Application of direct photometry to agricultural analysis

The applications of two direct‐reading spectrometers (porous‐cup spark method) to the analysis of agricultural materials are described: (1) a two‐channel instrument for the determination of 0.3–24 p.p.m. of magnesium in acetic acid and ammonium acetate extracts of soils and HCl extracts of plant materials; a coefficient of variation in direct analysis of about ±2.0% is found. The major composition of agricultural samples does not affect the determinations; (2) the eleven‐channel Hilger Medium Direct Reader for the determination in soil extracts of 0.1–24 p.p.m. copper, 1–400 p.p.m. manganese and 1–50 p.p.m. zinc, the coefficients of variation being ±1.10%, ±1.64% and ±7.01%, respectively. A tentative pelleted rotating disk method is given for the determination of zinc, boron, manganese and copper in ashed plant materials with coefficients of variation of ±1.9%, ±2.8%, ±3.3% and ±5.4%, respectively.