THE ALKAHEST OR UNIVERSAL SOLVENT
he production of a universal solvent or alkahest was one of the special problems of the alchemists in their general search for the philosopher's stone and the means of transmuting the so-called inferior metals into gold and silver. Their idea of the way in which it would aid them to attain these ends does not seem to be very clearly stated in any work that I have consulted; probably they thought that a universal solvent would wash away all impurities from common materials and leave in absolute purity the higher substance, which constituted the gold of the adepts. But whatever their particular object may have been, it is well known that much time and labor were expended in the fruitless search.
The futility of such attempts was very well exposed by the cynical sceptic, who asked them what kind of vessel could they provide for holding such a liquid? If its solvent powers are such that it dissolves everything, it is very evident that it would dissolve the very material of the vessel in which it must be placed.
When hydrofluoric acid became a subject of investigation it was thought that its characteristics approached, more nearly than those of any other substance known, to those of the universal solvent, and the very difficulty above suggested, presented itself strongly to the chemists who experimented with it. Not only common metals but glass and porcelain were acted upon by this wonderfully energetic liquid and when attempts were made to isolate the fluorine, even the platinum electrodes were corroded and destroyed. Vessels of pure silver and of lead served tolerably well, but Davy suggested that the most scientific method of constructing a containing vessel would be to use a compound in which fluorine was already present to the point of saturation. As there is a limit to the amount of fluorine with which any base can combine, such a vessel would be proof against its solvent action. I am not aware, however, that the suggestion was ever carried into actual practice with success.