SULPHUB. 



the same amount of sulphuric acid, but it is mixed with carbonic anhydride, 

 which is not wanted in many experiments. 



Sulphurous anhydride is very eagerly absorbed by water, 

 which takes up 40 volumes. This solution is an unstable 

 acid, like carbonic acid : 



Sulphurous anhydride. Water. Sulphurous acid. 

 S0 3 + H 3 = H 3 SO 3 



Yet many salts are formed by replacement of the hydrogen 

 in this acid; such salts are called sulphites, " ous " acids 

 making "ites," as you learned in 79. 



240. Bleaching Properties of Sulphurous Anhydride. It is 

 the sulphurous anhydride which is the bleaching agent when 

 straw goods are placed in a chamber in which sulphur is 

 burned. The gas unites chemically with the oxygen of the 

 coloring matter, and turns it white. The bleaching power 

 of this acid may be very prettily illustrated by holding a 

 red rose or peony over a burning stick of sulphur. The 

 coloring matter is not destroyed in bleaching, but there is a 

 chemical union between it and the acid ; and it is a union 

 that can be broken up either gradually by the action of light 

 and air, as is manifested in the return of color after a time 

 to the bleached articles, or quickly by the action of some 

 powerful agent, as sulphuric acid. We will give a single 

 illustration of the latter. If you pour a solution of sulphur- 

 ous anhydride in water into an infusion of logwood shav- 

 ings, the infusion loses its dark color ; but if you pour into 

 it a little sulphuric acid, the color will be at once restored. 



241. Sulphuric Anhydride, SO 3 . This body, which may 

 be considered as sulphuric acid less the elements of water, 

 is a glistening white solid. It can not be kept unless it be 

 shut in from the air in glass tubes hermetically sealed. On 

 exposure to the air it fumes violently, and soon becomes 

 fluid by attracting the moisture of the air. If it be thrown 



II 2 



