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CARBONIC ACID IN THE BREATH.
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lime-water and the other common water, and tubes which pass into the bottles and connect them. The apparatus is very rough,
Fig. 35.
but it is useful notwithstanding. If I take these two bottles, inhaling here and exhaling there, the arrangement of the tubes will prevent the air going backwards. The air coming in will go to my mouth and lungs, and in going out, will pass through the lime-water, so that I can go on breathing and making an experiment, very refined in its nature, and very good in its results. You will observe that the good air has done nothing to the lime-water; in the