"Aristotle had considered metals to be formed by the combination of moist and dry exhalations, and in the Jabirian works these... are... vapours of mercury and sulphur. The cause of the different metals was the... quality of the sulphur... The term sulphur ...as a component of metals probably referred to a volatile combustible material to which no... substance corresponded exactly. Likewise mercury... may... have been... an approximation to the other volatile liquid component of metals. ...The notion that metals contained a combustible principle persisted, and... provided the inspiration for the phlogiston theory."