Gold.
Gold is found to be unaltered, or there is at most a thin layer of silver chloride, which is the result of the action of sodium chloride upon the silver which the gold usually contains. Gold objects often have a red coating, which has been found to consist of ferric oxide, and is due to extraneous deposits which have been fixed by the silver chloride. I have not been able to prove the presence of gold chloride[78], and it does not appear possible that water containing sodium chloride can have the power of acting upon gold. If the ferric oxide is removed mechanically, some of the gold will naturally be removed with it, and this can be readily ascertained on analysis.
The degree of brittleness in objects of gold depends upon the changes which have taken place in other metals, especially silver, which are mixed with it.