212 Domestic Science 



dry a piece of yellow phosphorus as big as a large pea 

 and place it in a clean dry porcelain dish, P. 



Float this dish on the surface of the water in the 

 trough. Remove the stopper from a glass bell-jar, J3, 

 about 9 inches high, and lower the open end of the jar 

 into the water so that the dish is within the jar. Note 

 the level of the water-surface. 



Warm a glass rod gently in the Bunsen flame and, 

 passing it through the neck of the bell-jar, ignite the 

 phosphorus by touching it with the rod. At once 

 withdraw the rod and insert the glass stopper, S. 

 Hold the jar down for a few moments, as the action is 

 sometimes rather vigorous. Carefully observe how the 

 phosphorus burns, what sort of product is formed by 

 its combustion, what happens to that product, and 

 also any alterations which occur in the level of the 

 water-surface. When no further change seems to be 

 taking place within the jar, note the fraction of the 

 original air-space which is now occupied by water, and 

 the appearance of the gas remaining in the jar above 

 the water. Pour water into the trough till the water- 

 level is the same both outside and inside the jar. 



Warm the glass rod again, remove the stopper, and 

 try to ignite any phosphorus which remains. If the 

 experiment has been properly carried out this cannot 

 be done. Insert a lighted taper through the neck of 

 the bell- jar. It is at once extinguished. 



Exercise for Student. 

 Why is the pouring in of water to equalise the levels necessary ? 



From the above experiment it is clear that the whole 

 of the air does not take part in the burning of a candle 

 or a piece of phosphorus. 



