386 GASOMETRIC-MANOMETRIC METHODS 



3. Test for tight fitting by dipping the open end of the diver 

 into alcohol, blowing through the rubber tubing attached to II, and 

 then sucking a small drop of alcohol into the diver. If the drop is not 

 movable with equal ease in both directions, change the position of 

 the diver in III and repeat the test with alcohol until tight fitting 

 is obtained. 



4. Finally, blow out the alcohol and allow the diver to dry for a 

 few min. 



The Ball-Tipped Pipette. This pipette is very much the same 

 as the one used with microliter divers (page 360), except that it is 

 drawn out to an extremely fine thin-walled capillary. The ball is 

 formed by passing the pipette tip through a micro flame while com- 

 pressed air at 0.3-2 atmospheres is connected to the pipette. The 

 greater the pressure, the larger the hole that will be blown in the 

 ball, and the longer the flame, the larger the ball itself will be. The 

 dimensions, relative to the diver capillary are apparent from D, 

 Figure 135. 



(4) FILLING THE CAPILLARY DIVER 



Determining the Length of the Seals of Medium (Mi, Mo) to 

 be Used. First, the length of the column of medium {Ui) , which 

 placed in the diver will make the otherwise empty diver float, should 

 be calculated. It is most convenient to work with divers in which: 



Im= (0.4 to 0.5) Z„ 



where Id is the length of the diver. The value of Im may be calculated 

 from the following formula which was derived from that given by 

 Linderstr0m-Lang (1943, page 363): 



where / is the ratio of the weight of mercury to glass which was 

 determined in the selection of the diver capillary (page 383) and 

 (},gi and (j)M are the densities of the glass and medium, respectively 

 , (page 354) {cj,m = 1.325). 



As will be described later, the columns W, POi, P, and PO-j 

 are first placed in the diver in the order given. Mi and M2 are 

 placed last. The following conversion factors are used for the cal- 

 culation of the combined length of Mi and M2: 



