Hyposulphates, and Hyposolphites, compounds, the one of hyposulphuric and the other of hyposulphurous acid, with bases. Of these salts the only one of much interest is the hyposulphite of soda, which possesses the property of readily dissolving the chloride, bromide, and iodide of silver. It has been of great service in the preparation of daguerreotypes and photographs, being used to dissolve the sensitive salt of silver which remains unchanged after its exposure in the dark chamber of the camera. In chemical analysis also it is employed to distinguish between the earths strontia and baryta, precipitating the latter from its Solutions, but not the former. It has moreover been adopted as a medicine, and been found beneficial in cutaneous affections, in visceral obstructions, and in disease of the stomach attended with yeasty vomiting. The salt is prepared as follows: A pound of dry carbonate of soda, finely pulverized, is mixed with five ounces of flowers of sulphur, and the mixture is slowly heated until the sulphur melts. By constant stirring exposed to the air the sulphide of sodium, which first forms, is converted into sulphite of soda. This is dissolved in water and filtered.
The hot solution, concentrated by boiling, is then saturated with sulphur and allowed to cool, when it deposits large transparent crystals, which are the hyposulphite of soda, of composition represented by the formula Na2S2O3 + 5H2O. These are soluble in water, but not in alcohol. The hyposulphite of soda is the anti-chlor employed by paper makers for removing the last traces of chlorine from the bleached pulp. A delicate test for the presence of hyposulphurous acid is the brown red color produced by a few drops of perchloride of iron. - The hyposulphites, and especially the hyposulphite of soda, have been used in medicine for the destruction of animal and vegetable parasites and the arrest of fermentation. The diseases to which they have been applied are not only those which are demonstrably connected with parasitic growth or fermentation, as yeasty vomiting and parasitic affections of the mouth and skin, but also those where similar processes may be supposed to be essential factors; such are intermittent and other forms of malarial fevers, typhoid, purulent infection, glanders, cholera, and the contagious exanthemata.
Although favorable reports have been made of their action, general experience does not as yet appear to justify the hopes founded on theory, or the confident expectations of the physician most widely known as the originator of the treatment, Dr. Polli of Milan. No harm, however, has resulted from them, and the presumption in their favor is strong enough to justify their employment in connection with other treatment. The hyposulphite of soda may be given in doses of 10 or 20 grains, or more, three times a day, dissolved in water. The action of the sulphite is identical with or analogous to that of the hyposulphite, and it has been used for the same purposes.