THE STERILIZATION OF DRINKING WATER BY ULTRA- 
- VIOLET RADIATIONS: 
By Dr. Jutes 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 potable water. 
THE ULTRA-VIOLET RADIATION—THE QUARTZ MERCURY-VAPOR LAMP. 
A few general data will be first stated. The wave lengths (A) of 
light rays are generally measured in units which have received the 
designation of Angstréms (A. units). The Angstrém 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. units. 
erasiat, OF pie ta fener PEON at Bs oe eh ed oS oon a PSS de ta apie enb se 600. 000 
Solar spectrum: 
REN OO LEC UERET TOG tet Rt oe aad ae Nig wa Rtgeyy ayia emma ee 300. 000 
Limit of the visible red....-.-..- aM NS p fop adee 1M tetas Mp ns as Bie 7.610 
Lamatot the Visible vadletie cto EE DRA OU OS AOU eS 3. 970 
Lamith cmabe tilira-violetixs. Ay sisehe Salas tad. Kaa Tee eSh 3 2. 950 
Upper limit of the very bactericidal ultra-violet. ..............- Sates me 2. 800 
Metallic spectra: 
iitertor luWit OL the mercury spectrum... 2 es s<seenc nerve ede ste aue 2. 225 
iieniotaine metallic wltrasviolete +. Oi tae ees ee oe Res aU 1. 200 
Ordinary gas spectra: . 
inst ofithevextreme witra-vaoletis: .22820 Sl .bsd hk cbocs. Bcpeee-- 1. 039 
1 Translated by permission from Revue générale des Sciences pures et appliquées, Paris, April 30, 1911, 
pp. 332-338. 
