Fire and Heat 



73 



increase when the draft is increased by having a small opening at the 

 bottom and the top of the chimney? Does the fact that the candle 

 flame flickers uncertainly and is finally extinguished when the air is 

 shut off completely at the bottom and the top, prove that air is impor- 

 tant for burning ? Does it prove that air is indispensable to burning ? 



What proportion of the air is active 

 or unites with burning substances may 

 be determined in several ways. The 

 two ways which are suggested will bring 

 out the essential points. Both experi- 

 ments may be started at the same 

 time, though one requires several days 

 to give a satisfactory result. 



/n verted Jar 



Sack of Iron 



Filings 



-Water 



FIG. 20. The iron filings 

 becoming rusty or slowly oxi- 

 dizing use up a portion of 

 the air imprisoned in the jar. 



of the air is thus 



Exercise : Part of air used in combus- 

 . You will need two quart glass jars 

 with wide mouths ; a short piece of candle 

 fastened to a cork large enough to support it when floating and small 

 enough to enter the mouth of the jar ; three ounces of bright iron filings 

 tied in a bag of cheesecloth, and this fastened 

 to one end of a glass rod about five inches long ; 

 a piece of glass tubing bent as in Fig. 21. 



Moisten the bag and iron filings and arrange 

 over water in a granite pan, as in Fig. 20. 

 Mark the level of the water with a rubber band 

 or a sticker label. Let the jar stand undis- 

 turbed for several days, but observe frequently 

 and record heights of water level. When level 

 becomes stationary, mark it and test the resid- 

 ual air in the jar as directed in the next ex- 

 periment. 



Arrange glass tubing, which should be about 

 one inch high inside the jar, as in Fig. 21, and 

 fasten with rubber band. Use lime water or 

 caustic potash solution in the granite basin. 

 Light the candle and then cover carefully with 



the jar, forcing this down until the water runs into the shorter end 

 of the glass tube. Note that the water closes the tubing, thus pre- 

 venting the escape of air from the jar. Observe the behavior of the 

 candle flame. What does it show concerning the necessity of air to 



FIG. 21. How to ar- 

 range glass jar, glass tube, 

 and candle over water. 



