her under
one-eighth diameter and about an inch and a half long. This stem rests
in a guide at the end of a brass tube, the bulb contacting against the
other end which is approximately shaped. The bulb and its seating are
ground air-tight. A very light spring holds the bulb in position.

This valve is fitted into a metal or glass T piece, one limb of which
leads to the air reservoir and the other limb leads to the blowpipe jet;
the limb containing the valve leads to the tube through which the air is
blown in.

A convenient reservoir may be made from a fairly large football bladder.
A network of string should be fitted over the outside of the bladder and
the strings should terminate in a hook on which a weight can be hung, in
order to provide a means of adjusting the pressure at which the air is
delivered to the jet. This bladder should be washed out and allowed to
drain after use.

The air tube which passes from the valve to the mouth may conveniently
be made of brass, but, in order to avoid the continued contact of metal
with the lips of the operator, it should be fitted with a non-metallic
mouthpiece. It is an advantage from the point of view of portability to
have the air tube easily detachable from the T piece containing the
valve.

The blowpipe jets, of which there may be several with advantage, may be
made of glass tubing, bent to the most convenient angle and having an
enlargement or bulb at some point in the tube. This bulb serves as a
final condensing place for any traces of moisture that may escape from
the larger reservoir.

The whole device, blowing tube, reservoir, and T piece may be fastened
to a clamp, so that it can be secured on the edge of any table where
blowpipe work is to be carried out. If the blowpipe is to be used with
gas, the form of burner described under. "A Simple Form of Blowpipe"
will be found quite satisfactory.

_The Use of Oil, or Other Non-Gaseous Fuels._--Although gas, when
available, is usually preferred on account of its convenience, there are
several other fuels which give a hotter flame. They have, also, the
additional advantage of not requiring any connecting pipes; but each has
its own disadvantage.

One liquid fuel deserves special mention as being rather less desirable
than the others; this is alcohol. Although very convenient in use, it
has the disadvantage of being rather too highly inflammable and capable
of burning without a wick, thus involving a certain fire ris