THE STERILIZATION OF DRINKING WATER BY ULTRA- 

 VIOLET RADIATIONS. 1 



By Dr. Jules Courmont, 

 Professor of Hygiene in the Faculty of Medicine of Lyon. 



That solar light is capable of killing bacteria has been recognized 

 by Downes and Blunt, S. Arloing, Duclaux, and others. This action 

 is due to the ultra-violet portion of sunlight, that is, to the waves of very 

 small length, which are manifested by their chemical action rather 

 than their power of producing heat. Solar light, however, is rather 

 poor in ultra-violet rays, for they are to a great extent absorbed 

 by our atmosphere. Indeed their very limited bactericidal power 

 is scarcely comparable with the very great power possessed by the 

 untra-violet radiation given out by some artificial light sources, 

 notably by the mercury-vapor lamp, whose containing tube is made 

 of quartz. Only such sources as the latter are of practical applica- 

 tion to the sterilization of Dotable water. 



THE ULTRA-VIOLET RADIATION THE QUARTZ MERCURY-VAPOR LAMP. 



A few general data will be first stated. The wave lengths (X) of 

 .light rays are generally measured in units which haVe received the 

 designation of Angstroms (A. units). The Angstrom unit is equal 

 to 0.0000000001 meter. The following table gives the wave lengths 

 of a few different places in the spectrum: 



Spectrum of the Welsbach light: a. un it s . 



Limit of the infra-red GOO. 000 



Solar spectrum: 



Limit of the infra-red 300. 000 



Limit of the visible red 7. 610 



Limit of the visible violet -. . 3. 970 



Limit of the ultra-violet 2. 950 



Upper limit of the very bactericidal ultra-violet 2. 800 



Metallic spectra: 



Inferior limit of the mercury spectrum 2. 225 



Limit of the metallic ultra-violet ] . 200 



Ordinary gas spectra: 



Limit of the extreme ultra-violet 1. 030 



i Translated by permission from Revue generale des Sciences pures et appliqudes, Paris, April 30, 1911, 

 pp. 332-33S. 



235 



