MICROLITER DIVER TECHNIQUE 367 



meniscus comes to rest at the position of the microscope cross hair. 

 The appearance of the seal at this stage should be that shown in 

 Figure 128. (By drawing the seal below the final position, the glass 

 walls will be moistened and the lower meniscus will not be distorted. 

 The upper meniscus should also be well developed and for this 

 reason the seal should not reach the rim of the neck. When the two 

 menisci equally oppose one another's surface tension, the mouth 

 seal will stay in place.) 



5. Lower the diver stand quickly to remove the "air pipette" 

 from the diver, and fill up the mouth seal to the brim. Immediately 

 remove the solution which partly fills the air pipette when it is 

 taken out of the seal, and rinse with distilled water to prevent 

 clogging. 



Fig. 128. Placing of mouth seal. 

 Frnm Holter (1943) 



When the diver is submerged, the diluted medium in the seal is 

 displaced by the undiluted medium in the flotation vessel. This 

 displacement will be complete in a few min. with mouth seals 1-1.5 

 mm. long and 1 mm. in diameter. Should it be necessary to establish 

 the initial equilibrium pressure more quickly, and if the mouth seal 

 must be long and narrow, the equalization of the concentration of 

 the liquid in the seal must be speeded by displacing the liquid with 

 the flotation medium by rinsing. The rinsing process is carried out 

 by first drawing up into a glass tube, which has been drawn out to 

 a capillary about 10 mm. long and 0.2 mm. inside diameter, about 1 

 ml. of medium. Then the tip of the capillary is introduced into the 

 mouth seal and the medium in the tube is blown in to displace that 

 in the seal. 



If crystallization occurs in the mouth seal, equalization of the 

 diver will be delayed for hours, and displacement of the liquid by 

 rinsing may not help since crystals sometimes hide in the meniscus 

 edges and escape the rinsing current. 



The length of the mouth seal and the diver charge must be chosen 

 to give the diver the weight required for it to have an initial 

 equilibrium pressure of about 1 atmosphere. The weight may be 



