10 



GLASS APPARATUS IN COMMON USE 



formed. With the glass-cutting knife cut off whatever 

 may be necessary from the open ends to make the 

 tubes the required length. 



A rectangular block of "plasticine" (modelling clay) 

 into which the conical ends can be thrust makes a 

 very convenient stand for these small tubes. 



Capillary Pipettes or Pasteur's Pipettes (Fig. 13 a). 

 These little instruments are invaluable, and a goodly 

 a. b. c. supply should be kept on hand. They 

 are prepared from soft-glass tubing of 

 various-sized calibre (the most generally 

 useful size being 8 mm. diameter) in the 

 following manner: Hold a 10 cm. length 

 of glass tube by each end, and whilst 

 rotating it heat the central portion in 

 the Bunsen flame or the blow-pipe 

 blast-flame until the glass is red hot 

 and soft. Now remove it from the flame 

 and steadily pull the ends apart, so 

 drawing the heated portion out into a 

 roomy capillary tube; break the capil- 

 lary portion at its centre, seal the 

 broken ends in the flame, and round 

 off the edges of the open end of each 

 pipette. A loose plug of cotton- wool 

 in the open mouth completes the capil- 

 lary pipette. After a number have 

 been prepared, they are sterilised and 

 FIG i Ca ii s ^ ore< ^ i n batches, either in metal cases 

 lary pipettes. a, similar to those used for the graduated 

 pipettes or in large-sized test-tubes 

 sealed ends downward and plugged ends toward the 

 mouth of the case. 



The filling and emptying of the capillary pipette 

 is most satisfactorily accomplished by slipping a small 

 rubber teat (similar to that on a baby's feeding bottle 

 but not perforated) on the upper end, after cutting or 



