1 6 GLASS APPARATUS IN COMMON USE 



4. Heat the tube in this position in the peep flame 

 of the Bunsen burner, and draw it out into a hair-like 

 extremity. Snap off the glass tube, leaving about 

 5 mm. of hair-like extremity attached to the upper 

 capillary portion (Fig. 19, D). Allow the glass to cool. 



5. Lift up the bulb by the long capillary stem and 

 allow the mercury to return to its original position 

 an operation which will be facilitated by snapping 

 off the hair-like extremity from the long piece of 

 capillary tubing. 



6. Mark on the capillary stem with a grease pencil 

 the position of the end of the column of mercury 

 (Fig. 19, E.) 



7. Warm the capillary tubing at this spot in the 

 peep flame of the Bunsen burner, and draw it out very 

 slightly so that when cut at this position a pointed 

 extremity will be obtained. 



8. With a glass-cutting knife cut the capillary tube 

 through at the point "6," and allow the mercury to 

 run out. 



9. Now apply a thick layer of sealing wax to the 

 neck of the bulb. 



10. Take a piece of 5 mm. bore glass tubing and 

 draw it out as if making an ordinary Pasteur pipette. 



11. Break the capillary portion off so as to leave a 

 covering tube similar to that already used for the 

 smaller graduated pipettes. Into this covering tube 

 drop the graduated bulb and draw the capillary stem 

 down through the conical .extremity until further 

 progress is stopped by the layer of sealing wax. 



12. Warm the pipette in the gas flame so as to melt 

 the sealing wax and make an air-tight joint. 



13. Fit an india-rubber teat over the open end of the 

 covering tube, and the automatic pipette is ready for 

 use (Fig. 19, F). 



Sedimentation Pipettes (Fig. 20). These are prepared 

 from 10 cm. lengths of narrow glass tubing by sealing 



