SULPHUR. 87 



Sulphur dioxide is a colorless gas, having a suffocating, dis- 

 agreeable odor; it liquefies at a temperature of 10, and 

 solidifies at 60; it is very soluble in water, forming sulphur- 

 ous acid ; it is a strong deoxidizing, bleaching, and disinfecting 

 agent ; when inhaled in a pure state it is poisonous, when diluted 

 with air it produces irritation of the air-passages and coughing. 



Sulphurous acid, Acidum sulphurosum, H 2 S0 3 = 82. One volume 

 of cold water absorbs about 43 volumes of sulphur dioxide, or 

 100 parts by weight of water absorb 3.5 parts by weight of 

 sulphur dioxide. To make the officinal acid, the gas is to be 

 generated by heating charcoal and sulphuric acid in a flask, and 

 passing the gas through a wash-bottle containing water, into 

 distilled water for absorption. 



Thus obtained, sulphurous acid is a colorless acid liquid, which 

 has the odor as well as the disinfecting and bleaching properties 

 of sulphur dioxide; it is completely volatilized by heat. Sul- 

 phurous acid is a bibasic acid, the salts of which are termed 

 sulphites. 



Tests for sulphurous acid and sulphites. 



1. Sulphurous acid, or the gas liberated from sulphites, by the 

 addition of sulphuric acid decolorizes an acidified solution of 

 permanganate of potassium, in consequence of the deoxidation 

 of the latter. 



2. Similarly to the above, an acid solution of bichromate of 

 potassium is turned green by conversion of chromic acid into 

 chromic oxide. 



3. When sulphurous acid or sulphites are added to diluted 

 sulphuric acid and zinc (which evolve hydrogen), sulphuretted 

 hydrogen gas is liberated: 



H 2 SO 3 + 6H = H 2 S -f 3H 2 O. 



4. Chloride of barium added to solution of a sulphite produces 

 a white precipitate of sulphite of barium, soluble in diluted 

 hydrochloric acid; sulphate of barium is insoluble in hydro- 

 chloric acid : 



Na 2 SO 3 + BaCl 2 = BaSO 3 + 2NaCl. 



Sulphite Chloride Sulphite Chloride 



of sodium. of barium. of barium. of sodium. 



