Fire and Heat 77 



or any compound of similar nature. The air which combines 

 in burning or rusting is liberated from the burned or rusted 

 product by heat. 



A considerable amount of this gas is needed for study, and 

 it may be derived readily from several compounds which are 

 inexpensive and easily obtained. The most common is chlorate 

 of potash (potassium chlorate). To determine whether or not 

 this gives up the same gas, heat a few small lumps in a hard- 

 glass test tube. When the lumps are breaking down rapidly, 

 introduce a glowing splinter into the tube. What happens? 

 What does the result indicate as to the gas liberated? Does 

 it behave like the active part of air in supporting combustion? 



The gas which is produced from red lead and potassium 

 chlorate, and is supposed to be the active part of the air, 

 was probably first discovered by Scheele. Because it sustains 

 life, he named it " vital air/' and because it supports and is 

 indispensable to fire, he called it " fire air." Independently 

 of Scheele, Priestley discovered and gave a very complete de- 

 scription of its nature and behavior. Lavoisier, however, 

 gave it the name by which it is known to-day. He found it 

 present in many acids, and came to think of it as an " acid 

 former." He accordingly named it oxygen. What does the 

 term mean etymologically ? 



Exercise : Laboratory production of oxygen. To produce sufficient 

 oxygen for study, arrange apparatus as shown in Fig. 22. Put into 

 a large-diameter, hard-glass test tube a mixture of 10 grams of potas- 

 sium chlorate and 10 grams of powdered manganese dioxid. Close 

 the test tube with a one-hole rubber stopper, into which you have 

 inserted a piece of glass tubing about 4 inches long. Attach to glass 

 tubing a piece of rubber tubing 18 or more inches long ending in a 

 short piece of glass tubing. Arrange the jar in water so that you can 

 readily insert under its mouth the end of the glass tubing. Have 

 ready also three or four large bottles (eight to ten ounce capacity) 

 filled with water and covered with a square of glass. Apply heat care- 

 fully and gradually to the test tube, and when gas is escaping freely, 

 put end of glass tubing under the jar in the basin of water. The gas 

 bubbles through the water and, entering the jar, displaces the water. 



