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.
It is very seldom found in mineral waters, and then but in trifling quantities. The commercial magnesium nitrate liquifies readily, and is best kept in stock in solution 0r one part by weight in nine parts of distilled water. Filter. Specific gravity 1.075 to 1.076. A ready-made solution may be pre pared as follows: Dissolve 93.25 parts by weight of dry magnesium carbonate in 730 parts of pure nitric acid of 10° Baume, specific gravity 1.0685 at 15° 0.; dilute the neutral liquid to make it altogether 1000 parts of the specific gravity 1.075 to 1.076 at 15° C. This represents a 10 per cent, solution of magnesium nitrate. Of either solution the proportions will be 10 to 1.