174 SEVENTH REPORT—1837. 
the number of elements, nor the ratio between the positive and 
negative constituents was alike in the mutually replacing com- 
pounds. As, however, ammonia with an atom of water may be 
represented by (H,N +O) the oxide of ammonium ; this case was 
fairly considered as byno means decisive that isomorphous bodies 
are not necessarily analogous in constitution and represented by 
analogous formule. It may be, as many chemists have thought 
probable from other grounds, that potassium is itself a com- 
pound metal, and that potash, were its true constitution under- 
stood, may be analogous with ammonia. 
Other compounds, however, were discovered, agreeing in form, 
yet represented by formulz not reconcilable according to re- 
ceived views. Of these the earliest known were, that nitrate of 
soda and nitrate of potash, not then observed to be dimorphous, 
were severally isomorphous with cale spar and arragonite, and 
other examples have since been added chiefly by the researches 
of Mitscherlich. All the known groups of this kind are repre- 
sented in the following Table. TI call them monomorphous, to 
indicate that as groups with unlike formule they are not all 
known to assume more than one form. 
