Phosphors and Phosphorus in Early Danish Natural Philosophy by HELGE KRAGH Historisk-filosofiske Meddelelser 88 Det Kongelige Danske Videnskabernes Selskab The Royal Danish Academy of Sciences and Letters Commission Agent: C.A. Reitzel Det Kongelige Danske Videnskabernes Selskab udgiver følgende publikationsrækker: The Royal Danish Academy of Sciences and Letters issues the following series of publications: Authorized Abbreviations Historisk-filosofiske Meddelelser, 8 Hist.Fil.Medd.Dan.Vid.Selsk. (printed area 175 x 104 mm, 2700 units) Historisk-filosofiske Skrifter, 4 Hist.Filos.Skr.Dan.Vid.Selsk. (History, Philosophy, Philology, (printed area 2 columns, Archaeology, Art History) each 199 x 77 mm, 2100 units) Matematisk-fysiske Meddelelser, 8 Mat.Fys.Medd.Dan.Vid.Selsk. (Mathematics, Physics, (printed area 180 x 126 mm, 3360 units) Chemistry, Astronomy, Geology) Biologiske Skrifter, 4 Biol.Skr.Dan.Vid.Sel.sk. 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Reitzel • Copenhagen 2003 © Det Kongelige Danske Videnskabernes Selskab 2002 Printed in Denmark by Special-Trykkeriet Viborg a-s ISSN 0106-0481 ISBN 87-7876-347-9 Abstract Luminescent substances, whether organic or inorganic, have played a significant role in the history of science. Their role is here considered mainly within a Danish context relating to the period ca. 1640-1755. Thomas Bartholin’s De luce animalium of 1647 was the standard work of naturally occurring luminescent bodies in the early modem period. The discovery of elemental phosphorus in 1669 ushered in a new era, in the early phase of which Boyle and Leibniz were among the main investigators. Phosphorus came to Denmark through Leibniz and in early 1682 the substance was demonstrated before the king. The prepa­ ration of phosphorus, and scientific life in Copenhagen in general, can be followed through the Leibniz correspondence. A hitherto ignored work of Ole Borch of 1683, in which he describes the formation of phosphorus, is analysed and partially translated. Finally, attention is called to an essay on phosphorescence that Christian G. Kratzenstein wrote in 1754, the first of his many contributions to the proceedings of the Royal Danish Academy of Sciences and Letters. H e l g e K r a g h History of Science Department University of Aarhus Building 521, Aarhus 8000, Denmark [email protected] Contents 1. Introduction ............................................................................ 7 2. Historiographical considerations ........................................... 10 3. Lapis Solaris and other luminescent bodies ........................... 16 4. The discovery of a new phosphor ......................................... 25 5. The English phosphor ............................................................ 35 6. Some later perspectives .......................................................... 40 7. A sketch of chemistry in Denmark until 1660 ....................... 43 8. How phosphorus came to Denmark ....................................... 46 9. Ole Borch on phosphorus........................................................ 52 10. A contribution from the eighteenth century ........................... 62 11. Conclusion and sum m ary........................................................ 74 Full many a glorious morning have I seen Flatter the mountain-tops with sovereign eye, Kissing with golden face the meadows green, Gilding pale streams with heavenly alchemy. (Shakespeare, Sonnet 33) Verschwind in Flammen, Salamander! Rauschend fließe zusammen, Undene! Leucht in Meteoren-Schöne, Sylphe! (Goethe, Faust, part I) 1. Introduction Each of the 100 or so chemical elements has its own interesting history, which in many cases has been of profound importance to the economic and cultural developments that have shaped world history or national histories. Denmark, or before 1814 Denmark-Norway, has only a small share in this branch of chemical history, most notably in connection with the metallic elements of atomic numbers 13 (aluminium) og 72 (hafnium). Whereas impure aluminium was first isolated from alumi­ nous earth by H. C. Ørsted in 1825,1 the element hafnium was discov­ ered in Copenhagen as late as 1923, at Niels Bohr’s institute of theoret­ ical physics. However, in the latter case none of the discoverers, George Hevesy and Dirk Coster, were Danes.2 Hafnium was the first element ever which was identified by its atomic number, a defining property of a chemical element that had been discovered only a decade earlier. The subject of the present communication is phosphorescent sub­ stances, and more specifically the early history of phosphorus. This ele­ ment, number 15 in the periodic system, belongs to the seventeenth century, hence to a time when the modem notion of a chemical element (not to mention the atomic number) had no meaning. Although no Dane contributed to the process that led to the recognition of elemental phos­ phorus in the 1670s, it is worthwhile to trace how the history and pre­ history of phosphorus have interacted with Danish natural philosophy during the century. The period from about 1640 to 1680 has often been described as the first golden age of Danish natural philosophy, and so it should be no surprise that Danish scientists and philosophers took an early and active interest in the remarkable properties of phosphorescent substances. Among other things, the account that follows illuminates how international developments in natural philosophy were received and absorbed in a national context during the period of the Scientific Revolution. Although the paper is basically limited to the sevententh 1 J. Fogh, “Über die Entdeckung des Aluminium durch Oersted im Jahre 1825,” Det kgl. Danske Vidensk. Selsk., Mat.-Fys. Medd. Ill, 14 (1920), 1-17. Hans H. Kjølsen, Fra Ski­ denstræde til H. C. Ørsted Institutet (Copenhagen: Gjellerup, 1965), pp. 102-121. 2 Hevesy was Hungarian, and Coster was Dutch. A detailed account of the discovery of hafnium is given in H. Kragh, “Niels Bohr’s second atomic theory,” Historical Studies in the Physical Sciences 10 (1979), 123-186. See also H. Kragh, “Anatomy of a priority con­ flict: The case of element 72,” Centaurus 23 (1980), 275-301. 8 HIM 88 century, in the final section I briefly discuss a somewhat forgotten trea­ tise from the following century, written by the German-Danish experi­ mental philosopher and medical doctor C. G. Kratzenstein. This work, an attempt to systematize the knowledge of phosphorescent bodies within the framework of phlogiston-based chemistry, is of interest in itself but also illustrates how little progress had been made in the field of phosphors after a century of research. It may be useful to mention the modem meanings of what in the sev­ enteenth century was often referred to collectively as “phosphores­ cence”. Fluorescence, a name coined by George Gabriel Stokes in the mid-nineteenth century,3 denotes a process whereby absorption of opti­ cal energy is followed by an emission of light at longer wavelengths, hence smaller frequencies (Stoke’s law). Atomic electrons are excited from the ground state to a higher level, but decay to an energy level above the ground state. What were called phosphors in the seventeenth century were often fluorescent minerals which absorb the ultraviolet parts of sunlight and emit them in the visible spectrum. In its modem meaning, phosphorescence is closely related to fluorescence and mainly differs from it by the way in which the photonically excited electrons decay. Whereas in fluorescence the excited atom almost immediately decays to a lower energy state, in phosphorescence in can remain in the excited state for some