analogous Selenium Substitution Product of the same, 403 



Substance Q 7 * Barium Total percentage of 



taken. auipnur. Sulphate. Sulphur. 



0-785 0-151 2-112 56-36 



0-851 0-181 2-200 56-94 



0-519 0-114 1-315 56-93 



1-038 0-235 2-633 57-64 



0-910 0-206 2-284 57-26 



The residue is oxygen. 



Mean . . . 57-12 



The composition of this substance is expressed by the em- 

 pirical formula S 2 3 , which requires 57*14 per cent, of sul- 

 phur. This substance is therefore an oxide of sulphur con- 

 taining twice as much sulphur as the trioxide. Hitherto I 

 have not been able to form compounds of this substance, nor 

 to adduce facts from which an insight into the constitution of 

 the body might be obtained. This compound has not the 

 character of an acid anhydride, so far as I have yet ascertained; 

 t combines neither with water nor with metallic oxides, but 

 comports itself as an indifferent oxide, resembling some of the 

 oxides of nitrogen, 



I propose for this compound the name of Sulphur sesqui- 

 oxide, or Dithionie oxide. 



kxi insight into the constitution of this compound may pos- 

 sibly be obtained by studying its behaviour towards dry am- 

 monia ; it is, however, difficult to obtain a definite product of 

 this reaction, inasmuch as the compound which appears to be at 

 first formed suffers partial decomposition on account of the 

 heat produced in the action, notwithstanding that the tube be 

 carefully cooled. A peach-red-coloured substance is produced 

 in this reaction; but this body has not yet been obtained alto- 

 gether free from a yellow and a white substance simulta- 

 neously produced. When a mixture of these substances is 

 treated with water, sulphur is separated, and a solution is ob- 

 tained which contains sulphuric acid and polythionic acids 

 which show the characteristic reactions with silver salts. 



Behaviour of the Sesquioxide towards Sulphuric Acid. 

 The sesquioxide, as has been already mentioned, is insoluble 

 in pure sulphuric anhydride ; it is, however, very readily- 

 dissolved by a mixture of anhydride and hydrate, even when 

 the latter is present in very small relative quantities. The 

 blue compound cannot be separated from such a solution. 

 Crystals of anhydride separate from the solution in asbestos- 

 ike masses, which are more often coloured by the sesquioxide, 

 and which retain their colour for a considerable time if pro- 

 ected from the air and preserved in a cool place. The ses- 

 quioxide also dissolves in permanently liquid mixtures of anhy- 

 dride and hydrate, forming blue solutions which preserve their 



2E2 



