160 
to deliver 50. c.¢. of air per minute at a depth of 15 cm. in a 4 per cent. 
Ixnops 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. ¥ 
