Alloys of Gold

Alloying the metal with copper increases the hardness, elasticity, and tensile strength, but lowers the malleability, ductility, density, and melting-point. The alloys have a reddish tint. The minimum melting-point is 905° C., corresponding with 82 per cent, of gold and 18 per cent, of copper, the alloy of this composition being brittle. The British standard for coinage corresponds with eleven parts of gold in twelve of alloy, or 91.6 per cent. The alloys with silver are soft, malleable, and ductile, their properties being intermediate between those of the two metals. Below 37.5 per cent, of gold their colour is similar to that of pure silver. The solution of alloys of gold and silver in aqua regia is much facilitated by the presence of a mixture of ammonium nitrate and ammonium chloride. For additional alloys of gold reference should be made to the other volumes of this series.