On a Difficulty in Isomorphism. 43 j 



Not with manganafe of barytes . . . Ba Mn 



But with oxymanganate of barytes . . Ba Mn Mn 

 This discrepancy, which, occurring in such a case, ap- 

 peared to me very startling on the first perusal of your 

 paper, I propose to show, may be removed, by regarding 

 the salts in question, as we may reasonably do, notwith- 

 standing our preconceived notions to the contrary, to be 

 as much alike in constitution, as you have proved them to 

 be in form. 



That you may the better judge of the ground I proceed 

 on in offering such a suggestion, I may advert previously 

 to a change, similar, in its reasons, to the one I am going 

 to suggest — a change, however, which the notions of che- 

 mistry prevalent on the Continent do not admit or call for, 

 but which your paper is calculated to bring about in regard 

 to one point of doctrine, on which the British chemists 

 differ from the Continental. While, by both, the atoms 

 of oxygen, potassium, sulphur, and manganese, are held 

 at proportional weights, the atom of chlorine is held by us 

 at double the weight it is held by you. Between these two 

 views of the atomic weight of chlorine, the choice, I ap- 

 prehend, must be decided by your discovery, that the oxy- 

 manganate of potash corresponds in form with the oxy- 

 chlorate. Representing these compounds in their ultimate 

 components, we have, according to 

 Your view and ours, K + 8 O + 2 Mn oxymanganate of potash 



Yours .... K + 80 + 2C1 7 M . - . , 



Ours . . . . K + 8 0+ Ch joxychlorate of potash 



(Ch, representing our atomic weight of Chlorine, being 

 double CI, representing your weight of the same atom.) 



Your doctrine of Isomorphism — that is, the fact ascer- 

 tained in other instances, that, in compounds different in 

 some of their components, but agreeing in the number of the 

 atoms of those components, the resulting form is often the 

 same — this doctrine comes in between those two views, as 

 a witness on behalf of nature, to enable us to decide which 

 is true. The doctrine itself, indeed, I am well aware, is 

 little heeded by some chemists, who seem therein swayed 

 chiefly by a certain indolence that hinders them from let- 

 ting their attention dwell on difficulties, existing, no doubt, 



2 F 



