368 GASOMETRIC-MANOMETRIC METHODS 



adjusted by changing the length of the mouth seal. Should it be 

 necessary to change the volume of other liquids in the diver, the 

 equilibrium pressure can be kept constant by changing the volume 

 of the mouth seal according to the relationship: 



1 vol. aqueous soln. (d = 1) = 0.76 vol. medium (d = 1.325) 

 1 vol. paraffin oil (d = 0.87) = 0.64 vol. medium (d = 1.325) 



In order to replace the mouth seal with one of another vol., the 

 diver is removed from the flotation medium, rinsed on the outside 

 with distilled water, and dried with cloth or filter paper. Then the 

 mouth seal is removed with a pipette or filter paper rolls, and 

 replaced with a seal of water extending into the diver deeper than 

 the previous seal. This water seal is flushed with fresh water by 

 the rinsing technique (page 367). The water is removed, the 

 mouth is dried with hard filter paper, and the new seal of medium is 

 introduced. 



The length of the mouth seal may also be corrected by diluting 

 it with water, removing the excess with a roll of filter paper, and 

 then adjusting the position by means of an "air pipette" in a manner 

 similar to that employed when dealing with divers in anaerobic 

 experiments (page 373). 



Seal Stoppers. Linderstr0m-Lang and Holter (1942) pointed 

 out that the diffusion of gas through seals can be reduced consider- 

 ably by placing glass stoppers into the seal. The stopper consists 

 of a bit of glass rod having a diameter about 50-80 fi less than 

 that of the inside of the diver neck. The length of the stopper will 

 depend on the magnitude of the effect desired, but in general they 

 are used 2-3 mm. long. 



The solid stopper is the easiest to make but its weight may be 

 too great, making it more feasible to use hollow stoppers. Solid 

 stoppers can only be used with divers having a thin-walled neck 

 and a low center of gravity, since otherwise they render the diver 

 top-heavy. The hollow stoppers are made under a dissecting micro- 

 scope from a glass capillary of the proper outside diameter by fus- 

 ing one end shut in a micro flame, cutting off the capillary 0.5 mm. 

 longer than the stopper is to be, and fusing the open end shut. The 

 hot sealed end begins to bulge out due to the internal pressure 



