Nickel is extremely fusible ; its fusing point being higher than that of iron.
This metal is oxyded by exposure to the atmospheric air at a high tempera ture, though with difficulty. Its oxide is more easily obtained by exposure to heat with nitre ; it is of an apple green colour, and is obtained likewise of this colour by precipitation from some of its saline com binations. It appears to be the oxide at the minimum of oxydement; at least, ac cording to the experiments of Thenard, another oxide can be formed more high ly oxyded. It may be obtained by expos ing the green oxide to a red heat, or by heating it with oxymuriatic acid. It ap pears, therefore, to be too highly oxydiz ed to be capable of directly combining with any of the acids. According to Richter, oxide of nickel is reduced by heat alone ; and the only difficulty experienced is the intensity of the heat required to fuse the metal.
Nickel is oxydized and dissolved by a number of acids ; its solutions being ge nerally of a green colour and crystalliza ble.
The salts of nickel are decomposed by the alkalies, and the oxide, more or less free from the acid, is thrown down. If the alkalies are added in excess, they re dissolve it ; and with ammonia, in particu lar, soluble triple salts are formed. Pot ash and soda dissolve even a small quan tity of its pure oxide ; ammonia dissolves it in a much larger quantity.
Nickel combines with sulphur by fu sion. The compound has a yellow colour with some brilliancy. It is brittle and hard, and burns when strongly heated in contact with the air. Nickel is also dis solved by the alkaline sulphurets.
With phosphorus, nickel unites, either by projecting the phosphorus on the nick el at a high temperature, or by heating together phosphoric acid and nickel with a little charcoal. The nickel increases in weight one-fifth. The compound is of a white colour with metallic lustre, and ap pears composed of a congeries of prisms.
Nickel forms alloys with a number of the metals ; but our knowledge of these combinations is very imperfect.