Cobalt alums

The cobalt alums are isomorphous with those of iron and aluminium, and therefore, by the application of Mitseherlich s Law, they must be assumed to contain two atoms of cobalt, their generic formula being ... 

Ammonium Cobalt Alum, (bnff4)2S04.Co2(S04)3.24H20, was first prepared by Marshall,4 who, from a peculiar change in colour observed in the electrolysis of a solution of copper-cobalt potassium sulphate, was induced to electrolyse a solution of ammonium and cobalt sulphates, acidified with sulphuric acid in a divided cell. 

Potassium Cobalt Alum, K2S04.Co2(S04)3.24HaO, was obtained by Marshall mixed with potassium sulphate as blue octahedra in a similar manner to the preceding salt. 

Rubidium Cobalt Alum, Rb2S04.Co2(SO4)3.24H2O, and Csesium Cobalt Alum, Cs2S04.Co2(S04)3.24H20, have likewise been prepared by electrolysis,6 the alums forming at the anode. They crystallise out as minute, deep blue octahedra, stable in dry air, but decomposing in... 

CoS04,7H20. Few cobalt(III) oxy acid salts are known. 002(504)3,ISHjO is formed by electrolytic oxidation and forms alums Co(N03)3 contains co-ordinated nitrate (C0F3 plus NjOs). 

Hydrated cobalt III) sulphate, Co2(S04)3. JSHjO is obtained when cobalt(II) sulphate is oxidised electrolytically in moderately concentrated sulphuric acid solution it is stable when dry but liberates oxygen from water. Some alums, for example KCo(S04)2.12H,0 can be obtained by crystallisation from sulphuric acid solutions. In these and the sulphate, the cation [CofHjO) ] may exist it is both acidic and strongly oxidising. 

Despite the above similarities, many differences between the members of this triad are also to be noted. Reduction of a trivalent compound, which yields a divalent compound in the case of cobalt, rarely does so for the heavier elements where the metal, univalent compounds, or hydrido complexes are the more usual products. Rhodium forms the quite stable, yellow [Rh(H20)6] " ion when hydrous Rh203 is dissolved in mineral acid, and it occurs in the solid state in salts such as the perchlorate, sulfate and alums. [Ir(H20)6] + is less readily obtained but has been shown to occur in solutions of in cone HCIO4. 

Chemical precipitation is used in porcelain enameling to precipitate dissolved metals and phosphates. Chemical precipitation can be utilized to permit removal of metal ions such as iron, lead, tin, copper, zinc, cadmium, aluminum, mercury, manganese, cobalt, antimony, arsenic, beryllium, molybdenum, and trivalent chromium. Removal efficiency can approach 100% for the reduction of heavy metal ions. Porcelain enameling plants commonly use lime, caustic, and carbonate for chemical precipitation and pH adjustment. Coagulants used in the industry include alum, ferric chloride, ferric sulfate, and polymers.10-12... 

Cesium is determined as the tetraphenylborate, total cobalt as the anthranilate, sulfate as barium sulfate, and cobalt(III) by addition of the alum to excess of potassium iodide solution followed by titration with thiosulfate- Anal. Calcd. -for CsCo(S04)2-12H20 Cs, 22.2 Co, 9.82 S04, 32.0. Found Cs, 22.2 Co, 9.83 S04, 32.3 Co(III), 9.80. 

A powder which burns with a green flame is obtained by the addition of nitrate of baryta to chlorate of potash, nitrate of potash, acetate of copper. A white flame is made by the addition of sulfide of antimony, sulfide of arsenic, camphor. Red by the mixture of lampblack, coal, bone ash, mineral oxide of iron, nitrate of strontia, pumice stone, mica, oxide of cobalt. Blue with ivory, bismuth, alum, zinc, copper sulfate purified of its sea water [sic]. Yellow by amber, carbonate of soda, sulfate of soda, cinnabar. It is necessary in order to make the colors come out well to animate the combustion by adding chlorate of potash.15... 

An interesting scries of salts is afforded by the alums of trivalent iron, cobalt, rhodium, and iridium. These have the general formula... 

Both iron and cobalt, when trivalent, yield stable double sulphates with ammonium and the alkali metals, containing twenty-four molecules of water. These arc known as alums, and to them the general formula MaS04.Ba(S04).).2I.Ha0 may he ascribed. They usually crystallise in well-defined octahcdra. Nickel, on the contrary, does not yield salts of this type, since nickelie sulphate cannot exist. 

Cobalt, rhodium, and iridium yield sulphates of the type R2(S04)a, and these combine with sulphates of the alkali metals to produce alums, of the general formula MaS01.R2(S01)3.24H80. These are well-defined... 

Cobalt Blue consists essentially of oxides of cobalt and aluminium with more or less zinc oxide. It is obtained by calcining a mixture of alum and cobalt sulphate, and is used by artists in painting porcelain. Save for this it has now no commercial value.13 Cobalt blue is also known as Cobalt Ultramarine, Thenard s Blue, and King s Blue. 

Cobaltic sulphate, like the sulphates of rhodium and iridium, unites with the sulphates of the alkali metals to yield a series of well-defined, crystalline salts known as alums. These are isomorphous with those of iron, manganese, chromium, and aluminium, and form an interesting link between these metals and the central vertical column in Group VIII of the Periodic Table, of which column cobalt is the first member. 

Rhodium, like cobalt, iron, and aluminium, yields a well-defined series of alums. Application of Mitscherlich s Law of Isomorphism indicates that these have the general formula ... 

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