EXPERIMENTS IN RESPIRATION. 125 



with a cork having a tube (glass and rubber), so the gas can 

 be collected. Or the baking-powder may be placed in a saucer, 

 a funnel inverted over it, and a rubber tube slipped on the end 

 of the funnel for a delivery tube. Collect two jars' or tum- 

 blers of carbon dioxid. 



EXPERIMENT 5. Into ajar or tumbler of carbon dioxid 

 pour a little lime-water, and shake it vigorously, holding one 

 hand over the top of the jar. The lime-water is turned milky. 

 This is the test of carbon dioxid. 



EXPERIMENT 6. Pour a little lime-water into a jar, and 

 breathe through it by means of a glass tube. The lime-water 

 is rendered milky, thus showing the presence of carbon dioxid 

 in the expired breath. 



EXPERIMENT 7. Invert a jar over a burning taper. The 

 light is soon extinguished. Pour a little lime-water into 

 the jar, and shake it actively. Is carbon dioxid produced 

 by the burning taper ? The oxygen of the air unites with 

 the carbon of the taper and forms carbon dioxid. 



EXPERIMENT 8. Over a burning taper invert a clean, cold 

 jar. A film of moisture is seen on the inside of the jar. 

 This water vapor was produced by the burning of the taper. 



EXPERIMENT 9. Breathe into a cold glass jar. The mois- 

 ture from the breath is condensed on the inside of the jar. 



EXPERIMENT 10. Burn a watchspring in oxygen. Iron 

 oxid, or iron-rust, is the only product, while much heat and 

 light are given off. 



EXPERIMENT 11. Place a piece of watchspring in a glass 

 of water. The next day we shall find it has rusted. This 

 rust is iron oxid, the same as the iron oxid produced by the 

 rapid oxidation which we called combustion. 



EXPERIMENT 12. Burn a piece of magnesium ribbon. It 

 gives an intense white light, and the only product of the com- 

 bustion is a white ash, magnesium oxid. 



