Test-tube ends glass

Fig. II.5. Construction of a test-tube end. (a) A small section of the tube is melted and the halves pulled apart, (b) A small hot flame is used to melt excess glass, which is then pulled off with a cold piece of glass, (c) The end is heated evenly, removed from the flame when it is molten but before excess glass accumulates, and gently blown. (d) A finished product. The end should be hemispherical and the wall thickness uniform.

First close the tube by drawing out a point and making a neat hemispherical test-tube end. Then heat the glass, including the test-tube end until sufficient glass has been gathered. The mbe should have the appearance shown in Fig. 6.39a. 

FIG. 6.39. Blowing a bulb on the end of a tube. First prepare a test-tube end on a suitable piece of tubing and mark the required lengtlr on tire tube, (a) Shows the glass heated and gathered, ready to blow up. (b) Tire blown bulb witlr a side tube attached. Such a shape is difficult to preserve if the bulb is thin-walled. 

If preferred, suitable ignition tubes may be prepared by the student from soft glass tubing it is important that the thickness of the glass at the closed end be tmiform, otherwise the tube is likely to crack when heated. The simplest procedure is to blow a small bulb of uniform wall thickness at the end of the tube. The small test-tubes are available from all laboratory supply dealers... 

Make the melting-point tubes as described on p. 40 from a clean test tube the internal diameter should be about 4-5 mm. Cut off pieces about 5 cm. long. Close the lower ends by sealing as uniformly as possible, also keeping the walls as thin as possible. By drawing the softened glass away sideways avoid reducing the bore more than a little. 

Preparation of Red Phosphorus. (This experiment is prepared by one student who demonstrates it to the class.) Take a test tube with a drawn out end and fill it with carbon dioxide gas. Pour water heated to 30 °C into a mortar and lower a piece of white phosphorus into the water. Holding the phosphorus with pincers under the water, cut off a piece the size of a pea with a lancet or sharp knife. Rapidly dry the phosphorus with filter paper on a glass plate and lower it into the test tube filled with car-... 

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