262 



SILVER. 



when heated ; but it gradually absorbs the gas, and 

 is converted into the well-known compound for- 

 merly called horn silver, and afterwards muriate of 

 silver, though now with more propriety denomin- 

 ated chloride of silver. This chloride, however, is 

 more easily obtained by dissolving silver in nitric j 

 acid, and mixing the solution with a solution of | 

 common salt. A copious curdy precipitate falls. 

 When this precipitate is washed and dried, it con- 

 stitutes pure chloride of silver. Its specific gravity 

 is 5 1 29. It is one of the most insoluble substances 

 known, requiring no less than 3072 parts of water 

 for its solution. When exposed to the air, it 

 changes from white to a purple or blackish colour, j 

 It melts at 500 Fahr., and assumes, on cooling, 

 the form of a gray-coloured, semitransparent mass, 

 having some resemblance to horn, and for that 

 reason called luna cornea. A strong heat sublimes 

 it. When heated strongly in an earthen crucible, 

 it passes through altogether, and is lost in the fire; ! 

 but when mixed with about four times its weight | 

 of fixed alkali formed into a ball, with a little ; 

 water, and melted rapidly in a crucible well lined 

 with alkali, the silver is reduced, and obtained in 

 a state of purity. Chloride of silver is composed 

 of silver 13-75, and chlorine 4-50. A bromide and 

 an iodide of silver may be formed simply by adding 

 in the one case, a solution of a hydrobromate to 

 one of nitrate of silver, and in the other, a solution j 

 of a hydrodate. If one ounce of silver, one ounce 

 of phosphoric glass, and two drachms of charcoal, \ 

 be mixed together, and heated in a crucible, phos- 

 phuret of silver is formed. It is of a white colour, 

 and crystalline in its texture. It is composed of 

 four parts of silver and one of phosphorus. Heat 

 decomposes it by separating the phosphorus. When 

 thin plates of silver and sulphur are laid alternately 

 above each other in a crucible, they melt readily in 

 a low red heat, and form sulphuret of silver. Its 

 colour is black, and it crystallizes in small needles. 

 It is capable of being cut with a knife, and is more 

 easily fused than silver. It is well known that ' 

 when silver is long exposed to the air, especially in 

 frequented places, as churches, theatres, &c., it 

 acquires a covering of a violet colour, which de- 

 prives it of its lustre and malleability: this coating 

 is sulphuret of silver. Selenium appears to enter 

 into combination with silver in two different pro- 

 portions, forming seleniets. Arsenic forms an alloy 

 with silver in the proportion of sixteen of the 

 former to one hundred of the latter; it is steel- 

 gray, brittle, and tine granular. Silver may be 

 alloyed with antimony by fusion. Silver and iron 

 unite readily: the alloy has the colour of silver, 

 but it is harder, very ductile, and attracted by the 

 magnet. When 500 parts of good Indian steel are 

 fused along with one part of silver, the compound 

 is greatly improved for the purposes of cutting in- 

 struments. Melted lead dissolves a great quantity 

 of silver at a slightly red heat; the alloy is brittle 

 and lead-coloured. Silver is easily alloyed with 

 copper by fusion: the compound is harder, and 

 more sonorous than silver, and retains its white 

 colour, even when the proportion of copper exceeds 

 one half: the hardness is at its maximum when the 

 copper amounts to one fifth of the silver. The 

 alloy of silver and tin is very brittle and hard. 

 That of silver and mercury is formed by throwing 

 pieces of red hot silver into mercury heated till it 

 begins to smoke : it forms dendritical crystals, which 

 contain eight parts of mercury, and one of silver. 

 The most important combination amongthose of the 



acids and silver (the nitrate of silver} has been 

 alluded to above, in the description of the oxide <>*' 

 silver. Nitric acid is the proper solvent of this metal, 

 from which solution the other salts of silver are 

 obtained it dissolves more than half its weight of 

 the metal, the solution being attended with efferves- 

 cence: if the silver and the acid are pure, the 

 solution is limpid and colourless, exceedingly heavy 

 and caustic: it stains the skin, and all animal sub- 

 stances, of an indelible black colour; hence it is 

 often used to dye hair, c. ; when evaporated till 

 a pellicle begins to form on its surface, it deposits, 

 on cooling, transparent crystals of nitrate of silver, 

 in the form of six-sided, four-sided, or three-sided, 

 thin plates; but, by slow evaporation, the salt may 

 be obtained in short, right rhombic prisms of 129 

 31': its taste is intensely bitter and metallic, and 

 it is usually employed as a corrosive substance, 

 under the name of lunar caustic; it is soluble in its 

 own weight of cold, and in half its weight of hot, 

 water. From the solution, the silver is thrown 

 down in a metallic state by a great number of 

 bodies; for example, hydrogen, sulphurous acid, 

 sulphate of iron, proto-chloride of tin, carbon, 

 phosphorus, volatile oils, and many of the metals. 

 The specific gravity of lunar caustic is 3-52. When 

 heated, it readily melts, swells up, and then remains 

 liquid: in this state it is cast into small cylindrical 

 moulds by apothecaries, to be employed by surgeons 

 for the purpose of opening ulcers and destroying 

 fungous excrescences: as an escharotic, its action 

 is powerful, and it is greatly preferred to caustic 

 potash also, in consequence of its not be liable to 

 deliquesce and spread. Both the crystals and the 

 fused salt are anhydrous, consisting of 118 parts 

 oxide of silver, and 54 nitric acid : it detonates, 

 when heated with combustible bodies, and with 

 phosphorus it detonates on percussion. Sulphate 

 of silver is obtained with ease by mingling together 

 solutions of nitrate of silver and sulphate of soda: 

 it falls in the state of a white powder, which may 

 be dissolved in water, and crystalized: the crystals 

 are white and brilliant, and have the form of very 

 fine prisms : it has the peculiarly disagreeable taste 

 of the nitrate; is anhydrous, and composed of sul- 

 phuric acid 5, and oxide of silver 14 - 75. - Sulphite 

 of silver is obtained by mixing the solutions of 

 sulphite of ammonia and nitrate of silver. It 

 assumes the form of small, shining, white grains: 

 when exposed to the light, it assumes a brown 

 colour. Phosphate of silver is insoluble in water, 

 and is hence precipitated when a solution of phos- 

 phate of soda is added to a solution of nitrate of 

 silver. The salts of silver are decomposed by the 

 alkalies and the earths. Prussiate of potash, when 

 dropped into a solution of a salt of silver, occasions 

 a white precipitate; hydro-sulphuret of potash pro- 

 duces a black precipitate; and an infusion of nut- 

 galls gives a yellowish brown precipitate. A ful- 

 minating preparation of silver, similar to that of 

 gold, but more energetic, is prepared by dissolving 

 silver in nitrous acid, diluted with three parts of 

 water : to the solution lime-water is added as long 

 as any precipitation is occasioned; the precipitate 

 is washed and dried ; it is then allowed to remain 

 for several hours in liquid ammonia, when it 

 becomes a black powder; the liquor is decanted, 

 and it is allowed to dry in the air ; when completely 

 dry, such is its tendency to explosion, that it cannot 

 be touched, the slightest agitation causing it to 

 detonate; and so violent is the detonation, that 

 the experiment cannot be made with safety on more 



