§ =15.= The alchemists regarded the metals as composite, and granting this, then the possibility of transmutation is only a logical conclusion. In order to understand the theory of the elements held by them we must rid ourselves of any idea that it bears any close resemblance to Dalton’s theory of the chemical elements; this is clear from what has been said in the preceding chapter. Now, it is a fact of simple observation that many otherwise different bodies manifest some property in common, as, for instance, combustibility. Properties such as these were regarded as being due to some principle or element common to all bodies exhibiting such properties; thus, combustibility was thought to be due to some elementary principle of combustion--the “sulphur” of the alchemists and the “phlogiston” of a later period. This is a view which _à priori_ appears to be not unlikely; but it is now known that, although there are relations existing between the properties of bodies and their constituent chemical elements (and also, it should be noted, the relative arrangement of the particles of these elements), it is the less obvious properties which enable chemists to determine the constitution of bodies, and the connection is very far from being of the simple nature imagined by the alchemists. Aristotle’s Views regarding the Elements. § =16.= For the origin of the alchemistic theory of the elements it is necessary to go back to the philosophers preceding the alchemists, and it is not improbable that they derived it from some still older source. It was taught by Empedocles of Agrigent (440 B.C. _circa_), who considered that there were four elements--earth, water, air, and fire. Aristotle added a fifth, “the ether.” These elements were regarded, not as different kinds of matter, but rather as different forms of the one original matter, whereby it manifested different properties. It was thought that to these elements were due the four primary properties of dryness, moistness, warmth, and coldness, each element being supposed to give rise to two of these properties, dryness and warmth being thought to be due to fire, moistness and warmth to air, moistness and coldness to water, and dryness and coldness to earth. Thus, moist and cold bodies (liquids in general) were said to possess these properties in consequence of the aqueous element, and were termed “waters,” &c. Also, since these elements were not regarded as different kinds of matter, transmutation was thought to be possible, one being convertible into another, as in the example given above (§ 14). The Sulphur-Mercury Theory.