STERILIZATION OF OILS 55 



gillus and Mucor, Haughton and Davis (1914) noted only a 

 relatively small destructive effect of ultra violet radiation — in no 

 case greater than 20 per cent. They concluded, therefore, that 

 molds cannot be killed by ultra violet light except when present 

 in very small amounts. 



The method described above of exposing oil in open dishes to 

 the ultra violet radiation in order to produce sterility is not ap- 

 plicable practically. Numerous means suggest themselves of 

 sterilizing a liquid in thin films, such as flowing the oil over a 

 quartz plate placed directly over the source of ultra violet 

 energy, flowing the oil in open troughs beneath the lamp, etc. 

 all of which are limited by the fact that the oil is thus exposed to 

 contamination by dust, or likely to be heated unduly. The 

 method of exposure finally adopted was that of flowing the oil 

 through a spiral tube made of transparent quartz having a 

 bore of 3 to 3.5 mm. and extending the length of the mercury 

 vapor lamp. The oil within the spiral was kept cool by enclos- 

 ing the spiral in a gauze jacket over which ice water flowed 

 from a number of fine jets. With this arrangement, the oil at 

 the point of delivery never exceeded 60° in temperature, although 

 it was exposed at a distance of only one centimeter from the 

 lamp. Oil was fed into the spiral by gravity and the lower end 

 of the spiral extended into a sterile flask so that the oil from the 

 spiral could be collected under sterile conditions. One and a 

 half liters per hour of cotton seed oil can be sterilized with this 

 arrangement. The apparatus set up for use is shown in figure 1. 



With the above arrangement and with the mercury lamp 

 working at 48 to 60 volts, samples of olive oil emulsions of B. 

 siibtilis were run through the spiral, the time of exposure being 

 varied over several minutes. These experiments indicated that 

 eight minutes at a voltage of 48, or three and a half minutes at a 

 voltage of 60, secured effective sterilization. These results indi- 

 cate that the voltage at which the lamp is operating consider- 

 ably influences its effectiveness. The efficiency of the lamp 

 was therefore increased by insulating the cathode with asbestos. 

 By means of this arrangement the voltage across the terminals 

 was increased to 150. 



