the bulb tend to expand more than the
other, turn the expanded part to the bottom, pause for about a second,
both in rotating and blowing, in order that the lower portion may be
cooled by ascending air-currents; then continue blowing and turning as
before.

_Absorption Bulbs or Washing Bulbs._--These are made by an elaboration
of the processes given in the last paragraph, _g_, _h_, and _i_, Fig. 6,
illustrate this.

_A Thistle Funnel._--This is made by blowing a fairly thick-walled bulb
on a glass tube, bursting a hole by heating and blowing, and enlarging
the burst-out part by heating and rotating against a turn-pin.

_Bending Glass Tube._--Small tubing may be bent in a flat flame gas
burner and offers no special difficulty. Large or thin-walled tubing
should be heated in the blowpipe flame and a slight bend made; another
zone of the tube, just touching the first bend, should now be heated and
another slight bend made. In this way it is possible to avoid flattening
and a bend having any required angle can gradually be produced. A final
shaping of the bend may be made by heating in a large blowpipe flame and
expanding slightly by air pressure.

_Glass Spirals._--If a tube is heated by means of a long, flat-flame
burner, the softened tube may be wound on to an iron mandrel which has
previously been covered with asbestos. The mandrel should be made
slightly conical in order to facilitate withdrawal. It is desirable to
heat the surface of the asbestos almost to redness by means of a second
burner, and thus avoid undue chilling of the glass and the consequent
production of internal strain.

[Illustration: Fig. 7]

_A Thermo-Regulator for Gas._--Fig. 7, _a-e_, shows an easily
constructed thermo-regulator. The mercury reservoir, _a_, and the upper
part, _b_, are made by joining two larger pieces of tubing on to the
capillary. The gas inlet passes through a rubber stopper, in order to
allow of adjustment for depth of insertion, and the bye-pass branches,
_d_ and _e_, are connected by a piece of rubber tubing which can be
compressed by means of a screw clip, thus providing a means of
regulating the bye-pass.

_Use of Glass Rod._--Apart from its most common laboratory use for
stirring; glass rod may be used in building up such articles as
insulating feet for electrical apparatus or acid-resisting cages for
chemical purposes. Such a cage is shown by _f_, _g_ and _h_, Fig. 7.
Further, by an elaboration of the method of ma