LYCOS RETRIEVER 
Nickel: Heat
built 633 days ago
Nickel carbonate usually occurs as a light green crystalline solid or a brown powder. It dissolves in ammonia and dilute acids but is insoluble in hot water. It exhibits vigorous reaction with iodine, hydrogen sulphide or a mixture of barium oxide and air. It decomposes on heating before melting occurs.
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Nickel hydroxide occurs as either a fine green powder, green crystals, or an amorphous black powder. Its melting point is 230 °C and its vapour density is 3.2, Nickel oxide occurs as a green or black powder that becomes yellow when heated. Nickel oxide has a specific gravity of 6.7 and melts at 1960 °C.
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Nickel Salts.-Only one series of salts is known, namely those corresponding to the monoxide. In the anhydrous state they are usually of a yellow colour, whilst in the hydrated condition they are green. They may be recognized by the brownish violet colour they impart to a borax bead when heated in an oxidizing flame. The caustic alkalis added to solutions of nickel salts give a pale green precipitate of the hydroxide, insoluble in excess of the precipitant. This latter reaction is hindered by the presence of many organic acids (tartaric acid, citric acid, &c.). Potassium cyanide gives a greenish yellow precipitate of nickel cyanide, Ni(CN) 2, soluble in excess of potassium cyanide, forming a double salt, Ni(CN)2.2KCN, which remains unaltered when boiled with excess of potassium cyanide in presence of air (cf.
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