226 
THE GEOLOGIST. 
The combination of one equivalent of one of these monoxide bases 
•with one equivalent of the acid (R Si) foi'ms a neutral Silicate. If the 
Silica preponderates and the salt is an acid salt, then, when the Si is 
to the base as 2 : 1, it is called a bisilicate ; when 3:1a trisilicate, 
and so on. Conversely, when the base preponderates and the salt is 
basic, then, when the base is to the Si as 2 : 1 , it is called a blbasic 
silicate, when 3:1a tribasic silicate, and so on. This nomenclature 
is only applicable to the monoxide salts ; but it is also applied to the 
sesqui-oxide salts in the manner exjjlained below. 
It is found, howevei', that the chemical relations of silica-salts are 
not so adequately or simply expressed by a statement of the propor- 
tionate combination of these equivalents of bases and acids, as by 
tracing the ratio of the oxygen contained in the base to that contained 
in the acid. If we take b to be the number of equivalents of oxygen 
in the base, and a the number in the acid, the ratio between those 
{b : a) will always express the most important chemical relations of a 
silica-salt. For instance, in the simple silicate Wollastonite (Ca) Si 
there is one equivalent of oxygen in the base and two in the acid, hence 
6 : rt : : 1 : 2. In the compound silicate Oiihodase (K Si^ + =41 Si'') 
b:a:-A:\2. 
This relation can be expressed more compactly by dividing out the 
ratio, and taking the quotient, which we call the oxygen^quotient 
(abbreviated O.Q.). In Wollastonite O.Q. would equal - = \ = .5 ; 
it A 
b 4 
in orthoclase O.Q. = - = = •333. 
a 12 
The following table of the principal orders of silicate-salts will give 
a general idea of their relations — and particularly of the relation of the 
monoxide (R) salts to the sesqui-oxide (It) salts. It must be iinder- 
stood, however, that it is to a great extent theoretical, — many of the 
salts having no natural existence. It will be seen by this that a 
nomenclature devised for, and only strictly applicable to, the R salts is 
likewise applied to the R salts, which are aiTanged upon the others 
according to their O.Q. It will likewise be observed, and should 
always be borne in mind, that minerals of the same per centage of Si, 
may belong to very different orders of combination. 
