Isothiocyanates copper complexes

One of the earliest references to a reaction in solution, which, as we now realize, depends upon the formation of a coordination compound, was recorded by Pliny who stated that the adulteration of copper sulfate by iron sulfate could be detected by testing with a strip of papyrus soaked in gall-nuts, when a black colour developed if iron were present. A. Libavius (1540-1616) noted how ammmonia present in water could be detected by the blue colour formed with a copper salt and A. Jacquelain (1846) actually determined copper salts in terms of the blue colour formed on adding ammonia. Later developments used coordination compounds formed from ethylenediamine and other polyamines.3 T. J. Herapath determined iron(III) as its red isothiocyanate complex in 1852 and the basic procedure is used today.3... 

---