STUDY OF AIR. 9 



7. (By burning or oxidation is meant the chem- 

 ical union between oxygen and some 

 other substance.) How can you tell 

 when oxidation is going on? Name the 

 compounds that have been formed by 

 oxidation in the preceding experiments. 



3. STUDY OF AIR. (Dem.) 



Materials : Tray of water, flat piece of cork about two inches in 

 diameter, small porcelain dish (or bit of crockery), phosphorus, glass 

 jar with wide mouth, piece of glass to cover the jar, cylindrical grad- 

 uate. 



A. Preparation of nitrogen. 



i. Place the porcelain dish (or piece of crock- 

 ery) on the piece of cork and float the 

 latter on the water in the tray. Into 

 the dish put a piece of phosphorus twice 

 the size of a pea. Light the phosphorus 

 and then quickly cover it with the in- 

 verted glass jar, keeping the rim of the 

 latter about an inch below the surface of 

 the water. (See Fig. 2.) 



a. With what was the jar filled when it 



was placed over the burning phos- 

 phorus? 



b. As the phosphorus burns what do you 



see within the jar? What is the 

 composition of this substance? 

 How was it formed? (See Exp. 

 1, A, 5.) 



c. What ingredient, therefore, of the air 



is being removed? Why does the 



