30 



Prof. Sir C. A. Cameron and Mr. J. Macallan. [May 2, 



The Action of Sulphur upon Selenic Acid. 



When powdered sulphur is mixed with liquid anhydrous selenic 

 acid there is no action in the cold, but if the mixture is heated to 63° 

 the sulphur dissolves iu the a3id with production of an exceedingly 

 deep indigo-blue colour. There is some action, but slight, at 58°. The 

 body which is produced is very unstable, since it begins to decompose 

 at the temperature at which it is formed, with evolution of sulphur 

 dioxide, and reduction of the selenic acid to selenious acid. If water 

 is added when the colour has first developed, sulphur is deposited in 

 soft yellow flakes ; but after decomposition has commenced, the 

 addition of water throws down red selenium chiefly, owing to the re- 

 action between the sulphurous and selenious acids which are formed. 



A similar action has long been known to occur between sulphur and 

 sulphuric acid. In 1804 Bucholz (Gehlen's ' Neues Journal der 

 Chemie,' vol. 3, p. 7) discovered that sulphur dissolved in the latter 

 acid with the formation of a blue colour, the sulphur being re-precipi- 

 tated on addition of water. This reaction was subsequently inves- 

 tigated by Yogel, Schweigger, Berzelius, Wach, and Stein, and in 

 1875 Weber succeeded in isolating the blue compound (Poggendorffs 

 'Annalen,' vol. 156, p. 531), and discovered it to be a sesquioxide 

 of sulphur, S 2 3 , but very unstable, decomposing at ordinary tempe- 

 ratures with evolution of sulphur dioxide. 



The Action of Selenium upon Selenic Acid. 



A reaction takes place between selenium and anhydrous selenic acid 

 in the cold. The selenium dissolves in the acid with production, of 

 an intense and beautiful green colour. The presence of a minute 

 quantity of water prevents the colour from developing fully until the 

 acid is warmed. The acid is capable of dissolving a considerable 

 quantity of selenium. If kept in a closed vessel the colour thus pro- 

 duced is very permanent, being unaffected for months during summer 

 weather, but if the acid be heated to 75° the colour disappears, and 

 the selenic acid is found to be partly reduced to selenious acid. 

 Addition of water, when the colour has developed, throws down a 

 voluminous red precipitate of selenium ; and exposure to the air in an 

 open vessel for a few minutes is sufficient, from the same cause, to 

 change the green colour to red. It will be shown hereafter that this 

 green colour is probably caused by the formation of a new oxide of 

 selenium. Its production with the anhydrous acid affords a test for 

 the latter, which we have already made use of in the examination of 

 the effect of heat upon selenic acid. 



In 1827 Magnus found that selenium was dissolved by strong sul- 

 phuric acid, with development of a green colour, and was re-precipi- 

 tated on addition of water. Berzelius and Fischer subsequently 



