Chemical formulas of the Silicates. 253 
It will be remembered that the states of R in the oxyds RO, 
R#0*, RO2, RO?, RO® (which are equivalent to RO, 8(R;0), 
2(R}0), 3(RzO), 5(R10)), or in RS, R?S*, RS?, ete., were made, 
respectively, the «R, 6R, 7R, 5R, eR states, these symbols stand- 
ing severally for R, Rg, Ry, Ry, Ry in the above. 
e larger part of the silicates are included in two divisions: 
the Unisilicate, and the Bisilicate,* as recognized in the edition 
of my Mineralogy of 1854. The Unisilicates have, on the old 
system, the general formula k2Si, when only protoxyds are pres- 
ent, and (RS, #)*Si*, when part of the base is sesquioxyd, R* and 
® being mutually replaceable in different proportions. The 
Bisilicates have the corresponding formulas RSi and (R*,#)Si*. 
With &i, the formulas are R*Si, (R*, Si; and ReSiz, (Re, BSir. 
In writing these formulas on the new system, and adopting 
the system of symbols for the metal of the corresponding oxyds, 
| 4B, 8R, etc. (but dropping the « as unnecessary), the formulas 
above cited become 
for the ordinary Unisilicates (1) 2. 0, (2) & ER), 0. 
wee i sid 
for the ordinary Bisilicates (1) a . @@ ray pie 
The silicates of each division, whether containing sesquioxyds, 
or protoxyds, or both, have on this method essentially the same 
formulas.. Moreover the other states of oxydation may be in- 
troduced with the same facility, and thus the remainder of the 
Unisilicates and Bisilicates be included. We thus bring under 
to expressions 
Unisilicate Sil | Risilicate ped 
" (Ra, R, BR, 7R, mn),s ay sical (Ray R, BR, 7R,9R)) * 
much the larger part of the silicates, and exhibit to the eye the 
of unity among them, and the truth also that in inorganic 
hature the types of compounds are few and of the simplest kind. 
By means of fractional coéfficients the atomic ratios between the 
2, te., are easily indicated. 
By way of illustration I give below the special formulas of 
Various mineral species under these general formulas, together 
With those also of the Subsilicates. The list is made longer than 
ilicates, because they ex- 
the prefix ilieat diversity of significations in the new 
meta in the term metasilicate has a liversity ¢ 
istry, while etymologically hardly any significancy whatever. 
