SALMON— ON ROCKS. 227 



LIST OF THE PRINCIPAL SILICA SALTS. 















Formulas 



Formula 





Ratio of 

 6 : a 



O.Q. 



Fame of Salt. 



Wltll 



Monoxide 



with 

 Sesqui-oxid( 















bases. 



bases. 



1 



3 



1 



3.0 



Sexbasic v 





Jl6 Si 



R2 gi 



2 



2 



1 



2.0 



Quadribasic. i 





R* Si 



S Si 



3 



3 



2 



1.5 



Tribasic. 1 



S Basic. 



R^Si 





4 



1 



: 1 



1.0 



Bibasic. 



R2 Si 



R2 gi3 



5 



3 



: 4 



.75 



Sesqiiibasic. 





R3 gi2 



R Si2 



6 



2 



:3 



.666 



Four-thirds basic. 





R^ Si^ 



R^ Si9 



7 



1 



:2 





MONOSILICATE. 



Neutral. 



R 8i 



R Si^ 



8 



2 



5 



A 



Five-fourths silicate.^ 





R^ gis 



R^ Sii5 



9 



3 



:8 



.375 



Fom-thirds siUcate. 





R3 Si^ 



R Si^ 



10 



1 



3 



.333 



Sesquisilicate. 



VAcid. 



R2 Si^ 



R2 Si9 



11 



1 



.4 



.25 



Bisilicate. 



R Si2 



R Si6 



12 



1 



6 



.166 



Trisilicate. 





R Si3 



R Si» 



13 



1 



8 



.125 



Tetrasilicate. 





R 814 



R gl^2 



It will be remarked that the O.Q. of a neutral silicate is -5 ; and 

 that it increases as the base increases, and decreases as the silica 

 increases : or varies inversely as the acid. 



Besides its compactness, the expression of the order of silicate 

 minerals by means of the O.Q. has many other advantages. (1) It 

 affords a ready means of avoiding the confusion of the different 

 formulae of silicates arising from the acid having been assumed 

 until recently as a teroxide (Si) by the principal mineralogical 

 chemists. (2) It enables us to express exactly the condition of a 

 large class of intermediate and altered minerals, to which no regular 

 formulae could be applicable ; and thus to trace the metamorphoses 

 and genesis of many minerals and rocks. (3) And, generally, in the 

 case of complicated minerals, it avoids the necessity of setting up 

 formulae which are not statements of facts, but merely " the expres- 

 sion of the individual views of the chemist who devised them." 



itext to the O.Q., which expresses the general bearing of the base 

 to the acid, the most important relation is the ratio, in compound 



