This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
Magnesite contains about 52 per cent. of its own weight of carbonic acid. It is "carbonate of magnesia," that neutral salt which is very frequently and in great quantities found in North America and Europe. It is a white, hard mineral, and is decomposed even by strong acids but slowly, and the generating of gas takes more time than with any other material. It is, therefore, advantageous only when continuous apparatus is used. As ground powder it is frequently used in Europe in the manufacture of mineral waters, and is one of the most excellent and pure materials. In the United States it is too expensive, and marble dust and whiting comparatively so low in price, that it never may take an important place among the materials for producing carbonic acid gas in the mineral-water trade.
Magnesite is decomposed by the action of concentrated sulphuric acid. The residue is sulphate of magnesia (Epsom salt).