1750. J. Dolland, London, first made double achromatic compound lenses.
1757. Chloride of silver made by J. B. Beccarius.
1774. Dr. Priestly discovered ammonia to be composed of nitrogen and hydrogen; but ammonia is as old as the first decomposition of organic matter.
1777. Charles William Scheele observed that the violet end of the spectrum blackened chloride of silver more rapidly than the red end. Chlorine discovered.
1779. Oxalate of silver made by Bergmann.
1789. Uranium obtained from pitch-blende by Klaproth.
1791. Thomas Wedgwood commenced experiments with a solution of nitrate of silver spread upon paper and white leather, and obtained impressions of semi-transparent objects and cast shadows. Sir Humphry Davy joined him later.
1797. Nitrate of silver on silk by Fulhame.
1799. Hyposulphite of soda discovered by M. Chaussier.
1800. John William Ritter, of Samitz, in Silesia, observed that chloride of silver blackened beyond the violet end of the spectrum, thus discovering the action of the ultra violet ray.