On <i Difficulty in Isomorphism. 437 



BaMnMn = Ba + 8 + 2Mu 



NaS = Na + 40+ S 



But, as manganese is isomorphous with sulphur, we can, 

 better still, compare the two salts by taking- the ultimate 

 components of two atoms of sulphate of soda, thus : 



Ba Mn Mn = Ba + 8 O + 2 M n oxymanganate of bary tes . 

 2 Na S =2Na + 80 + 2S Sulphate of soda. 



Instead whereof I suggest, 



So+80 + 2S 

 (Where So stands for the atom of sodium, being, in weight, 

 double the received atom, which is represented by Na.) 

 Comparing together, as here we do, so much of each of 

 the salts as contains eight atoms of oxygen, we find two 

 atoms of manganese substituted, without affecting the 

 form of the compound, by two atoms of sulphur. This is 

 like substitution to what you have shown takes place in the 

 manganate and the sulphate of potash. Manganese and 

 Barium, in the proportion here assumed to be that of atom 

 for atom, may be regarded as possessing a like power of 

 ■substitution, since, taken in that proportion, and in suc- 

 cession, manganese, iron, calcium, barium, have been 

 found to re-place each other in compounds, without causing 

 an alteration in form. Therefore, we are sure that, in the 

 oxymanganate of barytes, the manganese is to the barium 

 in the proportion of two atoms to one. Again, the rela- 

 tion of the atoms of sodium and silver, in the proportional 

 weights generally assigned to these metals, may be regarded 

 as demonstrated by your discovery, that, in compounds, 

 these metals, in such proportions, may re-place each other, 

 without any change in the form. But I am aware of no 

 sufficient proof, heretofore adduced, establishing the rela- 

 tion of sodium or silver, in respect of atomic weight, to 

 manganese, to sulphur, to oxygen, or to barium, in such 

 a way, at least, as to forbid our either doubling or halving 

 the received atomic weights of sodium and silver. Thus, 111 

 the oxymanganate of barytes and the sulphate of soda, 

 while regarding the atomic weight of manganese as fixed, 

 we cannot doubt that the atomic weight of barium should 

 neither be halved nor doubled, but we are 'i"'"'' at liberty 



