(2) A similar oxide (flores jovis) is produced by burning tin in air at high temperatures or exposing any of the hydrates to a strong red heat.
Davy, inspired by his successful isolation of the metals sodium and potassium by the electrolysis of their hydrates, attempted to decompose a mixture of lime and mercuric oxide by the electric current; an amalgam of calcium was obtained, but the separation of the mercury was so difficult that even Davy himself was not sure as to whether he had obtained pure metallic calcium.
When substances readily combine with water to form hydrates, the heat of solution in water is usually positive; when, on the other hand, they do not readily form hydrates, or when they are already hydrated, the heat of solution is usually negative.
The alkalis are used almost exclusively in the condition of caustic lyessolutions of their respective hydrates in water.
Tin and antimony (also arsenic) are converted by it (ultimately) into hydrates of their highest oxides Sn0 2, Sb205 (As 2 O 5) - the oxides of tin and antimony being insoluble in water and in the acid itself.
