118 



L. F. Nilson, 



The foregoing exposition lias shown the incomparably strong- ten- 

 dency of selenious acid to form acid and overacid salts. The mode of 

 formulation, employed for them, points them out as compounds of neutral 

 selenite with anhydride (the waterfree salts), or with hydrate (the salts 

 containing water), in accordance with the most general and simple mode 

 of viewing the salts in question. Another mode would be to set them all 

 down as anhydrous salts, arising from new acids, formed by the union of 

 several molecules of selenious acid under partial loss of water. In this 

 sense, for example, the very remarkable salts of the sexivalent metals that 

 we have become acquainted with in the preceding investigation, would have 

 to be regarded as neutral salts of a six-basic tetraselenious acid: H 6 .0 6 .Se 4 5 , 

 formed by 4 mol. selenious acid, with the loss of 1 mol. water. But such 

 an assumption seems to me little authorized; it requires namely the 

 existence of a particular acid for every new stadium of saturation, and we 

 have seen in the preceding pages that selenious acid affords a great num- 

 ber of acid salts, of which the following 12 may be regarded as the re- 

 presentatives : 



1. 



5 / 4 -selenite: 



4Hg.0 2 .SeO+H 2 .0 2 .SeO. 



2. 



7a- 



>? 



Fe 2 .0 G .3SeO + H 2 .0 2 .SeO. 



3. 



3 A- 



>) 



2Am 2 .0 2 .SeO + H 2 .0 2 .SeO. 



4. 



Va- 

 %" 



') 



5Be.0 2 .SeO + 3H 2 .0 2 .Se.O. 



5. 



»a 



Cr 2 .O c .3SeO + 2H 2 .0 2 .SeO. 



6. 



7 A- 



;i 



2(Th.0 4 .2SeO) + 3H 2 .0 2 .SeO. 



7. 



%- 



>) 



5Hg 2 .0 2 .SeO + 4H 2 .0 2 .SeO. 



8. 



di- 



') 



Mg.0 2 .SeO+H 2 .0 2 .SeO. 



9. 



%- 



jj 



3Be.0 2 .SeO + 4H 2 2 .SeO. 



10. 



V-- 



11 



Th.0 4 .2SeO-f 3H 2 .0 2 .SeO. 



11. 



tri- 



)1 



Mg.0 2 .SeO-l-2H 2 .0 2 .SeO. 



12. 



tetra- 



11 



Zn.0 2 .SeO + 3H 2 .0 2 .SeO. 



On the other hand, the circumstance that the most part of these acid 

 salts, though formed at a higher temperature, contains water, seems to be oppo- 

 sed to such a view. Certainly, some of them lose their whole amount of 

 water at 100°, but this by no means proves that it is present in the compound 

 as crystallization-water, because selenious acid itself, at this temperature, 

 very easily becomes an anhydride. Particularly worthy of attention is the 

 composition of the acid selenites of the univalent metals; it is namely, as 

 already shown, of such a kind that they, without exception, may be re- 

 garded as consisting of R 2 .0 2 .SeO + nH 2 .0 2 .SeO. No one of them contains 



