176 CHEMISTRY. 



by means of which the paper, the wood, and the coal are 

 successively brought to the degree of heat requisite for 

 combustion. The following, then, is the order of these arti- 

 cles in relation to the degree of heat necessary to produce 

 their combustion tinder, sulphur, paper, wood, coal. If the 

 phosphorus so much used at the present day in the lucifer- 

 matches be put in this list, its place will be at the head of it. 



238. Sulphurous Anhydride, SO 2 . This gas is produced 

 whenever sulphur is burned. You are familiar with its 

 smell and its suffocating power. The gas un- 



mixed with air can not be breathed at all. It 

 extinguishes at once a lighted taper, as may be 

 seen when it is introduced into a jar of it, as 

 represented in Fig. 7& For this reason, when 

 a chimney takes fire, it may be extinguished by 

 sprinkling some sulphur upon the coals. The 

 sulphurous anhydride, rising, drives out all the 

 air, and, thus preventing the burning soot from being sup- 

 plied with oxygen, puts out the fire. The fact that the gas 

 is very heavy helps to produce this result, for while it fills 

 the chimney it is not disposed to pass rapidly upward. 



239. Preparation of Sulphurous Anhydride. This gas, though 

 easily obtained on a large scale by burning sulphur, is usually prepared in 

 the chemist's laboratory by heating copper with concentrated sulphuric acid. 

 The reaction is as follows : 



S u,phuricacid. Copper. 



2H 2 S0 4 + Cu = CuS0 4 + S0 2 + 2H 2 O 

 The sulphuric acid is decomposed, some of it furnishing S0 a and 2 to 

 form water with H 4 , while some of it forms copper sulphate with the metal. 

 Charcoal can be used in place of copper, the reaction being different : 



Pfli-hnn Sulphuric Sulphurous Carbonic WntPr 



acid. anhydride. anhydride. 



C + 2H 2 S0 4 = 2S0 2 + C0 2 + 2H S O 

 You see that more sulphurous anhydride is obtained by this method from 



