90 SULPHURIC ACID. 



where evil effects are feared from the communication 

 of disease. In all these cases sulphurous acid has 

 really a useful influence, as it seems able to destroy 

 a minute quantity of poisonous matter diffused through- 

 out the air ; but it must be remembered, that it can 

 have no power of improving air which is unwholesome, 

 in consequence of the presence of a large quantity of 

 carbonic oxide or carbonic acid, for in these circum- 

 stances, burning sulphur would only tend to make 

 the air worse, both by removing oxygen, and also by 

 adding sulphurous acid. 



177. The bleaching power of this acid may be very 

 well shown, by holding a lighted brimstone match 

 near a dark purple or blue flower, the color of which 

 will be immediately more or less destroyed, and we 

 may easily thus, either in part or wholly, render the 

 flower white. 



178. Sulphurous acid contains less oxygen than the 

 sulphuric acid; in fact, it stands in the same relation to 

 that acid, which carbonic oxide does to carbonic acid. 

 Sulphurous acid is formed whenever sulphur is burnt 

 in the air, because, under those circumstances, it is 

 not able to combine with enough oxygen to form the 

 more powerful acid. 



179. Sulphuric Acid is made by burning sulphur 

 mixed with nitrate of potash, which supplies it with 

 more oxygen than it could get by merely burning in the 

 air ; because the nitric acid in the nitre, when decom- 

 posed by the burning sulphur, gives rise to the forma- 

 tion of another compound of nitrogen and oxygen can- 



