Manual of basic techniques for a health laboratory - libdoc.who.int

40 Manual of basic techniques for a health laboratoryFig. 2.44 Heating the glass tubing before pulling thepipette— keep turning slowly;— stop when the glass becomes red hot.4. Stand the tubes in a beaker or a can, heated ends up,and leave to cool.Wash all the pieces of tubing prepared (following theinstructions given in section 3.5.1). Rinse and dry.5. Pulling the pipette is carried out as follows:— heat the middle of the length of tubing over theblue flame (Fig. 2.44);— keep rotating the tubing until the glass becomesred.Fig. 2.45 Pulling the pipetteFig. 2.46 Rounding off the ends of the pipetteby flaming6. Remove the tubing from the flame, still rotating it continuously, and pull the twoends apart slowly, keeping your hands perfectly level (Fig. 2.45). Pull the glass tothe length required (10–20cm).7. Leave to cool. Cut off the drawn portion at the exact length required. Round offthe sharp edges by holding them for a few seconds in the flame (Fig. 2.46).Alternatively, separate and seal the two pipettes by heating the pulled-out portionin the flame.Fig. 2.47 Rounding off theends of the glassrod by flamingMaking a stirring rod1. Use a glass rod about 5mm in diameter. Cut the rod into lengths of 15, 20 or25cm according to requirements, using a file (see Fig. 2.41).2. Round off the ends by rotating them over the blue flame of the burner, untilabout 1cm of the rod is bright red (Fig. 2.47).3. Flatten the heated end against the (dry) tiled working surface with a 500-g or1-kg weight (Fig. 2.48).4. Heat the other end and press it gently down on the tiled surface (Fig. 2.49).Glass rods can be used to decant liquids or to pour them slowly (see Fig. 3.52).