MICROLITER DR^R TECHNIQUE 375 



3. With stopcock M (Fig. 114) open to the atmosphere, place the 

 ground-glass joint on the vessel and then turn the stopcock to con- 

 nect the vessel to the manometer. 



4. Adjust the manometer to make the diver float, and see 

 whether the equilibrium pressure falls in the desired range. With 

 practice, one can judge the equilibrium pressure by the rate at 

 which the diver sinks. The position of the diver at the equilibrium 

 pressure is arbitrarily taken as that at which the top of the upper 

 air meniscus bordering the mouth seal coincides with the mark on 

 the vessel or the cross hair in the observing microscope. 



5. Again check to make sure no air bubbles are on the surface of 

 the diver. 



6. Rinse the mouth seal of the diver with medium as described 

 on page 367 if small effects are to be measured and especially if 

 narrow-neck divers with long seals are used. This need not be done 

 if large changes in gas vol. are to be measured. 



7. Use the manometer to place each flotation vessel vmder the 

 pressure at which the divers are to be kept between measurements, 

 i.e., "the basic pressure." This pressure should be high enough to 

 prevent the diver from rising and touching the flotation vessel. 

 (Holter found that a pressure 3-5 cm. over the equilibrium pressure 

 of the diver at the time is usually sufficient if the room tempera- 

 ture does not vary much.) 



8. At the proper times, make measurements of the equilibrium 

 pressure in the following manner: 



(a) Adjust the manometer to the basic pressure before opening 

 the stopcock of the flotation vessel. 



(b) Slowly reduce the pressure until the diver begins to rise. 

 Should the diver stick to the bottom so that it does not rise even 

 at a pressure of about 10 cm. less than the equilibrium pressure, 

 tap the neck of the flotation vessel lightly. Do not apply more 

 negative pressure to make the diver rise, since this may cause too 

 great a displacement of the neck seals. Tapping too hard may also 

 disturb the seals. 



(c) Regulate the pressure so that the diver remains at the 

 equilibrium position for at least 10 sec, and then read the manom- 

 eter to 0.5 mm. 



(d) Repeat the adjustment and reading. If the diver does not 

 change position during the time required for manometer readings 



