The chief service of iatro-chemistry to science consisted in its influence in bringing chemistry within the range of professional study, whereby a great extension in its pursuit was effected, with the result that a largely increased number of substances was discovered. Moreover, this wider experience of chemical processes familiarised workers with chemical phenomena in general, and thereby contributed to lay the foundations of a general theory of chemical action, which a succeeding age strove to complete. During the period of iatro-chemistry, which may be said to have extended from the first quarter of the sixteenth century to the latter half of the seventeenth, chemistry was advanced along practical lines by the labours of many men, chief of whom were Agricola the metallurgist, Palissy the potter, and Glauber the technologist. These men were primarily experimental chemists, who took little or no part in the fruitless polemics of the period, but followed their avocation in the true spirit of investigators, and thereby enriched science with many new and well-ascertained facts. =George Agricola=, born at Glauchau in Saxony in 1494, was a contemporary of Paracelsus. After studying medicine at Leipzig, he devoted himself to metallurgy and mineralogy, first at Joachimsthal, and published a number of works which were long deservedly regarded as the leading treatises on these subjects. In his _Libri_ XII. _de re Metallica_ he gives an account of what was known in his time respecting the extraction, preparation, and testing of ores. He describes the smelting of copper and the recovery of the silver which might be associated with it. He also describes methods of obtaining quicksilver, and of purifying it by treatment with salt and vinegar. He gives a full description of the method of obtaining gold by amalgamation, and of recovering the mercury by distillation. He gives accounts of the smelting of lead, tin, iron, bismuth, and antimony, and describes the manufacture of salt, nitre, alum, and green vitriol.