The right of levying seigniorage, however, was sometimes waived by the king to encourage his subjects to bring gold and silver to the mint, and several instances are recorded in which the aid of alchemists was called in to effect the transmutation of baser metals into gold.
39), although it is not known whether the term is identical with the more modern sal-ammoniac. In the form of sal-ammoniac, ammonia was known, however, to the alchemists as early as the 13th century, being mentioned by Albertus Magnus, whilst in the 15th century Basil Valentine showed that ammonia could be obtained by the action of alkalies on sal-ammoniac. At a later period when sal-ammoniac was obtained by distilling the hoofs and horns of oxen, and neutralizing the resulting carbonate with hydrochloric acid, the name spirits of hartshorn was applied to ammonia.
Though his writings abound in universal solvents and other devices of the alchemists, he made some real contributions to chemical knowledge.
The "symbols" for the elements used by Dalton, apparently suggested by those of the alchemists, have been rejected in favour of those which were introduced by Berzelius.
The curious signs on the coloured carboys in chemists' windows, which were commonly to be seen until the middle of the 19th century, were signs used by the alchemists to indicate various chemical substances.