242 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 



dier * has shown, by means of his chromo-actinometer, that every 

 quartz mercury-vapor lamp gradually loses its power of giving out 

 ultra-violet rays because of the increasing opaqueness of the quartz 

 tube. At the end of a service of about 500 hours, he states, the 

 lamp emits only one-seventh of its original quota of these rays. 

 This defect is without remedy and therefore decisive. If his results 

 are real, then immersion is necessary for cooling the lamp, so as to 

 prevent this change. 



Immersion, therefore, has these advantages, economy and long 

 service. 



It may be objected that since the immersion cools the lamp, with a 

 given current of electricity there will be a smaller amount of ultra- 

 violet rays emitted. This would be expected in accordance with the 

 results of Retchinsky (1906). However, a lamp thus cooled can be 

 made to emit just as much ultra-violet radiation as a warm lamp 

 (new and unused, see the experiments of H. Bordier) if a greater cur- 

 rent of electricity is used. The increased cost of this greater current 

 is practically of small importance compared with the increased 

 efficiency of the immersed lamp where all the radiation is utilized. 

 That is, though an immersed lamp uses a greater amount of elec- 

 tricity, it will sterilize a far greater amount of water. 



To sum up: The immersion of the lamp, economically considered, 

 is preferable. If the results of Bordier are confirmed, immersion will 

 be the only method giving a long life to the sterilizing power of 

 the lamps. 



NATURE OF THE PROCESS OF STERILIZATION OF WATER BY THE ULTRA- 

 VIOLET RADIATIONS. 



The ultra-violet rays kill the microbes in the water by a direct 

 bactericidal action, and not indirectly by a chemical modification of 

 the water. 



It might at first have been surmised that the sterilization was due 

 to the production of ozone. That is wholly untrue. With Th. 

 Nogier and Rochaix, 3 I have shown that during the time required 

 for sterilization (only a few seconds or a minute) not even a trace of 

 ozone was produced. If with a longer time it is produced, it would 

 be after sterilization had occurred and have nothing to do with the 

 latter process. It would never occur in practice. The production 

 of ozone is a separate laboratory process. Moreover, sterilization 

 will take place in the absence of oxygen. (Cernovodeanu and V. 

 Henri.) 



i H. Bordier, Quanti tome trie des rayons ultra-violets. Archives El. Med., No. 285, p. 396. 

 s J. Courmont, Th. Nogier et Rochaix. C. R. Ac. des Sciences, 12 juillet 1909. 



