GASES 151 



hausting its oxygen, then work downwards. If 3'ou begin at the 

 bottom of the mixture, as the gas comes oflf, it is liable to puff 

 the black dust up and choke the delivery tube. After once begin- 

 ning to make the oxygen, the lamp flame must not be taken 

 away from the test-tube while the delivery tube is under water. 

 The cooling of the tube will contract the gas, and water will rush 

 back and break the hot tube. 



All the apparatus may be held with the hands. One pupil 

 may attend to the bottles; one hold the test-tube, using a thick 

 handle of paper as a holder; anotlier may manage the lamp. A 

 stand and other conveniences may be used. For descriptions 

 and figures see anj' elementary text-book in chemistry. 



Note — Ever\f single operation of the above should be ques- 

 tioned about, and explained by the pupil, as every step is a good 

 lesson. 



Now that we have five or more bottles of oxygen, they may 

 be tested as follows: 



Into one bottIe,have one of the children insert alighted splinter. 

 Let the fire be extinguished except a small glow at the end. 

 Also have a small piece of lighted candle attached to a wire 

 thrust down into the jar. 



A piece of sulphur may be burned in the next jar. A little 

 cup made from a piece of crayon fastened to a wire can be used 

 to hold the lighted piece of sulphur while inserting it into the jar. 



A fine iron or steel wire may be burned. The wire may be 

 bent into a spiral form by wrapping it about a round lead pencil. 

 To one end of the wire attach a very small splinter, or bit of sul- 

 phur to serve as a lighter. The wood or sulphur is lighted, and 

 the wire thrust into the jar of oxygen. 



To burn charcoal, a charred splinter, or a glowing coal fast- 

 ened to a wire may be used. 



A brilliant effect is produced by heating a teaspoonful of 



