777 



SILVEK. 



SILVER. 



773 



dorsal fin, the external rays of the fins prolonged into a filament, and 

 four branchiostegous rays, but it possesses no ventral fins. This fish 

 is found at Rio de Palace, near Papayana, where it is known by the 

 name of Pescado Negro : it attains about 15 inches in length. 



Heterobranchus, Geoff. -The head is furnished with a rough bony 

 shield, which is flat aud broader than in the other Silurians, on account 

 of the lateral laminse furnished by the frontals aud parietals, which 

 cover the orbital and temporal bones. The barbules are eight in 

 number. The species inhabit the rivers of Africa, and some of those 

 of Asia. 



In some species the long dorsal fin is supported throughout by rays ; 

 these constitute the sub-genus Clarias, Val. ; and in others there is a 

 dorsal fin supported by rays, aud a second behind this, which is adi- 

 pose. To these the term Heterobranchus is restricted in the ' Histoire 

 Naturelle des Poissons.' 



Saccobranchus, CUT. and Val., ia founded upon the Silurus Singio 

 of Hamilton's ' Fishes of the Ganges," which possesses some interesting 

 peculiarities in its internal organisation, pointed out by Mr. Wyllie 

 in the 'Proceedings of the Zoological Society' for May, 1840. 



Plotonu, Lacdpfede, is distinguished by the elongated form of the 

 body and the possession of two dorsal fins, the hindermost being 

 supported by rays as well as the other. The species inhabit India. 



Anpi-'do, Linn., presents very singular characters, particularly in the 

 flattening of the head and in the dilatation of the anterior portion of 

 the trunk, which chiefly arises from that of the bones of the shoulder; 

 in the proportionate length of the tail ; in the small size of the eyes, 

 which are placed in the upper surface of the head. The species are 

 found in the tropical parts of South America. 



Chaca, Cuv. and Val., which is the next in succession in the 

 ' Histoire des Poissons,' is founded upon the Platystacm Chaca of 

 Buchanan Hamilton. It inhabits the rivers of India. 



Xisor is also founded upon a single species described under the name 

 fi. rhabdophorut by the author just mentioned, ia his 'Fishes of the 

 GhMfM? 



Loricaria, Linn., is distinguished by the head and body being 

 covered throughout by large angular bony plates. 



This genus is subdivided into two sub-genera. In the one (IJypo- 

 itomiu, Lacep.) there are two dorsal fins ; the hinder one ia small, and 

 provided with but one ray. In the second, to which Lace"pede restricts 

 the term Loricaria, there is but one dorsal fin. The species of both 

 Bub-genera are found in South America. 



SILVER, a metal which has been well known and highly valued 

 from the remotest period circumstances which are readily explained 

 by the facts of its occurring frequently native, and possessing great 

 lustre and fitness for immediate use without being subjected to any 

 metallurgic process. 



Native Silver occurs crystallised, arborescent, or dendritic, capillary, 

 reticulated, granular, and massive. The primary form of the crystal 

 is a cube. It has no cleavage. Fracture hackly. Colour white, but 

 externally often blackish, owing probably to the presence of a little 

 sulphur. Hardness 2'5 to 3. Lustre metallic. Colour pure white, 

 except when tarnished. Streak shining. Opaque. Specific gravity 

 1U'47. Malleable, but commonly less so than pure silver, probably 

 owing to an admixture of other metals. Soluble in nitric acid, and 

 the solution colourless when pure, but blue if copper be present ; and 

 if antimony, a white substance ; and if gold, a black one remaius 

 undissolved. Fuses into malleable' globules before the blow-pipe. 



Native Silver is met with in most parts of the world ; in the British 

 Isles, Germany, Hungary, in the north of Europe, but especially, and 

 in largest quantity, in Mexico and South America. Silver occurs in 

 mixture or combination with other metals. 



Antimonial Silver. Stibiuret of Silver. This occurs in crystals, in 

 grains, and massive. The primary form of the crystal is a right 

 rhombic prism. Cleavage parallel to the terminal plane and short 

 diagonal of the prism. Fracture uneven. Colour silver white, or, 

 when tarnished, yellowish-white. Streak silver white. Lustre metallic. 

 Opaque. Slightly malleable. Easily frangible. Hardness 3'5. Specific 

 gravity 9'44 to 9'8. Before the blow-pipe on charcoal it readily melts, 

 with the formation of white antimonial vapour, into a grayish globule, 

 which ia not malleable, but eventually pure silver ia obtained. It ia 

 not totally soluble in nitric acid, oxide of antimony remaining 

 undissolved. 



The Massive Varieties are amorphous, and have a granular or 

 foliated structure. 



Antimonial Silver ia found in clay-slate at Andreaaberg in the Hartz, 

 in Baden, near Guadalcanal in Spain, at Salzburg, and at Allemont in 

 France. 



The Andreasberg mineral (1), analysed by Vauquelin, and the 

 Baden (2), by Klaprotb, gave the annexed results : 



(1) (2) 



Silver 78 84-76 



Antimony .... 22 16-21 



_100 100 



Telluric Silver occura in coarse-grained masses. Colour gray. Lustre 

 metallic. Soft. Somewhat malleable. Specific gravity about 8'5. 

 It is dissolved by nitric acid, and when heated, and before the blow- 

 pipe on charcoal, gives a fused blackish mas*, containing specks of 

 metallic uilver. 



It is found at the silver-mines of Savdiuski, in the Altai Mountains, 

 Siberia. 



Its analysis by Rose gives 



Silver 62-42 



Tellurium 36-96 



Iron 00-24 



99-62 



Native Amalgam is a compound of silver and mercury. [MERCURY.] 

 A uriferotu Native Silver occurs crystallised in cubes, capillary, and 

 disseminated. Colour yellowish-white. Specific gravity 14'0 to 17'0. 

 Different varieties give the annexed results 



Fordyce. Klaproth. Boussingault. 



Silver 

 Gold 



72 



28 



34 

 64 



15-5 

 84-5 



17-6 

 82-4 



26 

 74 



3507 

 64-93 



100 98 100 100 100 100 



Arsenical Antimonial Silver, or rather Arsenio-Ferruginous Anti- 

 monial Silver. This substance occurs mammillated or in small globular 

 and reniform masses, and sometimes investing other substances. When 

 untarnished it is nearly silver-white, but is commonly tarnished 

 yellowish or blackish ; its lustre is metallic. It is harder than anti- 

 monial silver, but is sectile and brittle. Specific gravity 9-4. 



Before the blow-pipe antimony and arsenic are volatilised with the 

 alliaceous smell, and a globule of impure silver remains. Its localities 

 are nearly the same as those of autimouial silver. Klaproth obtained 

 from a specimen from Andreasberg 



Silver 12-75 



Antimony 4 



Iron 44-25 



Arsenic ....... 35 



96 



The native compounds of silver next to be described are those in 

 which it occurs in combination with the non-metallic elements. It 

 is not found simply combined with oxygen, nor at all with azote, 

 hydrogen, or fluorine. 



Chloride of Silver; Horn Silver; Muriate of Silver; Laxmannite. 

 This ore occurs crystallised and massive. Primary form of the 

 crystal a cube. No cleavage. Fracture uneven. Hardness I'O to 

 1-5. Yields to the pressure of the nail Streak shining. Specific 

 gravity 4'75 to 5'55. Translucent. Opaque. Lustre resinous. Colour 

 gray, yellowish, greenish, and blue of various shades. Malleable and 

 sectile. Fusible in the flame of a candle. Heated with potash by 

 the blow-pipe, yields a globule of metallic silver. Insoluble in nitric 

 acid, but dissolved by ammonia. When rubbed with a piece of 

 moistened zinc, the surface becomes covered with metallic silver. 



This ore occurs in various parts of Europe aud America, along with 

 others of the same metal. The largest masses, which are of a greenish 

 colour, are brought from Mexico and Peru. It is found in veins, 

 chiefly in primitive rocks. 



Two specimens from Peru (1) and from Saxony (2), analysed by 

 Klaproth, gave 



Chlorine 24 



Silver 76 



Oxide of Iron . . . . 

 Alumina . . . . . 

 Sulphuric Acid . . . . 



100 



Buttermilk Silver ; Earthy Corneous Silver. This is regarded as a 

 variety of the foregoing. It is described as being of a brownish colour, 

 with occasionally a tinge of green or blue. It is opaque, dull, with 

 au earthy fracture, and is soft, sectile, and heavy. It occurs massive, 

 and also investing other substances. It occurs only at Audreasberg, 

 in the Harz. 

 According to Klaproth, it is composed of 



Chlorine 8'2S 



Silver 24-64 



Alumina 67'08 



100 



Iodide of Silver ; fferreralile. Occurs massive in thin plates, which 

 are silver- or grayish-white, and which become bluish by exposure to 

 the air. Transparent. Translucent. Lustre resinous to adamantine ; 

 in thin lamina flexible and malleable. Melts on charcoal before the 

 blow-pipe, vapour of iodine being evolved, and globules of silver 

 remaining. It is found at Abarradon near Mazapil, in the state of 

 Zacatecaa, Mexico, in serpentine. 



Sulphuret of Silver ; Vitreous Silver; Silver Qlance; Henkelite. 

 Occurs crystallised aud massive. Primary form a cube. Fracture 

 fine-grained and uneven ; sometimes small and flat conchoidal. Colour 

 lead-gray; blackish when tarnished. Lustra metallic. Opaque. Hard- 

 ness 20 to 2'5. Malleable. Sectile. Specific gravity about 7'2. 



When heated by the blow-pipe, sulphur is expelled and silver 

 remains. It occurs in Saxony, Bohemia, and in great abundance in 

 Mexico. It has been occasionally found in Cornwall, aud in most 

 silver-mines. 



Analysis (1) by Klaproth, of a specimen from Freiberg ; (2) by 

 Berzelius : 



