Up: Glassmaking
Gilbert: 8 of 65
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Smooth both ends of the No. 6 piece in this
way.
Experiment 4. Practice with the blowpipe.
Hold the small end of the blowpipe just
inside the flame at one edge, about 1/8 inch above
the wick (Fig. 9), and blow air through the lamp
parallel to the top of the wick.
Keep your mouth closed on the blowpipe,
breathe through your nose, and practice keeping a steady
stream of air going for a long time. You will be able to do
this with a little practice.
Do you observe that the blowpipe flame is
pointed, also that it is made up of a pointed cone inside and a
lighter-colored cone outside? The hottest part of the flame is
inside the outer cone just beyond the point of the inner cone.
FIG. 10
CLOSING ONE END OF A TUBE
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The blowpipe flame is hotter than the lamp
flame because the heat of the burning alcohol is concentrated at
one point by means of the air blast, and because the alcohol is
more completely burned by the extra air.
Experiment 5. To close the end of a small tube.
Hold one end of a piece of No. 2 tube in
the blowpipe flame (Fig. 10), turn it slowly, and heat it until the
end closes. Does it close nicely?
Close one end of a piece of No. 4 in the
same way.
You can close No. 6 tubing in this way,
but it leaves a large lump of glass which may crack on cooling or
on reheating. You will practice closing No. 6 tubing later.
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