NITRATE OF SILVER.
427
Argen'ti Ni'tras.—Nitrate of Sil'ver.
History. —Geber ( Invent. of Verity, ch. xxi.) describes the method ofpreparing crystallized nitrate of silver. When this salt is fused, it istermed the infernal stone {lapis infernalis) or lunar caustic (causticumlunare).
Preparation. —In the London Pharmacopoeia it is directed to be pre-pared by dissolving one ounce and a half of silver in a mixture of onefluidounce of nitric acid and two fluidounces of distilled water. Thesolution is afterwards to be evaporated to dryness, and the dried nitratefused and poured into proper moulds.
The fusion may be more readily and safely effected in a Berlin porcelaincapsule over a spirit or gas lamp, by means of Griffin’s lamp furnace, thanin a crucible over a slow fire, as directed in the Pharmacopoeia .
The theory of the process is readily comprehended. Three equivalentsor 324 parts of silver abstract three equivalents or 24 parts of oxygenfrom one equivalent or 54 parts of nitric acid, thereby disengaging oneequivalent or 30 parts of binoxide of nitrogen, and forming three equiva-lents or 348 parts of oxide of silver, which unite with three equivalents or162 parts of nitric acid to form three equivalents or 510 parts of nitrateof silver.
leq.Binox.Nitrog. 30
3 eq. Oxygen_24
.324
. 162
RESULTS.
•leq.Binox.Nitrog. 30
— , 3eq.Ox.Silver 348
3eq.NitrateSiIver 510
Properties. —Nitrate of silver forms transparent, colourless crystals,whose primary form is the right rhombic prism. Its taste is stronglymetallic and bitter. When heated it fuses: if the temperature be in-creased, decomposition ensues ; nitric acid and oxygen are evolved, leav-ing metallic silver. It is soluble in both water and spirit. It does notdeliquesce: when exposed to the atmosphere and solar light it blackens,probably from the action of organic matter, hydrosulphuric acid, or watercontained in the atmosphere. Mr. Scanlan {Athenaeum, Aug. 25, 1838)finds that nitrate of silver in a clean dry glass tube, hermetically sealed,undergoes no change of colour by exposure to solar light: the contact oforganic matter readily occasions it to become black.
Characteristics. —It is known to be a nitrate by its deflagrationwhen heated on charcoal, and the evolution of nitrous fumes. Its charac-ters as a silver salt have been already described (p. 426.)
Composition. —Nitrate of silver is thus composed:—
Eq. Eq.Wt. Per Cent. Proust.
Oxide of Silver . . 1 . . 116 . . 68'23 . . 69'5
Nitric Acid . . . 1 . . 54 . . 31’76 . . 30'5
Nitrate of Silver . . ] . . 170 . . 99'99 . . 100’0
Purity. —Nitrate of silver should be white, and completely soluble indistilled water. By the action of organic matters it blackens froma partial reduction. The presence of copper may be detected in itssolution by the blue colour produced with caustic ammonia. The watery