Ultramikroanalyse II Die extinktiometrische Bestimmung des Magnesiums

The experimental technique employed in the determination of magnesium by means of tropaeolin 00, according to the method of Lang 4 ), is discussed, and several sources of errors are pointed out. The solubility of magnesium tropaeolinate in water was determined; the saturated solution was shown to contain 3.25 × 10 −7 g magnesium per cm 3 at 20°C and about 2 × 10 −7 g magnesium at 0°C. A convenient method for the determination of minute quantities of magnesium (10 −5 to 10 −7 grams) was worked out. According to this method magnesium is precipitated with a known quantity of tropaeolin 00, the precipitate is separated by centrifuging and the excess of dye is estimated by measuring the extinction of a portion of the supernatant liquid after the addition of sulphuric acid.