964 



SULPHUROUS ACID 



The sulphurous acid is passed through a wash-bottle, to remove any trace of sulphuric 

 acid which may come over, and then through a tube containing chloride of calcium, 

 if the gas be wanted dry ; it may then bo collected over mercury in the pneumatic 

 trough, or by displacement of air ; it cannot be collected over water, owing to its great 

 solubility in that liquid. 



2. By heating charcoal, or almost any organic substance, with concentrated sul- 

 phuric acid in tie same apparatus as above ; but in this case the sulphurous acid is 

 contaminated with a large quantity of carbonic acid, which, however, does not inter- 

 fere with it in many cases, as when employed in the manufacture of alkaline sul- 

 phites : 



C + 2(HO.SO S ) = CO 2 + 280= + 2HO. 



Charcoal. Sulphuric acid. Carbonic acid. 



C + 2H SO = CO 3 



Sulphurous acid. Water. 

 2S0 2 + 2B?0. 



3. By the combustion of sulphur or iron pyrites in oxygen gas or in atmospheric 

 air, and this is the process most generally employed on the large scale, as in the 

 manufacture of sulphuric acid. See STOPHURIC ACID. 



S 



0- = 



SO*. 



Sulphur. Oxygen. Sulphurous acid. 



Properties. At ordinary temperatures and atmospheric pressure sulphurous acid is 

 a colourless, transparent gas, possessing the disagreeable odour so well known to those 

 who have burnt a sulphur-match. It is neither combustible, nor a supporter of com- 

 bustion, and is always the product obtained by burning sulphur in air. It is a weak 

 acid, and is very soluble in water, that liquid at 60 Fahr. dissolving more than thirty 

 times its volume of the gas ; the solution of sulphurous acid, thus obtained, bleaches 



