Enamels and enamelling; an introduction to the preparation and ...

TESTING THE KAW MATERIALS AND ENAMEL MASS. 79
Consideration will be given to the nature of the blowpipe
flame, as many substances behave differently according as
they are heated in the inner or outer portion
of this flame.
The pointed blowpipe flame (Fig. 5) is produced by in-
serting the nozzle of the pipe in the flame of the spirit-lamp
.and blowing into it air inhaled through the nostrils and
forcibly expelled into the pipe by contracting the muscles of
Ke cheeks. On observing this conical flame it will be seen
FIG. 4.
FIG. 5.
to consist of two well-defined conical zones, one inside the
other. The inner cone, R, is highly luminous, whilst the outer
flame, o, is inferior in brightness but is blue in colour. The
former consists of gases which are capable of taking up oxy-
gen, whereas the outer cone, in addition to completely oxidised
bodies, contains free oxygen at a very high temperature.
The behaviour of these two parts of the blowpipe flame
towards various substances differs considerably, the properties
of the two flames being entirely opposite; the inner flame, R,