analogous Selenium Substitution Product of the same. 405 



quantity of the blue sesquioxide, which was dissolved in con- 

 centrated acid, was taken up by the liquid with the production 

 of a brown colour. This estimation of the sulphuric acid con- 

 tained in the mixture gave the following results: — 



Substance Barium Sulphate Percentage of 



taken. obtained. Sulphuric Acid. 



1-356 3-327 84-20 



1-400 3-475 84-32 



The liquid therefore contained sulphuric anhydride and 

 water in the proportion of 



6S0 3 and5H 2 ; 

 or anhydride and hydrate in the proportion of 

 lS0 3 and5H 2 S0 4 . 

 Such a solution may be diluted to a certain point without 

 losing the property of dissolving the sesquioxide with the pro- 

 duction of a brown liquid; but if this point be overstepped, a 

 decomposition takes place, the liquid becomes turbid and of 

 the colour of ordinary oil of vitriol, while sulphur is deposited. 

 The analysis of such a liquid showed that its composition 

 nearly agreed with that of the hydrate (H 2 S0 4 ). 



The blue sesquioxide is therefore dissolved with the forma- 

 tion of a brown liquid in an acid mixture containing an excess 

 of anhydride amounting to one fifth of that contained in the 

 first hydrate. 



Acid mixtures which are richer in anhydride dissolve the 

 sesquioxide with formation of blue or green liquids, while 

 acids whose concentration corresponds with that of the first 

 hydrate, or is somewhat less than this, decompose the sesqui- 

 oxide with the deposition of sulphur. 



The analogous Selenium Compound. 



Before describing the results of my experiments, I shall 

 give, as in the case of the sulphur compound, a short histori- 

 cal sketch of the work which has been done in connexion with 

 this substance. 



Magnus * first observed that selenium was soluble in oil of 

 vitriol. He stated that the solution is coloured green, that 

 the selenium dissolved as such, and that it is only upon warm- 

 ing the liquid, or upon allowing it to remain in moist air, that 

 the selenium undergoes oxidation, while sulphurous and sele- 

 nious acids are evolved. The statement, that the selenium is 

 dissolved without change, Magnus based upon the observation 

 that addition of water to the green liquid caused the deposi- 

 tion of almost the whole of the selenium, while from the liquid 

 which had been decolorized by boiling, no selenium, or but a 

 very small quantity, was thrown down by a similar treatment. 



*. Ann. vol. x. p. 491. 



