Tarnish definition

The first two are very soluble in water but the last is less so. Weaker bases inelude ammonium hydroxide where X is NH4. In faet every aeid ean generate a base by loss of a proton and the definition now ineludes any eompound eapable of donating eleetron pairs, e.g. amines. Bases turn litmus paper blue and show eharaeteristie effeets on other indieators. They are soluble in water, tarnish in air, and in eoneentrated form are eorrosive to the toueh. Common examples are given in Table 3.5. ... 

A solid state chemical reaction in the classical sense occurs when local transport of matter is observed in crystalline phases. This definition does not mean that gaseous or liquid phases may not take part in solid state reactions. However, it does mean that the reaction product occurs as a solid phase. Thus, the tarnishing of metals during dry or wet oxidation is considered to be a solid state reaction. 

Proust showed that the black tarnish forming on silver exposed to air is silver sulphide. He obtained lead dioxide (which he says was discovered by Scheele see p. 230) by the action of dilute nitric add on red lead, noticed the evolution of arsenic hydride when impure tin dissolves in acid, showed that the native oxychlorides of copper of Chile and Peru are definite compounds, rediscovered cuprous oxide, and prepared cuprous chloride he says that Pelletier had discovered stannous chloride and examined its action on solu-... 

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