the appli cation of heat. What remained was potassa in union with the acid.
This, when mixed with muriate of ammonia, and distilled, first yielded water and ammonia. Selenium then sublimed in small quantity. The residue, when washed, left a coarse brown powder. which was sele nium, and which was sublimed to free it from impu rities.
g The substance left after the distillation (d) was found to consist of baryta, copper, and tin, in union with the acid of selenium, and of arseniate of baryta.
Selenium is of different colours, according to the mode in which it is prepared. After bring fused, it has a deep brown colour, and metallic lustre. When allowed to cool slowly, its surface becomes rough. In the former case, the fracture is conchoidal, and pre sents the appearance of lead ; in the latter, it is granu lar, and resembles a piece of cobalt.