The analytical reagent dithizone has now been used in analytical chemistry for just over 50 years, and forms the subject of an extensive literature comprising well over 2200 papers. Research work on this reagent was first carried out by Hellmuth Fischer, originally as a purely personal interest — virtually a hobby. However, the Siemens organization at Erlangen, Germany, was fortunate indeed to be able to employ his expertise when they were faced with the problems of determining small amounts of metallic impurities in certain highly purified metals.1,2In this field, its great sensitivity and considerable selectivity made an immediate impact. The intense color of the reagent itself — and that of each of its metal complexes, their sparing solubility in water, but considerable solubility in organic solvents — led Hellmuth Fischer, and later many others, to elaborate liquid-liquid extraction procedures for concentrating and separating desired metals and to devise a whole variety of absorptiometric finishes. Selectivity was enhanced by a careful control of the pH employed in extractions, and by the use of masking agents.