ze that it
will pass easily, but not too easily, into _A_ or _B_. Expand this tube
at _D_, as shown in II., by softening the glass and gently compressing
it. The configuration of the enlarged tube as shown at _D_ may be
obtained by heating and compressing two or more zones of the tube that
are adjacent, one zone being less expanded than the other, so as to give
the sides of the imperfect stopper as nearly as possible the form shown
at _D_, which, however, is much less regular than may easily be
obtained. Seal off the head of the tube at _H_, and heat the glass till
it runs together into a nearly solid mass; compress this with a pair of
iron tongs to the flattened head _E_. In making _D_, aim at giving it a
form which will as nearly as possible correspond to that of the tube
into which it is to be ground, and make it slightly too large, so that
only the lower part at _D_ can be introduced into the mouth of _A_ or
_B_. Before it is ground, the stopper must be heated nearly to its
softening-point and annealed.

Moisten _D_ with a solution of camphor in recently distilled
turpentine, and dust the wet surface with finely-ground emery, then
gently grind it into its place till it fits properly. In this operation
the tail _G_, which should fit loosely into the tube _A_, will be of
assistance by preventing _D_ from unduly pressing in any direction on
_A_ in consequence of irregular movements. The stopper should be
completely rotated in grinding it. It must not be worked backwards and
forwards, or a well-fitting stopper will not be produced. Renew the
emery and camphorated turpentine frequently during the earlier part of
the grinding; when the stopper almost fits, avoid using fresh emery, but
continue to remove the stopper frequently at all stages of the
operation. That added at the earlier stages will be reduced to a state
of very fine division, and will therefore leave the stopper and mouth of
_A_ with smoother surfaces than fresh emery.[10]

[10] Mr. Gimmingham recommends giving stoppers a final polish with
rotten-stone (_Proceedings of the Royal Society_, p. 396, 1876).

NOTE.--The addition of camphor to the turpentine used for grinding glass
is very important. Notwithstanding its brittle nature, glass will work
under a file moistened with this solution almost as well as the metals.
Small quantities should be made at a time, and the solution should be
kept in a well-closed vessel, for after long exposure to the air it is
n