BEHAVIOR OF SOME SOIL INSECTS. l6l 



Glass Y's were inserted in each air line between the aluminum 

 coils and the apparatus for regulating the air flow. By means of 

 these Y's, cross connections of the different air lines could be made 

 or carbon dioxide could be introduced into the air. The carbon 

 dioxide was obtained from a tank of compressed carbonic acid 

 gas. The pressure was reduced and regulated by the use of a 

 pressure reducing valve. The gas passed from the pressure 

 gage through a rubber tubing to a two-way valve. By regulating 

 the size of these openings different proportions of the gas could 

 be passed into any two of the three air lines. The percentage of 

 carbon dioxide in the air was determined by collecting the mix- 

 ture in a burette over water and absorbing the carbon dioxide 

 with a solution of sodium or potassium hydroxide in a Hemple 

 pipette. Only a little work was done with ammonia and no 

 method was used for determining the per cent, in the air. Dif- 

 ferent gradients of ammonia air were secured by bubbling the 

 air in each of two lines through water bottles containing 1,000 

 c.c. of water to which had been added 30 c.c. and 60 c.c. respec- 

 tively of a i/ioN solution of ammonia. Air from each of these 

 lines turned moist litmus paper in a few seconds. 



The apparatus for measuring and regulating the air flow, in the 

 different thirds, of the cage, is new and was designed by Professor 

 V. E. Shelford and the writer. The principle involved is that 

 of measuring, by means of an inclined manometer, the static 

 pressure produced in a box or cylinder when the outlet is smaller 

 than the inlet. The apparatus, Fig. I, consists of three similar 

 parts, one part for each third of the cage. The air enters the 

 cylinders through the back, first, however, passing up to the top 

 of the back-board where there is a screw-clamp for regulating 

 the flow. Fig. 2 is a diagrammatic longitudinal section of the 

 cylinder showing its connections with the inclined manometer. 

 The cylinder is divided into two halves, each 3 inches long and 

 3 inches in diameter, which are constructed with a rim around 

 the outside of the adjacent ends in such a way that they can be 

 fastened together with thumbscrews. A thin circular diaphragm 

 or disk, with a small hole in the center, is placed between the 

 two adjacent ends and the connections are made air tight by a 

 rubber gasket on each side. The opposite ends of the cylinder 



