434 Doctor Clark to Professor Mitscherlich. 



plish that object, without going far to modify our concep- 

 tions of Oxygen-salts and Oxygen-acids. 



In various of your papers illustrative of Isomorphism, 

 you have proved that sulphur, selenium, chrome, and man- 

 ganese, have the power of re-placing each other, in com- 

 pounds, without affecting the resulting form, and that sil- 

 ver, in certain compounds, is re-placed, in like manner, by 

 sodium. The evidence that these conclusions rests upon, 

 cannot be better shown to be stable, than by putting it in 

 array. The salts in each of the four columns of the follow- 

 ing table, are like each other in form, but different, in that 

 respect, from any of the salts contained in the three other 

 columns. 



,„, , of Soda (Na). ,.„ , ... T „ of Silver with 



oj Potash. ^ Sih ^ <A ^ oj Sodawith Water. J Ammonia . 



Sulphate . . KS NaS NaS + 10HH 



AgS AgS +4NH 



Seleniate . . K §e Na Se NaSe+lOHH 



AgSe AgSe+4NH3 



Chromate . K Cr NaCWlOHH 



AgCr+4NHs 



•Manganate KMn 



In the foregoing table, the substituting power of manga- 

 nese has least of evidence to support it, in as far as this 

 metal occurs therein, as an element, only once. But what- 

 ever want of evidence may be supposed to arise hence, is 

 well supplied in the two following salts, alike in form and 

 constitution : — 



Ammoniacal chrome alum . . Am S + Cr Cr S 3 + 24 HH 

 Ammoniacal manganese alum Am S + Mn MnS 3 + 24 HH 



(Where Am is ammonium = N 2 H 3 ). 

 Now the discrepancy I have alluded to is this — 



The waterles? sulphate of soda . . Na S 

 and of course, the isomorphous salts Ag S, 

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



