COLLECTION OF GASES. 



163 



consists in first filling the bottle or jar (to be ultimately filled with, 

 gas) with water by immersing it therein in a tub or basin, and then 

 raising it bottom upwards partially out of the water, but so that the 

 mouth of the jar is still under water; or otherwise, by filling the 

 jar with water and corking it, or covering the mouth with the palm 

 of the hand, or with a saucer, and rapidly inverting it, and lowering 

 it till the mouth is under the water in the basin, the cork, hand, or 

 saucer being then removed ; if this is dexterously done, the jar 

 remains filled with water, not more than a comparatively insig- 

 nificant bubble or two of air entering during the operation. 



The jar thus filled with water, and partly raised out of the 

 basin, remains full of water in consequence 

 of the atmospheric pressure ; but if the delivery 

 tube of a gas generator producing an appropriate 

 kind of gas (such as hydrogen or oxygen), be 

 dipped into the basin and brought under the 

 mouth of the jar, the bubbles of gas passing out 

 at the end of the delivery tube will rise up into 

 and be caught in the jar, which will thus 

 be gradually filled with gas, which takes the 

 place of the water. When the jar is full, a 

 gas tray or saucer (fig. 70) is slipped under its 

 mouth whilst still immersed, and the saucer and 

 jar are then lifted out of the basin together, and 

 set by for use afterwards ; whilst another jar is 

 made to take the place of the first one, and is 

 similarly filled, escape of gas or entrance of air 

 being prevented by the water in the saucer which 

 "seals" the jar with a "water lute" or "hydraulic valve," a kind 

 of arrangement for closing temporarily the mouths of vessels con- 

 taining gas extensively used in another form 

 in coal gas works and chemical factories, 

 where gases of various kinds are dealt with. 

 As soon as one jar is thus filled, another may 

 be made to take its place, and thus several 

 may be filled in succession. 



To save the trouble of holding the jar 

 whilst filling with gas, a couple of half bricks 

 may be arranged side by side in the basin 

 half an inch or so apart ; the delivery tube is 

 made to pass into the vertical slit between 

 them, whilst the jar stands partly on one and partly on the other 

 brick in such a position that the bubbles rise up into it. At the 

 instrument-dealer's a pottery "bee-hive shelf" (fig. 71) may be 



Fig. 70. Bell jar 

 and Gas Tray. 



Fig. 71. Bee-hive 

 Shelf. 



