Wood Rays

WOOD RAYS (Wood), ultraviolet rays passing through special filters with minimal violet ray admixture. Wood initially (1903) used as filters for radiation from a mercury-quartz lamp solutions of nitroso-dimethyl-aniline salts in quartz cuvettes, which absorbed visible rays with a wavelength greater than 4,000 Å and invisible rays with a wavelength less than 2,700 Å; subsequently the cuvettes were replaced with glass containing nickel oxide. These rays between 3,000 Å and 2,700 Å are Wood rays. Recently Quarz-lampengesellschaft (in Hanau, Germany) has released a filter that attaches to the reflector of a standard Bach lamp, passing only negligible amounts of visible light and ultraviolet rays within the limits mentioned above. The material from which the filter is made is not precisely known; apparently it consists of an alloy of uviole glass with an admixture of nickel salts. Taking advantage of the fact that every body on which invisible rays fall reveals in darkness a characteristic, strictly specific fluorescence for itself, some researchers attempt to apply W. r. for determining the presence of various substances. These rays acquire known significance in forensic-medical investigations, making it possible: to detect the slightest traces of blood, without yielding to the most precise biological reactions; to recognize traces of seminal stains; to macroscopically differentiate bacterial cultures. Thanks to the different fluorescence caused by W. r., it is also possible to distinguish various metals and their salts, true gold from different alloys, true diamonds and pearls from fakes, various grades of fabrics, oils, paints, etc.