[HARRINGTON | MINERALOGICAL CHEMISTRY 11 
esters have been prepared. According to Tschermak, serpentine is one 
of its salts, and may be represented by the formula H,(MgOH),MgSi,0.,. 
Other chemists, however, explain the constitution of this mineral differ- 
ently. Clarke and Schneider, for example, regard it as an orthosilicate 
represented by the formula H,(MgOH) Mg,(SiO,),.' 
If, again, we consider four molecules of water eliminated from three 
molecules of orthosilicic acid, we obtain a polysilicic acid with the empi- 
rical formula H,Si,0,, thus : 

OH 
SON NES 
Si oH Si—_oy 
OH < 
Ou 
ZO i MAO 
Si — OH LEE 4H,0 — nS OH 
Où 
OI 0 
AOE. MON 
SIT OH SIT 9 
OI 
THREE MOLECULES OF ORTHO-TRISILICIC 
ORTHOSILICIC ACID. ACID: 
A compound having approximately this composition was prepared 
by the late Prof. Fremy of Paris.’ The polysilicates of Dana’s mineralogy 
are supposed salts of this acid. Orthoclase feldspar may be regarded as 
an ortho-trisilicate, and according to this view its formula is K AISi,O.. 
The silicic acids which we have discussed are then : 
(1) H,SiO, Orthosilicie. 
(2) H,SiO, Metasilicic. 
(3) H,Si,O, Meta-disilicic. 
(4) H,Si,O, Ortho-trisilicic. 
(5) H,Si,O, Ortho-disilicic. 
There is good evidence as to the existence of the first two, and 
fairly strong evidence as to the existence of 3 and 4. An ester or 
ethereal salt, (CH,),Si,O., of No. 5 has been prepared. Certain silicates 
have also been referred to it, but their constitution is probably better ex- 
plained in other ways. But even if we allow only four silicic acids it 
will be seen that the possibilities as regards variety of composition are 
very great ; for not only may there be both basic and acid salts of these 


1 Am. Jour. Sci., 40, 308, 1890. 
2 By decomposing potassium silicate solution by CO,, or SiF, by water, and drying 
the gelatinous precipitates so formed in vacuo, Fremy obtained a hydrate containing 
16°2 to 16°8 p.c. of water. The formula H,Si,0, requires 16°67 p.c. 
