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ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 



is solved through the use of such apparatus as we have described 

 using ultra-violet radiations. That of the sterilization of very great 

 quantities of water, as in the case of a city's supply, is now under study 

 but very near solution by the same means. 



CAN ALL LIQUIDS BE STERILIZED BY THE ULTRA-VIOLET RAYS? 



To this question I must answer, No. With Th. Nogier, I have 

 shown that substances rich in colloidal matter (wine, beer, cider, 

 bouillon, peptonized solutions, etc.) absorb very rapidly the ultra- 

 violet radiation. 1 Tins radiation will penetrate only a few millimeters 

 or fractions of a millimeter of such liquids, which therefore are not 

 sterilized. Even in the case of the most limpid beer, the clearest 



Fig. 2.— Vessel holding 115 liters for experiments on the sterilisation of water. 



white wine, a peptonized solution as transparent as water, steriliza- 

 tion does not result. Indeed, such liquids may be sterilized in the 

 laboratory either by exposing them in very thin layers or by stirring 

 them so that every portion comes in contact with the lamp. The 

 practical results of such methods are negligible; such sterilization 

 would be too costly. 



The water for our method must be clear; a muddy water would 

 not be sterilized. It would have to be filtered before entering our 

 apparatus. 



And so clear water is practically the only known liquid permeable 

 to the ultra-violet radiation and easily sterilized by it. 



1 J. Courmont et Th. Nogier, Sur la faible penetration des rayons ultra-violets a travers les liquids conte- 

 nant des substances colloides. Ac. des Sciences, 2 aoiit 1909. 



