Potassium sulphate, isomorphism

The rhombic bipyramidal crystals of potassium sulphate form an isomorphous group with those of the corresponding salts of rubidium and csesium. The axial ratios and mol. vol. are indicated in Table XXXVI the axial ratios and topical parame.ters of the three last-named salts were determined by A. E. H. Tutton.26... 

Certain halogen salts appear to be isomorphous with potassium sulphate and able to form alums with aluminium sulphate thus,... 

The anhydrous sulphate is a constituent of oceanic salt deposits, and is called thenardite. An isomorphous mixture with potassium sulphate is known as glaserite a double salt with magnesium sulphate as astrakanite, and with calcium sulphate as glauberite. 

Rubidium sulphate, Rb2S04.—The sulphate forms rhombic crystals isomorphous 2 with those of potassium sulphate, melting3 at 1074° C., the density at 20° C. being 3-6113, and at 60° C. 3-5943.4 It exists in two modifications,5 the transition-point being 657° C. The heat of formation from the elements is 344-68 Cal., and the heat of solution —6-66 Cal. at 15° C.6 The solubility 7 is given in the appended table ... 

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 solutions rich in potassium sulphate give mixed isomor-phous crystals of potassium sulphate the solutions rich in sodium sulphate give mixed isomorphous crystals of sodium sulphate fin y, intermediate solutions give a double salt whose formula is... 

E. Grosohufi placed the transition temp, at 666° and A. Hare, at 660°. The a-form is stable above 666°, and is completely miscible with the hexagonal form of potassium sulphate so that the high temp, form is itself hexagonal as the ordinary or j3-form of potassium chromate is completely miscible with the 8-form of potassium sulphate. Neither the f.p. cruwe, nor the transition curves. Fig. 42, shows a maximum or minimum. M. Amadori obtained a similar equilibrium diagram. Yellow potassium chromate, stable at ordinary temp., is isomorphous with potassium sulphate, and, therefore, cannot be separated from that salt by fractional crystallization. W. von Behren and J. Traube studied the dissolution and crystallization of the salt. R. KoUmann, G. Tammann and A. Sworykin, E. Mitscherlich, P. Groth,... 

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. ... 

This stated that compounds which crystallise in the same form (i.e. are isomorphous) are similar in atomic composition, and he quoted as examples the sodium phosphates and arsenates, in which an arsenic atom takes the place of a phosphorus atom. Mitscherlich used the fact that potassium selenate was isomorphous with potassium sulphate to deduce the formula of potassium selenate, and hence determine the atomic weight of selenium. Berzelius used the isomorphism of the sulphates and the chromates as evidence that the formula of anhydrous chromic acid was CrOj. He suggested that the lower oxide of chromium had a formula of Q2O3, and since this was isomorphous with the oxides of iron and aluminium, he was able to propose correct formulae for these compounds. 

It is not hydrolysed by water but reacts quantitatively with NaOH to yield sodium perchlorate and fluoride. It oxidizes iodides to iodine. Perchloryl fluoride reacts with ammonia to yield ammonium perchlorylamide NH4NHCIO3 [45a]. It reacts with potassium and caesium hydroxide to yield crystalline precipitates of K2NCIO3 and CS2NCIO3. It is isomorphous with metal sulphates, is explosive and very sensitive to flame, shock and friction. 

Isomorphism.—Although potassium telluratc, K./1YO, is not isomorphous with the corresponding sulphate, the hydrogen rubidium salts of sclenic and telluric acids arc isomorphous.7... 

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