without blackening the
glass when the directions for heating lead glass on pages 17-21 are
followed, should on no account be received. I am told that at some
places, where the water-supply is at very high pressure, it is utilised
for working blow-pipes by means of the apparatus described below, and
that some glass-workers find it advantageous to use such automatic
blowers. But after a little practice, the effort of working the blower
with the foot whilst manipulating the glass is not a source of serious
inconvenience. Indeed, as it gives a certain degree of control over the
flame without the use of the hands, the foot-blower is preferable. It is
worth while to describe an automatic blower, however.

=Automatic Blower= (Fig. 2).--A strong glass tube _A_ is welded into a
somewhat larger tube _B_ so that its end is about 2 mm. from the
contraction at _G_. _B_ has a side tube _C_ joined to it. The narrow end
of _B_ is fixed by an india-rubber cork to a strong bottle _D_ of two or
three litres capacity. The india-rubber cork also carries an exit tube
_E_, and _D_ is pierced near its bottom by a small hole at _F_.

[Illustration: FIG. 2]

In using the apparatus _A_ is connected with the water-supply, and water
passing through _G_, carries air with it into _D_. The water escapes
from _D_ by the opening at _F_, and the air is allowed to pass out by
the tube _E_, its passage being regulated by a tap. Fresh supplies of
air enter _B_ by _C_.

=Blow-pipe Flames=--_The Pointed Flame._--If the gas tap of a Herapath
blow-pipe be adjusted so that comparatively little gas can pass, and if
the foot-blower be then worked cautiously, a long tongue of flame ending
in a fine point will be produced (Fig. 3). This flame will subsequently
be described as the _pointed flame_. It should be quite free from
luminosity, and as the amount of air necessary for securing a pointed
flame is large, in proportion to the gas, there is excess of oxygen
towards the end _C_. By adjusting the proportions of air and gas,
pointed flames of various dimensions can be obtained with the same
blow-pipe. The part of a pointed flame to be used in glass-working is
the tip, or in some cases the space slightly beyond the tip.

[Illustration: FIG. 3.]

[Illustration: FIG. 4.]

_The Brush Flame._--If a large supply of gas be turned on and a
considerable blast of air sent into the flame, a non-luminous flame of
great size will be obtained (Fig. 4). In form it som