QUANTITATIVE ANALYSIS 445 It may occasionally happen, particularly if the solution is approaching saturation, that a small quantity of the crystalline solute separates at the top of the tube H in the zone Z, Le., immediately above the source of the heat. This may be prevented by placing a narrow oblong piece of asbestos paper, with slots cut in each end, horizontally between the tubes H and D, the slots fitting over the lower narrow ends of the condenser C and the cup F. Wait 2-3 minutes after the pellet has dissolved, and then again read the tapped thermometer. If three consistent readings are obtained, the heating can be stopped. It should be emphasised that the most accurate results are obtained if the thermometer readings are thus noted shortly after the rise in the boiling-point, as registered by the thermometer, is complete. An appreciably longer delay may produce inaccurate or inconsistent readings.
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