On a Difficulty in Isomorphism. 443 



The constitutions here assigned to the several salts imply, 

 among others, the three following suppositions: 



1. The basis of the barytic oxymangate contains, not 

 barytes, but the peroxide of barium, which has not in any 

 other instance been ascertained to constitute the basis of a 

 salt. 



2. The basis of the alkaline oxymanganate is not soda, 

 nor peroxide of sodium, but an unknown oxide of sodium, 

 with a third more oxygen than the peroxide, and, atom for 

 atom, a third more than even the acid with which it is 

 combined. 



3. The acid in each oxymanganate is not oxyrnanganic 

 acid, but the manganic. 



In the instance of the oxymanganate of barytes, the ex- 

 travagance of such suppositions is a little mitigated, by our 

 knowledge, that manganic acid is readily convertible into 

 the oxyrnanganic, and that peroxide of barium is an obtain- 

 able compound, although not ascertained to be the basis of 

 any salt. But analogy would extend like assumptions to 

 cases where no such circumstances of mitigation would exist. 

 For example, the oxychlorate of magnesia, whose formula 

 would become 



Mg CI* 

 would present us with a basis that is not magnesia, but an 

 unknown oxide of magnesium, and an acid that is not the 

 oxychloric, nor even the chloric, but some other, not 

 known, nor named. 



In the instance of the oxymanganate of soda, it might, 

 perhaps, be thought, that part of the difficulties that have 

 been enumerated might be avoided by allowing its formula 

 to remain unaltered — 



So Mn Mn 

 But, indeed, the difficulties would not thus be made fewer, 

 they would be merely of a different character. By retain- 

 ing this formula for the oxymanganate of soda, we would 

 be involved in the inconsistency of admitting the barytic 

 oxymanganate to contain the same acid as is in the man- 

 ganate either of barytes or of soda, while we assume that 

 the alkaline oxymanganate contains a different acid. 

 ( To be continued.) 



