CLASSIFICATION OF ELEMENTS. 1 U 



ric acid (HO, SO 3 + HO) with the sulphate of magnesia (MgO, 

 SO 3 + HO). The isomorphism of the salts of magnesia,, zinc, 

 cadmium and the protoxides of manganese, iron, nickel and 

 cobalt is perfect. But water has not been shewn to be iso- 

 morphous with these oxides, although it greatly resembles 

 oxide of copper in its chemical relations. Lime is not so closely 

 related as the other protoxides of this group, being allied to the 

 following class. But its carbonate, both anhydrous and hy- 

 drated, its nitrate and the chloride of calcium assimilate with 

 the corresponding compounds of the group ; while to its sul- 

 phate or gypsum, CaO., SO 3 + 2HO, one parallel and isomor- 

 phous compound, at least, can be adduced, a sulphate of 

 iron, FeO, SO 3 + 2HO (Mitscherlich), which is also sparingly 

 soluble in water like gypsum. 



Bismuth is placed in this class from its nitrate and sub- 

 nitrate, which are strictly analogous in composition to the ni- 

 trate and sub-nitrate of copper, but their isomorphism has not 

 been observed. The salts of the oxide of chromium, of alumina 

 and glucina are isomorphous with those of peroxide of iron 

 (Fe 2 O 3 ), with which these oxides correspond; and the salts 

 of manganic and chromic acids are isomorphous, and agree 

 with the sulphates. The vanadiates are believed to be isomor- 

 phous with the chrornates. Zirconium is placed in this class, 

 because its fluoride is isomorphous with that of aluminum and 

 that of iron, and its oxide appears to have the same constitu- 

 tion as alumina ; and yttrium and thorium solely because their 

 oxides, supposed to be protoxides, are classed among the 

 earths. 



Third Class. Barium, strontium, lead. The salts of their 

 protoxides, barytes, strontian and oxide of lead are strictly 

 isomorphous, and one of them, at least, oxide of lead is di- 

 morphous, and assumes the form of lime, and the preceding 

 class in the mineral plumbocalcite (Johnston) . But certain car- 

 bonates of the second class are dimorphous, and enter into the 

 present class, as the carbonate of lime in arragonite, carbonate 

 of iron in junckerite, and carbonate of magnesia procured by 

 evaporating its solution in carbonic acid water to dryness by 

 the water-bath (G. Rose), which have all the common form of 

 carbonate of strontian. Indeed these two classes are very 

 closely related. 



The Fourth class consists of potassium, ammonium, sodium, 



