Organic 2 Review Problem 433

Organic 2 Review Problem 433 - Carius tubing cautiously in...

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QUANTITATIVE ANALYSIS 417 those water-soluble compounds (e.g., halide salts) in which the halogen is ionic. The method, although long, is simple, the main difficulty for students being the preparation and sealing of the glass tube. Carius tubing is normally supplied in lengths of about 15 dcm. (5 ft.), sufficient for two tubes: the tubing is usually of about 2 cm. external diameter, whilst the thickness of the wall is about 3 mm. Carius tubing of good quality soft glass, if carefully prepared and sealed, is amply strong enough and has the great advantage of being easily worked in the ordinary air-gas blowpipe flame. Hard-glass tubing gives a much stronger sealed tube, but the latter has to be worked in an oxygen-gas blowpipe flame. For the actual estimation, heat the middle portion of a double length* of
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Unformatted text preview: Carius tubing cautiously in the blowpipe flame, starting first with a smoky flame and then increasing the proportion of air until a flame of maximum temperature is obtained, meanwhile rotating the horizontal tube (using both hands simultaneously, and not each hand in turn, for the rotation) in order to secure uniform heating. When the middle portion of the tube is quite soft, draw the two portions of the tube apart, so that two tubes similar to A (Fig. 72) are obtained, each being open at one end and drawn out to a fine tail at the other. Two Carius tubes can thus be made, although only one will be * A practical demonstration of the preparation and sealing of Carius tubes is of vastly greater value than any written description. FIG. 72....
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