Methods of air analysis / by J.S. Haldane.

  • John Scott Haldane
Date:
1920
Catalogue details

Licence: In copyright

Credit: Methods of air analysis / by J.S. Haldane. Source: Wellcome Collection.

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    stopper, which can then be easily removed or replaced without letting any air into the bottle. If the stopper is removed under water, which may sometimes be necessary with an awkwardly shaped stopper, the bottle should first be slightly warmed, so as to ensure that the pressure inside is positive, and no water enters; the neck is then at once closed by the middle finger and the bottle transferred to the mercury trough. The free end of the bent tube is now depressed below the mercury level and introduced into the neck of the bottle, and the tap of the burette is turned so as to allow the sample to be sucked into the burette. During this operation the bottle should be steadied with one hand ; as soon as the sample is sucked in the bottle becomes steady owing to the fact that mercury has been sucked up inside it, and support by the hand is no longer necessary. More than 20 c.c. of the sample should in most cases be taken in, after which the tap is com¬ pletely closed by a quarter-turn. The pressure inside the burette is now negative, and must be roughly adjusted to atmospheric pressure by raising the level¬ ling-tube. It is then safe to turn the tap so as to connect the burette with the potash pipette. If there was much negative pressure in the burette the potash might be sucked over on opening the tap. A positive pressure might, on the other hand, drive some of the sample into the potash pipette before the first reading was taken. The general procedure required when the sample is ■contained in a sampling tube will be evident from fig. 2.