The blowpipe enables us to get an oxidizing and a reducing flame of better form and greater power. To do this we cut off the air supply at the base of the burner and turn off the gas until the flame is about 1 cm. high; then upon introducing the blowpipe, and blowing a strong continuous jet of air across the Bunsen flame, we produce an oxidizing flame about 4-5 cm. in length. If the tip of the blowpipe be held outside of the Bunsen flame, and the pressure of the stream of air be diminished, we obtain a reducing flame.
Supports.—For supports, charcoal, platinum, and glass are chiefly used. The charcoal should be made from some light wood, such as alder. It should be well burnt, and should not scintillate or smoke.
The platinum supports are generally in the form of wire and foil. Platinum-tipped forceps are frequently employed in blowpipe analysis.
Glass is used in the form of tubing.
Hard glass tubing, 3 mm. bore, is drawn off into ignition tubes 7-8 cm. in length. Several dozen of these tubes should be made before commencing the tests of the next chapter.
Apparatus.—A small agate mortar, 4-5 cm. in diameter, should be provided in which to grind the samples to be examined.
The pestle, which should also be of agate, must be adapted to the mortar in shape and size.
Two pairs of forceps will also be needed.
One pair should be of steel, and the other pair of brass, with fine points.
Of other apparatus, the most necessary is:—