Some confusion of thought has been caused by the difference which has been made between the terms alchemy and chemistry and their applications. The word _alchemy_ is simply the word chemistry with the Arabic word _al_, which signifies _the_, prefixed, and the history of alchemy is really the history of chemistry--wild and erratic in its beginnings, and giving rise to strange hopes and still stranger theories, but ever working along the line of discovery and progress. And, although many of the professional chemists or alchemists of the middle ages were undoubted charlatans and quacks, yet did we not have many of the same kind in the nineteenth century? We may use the word alchemist as a term of reproach, and apply it to these early workers because their theories appear to us to be absurd, but how do we know that the chemists of the twenty-second century will not regard us in a similar light, and set at naught the theories we so fondly cherish? Only seven out of the large number of metals now catalogued by us were known to the ancients; these were gold, silver, mercury, copper, tin, lead, and iron. And as it happened that the list of so-called planets also numbered exactly seven, it was thought that there must be a connection between the two, and, consequently, in the alchemical writings, each metal was called by the name of that one of the heavenly bodies which was supposed to be connected with it in influence and quality. In the astronomy of the ancients, as is generally known, the earth occupied the center of the universe, and the list of planets included the sun and moon. After them came Mercury, Venus, Mars, Jupiter, and Saturn. To the metal gold was given the name of Sol, or the sun, on account of its brightness and its power of resisting corroding agents; hence the compounds of gold were known as solar compounds and solar medicines. As might have been expected, silver was assigned to Luna or the moon, and in the modern pharmacop[oe]ia such terms as lunar caustic and lunar salts still have a place. Mercury was, of course, appropriated to the planet of that name. Copper was named after Venus, and cupreous salts were known as venereal salts. Iron, probably from its being the metal chiefly used for making arms and armor, was dedicated to Mars, and we still speak of martial salts. Tin was named after Jupiter from his brilliancy, the compounds of tin being called jovial salts. The dull, leaden color of Saturn, with his apparently heavy and slow motion, seemed to fit him for association with lead, and we still have the saturnine ointment as a reminder of old alchemical times.