are prepared by heating and drawing out larger tubes.

[Illustration: FIG. 25.]

=Thistle Funnels= (Fig. 25).--Seal a moderately thick piece of small
glass tube at _A_, then heat a wide zone of it a little below _A_ by
rotating it horizontally in the blow-pipe flame till the glass softens,
and expand the glass to a bulb, as shown at _B_ of 1; during the
operation of blowing this bulb, the end _A_ must be directed to the
ground.

Soften the end _A_ and a small portion of _B_ as before, and, holding
the tube horizontally from the mouth, blow out the end _C_ as at 2. Heat
the end of _C_ gradually, till the glass softens and collapses to the
dotted line _dd_, and at once blow a steady stream of air into the open
end of the tube, rotating it steadily, till it is about to burst;
finally clean off the thin glass from round the edges of the funnel,
which should have the form shown at 3, and round them. An inspection of
a purchased thistle funnel will generally show that the head _B_ has
been formed from a larger tube sealed to _E_ at _f_.

[Illustration: FIG. 26.]

=Closing Tubes containing Chemicals= for experiments at high
temperatures.--Tubes of the hard glass used for organic analyses answer
best for this purpose; the operation of drawing out the end of such a
tube is practically identical with what has been described under the
head of choking, p. 35. A well-sealed tube presents the appearance of
that shown by Fig. 26.

In order to secure a thick end to the point of the tube _a_, about an
inch or so of the tube near the contracted part should be warmed a
little, if it is not already warm, at the moment of finally sealing it;
the contraction of the air in the tube, in consequence of the cooling of
the warm tube, will then ensure the glass at _a_ running together to a
solid end when it is melted in the flame.

If it will be necessary to collect a gas produced during a chemical
action from such a tube, make the contracted end several inches long,
and bend it into the form of a delivery tube. It will then be possible
to break the tip of this under a cylinder in a trough of liquid.

=In order to explain the construction of apparatus consisting of several
parts=, it will be sufficient to take as examples, two very well-known
instruments, and to describe their construction in detail. From what is
learned in studying these, the student will gather the information that
is wanted.

[Illustration: FIG. 27.]

1. _To