quickly that you have the latter all hot at once.
Put down the blow-pipe, and, using both hands, press the tubes
together (which wooden clips will readily allow), and after seeing
that the glass has touched everywhere, pull the tubes a trifle apart.
Apply the blow-pipe again, passing lightly over the thin parts, if
any, and heating thicker ones; having the end of the rubber tube in
his mouth, the operator will be able to blow out thick places. When
all is hot, blow out slightly, and having taken the flame away, pull
the tubes a little apart, and see that they are straight.

Throw an asbestos rag over the joint, loosen one pair of the clamps
slightly, and leave the joint to anneal. It is important that the
least possible amount of glass should be heated, hence the necessity
of having the ends well prepared, and it is also important that the
work should be done quickly; otherwise glass will flow from the upper
side downwards and no strong joint will be obtained.

Fig. 17. Tube being opened at one end.

Sec. 24. To weld Tubes of very small Bore.

If the bore is not so small as to prevent the entrance of the point of
the iron nail, get the ends of the tubes hot, and open the bore by
inserting the end of the nail previously smeared over with a trace of
vaseline. Work the nail round by holding the handle between the thumb
and first finger of the right hand, the tube being similarly placed in
the left. The tube and nail should be inclined as shown in the
sketch.

Never try to force the operation; the nail soon cools the glass, so
that only a very short time is available after each heat; during this
the tube should be rotated against the nail rather than the nail
against the tube. Be careful not to heat a greater length of tube
than is necessary, or the nail will, by its component of pressure
along the tube, cause the latter to "jump up" or thicken and bulge.
Both ends being prepared, and if possible, kept hot, the weld may be
made as before, and the heating continued till the glass falls in to
about its previous thickness, leaving a bore only slightly greater
than before.

It is in operations such as this that the asbestos box will be found
of great use. As soon as one end of the weld is ready cool it in the
flame till soot deposits, and then plunge it into the asbestos. This
will cause it to cool very slowly, and renders it less likely to crack
when again brought into the flame. Turned-out ends, if the gl