SULPHUR. 1()3 



Tests for sulphurous acid and sulphites. 



(Sodium sulphite, Na 2 SO 3 , may be used.) 



1. Sulphurous acid, or the gaseous sulphur dioxide liberated from 

 sulphites by the addition of sulphuric acid, decolorizes an acidified 

 solution of potassium permanganate, in consequence of the deoxida- 

 tion of the latter. 



2. Similarly to the above, an acid solution of potassium dichromate 

 is turned green by conversion of chromic acid into chromic oxide. 



3. When sulphurous acid or sulphites are added to diluted sul- 

 phuric acid and zinc (which evolve hydrogen), hydrogen sulphide is 



liberated. 



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



4. Barium chloride added to a neutral solution of a sulphite pro- 

 duces a white precipitate of barium sulphite, soluble in diluted hydro- 

 chloric acid ; barium sulphate is insoluble in hydrochloric acid. 



Na. 2 SO 4 + BaCl 2 = BaSO 3 + 2NaCl. 

 Sodium Barium Barium Sodium 



sulphite. chloride. sulphite. chloride. 



5. Silver nitrate produces a white precipitate of silver sulphite, 

 which darkens when heated, metallic silver and sulphuric acid being 



formed : 



Ag 2 S0 3 + H 2 = 2Ag + H 2 S0 4 . 



6. A strip of paper, moistened with mercurous nitrate solution, 

 turns black when suspended in sulphur dioxide. 



Sulphur trioxide, SO 3 = 8O (Anhydrous sulphuric add). This 

 is a white, silk-like solid substance, having a powerful affinity for 

 water; it may be obtained by the action of phosphoric oxide on 

 strong sulphuric acid, or by passing sulphur dioxide and oxygen 

 together over heated platinum-sponge ; it is of scientific interest only. 



Sulphuric acid, Acidum sulphuricum, H 2 SO 4 = 98 (Oil of 

 vitriol, Hydrogen sulphate). There is no other acid, and perhaps no 

 other substance, manufactured by chemical action which is so largely 

 used in chemical operations, and in the manufacture of so many of 

 the most important articles, as is sulphuric acid. 



Sulphuric acid was accidentally discovered in the fifteenth century, 

 and was then obtained by heating ferrous sulphate (green vitriol) in 

 a retort. To the liquid distilling over, the name of oil of vitriol was 

 given, in allusion to the thick or oily appearance, and the green 

 vitriol from which it was obtained. 



