Ferrid-cyanide of Potassium. Ferricyanide of Potassium. Into a dilute solution of the above prussiate of potash, a current of chlorine gas is passed, till the solution ceases to give a blue precipitate with persalts of iron. It is then evaporated, crystallized, and recrystallized till quite pure. [M. Posselt advises to add a few drops of solution of potash to the boiling liquor, to decompose the green matter that is formed; to filter the hot solution, to separate some peroxide of iron which is thrown down, and to let the liquor cool very slowly.] Or, boil yellow prussiate of potash with 12 or 15 parts of water, and while boiling add good chloride of lime until a filtered sample no longer yields a blue precipitate with persalts of iron. Filter quickly, and add carbonate of potash till the liquid has a faintly alkaline reaction, then evaporate for crystallization. - Chemist, vol. viii. PRUSSIAN Blue. Berlin Blue. Percyanide,ferrocyanide, or ferro-prussiate of iron. Commercial Prussian blue is made by adding to a solution of prussiate of potash, or of prussiate cake, a solution of 2 parts of alum and 1 of sulphate of iron, washing the precipitate repeatedly with water to which a little hydrochloric acid has been added, and exposing it to the air till it assumes a deep colour. A purer kind is made by adding a solution of persulphate or perchloride of iron to a solution of pure ferro-prussiate of potash. Turnbull's Prussian blue (ferrid-cyanide of iron) is made by adding a solution of red prussiate of potash to one of proto-sulphate of iron; or by adding proto-sulphate of iron to a mixture of yellow prussiate of potash, chloride of sod;;, and hydrochloric acid.