polarograph, which is applicable to most zinc alloys provided that the cadmium : indium ratio does not exceed 10:x. If this ratio is exceeded then the indium concentration may be reported as less than l/&h of the cadmium content. 2. A "collection" method applicable to zinc and to zinc alloys provided that their aluminium content is less than 0.01 "A,.
- A method using an iodide base electrolyte which will determine indium in zinc or in zinc alloys in which lead is absent, or is less than r/&h of the indium concentration.
'. 4. A co-precipitation method which is applicable to almost all zinc alloys, but which is much more lengthy than those mentioned above.
For routine work, the cathode-ray method is the best and this could easily be extended to give determinations of copper, lead ancl cadmium in the same solution. Sl.J&IMARY In this paper, the clevclopmcnt of a co-precipitation method for the separation of indium from zinc alloys is clcscribcd and a method for the dctcrmination of intlium clown to 0.5 p.p.m. in mazak alloys is prcscntcd. Results obtained in trials of this method arc given anti the final conclusions regarcling this and previously tlevclol~cd methods arc incluclcd. f G. I:.