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MINERALOGICAL REMARKS. 283
and ftrike fire difficultly with a fteel. The fpecific gravity of the
tranfparent kind is to water as 2,3651 to 1,0000, of the opake kind
as 2,3592, and of the mountain-rock as 2,3333. One of thefe clear
pebbles, which weighed feventy-five grains, was repeatedly made red
hot in a covered crucible, and each time quenched in cold water ; by
this operation it became white, and fomewhat fpongy on its furface ;
in the middle neither its clearnefs nor tranfparency was changed in
the leaft. I then broke it into {mail pieces, and placed them once
more for two hours in a ftrong red heat, by which not the leaft
change was now produced on their new furfaces, but they remained
conftantly clear, with the edges fharp and tranfparent. After all this
Jong procefs in the fire, I only found a lofs of one grain in weight.
The pebble which had been thus treated was ground very fine,
and fifty grains of it were placed in a crucible with three times its
weight of decompofed mineral alkali, and heated as much as pofble
for three hours, (yet) without fuffering it to melt: then the cooled
white fubftance was fuperfaturated with aqua regis, and boiled for a
few hours in a fand-bath ; then filtered, and the undifolved filiceous
earth carefully wafhed with diftilled water; then dried,and at laft ftrong¬
ly heated in a crucible. This then weighed thirty-feven grains.
Fourthly, A little dry phlogifticated alkaline falt was added to the filter¬
ed folution, and Pruffian blue was then precipitated; eight grains were
required. to its entire precipitation. Then all was ‘boiled in a retort
till it was reduced to a few ounces, then filtered, the Pruffian blue
002 well
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