40 Ur. W. Odliug on the Doctrine of Equicalents. 



that an atom of the same element under different conditions has 

 several different representative values. Thus^ if we take three 

 atoms of chlorhydric acid, H-'^CFj we can replace the three 

 atoms of hydrogen by three atoms of potassium, to obtain three 

 atoms of chloride of potassium, K'^ CP. But in three atoms of 

 chlorhydric acid, H^ CP, we can also replace the three atoms of 

 hydrogen by one atom of bismuth, and thereby obtain the body 

 BiCP, or terchloride of bismuth ; whence it is evident that the 

 atom of bismuth is equivalent to, or is the representative of, 

 three atoms of hydrogen or of potassium ; and we find in general 

 that the different elements have different replaceable values or 

 equivalents. Taking the atom of hydrogen as the unit of equi- 

 valency, the atom of bismuth has a threefold equivalency. To 

 facilitate comparison, I proposed some few years back, that mode 

 of indicating differences in equivalent value which has now come 

 into very general use, namely, by the use of one or more dashes 

 placed to the riglit or left of the symbol, so as to establish a 

 difference to the eye between the atom of a body and its 

 equivalent or substitution value, as shown in the following 

 formulcE :- ^Vg'^ PO^ Phosphate of silver. 



Bi'" P04 Phosphate of bismuth. 

 It not unfrequently happens that the same element has more 

 than one equivalent. For instance, an atom of platinum, with 

 the atomic weight 98 'S, sometimes replaces one, sometimes two 

 atoms of hydrogen. Thus we have the compounds — 



Platinous chloride Pt' CI analogous to HCl. 



Platinic chloride Pt" CP analogous to H- CP. 



Platosamine . NH^Pt' T , , ,tuq 



Platinamine . NH Pt" | analogous to NH^. 



Diplatosaminc . IV^H^Pt' ~| , , oattt«? 



Ditlatinamine . N^H^pt'/ |a"'^%0'^s to 2NIP. 



Again, the atom of iron, with the atomic weight 28, is sometimes 

 equivalent to one, sometimes to | of an atom of hydrogen, thus: — 

 Ferrous chloride . , Fe' CI analogous to IICl. 



Ferric chloride . . . FFe"' CP analogous to H^ CP. 

 Ferro- sulphate of potash Fe' K' SO'* analogous to H^ SO"*. 

 Iron-alum .... FFe'" K' S^O^ analogous to 211280". 

 And similarly with several other metals. 



As a further illustration of equivalents, three atoms of hydro- 

 gen may be equally well replaced by 



Three atoms of potassium K'^ 



One atom of potassimu + one atom of platinum K' Pt" 

 Two atoms of iron (ferricum) ..,.,. FFe'" 



One atom of bismuth Bi"' 



!Six atoms of mercury (diiuercurosuni) . . . ^^llg^' 



