ther before the flame, and they can also be drawn into
smaller tubes when softened by heat.

In order to make a side connection as in a T piece, a ring of silica
should be applied to the tube in the position fixed upon for the joint.
This ring must then be slightly expanded, a new ring added, and so on,
till a short side tube is formed. To this it is easy to seal a longer
tube of the required dimensions. It is thus possible to produce Geissler
tubes, small distilling flasks, etc. Solid rods of silica are easily
made by pressing together the softened ends of the fine rods or threads
previously mentioned. Such rods and small masses can be ground and
polished without annealing them.

=Quartz Fibres.=--These were introduced into physical work by Mr. Boys
in 1889. They may be made by attaching a fine rod of vitrified quartz to
the tail of a small straw arrow provided with a needle-point; placing
the arrow in position on a cross-bow, heating the rod of silica till it
is thoroughly softened and then letting the arrow fly from the bow, when
it will carry with it an extremely fine thread of silica. A little
practice is necessary to ensure success, but a good operator can
produce threads of great tenacity and great uniformity. Fuller accounts
of the process and of the various properties and uses of quartz fibres
will be found in Mr. Boys' lectures (Roy. Inst. Proc. 1889, and Proc.
Brit. Assn. 1890), and in Mr. Threlfall's Laboratory Arts.

INDEX.

Air-traps, 69.
Annealing, 23.
Apparatus needed for Glass-working, 11.
Appendix, 82.

Beginners, Failures of, 22.
Bellows, Position of, 3.
---- Various forms of, 7.
_See also_ Blower.
Bending Glass Tubes, 28.
Blower, Automatic, 8.
Blow-pipe, Cheap form of, 4.
---- Dimensions of, 4-5.
---- Fletcher's Automaton, 6.
---- Fletcher's Compound, 6.
---- Gimmingham's, 6.
---- Herapath's, 6.