LESSONS IN CHEMISTRY 7 



phosphorus, we are unable to make it burn, however vigor- 

 ously we may rub it against a rough surface. When, how- 

 ever, we touch a heated nail to the sulphur, the latter 

 catches fire and burns with a pale blue flame, giving off the 

 same suffocating smell that we perceived when the match 

 head was aflame. 



In the burning of sulphur a process is going on similar to 

 that already described in the case of phosphorus. The 

 heated sulphur combines with a certain amount of the oxy- 

 gen of the air, and an invisible gas is made which we 

 recognize by its pungent odor. This new substance, being 

 composed of sulphur and oxygen, is called oxid of sulphur. 

 Our experiment teaches us that sulphur does not combine 

 with oxygen as readily as does phosphorus, for the former 

 could not be lighted by friction. The heat caused by the 

 burning phosphorus on the match tip is sufficient, however, 

 to set fire to the sulphur. 



Water. We are now ready to study the composition of 

 wood itself, and to note the changes that take place when it 

 is burned. If we hold a lighted match stick just beneath 

 the mouth of a dry tumbler, we soon notice that the inside 

 of the glass is covered with a film of moisture. Water, 

 then, is the first substance produced in the process of burn- 

 ing wood. 1 It goes into the air in the form of vapor and is 

 then condensed by the cool surface of the glass. 



Carbon and Carbon Dioxid. On extinguishing the flame of 

 a burning match, we find that the wood has been converted 

 into a black, brittle substance; this we call carbon. As was 

 the case with sulphur, it is impossible to make the carbon 

 burn by the heat of friction. If, however, we put the 

 charred wood into a hot flame, the carbon catches fire, 

 gradually disappears, and nothing remains but a powdery, 

 gray ash. The same result is obtained if we allow a match 

 to burn as long as it will, since the carbon is then heated 

 red hot by the burning phosphorus and sulphur. In this 

 1 We shall prove later that water is an oxid of a gas called hydrogen. 



