PIPETTES. 457 



drawn-out portion should be about 40 cm. (16 in.) long. 

 This is then heated in the middle, and, as a result, two 

 sealed pipettes are thus obtained (Fig. 61, c or d). 



Frequently, it is desirable to transfer a liquid or a sus- 

 pension from one tube to another. For small quantities 

 the ordinary pipette (c or d) can be used direct. For larger 

 quantities a bulb should be blown into pipettes c or d, thus 

 giving pipette d. While it requires a great deal of practice 

 to blow a perfect bulb, still a serviceable one can be made 

 without much difficulty. 



a 

 4 



FIG. Gi. Drawn-out tube pipettes of Pasteur, a Plugged, sterile tube as kept in 

 stock; b The same heated 'at x in blast-lamp, drawn out; then sealed at x\ c and ^com- 

 pleted pipettes; e The same with bulb. 



A narrow flame of the blast-lamp is directed at the tube a short 

 distance above the point where it begins to narrow. The tube is 

 slowly turned until the glass softens; whereupon the ends are slightly 

 pushed together so as to form a thick ring of glass. One or two addi- 

 tional rings are made in this way. A large flame is then turned on 

 so as to melt the thickened zones of glass. When the glass is per- 

 fectly soft the end is brought rapidly to the mouth and the bulb is 

 blown. The glass tube should be turned, slowly and steadily, while 

 heating and also while the bulb is being blown. The bulb pipettes 

 can often be used to better advantage if the capillary is bent at right 

 angles just below the bulb. 



When a pipette is to be used the mouth end should be heated in 

 the flame for a few moments. This is to prevent possible infection. 

 The lower end of the capillary tube is then scratched with a file or 

 glass-cutting knife and the sealed end removed. The end may be 



