t descriptions of operations
before the blow-pipe.

Before proceeding to work with soda glass, the student should not only
verify by experiments what has been already said, but he should
familiarise himself with the action of the blow-pipe flame on lead glass
by trying the glass in every part of the flame, varying the proportions
of gas and air in every way, repeating, and repeating, his experiments
until he can obtain any desired effect with certainty and promptitude.
He should practice some of the simpler operations given in Chapter III.
in order to impress what he has learned well on his mind.

=Management of Soda Glass.=--In working with soda glass the following
points must be constantly kept in mind. That as it is much more apt than
lead glass to crack when suddenly heated, great caution must be
exercised in bringing it into the flame; and that in making large joints
or in making two joints near each other, all parts of the tube adjacent
to that which, for the moment, is being heated, must be kept hot, as it
is very apt to crack when adjacent parts are unequally heated. This may
be effected by stopping work at short intervals and warming the cooler
parts of the tube, or by the use of the brick or block of wood to check
radiation, or even by placing a supplementary blow-pipe or Bunsen burner
in such a position that its flame plays upon the more distant parts of
the work, not coming sufficiently into contact to soften the glass,
however, but near enough to keep it well heated. Lastly, to prevent the
finished work from falling to pieces after or during cooling, the
directions given under the head of annealing must be carefully carried
out.

In very much of his work the glass-blower is guided more by the _feel_
of the glass than by what he sees. The power of feeling glass can only
be acquired by practice, and after a certain amount of preliminary
failure. As a rule I have observed that beginners are apt to raise their
glass to a higher temperature than is necessary, and that they employ
larger flames than are wanted. If glass be made too soft it may fall so
completely out of shape as to become unworkable except in very skilful
hands. The following rules, therefore, should be strictly adhered to.
Always employ in the first instance the smallest flame that is likely to
do the work required. In operations involving _blowing out_ viscous
glass, attempt to blow the glass at low temperatures before higher ones
are tried