THE NON-METALLIC ELEMENTS: SULPHUR 



69 



anhydride of this new acid, and is it possible to obtain it by 

 the oxidation of sulphurous anhydride ? 



To investigate these questions, fit up the apparatus figured. 

 In the combustion tube D, near the drawn-out end, place some 

 platinised asbestos, i.e. asbestos on which platinum h'as been 

 deposited in a finely divided state. In C place a strong 

 solution of sulphurous acid (supplied). Allow water to syphon 

 from A to B in order to drive air through the solution of 

 sulphurous acid, so that a mixture of air and sulphurous 

 anhydride, evolved from the acid, will pass through D. 



Fig. 28. 



Now heat the platinised asbestos in D. Judging from 

 the altered smell and appearance of the issuing vapours, 

 is oxidation of the sulphurous anhydride now taking place? 

 Allow the asbestos to cool, and heat an empty portion of the 

 tube. Does oxidation now occur ? Now heat the platinised 

 asbestos again, and pass the vapours into water by means of a 

 glass tube attached to D. Note whether an odourless acid 

 solution is obtained similar to that formed by the slow action 

 of the air on solution of sulphurous acid. 



This experiment indicates that sulphurous anhydride and 

 oxygen do not combine under ordinary conditions even when 

 heated, but combine when brought into contact with hot 



