HEATING THE HOME 13 



show that substances burn much more vigorously in it than 

 in air. 



Before a substance will burn, it must be heated to a cer- 

 tain temperature called the kindling temperature. In 

 kindling fires, substances are first used with a low kindling 

 temperature, such as paper, then this sets fire to a substance 

 with a higher kindling temperature, like wood, and finally 

 the wood in burning heats up a substance like hard coal with 

 a still higher kindling temperature, till it, too, burns. 



DEMONSTRATION 4 



Purpose. To prepare oxygen and study its properties. 



Apparatus. Test tube, glass tubing about eighteen inches 

 long, pneumatic trough, four wide-mouthed glass bottles, po- 

 tassium chlorate, manganese dioxid, oxone, sulfur, iron picture 

 wire, deflagrating spoon. 



Directions. A. Preparation of oxygen. i. Fill the test 

 tube half full of a mixture of equal parts of potassium chlorate 

 and manganese dioxid. Insert a stopper with a hole. Bend 

 the glass tube about three inches from one end to make an acute 

 angle, and at the same distance from the other end bend it to 

 make an obtuse angle. Insert the end with the acute angle, in 

 the hole of the stopper, and put this in the test tube. Support 

 the tube on the ring of a ringstand. Place the other end of 

 the tube under the shelf of the pneumatic trough. Fill the 

 trough with water to cover the shelf. Fill four wide-mouthed 

 bottles with water and invert on the shelf. 



2. Heat the test tube gently, allowing the first bubbles to es- 

 cape. Then place one bottle with the mouth over the opening 

 in the shelf so as to collect the gas. When the water has all 

 been forced out, remove the bottle and put another in its place. 

 In this way fill four bottles. 



3. In place of potassium chlorate and manganese dioxid 

 oxone may be used. The advantage of using this is that it is 

 not necessary to heat the substance. It may be placed in a 

 bottle and when water is added, oxygen is given off at once. 



