Photochemical activity of ultra-violet light: Anon. (Metallurgical and chemical engineering, vol. 18, no. 1, p. 43, January 1, 1918)
- Publisher
- Elsevier Science
- Year
- 1918
- Tongue
- English
- Weight
- 75 KB
- Volume
- 186
- Category
- Article
- ISSN
- 0016-0032
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✦ Synopsis
I918.)--The photochemical activity of invisible light-waves existing beyond the visible violet of the spectrum has long been a recognized fact, and considerable research has been made to determine the nature and extent of the reactions produced. The shortest wave-length of light perceptible to the eye is about o.39(x)]~ , in the violet end of the spectrum. Rays of shorter wave-length vary in their activity and effect. Berthelot divided them into four groups : ( I ) Wave-lengths 0. 4 to o.3~, comprising the ultra-violet rays that reach the earth's surface in sunlight. These rays are similar to the violet raysof the visible spectrum.
(2) Wave-lengths 0. 3 to o.2~, medium rays of strong photochemical effect, producing marked chemical and physical changes. (3) Wavelengths 0.2 to o.I5~ , useful in synthetic processes. (4) Wave-lengths o.15 to o.I~, comprising an ultra-violet region which is little known.
Among the physical and chemical effects produced by ultra-violet light are many of practical value, affording quick tests for certain properties, and acceleration of certain chemical reactions. The sterilization of liquids such as water and milk, and of semi-solids like edible fats, is readily accomplished by ultra-violet rays. Exposure of only a fraction of a second under proper conditions is required for complete sterilization. Most dyes fade rapidly under treatment with ultra-violet light, and some remain fast. Fabrics like cotton, rubber, oil-cloth, etc., reveal in a comparatively few minutes the deterioration that otherwise would not become apparent for days in ordinary light. Numerous organic substances are bleached by its action.
Chemical reactions produced by ultra-violet light are many and varied. Chlorine derivatives of toluol are produced in greatly increased yields and without undesirable by-products if the reaction proceeds in the presence of ultra-violet rays. Other chlor-substitution organic products are formed with greater facility, in greater quantity, and of higher degree of purity if ultra-violet light enters into the reaction. The halogen elements generally seem sensitive to this force and enter into synthetic reactions rapidly under its influence. Cyanogen is converted into para-cyanogen, sulphur and phosphorus show allotropism, organic compounds undergo isomeric changes, hydrolytic reactions are accelerated, and numerous other changes occur under influence of ultra-violet rays.
The production of these rays in a manner suitable for application in the arts has been the subject of considerable invention. They are given off in concentrated form from a mercury-vapor lamp, but, since glass is impervious to them, it is necessary to construct the lamp of quartz if the rays are to be used.
An improved form of quartz mercury-vapor lamp which embodies new features in construction and application is manufactured by the R. U. V. Company, New York City. This lamp produces an ultra-violet component several tirnes stronger than that yielded by other forms of quartz mercury-vapor lamps. The wave-lengths of its light have been measured as low as o.I8~, indicating a high degree of activity according to Berthelot's classification given above.