Ammonium sulphate, crystal isomorphism with potassium

Silver chromate is almost insoluble in water, glacial acetic acid, and in solutions of potassium chromate, but soluble in those of ammonia, caustic alkalies, nitrates, and in dilute acetic acid. A concentrated solution of ammonium nitrate is a good crystallising medium for silver chromate. With chlorine, above 200° C., silver chloride, chromium trioxide, and oxygen are produced. The solution in ammonia contains the compound Ag2Cr04.4NH3, which forms crystals isomorphous with the corresponding ammoniacal sulphate. ... 

Potassium sulphate and ammonium sulphate are two isomorphous salts when masses of these two salts are left a long time in contact with an aqueous solution the crystals of both cease to be distinct, and at last there rest only mixed cr3rstals, containing both sulphate of potassium and ammonium sulphate. 

Rudorff s experiments, compared with the theorems of J. Willard Gibbs, show us that the mixed crystals should be considered not as two phases, but as a single phase these crystals are not therefore, as many writers have supposed simp y mechanical mixtures, a juxtaposition or a mixing of crystalline particles of potassium sulphate and cr3nstalline pa tides of ammonium sulphate in them the two component salts are physically mixed in a manner as intimate as for an aqueous solution every volume, however small which may be cut from one of these crystals, contains a certain quantity of each one of these salts these mixed crystals, formed by two isomorphous bodies, constitute, according to the... 

The octahedral, cubic crystals are violet to black in colour, and appear ruby-red in thin layers and J. H. Kastle found that the intensity of the colour is very much reduced at liquid air temp. F. Klocke, C. F. Rammelsberg, C. von Hauer, and J. W. Retgers showed that the crystals are isomorphous with other alums, for they show similar corrosion figures. E. Dittler obtained overgrowth with potassium aluminium sulphate. T. V. Barker found a close connection between parallel overgrowths in chrome-alum, potash-alum, and ammonia-alum and the mol. vols which are respectively 542-2, 541-6, and 552-2. C. von Hauer found that with the introduction of a crystal of iron-alum in a sat. soln. of chrome-alum nearly all the latter separates out while L. de Boisbaudran found that a sat. soln. of basic ammonium aluminium alum does not affect the octahedral faces of the... 

Mitscherlich also measured the angles of the crystals of double sulphates of potassium and ammonium with magnesium, ferrous iron, manganese, zinc, copper, cobalt and nickel. This established the isomorphism of potassium and ammonium sulphates. He found that the double potassium sulphates had one proportion of water more than the double ammonium sulphates, and also obtained a salt crystallising in beautiful and large octahedra with exactly the same composition as alum but containing ferric oxide instead of alumina (ferric alum). He says he hoped to show that a study of crystallisations would give the compositions of bodies as certainly and definitely as chemical analysis . A letter from Humboldt to Mitscherlich said this beautiful work had exposed the incorrectness of Haiiy s view. ... 

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