AUTOMATIC PIPETTES 15 



a small Pasteur pipette with a hair-like capillary 

 extremity. 



2. With a standard pipette fill 100 c.mm. into the 

 neck of this pipette, and make a scratch with a writing 

 diamond at the upper level (a) of the mercury meniscus 

 (Fig. 1 9, A). 



FIG. 19. Making throttle pipettes large capacity 



Now force the mercury down into the capillary stem 

 as far as it will go, so as to leave the upper part of the 

 tube in the region of the diamond scratch empty 

 (Fig. 19, B). 



3 . Heat the tube in the region of the diamond scratch 

 in the blowpipe flame, and removing the tube from 

 the flame draw it out so that the diamond scratch now 

 occupies a position somewhere near the centre of this 

 new capillary portion (Fig. 19, C). 



