it08 Mr. R. Phillips's Observations 



" Now the discrepancy I have alluded to is this : 



The waterless sulphate of soda . . Na S 



and of course, the isomorphous salts Ag S, 



Na Se, Ag Se, you found to be of like form, 



Not with manganate of barytes . . . Ba Mn 



But with oxymanganate of barytes . . Ba Mn Mn. 

 " This discrepancy, which, occurring iii such a case, appeared 

 to me very startling on the first perusal of your paper, I pro- 

 pose to show, may be removed, by regarding the salts in ques- 

 tion, as we may reasonably do, notwithstanding our precon- 

 ceived notions to the contrary, to be as much alike in constitu- 

 tion as you have proved them to be in form." 



After some further observations Professor Clark proceeds : 

 ** While abiding by this your doctrine, and proceeding on a 

 like principle to what has just now been illustrated in the 

 case of the oxymanganate and the oxychlorate of potash, it is 

 possible, I conceive, to remove that unlikeness of constitution, 

 so apparent in the following salts of like form : 



The oxymanganate of barytes . . . Ba Mn Mn 



The waterless sulphate of soda . . Na S 

 These two salts we may better compare, unswayed by any 

 theory, by regarding them in their ultimate components, 

 thus: 



Ba Mn Mn = Ba -f 80 + 2Mn 



NaS =Na + 40 + S 



But as manganese is isomorphous with sulphur, we can, 

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

 ponents of two atoms of sulphate of soda, thus : 



Ba Mn Mn = Ba + 8 O + 2 Mn oxymanganate of barytes. 



2 Na S = 2Na4-804-2S 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 we here 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 com- 

 pound, by two atoms of sulphur." 



This proposal, as Professor Clark says of the difficulty 



