STATE GEOLOGIST. 29 
the particles in contact with the basic matter, as well as the crystalline or 
amorphous condition. While in the discussion of chemical reactions it is 
always assumed that molecule is in contact with molecule, this ideal con- 
dition is never realized except in solutions and fusions. In the manufac- 
ture of glass, the sand is ground finely and is intimately mixed with the 
fluxes, soda and lime. On exposing the mixture to a high temperature 
the fine particles of silica will be the first to unite with the flux, forming 
a readily fusible silicate, which later draws the coarser particles into 
solution. Similarly in preparing artificial silicates from crystalline silica 
without actual fusion, the first consideration must be fineness of grain. 
Coarse particles and crystalline fragments are of no value for the reaction. 
‘The range of size allowable for the quartz fragments in the preparation 
of hydraulic mixtures has been examined by the writer in a series of 
experiments quoted elsewhere. At this stage it suffices to say that quartz 
grains whose diameter averages more than 0.005 of an inch are practically 
inert, since their reaction with the basic substance remains only superficial. 
This question of size is of the utmost importance in practice, since for all 
artificial cements the quartz must be ground to the required fineness, an 
operation which means a certain expenditure for power and wear and tear 
of machinery. 
Amorphous Silica. —When quartz is fused with sodium: carbonate 
it dissolves in the latter, forming a sodium silicate readily soluble in water. 
if we treat the fused mass with water, dissolving it completely, and 
acidify it we obtain on concentration a precipitate of silicic acid, 
gelatinous in character. We have thus transformed by fusion the insol- 
uble crystalline silica into the soluble state, for on treating the separated 
silicic acid with a hot sodium carbonate solution, it will be found to go 
into solution without difficulty. The colloidal silicic acid, on being brought 
in contact with hydrated lime, will slowly harden, producing a cement, 
the substance formed being a hydraulic calcium silicate. 
The hydrous silicic acid prepared as above does not correspond to 
any definite composition, but may be represented by the general formula, 
SiO,-+xH,O, the water held chemically being dependent on the conditions 
of concentration, temperature, acidity, etc., which prevailed during the 
precipitation of the substance. The chemical activity of the colloid during 
its hydrous state is proportional to the number of molecules of water 
fixed chemically, or the amount of water thus keld, though silicic acid in 
no case can ever be considered a strong acid compared with nitric or 
hydrochloric acids. 
Thus we may have the following and many other silicic acids: 
H,SiO,, meta-silicic acid, bi-valent. 
Combining two molecules of meta-silicic acid and imagining one 
molecule of water split off, we. have: 
2H,5i0O,—_H,O=H,Si1,O,, meta-disilicic acid. 
By adding one molecule of water to the meta-silicic acid we obtain 
further: 
TE oi©, OT, >10,, ortho;silicre acid, 
