Light-sensitive paper, making

Make some more light-sensitive paper for the experiment on page 83. Don t make any images on this batch, though. Just soak some index cards in a sodium chloride solution, then in a silver nitrate solution, let them dry in a dark place, and store them in a black envelope. 

Turnbull s Blue. An inorganic blue pigment made by the reaction of a ferrous salt and potassium ferricyanide [Fe3Fe(CN)6]2. One of its important uses is in making blueprints, in which sensitized paper containing ferric ammonium citrate and potassium ferricyanide is exposed to light, the ferric ions being thus reduced to ferrous ions. 

---