A method is described for the flame-photometric determination of 0 to 60 p.p.m. of calcium in solutions containing 4 per cent. w/w of sodium. Calcium is adsorbed from 100ml of solution on a column of sodium-form Chelex-100 chelating resin ; sodium is selectively eluted with hydrochloric acid at pH 2.4. Adsorbed calcium is eluted with 2 N hydrochloric acid and the resin washed with distilled water. The eluate and washings are diluted to 100m.l and the calcium determined on a Unicam SPQOO flame photometer.Magnesium, zinc, nickel, barium, mercury, manganese, copper and iron, present separately in concentrations of 26 p.p.m. or collectively in concentrations of 5 p.p.m. each, do not interfere. Aluminium depresses the amount of calcium found.The method has been used to determine calcium in simulated sea water.

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Very dilute solutions containing zinc sulphate, sodium and sulphuric acid were passed down a column of Zeo‐Karb 225 cation‐exchange resin, and the volume at which zinc first appeared in the effluent (breakthrough volume), together with the volume at which the concentration of zinc in the effluent became equal to its concentration in the influent (equivalent volume), were determined.