A Critical Study on the Methods of Water Analysis (X)

Calcium and Magnesium

Abstract

1. Calcium: The method of determining calcium in water is based on the permanganatometry of its oxalate. In this method, the oxalate of calcium is treated with dilute sulphuric acid and the liberated oxalic acid is then titrated with the standard solution of potassium permanganate. The author studied the influence of the coexistence of magnesium with calcium, since magnesium is the most common contaminating substance in this method. The experimental result shows that the small content of magnesium (<10mg Mg/L) has no appreciable influence upon the determination of calcium.
2. Magnesium: Magnesium is determined by the titration of its quinolate, proposed by Berg. Magnesium is precipitated in an ammoniacal medium with the alcoholic solution of oxine (8-hydro-xyquinolin). The precipitate is filtered and then dissolved with a little hydrochloric acid, and it is titrated with the standard solution of potassium bromate, a few drops of indigo-carmin or methyl red being added as indicator.
Magnesium can be almost completely separated from calcium with oxine. As for the magnesium determination of water containing less than 20mg of calcium per litre, this method appears to be quite useful, and also it seems to be suitable for the routine work in limnology.