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.
Sulphate of magnesium should be kept in well-closed vessels. Small, colorless, right-rhombic prisms, or acicular needles, slowly efflorescent in dry air, odorless, having a cooling, saline and bitter taste, and a neutral reaction. Soluble in 0.8 part of water at 15° C. (59° F.), and in 0.15 part of boiling water; insoluble in alcohol. When heated, the salt gradually loses nearly 44 per cent, of its weight (water of crystallization), and at a strong, red heat it fuses, congealing on cooling to a white mass, which amounts to 48.7 per cent of the original weight.
One part by weight of sulphate of magnesium in nine parts of distilled water. Filter. Specific gravity 1.050 at 15° C, containing 10 per cent, of hydrous magnesium sulphate, the commercial salt. Proportion 10 to 1.