TENSION-EQUALIZER UNIT. 



29 



filled with dilute barium-hydroxide solution. Through one hole of 

 the rubber stopper is inserted a glass tube which extends below the 

 surface of the liquid; in the other hole is a short piece of glass tubing. 

 The end of the long glass tube is connected to a point in the piping just 

 beyond the third water-absorber, while the short glass tube is connected 

 to the piping going directly to the intake of the rotary blower. The 

 method of testing is explained in detail on page 32. 



Moistener. — The air leaving the last water-absorber is absolutely dry 

 and also has a slight odor of acid which, if not removed, would be 

 extremely irritating to the respiratory tract of the subject. To moisten 

 the air sufficiently for comfortable respiration and to remove the acid 

 fumes, a part of a Kipp genera- 

 tor is used containing a solution 

 of sodium bicarbonate. (See fig. 

 7.) The vessel is closed with a 

 rubber stopper in which is in- 

 serted a brass tube with a number 

 of perforations in its lower end, 

 this tube dipping sufficiently into 

 the liquid in the vessel for the 

 perforations to be covered. More 

 recently sodium carbonate has 

 been substituted for the sodium 

 bicarbonate, as the latter gives 

 off traces of carbon dioxide which 

 may vitiate the results of the 

 experiment. At the rate of 35 

 liters per minute, the air is satu- 

 rated to about 65 per cent with 

 this arrangement and the acid 

 fumes are very efficiently re- 

 moved. 



Oxygen supply. — The oxygen for this apparatus has been supplied 

 mainly by admission from a weighed cylinder. In the spring of 1911 

 the method of admission through a 1-liter Bohr meter was substituted, 

 and this has since been used entirely. A more detailed description 

 of both of these methods and a discussion of their merits will be given 

 in the description of the spirometer unit of this apparatus. 



Manometer. — In order to be absolutely certain that the volume of the 

 air in the apparatus is the same at the end as at the beginning, it is 

 necessary to have some method of measuring it. Instead of using the 

 volume of the tension equalizer for this purpose, it is measured by de- 

 termining the pressure on the tension equalizer with a very delicate 

 Topler 1 manometer. This manometer has a glass tube bent in the arc 



Fig. 7. — Moistener. 

 Air enters at top of upright tube, passes through 

 holes into the water, and out of the side outlet in 

 upper bulb. 



*A. Topler, Wiedemann's Ann. d. Physik u. Chem., 1895, 56, p. 609. 



