28 ANNUAL REPORT 
more or less readily, according to the crystallization and size of grain, by 
caustic potash and soda solutions. In time, finely pulverized quartz 
unites completely with the caustic bases, forming hydrous silicates of 
potassium or sodium. When fused with potassium or sodium carbonate 
it combines readily with these, producing anhydrous silicates, which again 
are soluble in water. 
When quartz is heated to red heat or above, molecular changes 
take place expressed by peculiar changes in volume, the material expand- 
ing, as has been shown by Chatelier, in a seemingly irregular manner. 
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Fig. 1. Chatelier’s Curves, showing the expansion of various forms of silitca. 
These molecular changes, expressed by the expansion, tend to trans- 
form the crystalline mass to the non-crystalline or amorphous state. In 
practical experience this phenomenon is familiarly known in the manu- 
facture of Dinas or silica brick, which are invariably found to increase in 
volume when exposed to higher temperatures. Likewise in the manu- 
facture of bricks from clay high in sand, which, instead of shrinking, as 
most clay bricks do, expand in the kiln often to the surprise of the maker. 
The same fact is applied in the grinding of quartzitic rocks for the pottery 
industry, which, before being crushed and ground, are calcined and 
quenched in water while still hot. 
But heat assists in bringing about the union of crystalline silica 
with practically all bases. While the hydrated silicic acid is a most feeble 
acid, the anhydrous silicon dioxide at higher temperatures becomes the 
most active and powerful acid, being able to unite with bases in a great 
number of proportions. In the formation of silicates the physical charac- 
ter of the silica, as well as of the reacting base, is of vital importance in 
governing the chemical reactions taking place. ‘This refers to the size of 
