Inquartation is a method of separating metallic gold from silver by the use of concentrated nitric acid. It works because silver and other base metals are soluble in the acid, whereas gold and other noble metals are not. In practice inquartation actually causes a parting of the metals. It is necessary for the exposed metal to have a large surface area, which can be achieved by granulation of the metal. It is also necessary to add some base metals to the reaction, so that the gold constitutes a quarter of the metals present. Placer gold, found in surface sediment, can be used as is, but lode gold must be extracted from its gangue minerals first.
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Things you need
- Nitric acid
- Filter paper
- Stirring Rod
- Metal Shears
- Laboratory stand
- Muffle furnace
- Crucible and lid
- Rubber gloves
- Eye protector
Granulate the gold into fine particles using the metal shears. Placer gold usually doesn't require this step unless there are nuggets present. The reason for reducing the gold to small particles is to expose as much of its surface area as possible to the action of the nitric acid.
This process is used for the small scale refining of gold, which mirrors the fire assaying process in liquid chemical form. In practice inquartation is limited to batches of metal weighing less than 4kg. The process yields gold that exceeds 99.9 per cent fine.
Mix one part of the nitric acid with two parts of deionised or distilled water in a beaker. This is your working solution; to this, slowly add the granulated gold pieces in a ratio of 1g of gold to 4g of your working solution. The nitric acid dissolves the silver that is alloyed with the gold, as well as any other base metals contained in the gold. Gold itself is not affected by the nitric acid and settles at the bottom of the beaker; it can be later filtered out of the nitric acid.
The reaction of the silver with the nitric acid will produce large quantities of hydrogen and other gases capable of forming an explosive mixture when mixed with air. Do this process only in a well ventilated place while wearing rubber gloves and eye protectors.
The working process generates a continuous stream of bubbles as the acid reacts with the silver, converting it to silver nitrate. For the process to reach its conclusion takes time, during which the gold should be stirred occasionally until no more bubbles are observed. The solution should be allowed to sit for another half hour with occasional stirring.
Pour the finished solution through a paper filter to recover the gold particles, and save the silver nitrate solution for further treatment. The gold particles and filter paper are placed into a porcelain crucible and fired in a furnace that melts the gold. The filter paper is completely destroyed in the furnace. The gold forms a button at the bottom of the crucible.
The silver nitrate solution can be treated with common table salt that causes the silver to precipitate from solution as silver chloride. The filtrate of silver chloride can then be treated the same way as the gold in a furnace to reduce the silver chloride to metallic silver.
In this fashion gold can be separated from silver, and both metals can be recovered for later use.
Tips and warnings
- The process goes faster if gently heated in the sun.
- Nitric acid can cause severe burns.
- Wear rubber gloves and eye protectors when using this process.
- Do not try to heat with a flame.
- Only perform this process in a well ventilated area.
- Hydrogen gas and air make an explosive mixture.
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