APPENDIX A 



ELEMENTARY GLASS BLOWING WITH BUNSEN FLAME ^ 



The glass used should be that known as " soft," " soda," or Thuringian glass. 

 It is supplied in tube or rod form by all dealers in laboratory apparatus, and in 

 lengths of from 4 to 5 feet. 



I. Pasteur pipette. — Method of preparation. — (i) Lengths of soft glass tubing 

 of about 25 cm. in length and 5-7 mm. internal diameter as shown at a on 

 Fig. 35, are plugged lightly at each end with cotton-wool, and then sterilised 

 in the hot air steriliser at 1 50° C. for one hour. A number of these should be 

 prepared at the same time and held ready in a box or other receptacle. The 

 ordinary lengths of glass tubing as supplied by laboratory furnishers will be 

 found to cut up into four of these lengths, each of which will make two 

 pipettes. 



(2) Holding the tube near its extremities between the first two fingers and 

 thumb of each hand, and at an angle of about 30^ from the vertical so as to 





=0 



O-j — 



■ — rj 



Fig. 35. — Method of making a Pasteur pipette. 



Utilise as great a length of flame as possible, turn it steadily with a constant 

 motion in the large flame of a Bunsen burner in such a manner that 3 to 4 

 inches in the centre of the tube will soften under the influence of the heat. 



(3) As soon as the glass is sufficiently softened, withdraw the tube from the 

 flame, and, holding it horizontally, draw the ends steadily apart until the heated 

 portion assumes the form shown at b on the figure. The interior dimensions of 

 the capillary portions of the pipette will depend upon (i) the length of tube which 

 has been softened, and (2) the rapidity with which the above action is carried 

 out. The smaller the portion of the tube heated, and the more rapid the draw- 

 ing apart, the finer will be the capillary portion of the pipette. 



(4) Divide the drawn-out portion of the tube at its centre and seal off" the 



* The ordinary laboratory Bunsen burner will be found sufficient, but one 



giving as large a flame as possible is recommended. 

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