I. They believed in the alcahest, or universal solvent. Taking that

epithet, even in its most literal signification, it has simply to be stated, that modem chemistry has actually realised it. The element fluorine is nothing less than the alcahest. Lavoisier once expressed his surprise that it should 28
ALCHEMY AND THE ALCHEMISTS.
lever have occurred to the masters that no vessel on earth could hold the iniversal solvent, because it would solve the vessel too ! That is precisely ;he difficulty to contend with in the attempt to isolate fluorine. It is a jood many years now that it has been well understood by chemists that Derbyshire spar is composed of calcium — the metal of which quicklime is the rust or oxide — and of fluorine, another element, the latter of which ingredients could not be presented separate, just because no substance could withstand the intensity of its chemical action. No one doubted the existence of fluorine — thanks to Davy’s discovery of iodine, and the sagacity of Ampere — notwithstanding of the circumstance that it could not be handled and seen, owing to its irresistible powers of solution. It at length occurred to two brothers of the name of Knox, that vessels cut out of fluor-spar itself, seeing it is a substance already saturated with fluorine, might serve the purpose of catching some fluorine in ; and their experi- ments have been in a great degree successful. Faraday has also experi- mented on this subject. Fluorine seems to be an orange-coloured gas ; clilorine is a green gas ; iodine is a solid at ordinary temperatures, but a
I gentle heat converts it into a deep pui'ple vapour. Bromine is hquid, and
I resembles iodine vapour when in the gaseous state ; but it is more ruddy than purple. These four elements are deeply connected with one another ; but be that connection what it may, and even suppose that fluorine has not
I yet been separated in the state of absolute chemical purity, it cannot be denied that there lies the alcahest of old alchemy.