QUANTITATIVE ANALYSIS 481 designed to ensure that the carbon dioxide and water vapour are swept out of the combustion tube and transferred quantitatively to the absorption tubes. The carbon dioxide is swept out and absorbed more rapidly than the water vapour. This is due in large part to the tendency of the water vapour to condense in the beak of the combustion tube and/or the side-arm of the water absorption tube R. The two heating hooks Q are left in their original position until 120 ml. of water have been collected, they are then separated and placed one on each side of the piece of rubber tube which connects beak and side-arm, and just touching it. They remain here until a total of 190 ml. has been collected, and are finally placed on the absorption tube side-arm while the last 60 ml. pass, thus ensuring that all the water is driven over from the side-arm into the absorption tube R. If all the water has not been driven over when 250 ml. of oxygen have passed, this sweeping-out process should be continued until this has been achieved. At the end of the sweeping out, the tap
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