Platinocyanide, barium

By double decomposition of the metallic sulphate with barium platinocyanide solution. Thus, for example, the magnesium salt was first prepared by Martius as follows ... 

It is not easy to account for this isomerism according to the ordinary methods of representation of the structure of the platinocyanides. Since samples of anhydrous barium platinocyanide, derived from the isomeric tetrahydrates respectively, are equally fluorescent, it seems fairly certain that any scheme must take into consideration the combined water. Levy therefore suggests that the isomerism of the tetra-hydrate may be accounted for by assuming that two molecules of water are attached to the barium and two to the platinocyanide radicles, since, in the case of the latter radicles, two alternative positions are possible, namely ... 

Aluminium Platinocyanide, Al2[Pt(CN)4]3, is prepared by addition of an aqueous solution of aluminium sulphate to one of barium platinocyanide. The barium sulphate is removed by filtration and the clear liquid allowed to crystallise. The salt separates out in blue, deliquescent laminse.3... 

Barium platinocyanide tetrahydrate can exist in two isomeric forms, which, however, are crystallographically identical. They differ in colour, density, and in fluorescence, as indicated in the following table 2 ... 

When a solution of barium platinocyanide is allowed to crystallise after adding a trace of barium cyanide or barium hydroxide to it, crystals of the green 8-salt axe obtained. If, on the other hand, a trace of hydrogen cyanide, hydrogen chloride, tartaric or acetic acid, or cyanoplatinous acid is present instead, crystals of the yellow a-salt are deposited. 

Barium platinocyanide, after prolonged exposure to radiation from radium compounds, becomes brown or red and loses its fluorescent properties. The only way to completely restqje the red crystals to their fluorescent state is by solution and recrystallisation,1 although gentle heating will partially restore them. This is well illustrated by the following table ... 

Levy5 has shown that two isomeric varieties of the pentahydrate exist, analogous to the two isomerides of the tetrahydrate of barium platinocyanide. The a-salt may be described as golden yellow with green fluorescence on the pyramid faces, whilst the (3-salt shows a green fluorescence on all faces, which is particularly intense on the tops of the crystals. The crystalline characters of the two isomerides are identical. 

The a-salt is obtained by crystallisation from a solution containing a small quantity of acid, and the (3-salt from one containing some hydroxyl or cyanide ions, precisely as in the case of the a and [3 barium platinocyanides. 

Indium Platinocyanide, In2[Pt(CN4)]3.2H20, is prepared3 by boiling solutions of barium platinocyanide and indium sulphate together, filtering off the barium sulphate and allowing to crystallise out. It yields white, hygroscopic leaflets. 

Potassium Barium Platinocyanide, BaK2[Pt(CN)4]2.Aq, is obtained by crystallising mixed solutions of barium and potassium platino-cyanides. In appearance it resembles the sodium potassium salt.3... 

Radium Barium Platinocyanide.—-Since the majority of platino-cyanides fluoresce under the influence of radiations from radioactive substances, the radium salt should be self-luminous. The radium barium salt was prepared1 by dissolving radioactive barium chloride in water and boiling the solution with excess of silver platinocyanide. After filtering off insoluble silver salts the solution was allowed to crystallise in a desiccator. 

The crystals deposited last were reddish in colour, and brightly luminous at first, but the intensity of their luminosity gradually diminished, and the reddish tint deepened in colour. No doubt this is attributable to alteration of the barium platinocyanide in the complex, since the free salt upon exposure to radium radiations undergoes some change, resulting in a weakening of the fluorescence as has already been pointed out (see p. 321). 

Uranyl Platinocyanide, U02.Pt(CN)4.4(or 5)H20, has been prepared 6 by double decomposition of solutions of uranyl sulphate and barium platinocyanide. The green, filtered solution, upon evaporation at room temperature in a desiccator, deposits red crystals possessing a strong green metallic reflection. 

Rontgen s critical discovery was made in 1895 when he happened to observe that, as a cathode-ray tube was being operated in a darkened room, paper covered with barium platinocyanide lying some distance from the tube lit up with brilliant fluorescence. The fluorescence of barium platinocyanide was used at that time to establish the presence of invisible rays of the solar spectrum (such as ultraviolet). However, on this occasion, the tube had been surrounded by a close-fitting shield of black cardboard, quite opaque to ultraviolet light or sunlight. 

FIG. 21, X-ray apparatus used by Rontgen consisted of (A) high-voltage induction coil (B) paper painted with barium platinocyanide, which glowed when struck by rays (C) the tube surrounded with a cylindrical black cardboard cover (D) the cathode, which emitted electrons. 

If the (much dearer) chemical, barium platinocyanide be used, tne phosphorescence is much stronger and of a greenish tinge. It is with this chemical that X Ray screens are coated. Another chemical almost equally brilliant (phosphorescing blue) is potassium platinocyanide it is also equally dear. 

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