324 THE GROWTH OF PLANTS AND ANIMALS 



tumbler or wide-mouthed bottle filled with air, which should be 

 steadied if it tends to tip. Note formation of phosphorus 

 oxide (Pa Os). Allow this to dissolve out, that nitrogen may be 

 left pure. Then cover glass with tin, place it upright and test 

 with lime water and with a burning stick. Compare with car- 

 bon dioxide. 



4) Water manufacture: 



Burn a match, or, better, a candle under bottom of a clean 

 tin cup filled with ice water. Compare with result obtained in 

 5, part 1. 



5) Proportion of organic matter in soil: 



a) Weigh out 1 oz. of each sample of soil, as leaf mold and 

 garden soil, and label each. Dry in oven for several hours, 

 with heat low enough not to burn paper upon which they are 

 placed. Reweigh and explain loss of weight. 



b) Put dried samples in an iron spoon and place in a hot 

 fire until samples have been at red heat for 5 or 10 min. Allow 

 to cool and reweigh. What does loss of weight equal and of 

 what does residue consist? 



