Van Helmont regarded water as the primary element out of which all things are produced. He denied that fire was an element or anything material at all, and he did not accept the sulphur-mercury-salt theory. To him is due the word “gas”--before his time various gases were looked upon as mere varieties of air--and he also made a distinction between gases (which could not be condensed)[79] and vapours (which give liquids on cooling). In particular he investigated the gas that is now known as carbon-dioxide (carbonic anhydride), which he termed _gas sylvestre_; but he lacked suitable apparatus for the collection of gases, and hence was led in many cases to erroneous conclusions. [79] It has since been discovered that all gases can be condensed, given a sufficient degree of cold and pressure. =Francis Mercurius van Helmont= (see plate 12), the son of John Baptist, born in 1618, gained the reputation of having also achieved the _magnum opus_, since he appeared to live very luxuriously upon a limited income. He was a skilled chemist and physician, but held many queer theories, metempsychosis included. Johann Rudolf Glauber (1604-1668). § =58.= =Johann Rudolf Glauber= was born at Karlstadt in 1604. Of his life little is known. He appears to have travelled about Germany a good deal, afterwards visiting Amsterdam, where he died in 1668. He was of a very patriotic nature, and a most ardent investigator in the realm of Chemistry. He accepted the main iatro-chemical doctrines, but gave most of his attention to applied Chemistry. He enriched the science with many important discoveries; and crystallised sodium sulphate is still called “Glauber’s Salt.” Glauber, himself, attributed remarkable medicinal powers to this compound. He was a firm believer in the claims of Alchemy, and held many fantastic ideas. Thomas Vaughan (“Eugenius Philalethes”) (1622-1666.)