ALCHEMISTS AND IATROCHEMISTS When the Arabs conquered Egypt in the 7th century and over ran Syria and Persia, they brought a new spirit of enquiry to bear on the old 'civilizations they subdued. The great name that stands out in the alchemic period is that of Jabir—probably the same Geber of the Latin books Summa Perfectionis and Liber Fornacum of which the existing mss. date from the i 3th century. Jabir ibn Hayyan accepted the Aristotelian doctrine of the four elements, but to these he added the special chemical elements mercury and sulphur, by which he meant not so much the two elements as met with in nature, but rather the principles giving metals their unalterable property, and the earthly impurity that it was possible to cleanse them from. Gold, unaltered by fire, contained a very pure mercury ; lead and copper contained much sulphur. That gold could be extracted from copper pyrites, and that silver remained when galena was long roasted, were regarded as evidence that the lustrous crystals of pyrites and galena, looked on as metals, had been transmuted by purification from the sul phur or dross into the nobler metals.
The two alchemic elements were thus introduced; the third element "salt"—representing the residue that remained fixed after calcination—was added by the iatrocL mists. These three ele ments constituted the tria prima of Paracelsus and his disciples of the 16th century. Jabir himself seems to have believed in the philosopher's stone, and the term Kimya may have signified the secret powder which had to be projected on the molten metal to cause transmutation.
A century after Jabir came Rhazes, physician and chemist ; and he was followed by Ibn Sina, better known as Avicenna, who knew that metals could be changed in colour, but not really altered in substance.
In the 1 i th century Mansur distinguished between patron (sodium carbonate) and qali (potassium carbonate). He describes the preparation of a plaster of Paris, for use in surgery, by heat ing gypsum and mixing it with white of egg.
When the Arabs penetrated into Spain they brought with them their chemical knowledge and their love of learning. Through the Arab universities founded in Spain, the knowledge not only of alchemy, but also of much of Greek thought first illuminated the backward States of Europe. We cannot be sure of the origin of many of the Latin texts of the 12th and following centuries. It is said that the book translated from the Arabic by Robert of Chester in 1144 contains passages which occur in the earlier alchemist mss. It is even probable that the names which figure largely among the early chemists in Europe—Albertus Magnus, Roger Bacon, Raymond Lully, Vincent de Beauvais—are those of writers who made known not so much their own chemical ex perience as that of the Arabian alchemists. Albertus takes the same view as Avicenna concerning "chemical gold"—it is a super ficial imitation, not real gold.
Paracelsus, the son of a physician, studied at Basle and at Wurzburg, and after wandering through Europe returned to Basle in 1526 and was appointed professor of medicine. His first public act was to burn the works of Galen and of Avicenna, the great handbooks of medicine, and to proclaim that chemistry was not concerned with the transmutation of metals but was the hand maid of medicine. His reckless use of inorganic salts—many of them poisonous—led to his expulsion from Basle.
Contemporary with the restless and dogmatic Paracelsus, Agric ola devoted many years to the study of ores and the preparation of pure metals and salts from them. His De Re Metallica records many first-hand experiments—on the amalgamation pro cess of extracting gold, on the properties of bismuth, on flame tests for various metals. A little later Libavius, a German phy sician, published his Alchymia, which may be regarded as the first European textbook of chemistry. Coming later still, Glauber made his reputation as a great practical chemist : he gave a clear description of the mineral acids and of aqua regia (q.v.), and he left his name attached to sodium sulphate.
Last of the iatrochemists came van Helmont, regarded by many as the link between the alchemists and the modern chemists. He rejected the tria prima of Paracelsus and the four elements of Aristotle, going back to the older doctrine of Thales that water was the origin of all things. His well-known experiment of grow ing a willow-shoot in dried earth, and watering it regularly until it had gained many pounds in weight without receiving any ap preciable nutriment except from the water, is recalled now with a feeling that Nature had a sense of irony in deceiving the man who discovered carbonic acid gas.
He showed that an air was given off when an acid acted on limestone or potashes, and that this air extinguished a flame. The same air he found was produced in fermentation and occurred naturally in the Grotto del Cane. In his endeavours to prepare the air in closed vessels he discovered the enormous force de veloped by it ; Ideo, nominis egestate, he writes, halitum ilium Gas vocavi, non longe a Chao veterum secretum (Opera Omnia, Frankfurt, 1682, p. 69) . The term gas sylvestre, applied to carbon dioxide, meant the wild chaotic air that could not be coerced into vessels. Van Helmont found he could make an inflammable air, gas pingue, by heating animal matter, but he did not further distinguish between his gases.