Alkahest

Alkahest is a hypothetical universal solvent, having the power to dissolve every other substance, including gold. It was much sought after by alchemists for what they thought would be its invaluable medicinal qualities.

Etymology

The name is believed to have been invented by Paracelsus from Switzerland, who modeled it on similar words taken from Arabic, such as ‘alkali’. Paracelsus' own recipe was based on caustic lime, alcohol, and carbonate of potash. He believed that alkahest was, in fact, the philosopher's stone.

Issues with a "universal solvent"

A potential problem involving alkahest is that, if it dissolves everything, then it cannot be placed into a container because it would dissolve the container. However, the alchemist Philalethes specifies that alkahest dissolves only composed material into their constituent, elemental, parts. The old remark, "Spit is the universal solvent” mocks a very old idea that, somewhere, there might be found a solvent that will dissolve anything. In modern times, water is sometimes called the universal solvent as well, because it can dissolve a large variety of substances, due to its chemical polarity.