theory in later centuries. This was the theory of the five elements—fire, air, water, earth and ether or essence. It seems very probable that this theory was derived originally from ancient Hindoo philosophy, because in ancient Hindoo classics it is more completely elaborated than by Aristotle. The four elements—air, fire, water, earth—were not considered as distinct elementary substances, according to our modern definition of an element, but rather as determining qualities.
Thus fire combined the qualities of warmth and dryness; air—warmth and moistness; water—cold and moistness; earth—cold and dryness. All substances were considered as combinations of these elementary qualities, or in some sense as composed of these elements. The fifth element, ether or "essence," was more subtle and less clearly defined. It was supposed to be capable of taking all forms, and finally came to be identified with the "materia prima," or primal matter, out of which all other forms of matter were supposed to be born.
The Aristotelian notion of the four elements also implied the possibility of the change of one element to another. Thus when water evaporated by heat it became air; that is, by the addition of warmth, it changed from cold and moist to warm and moist, the properties of air. This idea among later alchemists served to justify the notion of the transmutability of the elements, that will-o'-the-wisp of chemists for many centuries. But this idea of the possibility of transmuting one element into another as of the baser metals into gold and silver received greater vitality from the observations and experiences, of the metallurgists upon the occurrence, preparation and alloys of the metals,
The metals known to the ancients were seven in number, gold, silver, lead, mercury, iron, copper and tin, though they were not considered as elements. Other metals indeed entered into their alloys, but they were not recognized by them as separate or distinct from those already named. Arsenic was known, though not considered as a metal. Bismuth and zinc and antimony began to be recognized as distinct substances about the beginning of the sixteenth century. As methods of analysis were rudimentary even at this later date, and as there was no realization of the concept of an element of unvarying composition and properties, and as the metals were obtained in varying degrees of purity or admixture, it can be understood how the changes in appearance and properties of the metals, as obtained from their ores, was believed to be due to a partial transmutation in the Aristotelian sense.
In the alloying of various metals, the character of the alloys was changed in ways that easily suggested actual changes in the character of the metals themselves. Thus we know that the Egyptians considered certain alloys of gold and silver as a distinct metal "electrum." The frequent occurrence of some gold in silver as obtained from its ores also easily suggested the idea that this gold had in some way been produced from the silver.