The mineral composition of apples. V.—The determination of sodium and its distribution in the fruit

The determination, with an E.E.L. flame photometer, of sodium in the seeds, pulp, peel and stems of apples is subject to errors owing to the presence of calcium, potassium and magnesium. In the absence of phosphate, values which are too high by as much as 50% may be obtained. Phosphate is present in the ash of the seeds, pulp and peel of Cox's Orange Pippin apples in amounts sufficient to suppress completely the effect of calcium, but the amount in the ash of the stems is insufficient to do so and errors of about 10% may arise. The sum of interferences due to potassium and magnesium in the ash of any part of the apple results in positive errors of up to 7%. Apart from slight variations near the surface, sodium concentrations in median transverse sections of apples rise from the surface of the fruit to a maximum at 5 mm inside and then fall towards the centre. The variations within the outer 3 mm appear to be characteristic of individual apples and unrelated to orchard treatment and time in store.