CHEMISTRY OF RESPIRATION. 123 



produce the changes in the air that passes through the lungs, 

 we must know something about the gases that are the con- 

 stant components of that which we breathe. 



EXPERIMENTS ILLUSTRATING THE CHEMISTRY OP 

 RESPIRATION. 



MATERIALS. Soup-plate or basin, two quart fruit-jars, 

 piece of phosphorus half the size of a pea, chalk crayon, strip 

 of sheet-lead one inch wide and eight inches long, fine wire 

 one foot long, pail of water, cup, matches, watchspring, mag- 

 nesium ribbon four inches long, two horse-radish bottles, four 

 tumblers (two should be kept in a cool place), lime-water (pre- 

 pared a day or two beforehand, by putting a piece of quick- 

 lime about the size of a hen's egg into a quart of water ; pour 

 off the clear liquid for use in experiments), wax tapers, rubber 

 tubing (two feet), bellows, splints, corks, apparatus for gene- 

 rating oxygen and carbon dioxid (consult any chemistry). 



CAUTION. Always handle phosphorus with forceps, not 

 with the fingers. Cut it under water, in a plate. 



PREPARATION. Hollow out the large end of the crayon, 

 and wire it to one end of the lead strip. Bend the strip so 

 that the crayon cup will be held at half the height of the jar, 

 and set it on the plate. Lay the piece of phosphorus in the 

 chalk cup made of the crayon ; pour a little water into the 

 plate. 



EXPERIMENT 1. Ignite the phosphorus, and lower the in- 

 verted jar over it. Keep the mouth of the jar covered with 

 water, adding more if some of the water is drawn up into the 

 jar. 



EXPLANATION. - The phosphorus in burning unites with 

 the oxygen of the air, forming a white cloud of phosphoric 

 oxid. This is gradually absorbed by the water, and the pres- 



