METHOD OF COLLECTING GASES.

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downwards, scarce any of it will enter the glass, because itsentrance is opposed by the elasticity of the included air ; but ifthe vessel be turned with its mouth.upwards it immediately fillsand the air rises in bubbles to the surface. Suppose this opera-tion to be performed under one of the jars or receivers whichare filled with water and placed upon the perforated shelf, theair will ascend in bubbles as before, but instead of escaping, itwill be caught in the upper part of the jar and expel part of thewater it contains.

In this manner we see that air may be emptied out of one ves-sel into another by a kind of inverted pouring, by which meansit is made to ascend from the lower to the upper vessel. Whenthe receiving vessel has a narrow neck the air may be poured ina similar manner through an inverted funnel inserted in itsmouth.

If the air is to be transferred from a vessel that is stopped likea bottle, the bottle must be unstopped with its orifice down-wards in the water; and then inclined in such a manner that itsneck may come under the perforated excavation of the shelf.The gas will escape from the bottle and passing into the vesseldestined to receive it, will ascend in it, in the form of bub-bles.

In whatever manner this operation is performed, the necessityof the excavation in the lower part of the shelf may be readilyconceived. It is as mentioned before destined to collect the gaswhich escapes from the vessel, and direct it in its passage to-wards the vessel adapted to receive it. Without this excavationthe gas, instead of proceeding to the place of its destination,would be dispersed and lost.

The vessels or receivers for collecting the disengaged gasesshould be glass cylinders, jars, or bell-glasses of various sizes;some of them should be open at both ends, others should be fit-ted with necks at the top, ground perfectly level, in order thatthey may be stopped by ground flat pieces of metal, glass, slate,

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