Gravimetric Analysis

Gravimetric Analysis. Quantitative analysis - i.e. the determination of the amounts of the several known constituents present in a compound substance or mixture of substances - may be divided into two great branches, volumetric and gravimetric analysis. In the latter the determination is made by converting the particular constituent which is to be determined into some form of combination, the composition of which is accurately known, which can be obtained pure from the original substance, and the weight of which can be accurately determined. Thus, suppose it were required to determine the quantity of e.g. sulphuric acid combined with metals in a sulphate, a known weight of the substance would be dissolved in dilute hydrochloric acid and a solution of barium chloride, BaCl2, added. By this means a white precipitate of sulphate of barium is obtained, which can be collected on a filter paper, dried, and heated strongly, so that no moisture remains, and the paper is completely burnt. As the resulting mass contains 41-2 per cent. of SO,, or corresponds to 42-1 per cent. of sulphuric acid, the quantity of this acid in the original body is easily determined.