For reasons which need not be described here, van Helmont studied with particular interest the various modifications in which carbon is capable of occurring in nature - among them carbon's combustion product, carbon dioxide. It was his observations of carbon dioxide which made him aware of a condition of matter whose properties caused him the greatest surprise. For he found it to be, at the same time, 'much finer than vapour and much denser than air'. It appeared to him as a complete 'paradox', because it seemed to unite in itself two contradictory qualities, one appertaining to the realm of 'uncreated things', the other to the realm of 'created things'. Unable to rank it with either 'vapour' or 'air' (we shall see presently what these terms meant in van Helmont's terminology), he found himself in need of a special word to distinguish this new state from the other known states, both below and above it. Since he could not expect any existing language to possess a suitable word, he felt he must create one. He therefore took, and changed slightly, a word signifying a particular cosmic condition which seemed to be imaged in the new condition he had just discovered. The word was CHAOS. By shortening it a little, he derived from it the new word GAS. His own words explaining his choice are: 'Halitum ilium GAS vocavi non longe a Chaos veterum secretum.' ('I have called this mist Gas, owing to its resemblance to the Chaos of the ancients.')²