SULPHUROUS ACID. 3 1 1) 



peroxide of hydrogen, and is decomposed or preserved by si- 

 milar agencies. 



Sulphur is readily inflamed, taking fire below its boiling 

 point and burning with a pale blue flame, and the formation of 

 suffocating fumes, which are sulphurous acid gas. It exhausts 

 the oxygen of a confined portion of air by its combustion, 

 more completely than carbonaceous combustibles, and on that 

 account, and partly also from a negative influence which 

 sulphurous acid has upon the combustion of other bodies, 

 it may be employed in particular circumstances to extinguish 

 combustion ; a handful of lump sulphur being dropt into a 

 burning chimney as the most effectual means of extinguishing 

 it. Sulphur unites directly with oxygen only in the proportions 

 of sulphurous acid, but several compounds of the same ele- 

 ments may be formed, which are all acids ; namely 



Hyposulphurous acid S 2 O 2 



Sulphurous acid. . . . . S O 2 

 Hyposulphuric acid. . . . . S 2 O 5 

 Sulphuric acid. S O 3 



Uses. From its ready inflammability sulphur has long been 

 applied to wood -matches. But its most considerable applica- 

 tions are in the composition of gunpowder and other deflagrat- 

 ing mixtures, and in the manufacture of sulphuric acid, which 

 there will again be occasion to notice in a more particular 

 manner. 



SULPHUROUS ACID. 



Eq.4Ql.lJ, or 82.12; SO 2 ; density 2210.6 5 combining 

 measure [ ^). 



Sulphurous acid was distinguished as a particular substance 

 by Stahl, and first recognized as a gas by Dr. Priestley. It was 

 subsequently analyzed with accuracy by Gay-Lussac and by 

 Berzelius. 



Preparation. When sulphur is burned in dry air or oxygen 

 gas, sulphurous acid is the sole product, and the gas is found to 

 have undergone no change in volume. But sulphurous acid is 

 more conveniently prepared by heating oil of vitriol upon mer- 

 cury or copper, either of which becomes an oxide at the expense 



