404 Prof. R. Weber on a new Oxide of Sulphur and an 



colour for weeks when kept in sealed tubes in a cool place. 

 The colour of these solutions, however, gradually changes 

 from blue to green, then to brown, and finally to the appear- 

 ance of ordinary oil of vitriol. From solutions containing a 

 large quantity of sesquioxide relatively to the amount of anhy- 

 dride present, sulphur is slowly precipitated as the colour of 

 the liquid changes ; if, on the other hand, the proportion of 

 anhydride be large, the solutions remain clear. Sulphurous 

 acid is an invariable product of the decomposition of these 

 solutions. If slightly fuming (or English) sulphuric acid be 

 added in small quantities to the blue liquid just described, the 

 colour changes to green, and, on further addition of acid, to 

 brown, until finally sulphur is deposited and sulphurous acid is 

 evolved. Like changes of colour are brought about by the addi- 

 tion of sulphur in successive small quantities to the blue liquid. 

 By cooling the liquid which has been saturated with sulphur, 

 that element separates out, partly in a crystalline and partly in 

 an amorphous form. I have found that the brown liquids are 

 much less stable than the blue, inasmuch as they lose their 

 colour even after 24 hours. Heat hastens the decomposition 

 of the dissolved sesquioxide ; it likewise influences the colour 

 of the solution. A cold solution, which was coloured brown, 

 became green when heated, but returned to its original colour 

 upon cooling. The brown liquid, obtained either by the action 

 of hydrated sulphuric acid upon the sesquioxide, or by acting 

 on a solution of the same body with sulphur, contains a larger 

 amount of sulphur proportionally to anhydride than is found 

 in the sesquioxide. A brown substance is also produced by 

 the action of the vapour of anhydride upon an excess of dry 

 sulphur: this substance in the dry state is very unstable. By 

 allowing vapours of the anhydride to act upon sulphur, the 

 latter is momentarily coloured brown, but the colour quickly 

 disappears. 



Dry sulphur quickly brings about the decomposition of the 

 dry sesquioxide. I have not been so fortunate as to isolate 

 this horn-coloured substance ; and indeed I doubt whether it 

 is a true oxide of sulphur, but rather incline to the view that 

 sulphur behaves towards the blue sesquioxide in a manner 

 similar to that observed in the cases of selenium and tellurium, 

 which, when added to the chlorides of these elements, dissolve 

 therein to a large extent. 



I have determined the composition of the mixture of sul- 

 phuric anhydride and hydrate, in which the sesquioxide dis- 

 solves with the production of a brown liquid, the colour of 

 which, on the smallest addition of anhydride, changes to blue. 

 For this purpose English sulphuric acid was added to a quan- 

 tity of the anhydride, containing hydrate, until a small 



