ABSTRACT
An exciting period for analytical chemists was inaugurated at the end of 1859 when the Heidelberg chemist Robert Bunsen and his physicist colleague Gustav Kirchhoff showed how flame colours could be analyzed prismatically to produce an emission spectrum that was unique to the element present in the flame. Such ‘signature tunes’ offered a new and extraordinarily accurate and delicate alternative to the classical methods of qualitative analysis that Crookes had learned as a student at the Royal College of Chemistry. Spectroscopy, as it became called, also offered the prospect of detecting elements hitherto hidden to science by revealing lines that did not belong to any of the known elements. When pursuing photographic chemistry Crookes had been excited by Herschel’s hint in his presidential address to the British Association meeting at Leeds in 1858 that he had possibly discovered a new arsenic-like element with photographic properties. Although a complete muddle as far as finding elements, Herschel’s investigations, with Crookes’ help, revealed the significance of exposure times in silver-salt photography.2 The episode illustrates how keen Crookes was to identify new elements optically, as well as his hopes of finding a revolutionary new photographic method.
