QUANTITATIVE ANALYSIS 489 easier to lift the reservoir J out of its rim for raising and lowering, rather than ftinning the ring up and down the central stand on each ocasion). Tap T 1 is 0ow cautiously opened to such an extent that not more than one bubble of gas per second passes, and these bubbles are observed carefully as they rise in the nitrometer tube. Bubbles containing a large proportion of air are not absorbed, guffer little diminution in size and rise rapidly up the tube. Bubbles of carbon dioxide, however, are absorbed, diminish in size and rise more and more slowly as they ascend. When all the air has been swept out of the combustion tube, the so-called micro-bubbles are obtained; these should almost disappear and not be larger than a fine dust; they swirl in the wide part of the nitrometer as they rise, instead of travelling straight upwards, and they rise extremely slowly. These bubbles are so small that it should be possible to collect them for upwards of half an hour before any detectable volume is registered on the nitrometer
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