An Acid Test is the established process of finding out beyond any doubt if a thing is genuine or not. Gold is one of the few precious metals that isn't affected by the majority of acids. However, it does react with a mixture of hydrochloric and nitric acids which was given the Latin name "Aqua Regia", meaning "royal water", in the middle ages, as it dissolved the king of metals. The first recorded use of the phrase as an idiom was as the World War One drew to a close, when US President Woodrow Wilson said to Congress, "The treatment accorded Russia by her sister nations in the months to come will be an acid test of their goodwill".