Johann Heinrich Schultz is credited with the discovery that certain silver salts, most notably silver chloride and silver nitrate, darken in the presence of light. In an experiment conducted in 1724 he determined that a mixture of silver and chalk reflects less light than untarnished silver. Though his discovery did not provide the means of preserving an image - the silver salts continued to darken unless protected from light - it did provide the foundation for further work in fixing images by such researchers as Thomas Wedgewood and Sir Humphrey Davy. Silver chloride (also called silver(I) chloride) is a chemical compound with chemical formula AgCl. ... Silver nitrate is a chemical compound with chemical formula AgNO3. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye, or in a more general sense, any electromagnetic radiation in the range from infrared to ultraviolet. ... Events January 14 - King Philip V of Spain abdicates the throne February 20 - The premiere of Giulio Cesare, an Italian opera by George Frideric Handel, takes place in London June 23 - Treaty of Constantinople signed. ... General Name, Symbol, Number silver, Ag, 47 Chemical series Transition metals Group, Period, Block 11, 5, d Density, Hardness 10490 kg/m3, 2. ... The Needles, part of the extensive Southern England Chalk Formation Chalk is a soft, white, porous form of limestone composed of the mineral calcium carbonate. ... Humphry Davy Sir Humphry Davy (December 17, 1778 - May 29, 1829), often incorrectly spelled Humphrey, was a Cornish chemist. ...