MICROLITER BURETTES 



257 



In the type 2 (Lindersti'0m-Lang and Holter, 1933a), shown in 

 Figure 83, the mercury is separated from the standard solution by 

 an air space. This instrument is used for solutions which might be 

 affected by contact with mercury. When the screw S is manipulated, 

 the right mercury column, which is open to the air, is raised or 

 lowered, and this results in a small positive or negative pressure over 

 the left column. In this way liquid can be delivered from, or drawn 

 into, the burette. 



The type 1 burette can be connected to a permanent reservoir of 

 standard solution as shown in Figure 84 ( Linderstr0m-Lang and 

 Holter, 1933b). 





^ 



L^ 



8. Burette, type 

 with reservoir. 

 Frovi hinder str0m-Lang 

 and Holter (1933b) 



Fig. 85. Glass bead used 



to exclude air during titration. 



From hinder sir 0m-Lang, Weil 



and Holter (1935) 



Reduction of evaporation and protection from the air during 

 titration is afforded by the loosely fitting glass cap around the tip 

 of the burette held suspended by two threads (Fig. 82). This effect 

 may also be obtained by passing the tip of the burette through a 

 glass bead, P (Fig. 85) , which rests on the top of the titration vessel 

 (Linderstr0m-Lang, Weil, and Holter, 1935). The glass bead may 

 be dipped into paraffin oil first in order to effect a better seal to the 

 titration tube. In order to carry out titrations in an atmosphere free 



