34 Prof. H. Rose on the different States of Silicie Acid, 
produced by the action of a very elevated temperature below 
the point of fusion, as occurs sometimes in the devitrification 
and crystallization of glass. Some experiments of Prof. Rose 
show the equal impossibility of sustaining this view. These ex- 
periments were made in a porcelain kiln, where the temperature 
rises to and remains during eighteen hours at about 2000° Centi- 
grade (according to M. Elsner), after which the substances thus 
heated cool very slowly. 
A erystal of quartz perfectly transparent did not undergo any 
alteration by this test ; its density of 2°651 was afterwards found 
to be 2-650. A crystal of the same quartz, the angularity of 
which was intact, but the inferior extremity of which was cracked, 
did not sustain any alteration im the intact portion, but became 
whitish and brittle in the part which was already fissured. Those 
portions which had become opaline, possessed a density of 2-613, 
which indicated the passage of the quartz to a modification less 
dense. Lastly, a crystal of very pure quartz was submitted to 
the same test, after having been previously reduced to a very fine 
powder. This powder subsided considerably, without however 
cohering, and its density fell to2°394. It was exposed a second 
time in the furnace, and the density became 2°329. 
A fragment of blackish flint, density 2°591, was submitted to 
the same process. Without changing its form, it became white 
and capable of very easy pulverization. The density of an entire 
fragment was found to be 2°218; that of the fine powder 
2°237. 
It results from these experiments that crystallized silica passes 
gradually into the amorphous modification when it is exposed to 
an elevated temperature below its point of fusion. They prove 
also that a more perfect crystalline state opposes a greater 
resistance to this transformation, as it does to the action of 
solvents. 
The amorphous modification is not produced merely by the 
action of great heat upon crystallized silica ; it is obtained also on 
fusing the same with an alkali and afterwards decomposing the 
alkaline silicate by an acid, and generally whenever a natural or 
artificial silicate is decomposed by an acid. 
Here the author signalizes various phenomena which are ob- 
served during this decomposition. Sometimes the silica remains 
in solution, sometimes it becomes separated in the pulverulent 
state, sometimes it determines the coagulation of the liquor into 
a gelatinous mass. He also signalizes the influence of calcina- 
tion on certain silicates,—sometimes rendering undecomposable 
by acids those which were previously decomposed with facility, 
sometimes, on the contrary, facilitating their decomposition. 
These facts have led certain chemists to suppose the existence of 
