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Aqua regia is primarily used to produce chloroauric acid, the electrolyte in the Wohlwill process for refining the highest purity (99.999%) gold. Aqua regia is also used in etching and in specific analytic procedures. It is also used in some laboratories to clean glassware of organic compounds and metal particles.
Generally, the preparation of this material involves gold being dissolved in aqua regia, then reacted with a solution of tin(II) chloride. The tin(II) chloride reduces the chloroauric acid from the dissolution of gold in aqua regia to a colloid of elemental gold supported on tin dioxide to give a purple precipitate or coloration.
After removing the solid gold other elements like silver and copper may be extracted from the liquid. To get the gold to a very high level of purity (999 fine gold) it is sometimes processed further with aqua regia to effectively remove all the impurities. Aqua regia was also used for parting.
The resulting gold is 99.999% pure, and of higher purity than gold produced by the other common refining method, the Miller process, which produces gold of 99.5% purity. [ 1 ] [ 2 ] [ 3 ] For industrial gold production the Wohlwill process is necessary for highest purity gold applications.
Fulminating gold – a number of gold based explosives which "fulminate", or detonate easily. – gold hydrazide, formed by adding ammonia to the auric hydroxide. When dry, can explode on concussion. – an unstable gold carbonate formed by precipitation by potash from gold dissolved in aqua regia. Galena – lead(II) sulfide. Lead ore.
This method has been used since ancient times. In modern times, additional tests can be done. The trace will react in different ways to specific concentrations of nitric acid or aqua regia, thereby identifying the quality of the gold: 24 karat gold is not affected but 14 karat gold will show chemical activity.
A visualization of the aqua fortis (nitric acid) and aqua regia acid tests on zinc, copper, silver, and gold. Testing for gold with acid capitalizes on gold's status as a noble metal, resistant to corrosion, oxidation, or acid. The procedure includes rubbing the gold-colored item on black stone, leaving a visible mark.
Very dilute amounts of powdered gold or platinum were dissolved in aqua regia [42] and added to spirits of tar for platinum and a mixture of turpentine, flowers of sulfur and linseed oil for gold. The mixture was applied to the glazed ware and fired in an enameling kiln, depositing a thin film of platinum or gold. [43]