360 



GASOMETRIC-MANOMETRIC METHODS 



close off the rubber tubing with a pinchcock. Heat the jacket tube 

 cautiously with a gas flame in the region of the braking tip; this 

 will cause the water in the tip to evaporate and the warm air will 

 clear the fine channel. If the tip becomes filled with a salt solution, 

 it will usually be necessary to draw a new tip. Obviously, it is 

 desirable that the pipette be rather long when first made. 



D 



A 



E 



B 



Fig. 123. 



Fig. 124. 



Fig. 125. 



Fig. 123. Braking pipette. From Holier (1943) 

 Fig. 124. Ball-tipped pipette. From Holler (1943) 



Fig. 125. Ball joint for holding pipettes. A, Supporting discs; B, metal 

 springs; C, supporting rail. From Holler (1943) 



Type 4 Pipette. The ball-tipped pipette (Fig. 124) is used to 

 deposit a drop of liquid at a definite place in a very narrow diver 

 neck (<0.7 mm. diameter) or in a fine capillary. The stem attached 

 to the ball has an outer diameter of 0.15-0.25 mm. and the ball 

 itself a diameter of 0.2-0.4 mm. 



The pipette is made by drawing out a glass capillary from a piece 

 of tubing of medium wall thickness, sealing the tip by fusing, and 

 connecting the pipette with rubber pressure tubing to a source of 

 compressed air at 0.5 to 2 atmospheres (depending on the size of the 

 ball to be made). The sealed tip is brought close to a micro flame; 

 when the glass becomes soft enough it blows out into a ball which 

 perforates at the softest point. 



