SPIROMETER UNIT. 



35 



Oxygen is admitted after the air leaves the carbon-dioxide absorber 

 and between this point and the spirometer connection is made with 

 the respiratory tract of the subject. The general plan of the apparatus 

 with its different parts is shown in figure 10. From the rotary pump 

 the air passes in turn into a trap, two Williams bottles containing sul- 

 phuric acid, a soda-lime container, a sulphuric-acid container or Will- 

 iams bottle, a can containing dry sodium bicarbonate to remove acid 

 fumes, and finally reaches the respiratory tract of the subject. From 

 there it passes into the spirometer and returns to the rotary pump or 

 blower. 



FIG. 10. Detailed plan of ventilation system in spirometer unit. 

 DESCRIPTION AND USE OF PARTS. 



Rotary blower. The rotary blower in this apparatus is the same as 

 that used in the tension-equalizer unit, and described in that connec- 

 tion (see p. 24). 



Trap. In using the apparatus a stoppage occasionally occurs which 

 is due either to improperly packed soda-lime containers or to improper 

 manipulation. If pressure is developed in the air-circuit beyond the 

 blower, which can not be released when the ventilation is stopped, the 

 acid from the two Williams bottles will be forced back into the blower. 

 In order to avoid the delay in experimenting required to remove this 

 acid, it has been found advisable to insert a trap for catching the acid 

 when such pressure occurs. For this purpose an empty Williams bottle, 

 reversed, has been inserted in the air-circuit, and thus, when pressure 

 occurs, the acid will run up into the tube which extends to the bottom 

 of the bottle. This empty bottle is sufficient to retain all acid which 

 may come into it due to back pressure. 



Water-absorbers. For absorbing the water-vapor from the expired 

 air and from the air of the apparatus, two Williams bottles in series are 

 used, each filled with 450 c.c. of strong commercial sulphuric acid. 



