of the main tube. This must be carefully
annealed. It is more important that the walls be thick than that the end
be nicely rounded: it may indeed be left somewhat conical in shape.

At a point about two inches from the open end of the tube, it is slowly
warmed and finally heated to the softening point. Grasping the open end
with a pair of crucible tongs, it is cautiously pulled out, a little at
a time, usually during rotation in the flame, to make a constriction of
moderate wall-thickness, but of sufficient internal diameter to admit
the tube containing the substance. After annealing this, cooling and
cleaning the tube, the acid and salt are introduced (the former by means
of a long-stemmed funnel) and the tube is inclined and rotated about its
axis so that the acid wets its surface about half way up from the
bottom. The substance is now weighed out in a piece of thin-walled glass
tubing, closed at one end, and about two inches long. Inclining the
large tube at a suitable angle, the small one is introduced, closed end
first, and allowed to slide down the walls of the large tube until it
reaches the place where the acid has wet the tube. Here it will stop,
and if the tube is kept inclined during the rest of the operation it
will roll around inside the tube at this point and thus not get down
where any acid is likely to get into it and produce any pressure by
decomposing it before the open end of the tube is sealed. Now the tube
is held in an inclined position, taking care that the acid does not
reach up to the substance, the constricted portion cautiously warmed and
shrunk. It is finally shrunk and drawn out into a somewhat elongated
cone, with walls as thick as the rest of the tube, and when this is
accomplished the end of the cone is sealed and the waste piece drawn
off. Anneal with great care, and cool in such a position that the acid
cannot reach the hot glass. The shrinking of this cone takes a good deal
of patience, and is one of the most important parts of the process. If
the walls are left too thin, the tube may burst when heated, and the
whole labor is lost. If care is taken, the same tube can be used for a
number of determinations, until it becomes quite short.

INDEX

Annealing glass, 4, 24

Bellows, 4

Bending glass, 8

Blowing glass, 13, 19, 20, 21, 24, 29, 31
with a rubber tube, 22

Blowpipe, 4

Bulb at end of tube, 28
in middle of tube, 32
very large, 32