Researches on the Salts of Selenious Acid. 



77 



analogous to those of the bivalent metals; but the acid salts, formed by 

 the decomposition of the former when heated, and the basic salts, seem to 

 partake more of the properties of the metal-group, to which we shall here- 

 after come; although it may be, that this circumstance only indicates that 

 the hydrate of glucinum is possessed of very weak basic properties. 



Ziuc, though affording a tetraselenite, gives no diselenite, which, no 

 doubt, is dependant upon the different solubility of the neutral salt and the 

 tetraselenite. 



The selenites of mercury make remarkable exceptions from the re- 

 gularity generally observable within the group of the bivalent elements; 

 the mercurous selenites, by their decided tendency to grow basic, even with 

 excess of acid, and by forming an acid salt, as extraordinary as 9 / 6 -selenite; 

 the mercuric selenites by their disinclination to yield acid salts, 5 / 4 -selenite 

 being the only one obtained, and under circumstances when the other me- 

 tals of the group have given di-, tri-, or tetraselenite. 



Also cadmium is very interesting and irregular with regard to its 

 selenites, being the only bivalent metal which has afforded an acid salt 

 such as 



3Cd.0 2 .SeO+H 2 .0 2 .SeO, 



a composition very characteristic of the sexivalent metals within the follow- 

 ing group, which, almost without exception, give salts of the composition 



R 2 .0 G .3SeO -f H 2 .0 2 .SeO +xaq. 



Cadmium moreover gives a sesquiselenite, within this group single in its 

 kind; also in this respect, it has a correspondency within the following 

 group in the sesqui-selenites of aluminium, didymium and indium, whereas 

 no bivalent metal, among the univalent only ammonium, has given such a 

 salt. Owing to its selenites as well as its known sulphate, cadmium thus 

 forms a notable link of union between the bivalent and the sexivalent me- 

 tals, to the latter of which I shall now pass. 



