The mineral composition of apples. I.—Introduction, sampling methods and ashing techniques

Methods which are now widely used to determine the mineral composition of leaves are not necessarily those which are the most suitable for determining the composition of apples. Differences between the chemical composition of fruit and leaf in respect of general composition, and in the ranges and ratio of concentrations of mineral elements, affect the suitability of methods. Methods of sampling and of preparing samples by freezing and grating, and sources of contamination are described. Descriptions of three methods of ashing apple tissue, with nitric acid or nitric and perchloric acids, and by heating in platinum crucibles at 900°G are given. A combustion procedure using an oxygen flask with electrical ignition and magnetic stirring for fume recovery in hydrochloric acid is also described. Comparisons of the methods for samples of frozen, grated apple showed that ashing large sub‐samples with nitric acid gave the most reproducible results. Dry ashing at 900°G gave results comparable with the use of the other methods. Differences due to the shape of crucible and also losses of potassium and sodium with prolonged heating at 900°G are discussed. The effects of filtration and of storage on ash solutions are described. The combustion procedure is quicker than the other methods but is unsuitable for the determination of sodium, and calcium results are slightly less reproducible.