THE HALDANE GAS-ANALYSIS APPARATUS 117 



the mercury assures saturation of the air with water vapor. Time 

 for drainage must be allowed before making readings. 



A very serviceable sampling tube for the transfer of air can be 

 made from a 30 c.c. ground-glass syringe, to which is attached 

 a two-way stopcock. The dead space in these syringes is washed 

 out by working the piston back and forth several times. A thin 

 coating of vaseline prevents leakage of the gas. We have found 

 that these sampling tubes will retain a sample of expired air with- 

 out change up to eight hours. 



Manipulation of Apparatus. The sampling syringe 20 is 

 attached to opening 2 of the burette, and its stopcock 17 opened 

 to atmospheric air. The level of the mercury is raised to the level 

 of the stopcock of the syringe and is then turned so that syringe 

 and burette are in communication. The bulb of mercury is lowered 

 so that the mercury falls in the burette. This draws the piston 

 of the syringe with it, and fills the burette with air from the 

 syringe. It is advisable to put a little positive pressure on the 

 piston of the syringe in the maneuver to prevent possible leakage. 

 When all of the air is in the burette a slight positive pressure is 

 produced in the burette by gently pressing on the piston, and 

 immediately thereafter the stopcock on the syringe 17 is again 

 turned to the original position. This allows the pressure of air 

 in the burette to come to that of the atmosphere. The height of 

 the mercury is now adjusted to a convenient height in the burette 

 by closing cock 7 and turning the milled screw 6. The cock 8 is 

 now made to communicate with the absorption bulbs. If the air 

 in the burette is at atmospheric pressure, no change wih 1 occur 

 in the level of the fluids. The reading is then taken on the burette. 



The next step in the analysis consists in turning stopcock 8 

 to communicate with the caustic soda solution in bulb 9, and 

 the leveling tube 5 is raised, forcing mercury into the burette 

 and the air into bulb 9. The gas is passed back and forth several 

 times until absorption is complete, as can be determined by the 

 fact that the level of the mercury in the burette remains constant 

 when the fluid in the bulb is returned to its original level 13 on 

 the stem. In this adjustment it is convenient to make the gross 

 leveling by the mercury bulb and the fine leveling by closing 7 

 and turning 6 until the fluid in 9 is at the original height. The 

 reading on the burette indicates the loss in volume due to the C(>2 

 absorbed. 



