K. J. Ru.SSELL AND A. AlM'I.KVAKD 43 



sliding oil a fixed brass rod {(i) in front of the water jaeket (F) wliic-h 

 surrounds the measuring tube, and an electric liglit Ijeliind, enable 

 accurate readings to be taken. The laboratory vessel also allows of 

 analyses being made by absorjition with small quantities of reagents. 

 A simple apparatus for teaching purposes. For teaching and demon- 

 stration purposes the apparatus in Fig. 17 is very useful. A piece of 



1 



A 



Fig. 17. A]>paratus for demonstrating the pressure of CO.; in soil air. 

 .1-1, aspirator. B, |" gas pipe driven into .soil. 



C, tube of saturated bar3rta water open to air. 



D, „ „ „ „ connected to soil. 



half inch gas pipe is driven 6 inches into the soil and connected through 

 a tube of baryta water to a large bottle of water fitted with a syphon 

 tube so that it can act as an aspirator. A second tube of baryta water 

 open to the atmosphere is also attached to the bottle. Set the aspirator 

 going and arrange the clips so that air bubbles pass through both baryta 

 tubes at the same rate. In a short time the one connected with the 

 soil shows turbidity while the other open to the air is still clear. 



