SIL
( 294 ) SIL
mined with a magnifier, appear to "be compofedof truncated odtohedrons.
The above curious fubftance was difcoveredSby Welter, and is by him called the bitterprinciple, and he fuppofes it to be generallyproduced by the aftion of nitric acid on animal•matters, and. is perhaps the fame fubftancewhich caufes .the bitternefs of bile,
•It has not been further examined.
SILVANITE. See Tellurium.
SILVER. Silber, Germ. Urgent, Fr.
Silver is a metal of a pure white colour, verymalleable, foft, fufible at a full red heat, butnot oxydable by expofure to the air while melt-ed. It is foluble with eafe in nitrous acid, andprecipitable from its folution in the form of a■white curd by muriatic acid, or any of theneutral muriats.
§ i. Ores of Silver .*
Sp. x. Native Silver. Gediegen Silber, Wern.Argent Natif, Broch.
Its colour is filvery white, but externally it is.often yellowifh and brownilh, in confequenceof being tarnifhed by fulphureous vapours. Itoccurs maffive, difleminated, in plates, inrounded pieces, alfo capillary, filiform, reticu-lated, arborefcent and cryftallized. The formsof its cryftals are,
1. The regular odtohedron,
3. A folid, compofed of the two former,and generally reprefented as a double fix-fidedpyramid, with truncated fummits.
The cryftals are ufually very fmall, andgrouped together. The furface of the cryftalsis fmooth, that of the plates is drufy, thefiliform and capillary varieties are commonlylongitudinally ftriated. Its fuperficial luftre ismetallic, varying from Ihining to glimmering,according to the fmoothnefs or roughnefs ofthe furface. Its fradture is hackly, it acquiresa bright Ihining metallic luftre by fridtion. Itis opake, foft, duciiJe, flexible but not elaftic.Sp. gr. about 10.
The above is the defcription of pure nativefilver, it is not unfrequently however alloyedwith gold in various proportions; a fpecimenanalyfed by Dr. Fordyce afforded 28 per cent..,of this latter metal; in this cafe the colour ap-proaches to that of pale brafs, and its fpecificravity is greater than that of pure filver.ometimes alfo native filver is mixed with? fmall proportion of copper by which it
• An. Cliim. tom. *£. * Kirwaa.
acquires a tinge of red, and is fenfibly harderthan when pure.
The moll recent of the primitive rocks arethofe in which native filver principally occurs?it has been found alfo in ftratified mountains.It occurs chiefly in veins accompanied byquartz, heavy fpar, and calcareous fpar, by va-rious other ores of filver, as well as fpathofeiron, arfenical pyrites and cobalt, &c.
This ore is abundant in Peru and Mexico ,where folid maffes of filver have been foundweighing 30 or 40 lbs. In Europe it is foundmolt plentifully in Saxony , Bohemia, andSwabia. The mines of Kdngsberg in Norway ,which ufed to furnilh this ore are now almoftentirely exhaufted. The Hungarian minesafford a confiderable quantity of this ore, andit has been recently difcovered in Cornwall .In Alia and Africa filver appears to be lefsplentiful than gold.
Sp. 2. Silver Amalgam . For an accountof this ore fee Mercury, ores of.
Sp. 3. Antimonial Silver. Spiefglas Silber tWern. Argent Antimonial, Broch.
Its colour is tin-white, approaching more orlefs to filver-white; by expofure to the air it isoften fuperficially tarnifhed, and then exhibitsvarious iridefcent colours. It occurs in mafs,difleminated, in kidney-fhaped maffes, or cryftal-lized: the forms of its cryftals are the following.
x. The regular hexahedral prifm: fometimesthe prifm is very fhort fo as to become tabular:fometimes its lateral edges are truncated, whichgives it a cylindrical appearance.
2. A fomewhat oblique four-fided prifm,which is often nearly cubical.
The cryftals are fmall and very fmall; theprifms are longitudinally ftriated, but all theother faces are fmooth. Externally it is gliften-ing, internally it is brilliant, with a metallicluftre. Its fradture is lamellar in one dire&ion,but in others is flat conchoidal. It prefentsgranular concretions of various fizes. It ac-quires a luftre by friction; is moderately hardand brittle. Sp. gr. 9.44—10.
Before the blowpipe on charcoal this mineralreadily enters into fufion, the antimony thenflies off in a white vapour, with its peculiarodour, and there remains a globule of filverfurrounded with a brownilh flag, which coloursglafs of borax green.
It has been analyfed by Selb, Klaproth ,Vauquelin and Abich, with the followingrefults. 6
Emmerling. JBrochant, Jamefon. Hauy.