160 



to deliver 50. c c. of air per minute at a depth of 15 cm. in a J per cent. 

 Knops solution at the expense of 50 c. c. of water. At this rate less than 20 

 gallons of water per day would be used with the apparatus running con- 

 tinually. 



The apparatus as now in use is designed for the aeration of water cul- 

 tures, but its wide range of adjustment and its economy will permit its 

 being used for many other purposes. Various devices may be attached at H 

 for changes of temperature, humidity, or chemical nature of the air, pro- 

 vided that allowance be made for the increased pressure that may be 

 necessary. 



Where it is desired that the stream of air be carefully guarded from 

 outside contamination, this apparatus is clearly the superior of any by 

 means of which the air is drawn through tubes by an aspirator at the end, 

 for it is a decided advantage in such cases to have the pressure, which 

 determines the direction of any possible leakage, outward rather than 

 inward. 



Indiana University, 



Bloomington, Indiana. 



