HOW TO MAKE A FIRE 183 



become a household necessity. This is the clinical ther- 

 mometer which is used in order to detect any change in 

 the temperature of the body from normal, or 98.6 degrees. 

 Body temperature changes are the surest indication that 

 something is wrong within, for fever always shows the 

 presence of toxins or poisons in the blood, and may mean 

 serious illness. In case of a high temperature or fever a 

 physician should always be called. 



Study of a match. Fire making has improved greatly 

 since the days when the Indian rubbed a pointed stick 

 into a hole in another stick in order to obtain a light 

 through the heat evolved by the rapid rubbing or friction. 

 The flint and steel of our forefathers made use of per- 

 cussion in obtaining fire, and the modern friction match 

 makes scientific use of the different kindling temperatures 

 of different substances. We have seen that phosphorus 

 kindles at a lower temperature than most substances, but 

 white phosphorus is poisonous and its use in making 

 matches has been prohibited by law, so that the ordinary 

 match head now contains a mixture of a phosphorus com- 

 pound combined with potassium chlorate, powdered glass 

 or sand, and glue. By rubbing this enough heat develops 

 so that it. lights. In the safety match the head is made up 

 of some substance that burns at a low temperature while 

 red phosphorus is placed on the box, combined with sand or 

 powdered glass to give it a rubbing surface. This prevents 

 the match from being lighted without the phosphorus on 

 the box to aid it in its ignition. 



How to make a fire. The following simple experiment 

 will show one factor necessary to start a fire. Cover a 

 burning candle with a lamp chimney so that it is closed 

 at the bottom but open at the top. The candle gradually 



