SALMON— ON ROCKS. 227 
LIST OF THE PRINCIPAL SILICA SALTS. 
Ratio of 
b : a 
O.Q. 
Name of Salt. 
li^ATTTin lap 
with 
Monoxide 
X VI lii t* ICTj 
with 
Sesqui-oxid( 

1 
3 
1 
3.0 
Sexbasic \ 
R" Si 
S2 gi 
2 
2 
1 
2.0 
Quadribasic. i 
R* Si 
* Si 
3 
3 
2 
1.5 
Tribasic. 1 
'.Basic. 
R3 Si 
e Si 
4 
1 
1 
1.0 
Bibasic. 
R2 Si 
gi3 
f) 
3 
4 
.75 
Sesquibasic. 
R3 gi2 
S Si' 
6 
2 
3 
.666 
Four-thii'ds basic. 
R^ Si^ 
gia 
7 
1 
:2 
.5 
MONOSILICATE. 
Neutral. 
R 8i 
R gi3 
8 
2 
:5 
.4 
Five-fourths silicate.\ 
R^Si^ 
Siis 
9 
3 
:8 
.375 
Four-thirds silicate. 
R3 Si* 
R gi^ 
10 
1 
:3 
.333 
Ses(iuisilicate. 
sAcid. 
R2 Si» 
R2 gi9 
11 
1 
:4 
.25 
Bisilicate. 
R Si-^ 
R gi« 
1-2 
1 
:6 
.166 
Trisilicate. 
R Si3 
R Si' 
13 
1 
8 
.125 
Tetrasilicate. 
R Si^ 
R gi>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 
formulee 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 minei'als and rocks. (3) And, generally, in the 
case of complicated minerals, it avoids the necessity of setting up 
formula3 which are not statements of facts, but merely " the expres- 
sion of the individual views of the chemist who devised them." 
Next to the O.Q., which expresses the general bearing of the base 
to the acid, the most important relation is the ratio, in compound 
