CLASSIFICATION OF ELEMENTS. 145 



tal to one of sulphur (Johnston ubi supra). But the division 

 of the equivalents of sodium, potassium and ammonium which 

 would follow that of silver, and the consideration of potash 

 and soda as suboxides are most violent assumptions, and not 

 to be lightly entertained. 



It has been inferred that lime with an atom of water is pro- 

 bably isomorphous with potash and soda, because CaO + HO 

 appears to replace KO or NaO in mesotype, chabasie and 

 other minerals of the zeolite family. 



Fifth Class. Chlorine, iodine, bromine, fluorine. These 

 four elements form a well defined natural family. The three 

 first are isomorphous throughout their whole combinations, 

 chlorides with iodides, chlorates with iodates, hyperchlorates 

 with hyperiodates, &c. ; and such fluorides also as can be 

 compared with chlorides appear to affect the same forms. It 

 is connected with the second class through hyperchloric acid ; 

 the hyperchlorates being strictly isomorphous with the hyper- 

 manganates. But the formulae of these two acids are 



Cl O 7 and Mn 2 O 7 , 



one atom of chlorine replacing two atoms of manganese. Or, 

 this class has the same isomorphous relation as the preceding 

 class to the others. And such I shall assume to be its true re- 

 lation, although halving the atomic weight of chlorine, which 

 would give two atoms of chlorine to hyperchloric acid, is not 

 so improbable a supposition as dividing that of sodium ; still it 

 would lead to the strange conclusion that chlorine enters into 

 its other compounds, as well as into hypermanganic acid, 

 always in the proportion of two atoms; for that element is 

 never known to combine in a less proportion than is expressed 

 by its presently received equivalent. It appears that a salt has 

 been casually observed to occur in the preparation of hyper- 

 manganate of potash having exactly the figure of chlorate po- 

 tash, and containing a corresponding acid of manganese in 

 which two of rnetal still represent one of chlorine as in hy- 

 permanganic acid.* 



Sixth class. Nitrogen, phosphorus, arsenic, antimony ; 

 also composing a well marked natural group, of which nitrogen 

 and antimony are the two extremes, and of which the analogous 



* Liebig's Introduction to the First Elements of Chemistry, by Richardson, 



-page 87. 



1, 



