ary shaping of the plug. If
but few plugs are to be ground it is unnecessary to provide a means of
rotating the moulds, as the plug may be held in the hand and ground into
the mould in a manner similar to that used in the first method of
stoppering.

[Illustration: Fig. 14]

When the socket and plug have been ground, by the successive use of
cones and moulds, to the desired angle, so that they correspond almost
exactly, the plug is given its final fitting into the socket by
grinding-in with a fine abrasive, in the manner first described.

_Stopcocks._--Although it would be more strictly in keeping with the
form of this book to divide the making of stopcocks into two parts;
shaping by heat and grinding, we will consider the whole operation here,
and take for our example a simple stopcock such as that illustrated by
Fig. 14.

The "blank," _f_, that is the socket before grinding, is made by drawing
out a piece of fairly thick-walled tubing into the form shown by _a_.
Two zones on this tube are then heated by means of a small, pointed
flame, and the tube is compressed along its axis, thus producing two
raised rings as shown by _b_. Two zones, slightly towards the outer
sides of these two raised rings are heated and the tube is drawn while
air pressure is maintained within. This produces two thin-walled bulbs
or extensions similar to those shown by _c_. One of these extensions is
now broken off by means of a sharp blow with the edge of a file or
other piece of metal, and the edges of the broken glass are rounded in
the flame. The other extension is left to serve as a handle. We have now
a piece of glass like that shown by _d_. Now heat a spot on the side of
this, medially between the raised rings, until the glass is on the point
of becoming deformed, and bring the intensely heated end of a smaller
tube in contact with the heated spot. Without disturbing the relative
positions of the two tubes, press the smaller tube down on a thin steel
wire, so that the wire passes along the tube and enters the soft glass;
thus forming a projection inside the sockets as shown by _e_. The wire
must be withdrawn, again immediately. When the wire has been withdrawn,
heat the place where it entered to dull redness, in order to relieve any
strain; break off the thin extension, which up to the present has served
as a handle, round off the broken edges in the flame, and join on and
indent a similar piece of small tubing to the opposite side of