Termokolory colors are sensitive to temperature changes. The commercially available chemicals under consideration as Ag 2 [HGI 4 ] (reversible change yellow red at about 60 ° C) and Cu 2 [HgI 4 ] (red black reversible change at about 90 ° C).
The starting material for the preparation of these termokolorů is HgI 2
Preparation of Cu2[HgI4]
In 25 ml of water dissolve 3.3 g of potassium iodide and the solution Dissolve 4.5 g of mercuric iodide. To the resulting solution slowly and with stirring add a solution of 5 g of copper sulphate pentahydrate in 40 ml water. The reaction mixture acquires a red color, sometimes with a little eliminate red precipitate. To a solution of introducing 10 minutes gentle stream of carbon dioxide (for example, it is obtained by reacting sulfite and dilute sulfuric acid) - exclude red product. Precipitate was filtered and washed thoroughly with water.
HgI2 + 2KI + 2CuSO4 + SO2 + 2H2O --> Cu2[HgI4] + K2SO4 + 2H2SO4
Instead of carbon dioxide can be added to the reaction mixture, the amount of sulfite.