Researches on the Salts of Selenious Acid. 



9 



From them, acid salts have been prepared, in most cases by treating with 

 the necessary quantity of selenious acid tor forming di- and tetraselenites; 

 in this manner, many metals, besides di-, also give tetraselenites; some, as 

 magnesium, glucinum, cobalt, instead of tetraselenites, afford triselenites, 

 some others have yielded sesquiselenites, for instance ammonium, alu- 

 minium, cadmium, didymium, formerly unknown stages of saturation of 

 selenious acid. Moreover, acid salts have been obtained also in other stages 

 of saturation; this is especially the case with those which form sesquioxides, 

 of which group 4 / 3 -selenites seem to be particularly characteristic; more 

 seldom, they give 5 / 3 -selenites. That a metal does not give any acid salts 

 may be looked upon as a very rare exception. Berzelius' supposition 

 that all acid salts would be soluble in water, is not supported by experi- 

 mental evidence; on the contrary, it is not unusual that insoluble acid salts 

 occur, as well of the heavy metals, as of the earth-metals. His statement 

 that selenious acid shows very little tendency to form basic salts, must also 

 be submitted to some correction. It happens namely very often that, on 

 mixing neutral solutions, basic salts are precipitated; this is the case with 

 glucinum, aluminium, chromium, iron, indium, uranium, cerium, lanthanum, 

 didymium etc. Such selenites as are but sparingly, or not at all soluble 

 in water, for the most part, readily dissolve in hydrochloric acid ; some few, 

 however make an exception from this rule; this is especially the case with 

 selenite of zirconium, which can be dissolved, only when heated for a very 

 long time with the warm acid. Sometimes the salt, on dissolving in 

 hydrochloric acid, yields free selenium. That this is the case with the 

 ferrous and mercurous selenites, has been already some time known; the 

 salts of thallium present the same phaenomena, which depends on an oxida- 

 tion, at the expense of the selenious acid, into ferric, mercuric etc. salts 

 that are dissolved. For the same reason, a stannous selenite cannot exist. 



After these general remarks, and before entering upon the descrip- 

 tion of the different compounds, I will first give an account of the analy- 

 tical methods applied, in order that I may not be obliged in every parti- 

 cular case to state the mode of determining the composition. 



ANALYTICAL METHODS. 



Berzelius, in his analyses, has not determined selenious acid other- 

 wise than as a loss. On accounting for the analyses of the selenites of 

 sodium, he mentions an unsuccessful attempt to precipitate selenium from 



Nova Acta Reg. Soc. Sc. Ups. Ser III. 2 



