AYERS AND JOHNSON: DESTRUCTION OF BACTERIA 



161 



from 3000 to 2000 Angstrom units possessed a powerful bacteri- 

 cidal power and have endeavored to make a practical use of this 

 fact. Water when clear has been successfully treated by the ultra- 

 violet rays but when appUed to milk the attempts to obtain a 

 sterile product have not been so successful. 



The object of the present work has been to determine if it is 

 possible to steriUze milk by the ultraviolet rays and also how 

 practicable the process would be. 



In these experiments milk was exposed over two drums revolv- 

 ing in troughs in such a manner that milk was picked up from a 

 trough in a thin layer by one drum, then taken off by a scraper 

 and conveyed to a second tank where it was picked up by the 

 second drum. After going over the second drum, the milk was 

 collected by a second scraper which conveyed it to a sterile flask. 



This apparatus enabled us to obtain layers of milk of different 

 thicknesses by rotating the drums at various rates of speed which 

 also, of course, varied the length of exposure. 



The ultraviolet rays were generated by a quartz mercury 

 vapor lamp operating on a 220 volt direct current circuit taking 

 3.5 amperes. The light tube of the lamp was at a distance of 

 four inches above the surface of the drums. In general, it may 

 be said, that the thickness of the layer of milk exposed averaged 

 about 0.1 mm. The length of exposure over the two drums 

 was about two seconds, when the drums were making 20 to 24 

 R.P.M. and about one second at 50 to 56 R.P.M. 



