reflector. For ordinary work, an annealing
oven is not necessary, but one is described on page 60 in connection
with the special cases where annealing is desirable.

Fig. 3 illustrates the tools and appliances. _a_ is an end view of the
desirable form of file, and shows the best method of grinding the edges
in order to obtain a highly satisfactory tool. _b_ is a glass knife,
shown both in perspective and end view, it is made of glass-hard steel
and should be sharpened on a rough stone, such as a scythe-stone, in
order to give a slightly irregular edge. _c_ is a small turn-pin which
may be made by flattening and filing the end of a six-inch nail. _d_ is
the large turn-pin and consists of a polished iron spike, about five
inches long and a quarter of an inch diameter at its largest part. This
should be mounted in a wooden handle. _e_ and _f_ are carbon cones. A
thin rubber tube is also useful; it may be attached to the work and
serve as a blowing tube, thus obviating the necessity of moving the work
to the mouth when internal air pressure is to be applied. In order to
avoid undue repetition, the uses of these tools and appliances will be
described as they occur.

[Illustration: Fig. 3]

Glass, as usually supplied by chemical apparatus dealers is of the
composition known as "soda-glass." They also supply "hard" or
"combustion" glass, but this is only used for special purposes, as it is
too infusible for convenient working in the ordinary blowpipe flame.

Soda-glass consists primarily of silicate of sodium with smaller
quantities of silicate of aluminum and potassium. Its exact composition
varies. It is not blackened, as lead glass is, by exposure to the
reducing gases which are present in the blue cone of a blowpipe flame,
and hence is easier for a beginner to work without producing
discolouration.

Further notes on glasses will be found on page 55, but for ordinary
purposes soda-glass will probably be used.

CHAPTER II

Easy Examples of Laboratory Glass-Blowing--Cutting and
Sealing Tubes for Various Purposes; Test-Tubes,
Pressure-Tubes, Tubes for High Temperature
Experiments--Thermometer-Bulbs, Bulbs of Special Glass,
Pipettes, Absorption-Bulbs or Washing-Bulbs--Joining Tubes;
Branches, Exhaustion-Branches, Branches of Dissimilar
Glass--Blowing Bulbs; A Thistle Funnel; Cracking and
Breaking Glass; Leading and Direction of Cracks--Use of
Glass Rod or Strips of Wi