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



Fischer * differed from Magnus in his interpretation of the 

 formation of the green liquid already mentioned. He sup- 

 posed that this liquid contained a coloured oxide of selenium , 

 and that the violet liquid obtained by replacing tellurium for 

 selenium, contained a coloured oxide of tellurium dissolved in 

 acid, and that these oxides were decomposed by water with 

 precipitation of the elements selenium and tellurium. He did 

 not think it probable that a mere solution of these elements 

 should be possessed of a colour so different from that of the 

 elements themselves; and he further strengthened his position 

 by pointing out that a considerable part of the dissolved tellu- 

 rium remained unprecipitated on the addition of water. 



Magnus f found that about 2 per cent, of the selenium 

 which had been dissolved was not precipitated by water. The 

 strife as to the nature of this selenium solution has not hitherto 

 been brought to an end, because no direct proof could be 

 brought forward by either side, and also because no coloured 

 oxide of selenium was known. By the action of selenium 

 upon pure sulphuric anhydride, I have succeeded in obtaining 

 a compound analogous to dithionic oxide, in which one 

 atom of sulphur is replaced by one atom of selenium. This 

 substance dissolves in fuming and also in English oil of vitriol, 

 with the production of a deeply green-coloured liquid, which 

 is possessed of the properties of the coloured liquids which 

 have been already mentioned. 



Preparation of the Compound. 



The behaviour of selenium towards ordinary sulphuric an- 

 hydride is similar to that of sulphur : it dissolves easily 

 therein ; but the compound which is produced cannot, any 

 more than the dithionic oxide, be separated from this solution. 

 In the pure anhydride (prepared as I have already described) 

 selenium is gradually converted into a dark green viscid tar- 

 like mass, which is denser than the anhydride. By main- 

 taining a temperature of 15° to 17° C, and using a small 

 quantity of selenium, the production of this substance is ac- 

 companied by the evolution of but a very small quantity of 

 sulphurous acid, formed by the partial decomposition of the 

 substance. The tarry drops of the selenium compound do not 

 dissolve in an excess of anhydride, which remains uncoloured, 

 and can be separated by decantation. Inasmuch as heat is 

 produced in this reaction, means must be adopted for cooling 

 the anhydride, without, however, causing its solidification. 

 The anhydride used in the preparation of the compound was 

 contained in a glass tube about 6 millims. wide ; small pieces 

 of porous selenium were successively dropped into the tube, 



* Pogg. Am, vol. xii. p. 153, vol. xvi. p. 118, t Ibid. vol. xiv. p. 328. 



