In many scientific investigations and technical operations it is necessary to know not only the total amount of an element of interest but also the amount of its different valencies , combinations or mineralogical forms. The diff-erent phases or forms of an element can usually be obser-ved of course by microscopical examination, X-ray diff-raction or other physical means . The frequent difficulty of obtaining by these techniques a rapid quantitative measure of the phases present. has led to the dcvelopiucut of many chemical procedures, based principally on a sele-ctive solvent , a chelate, resin or other isolating agent. The chemical approach , though it may suffer from certain deficiencies in accuracy and precision , has the merit
of quickly providing a reasonable satisfactory result. It does not require expensive and complicated instruments or workers with long experience in the interpretation of data . The popularity of chemical phase analysis in indu-strial practice, therefore , is not difficult to understan
