Full text: Vol. II (2)

188 
DIAMOND. 
known. It is therefore employed for sawing and boring the hardest 
stones, and for engraving seals. For this purpose it is reduced to 
powder. 
This powder is uſed in the fame manner as sand, emery, or other 
cutting powders, are employed by the lapidaries, viz. by moistening 
it with empyreumatic oil, and applying it to their wheel or drill ; 
or the metal point used by the seal engravers, like a crayon. The 
metal employed for this purpose is the purest and softest iron. This 
takes faſt hold of the diamond powder,—it being pressed into it by 
the force exerted in the operation : And the little particle never 
quits its place to roll about, but is carried along by the tool, acting 
like the tooth of a file, and tearing up whatever it touches. There 
is something curious in the way in which diamond acts in cutting 
common glaſs. The glazier’s diamond is by no means ſharp pointed. 
I have seen them as blunt and round and fmooth as the head of a 
large pin ; yet this, with a moderate preffure, causes the plate to 
ſhiver under it wherever it is drawn. This is by no means a crack; 
but the glafs being made somewhat weaker there, splits imme 
diately, when gently patted on the other side with a hard body. 
4. The diamond is still more distinguished from the rest of the 
gems by its chemical properties, or the effects produced on it by 
heat and mixture with other bodies. The utmost violence of heat, 
even that of a burning mirror, does not induce the leaft appearance 
of fusion. Its asperities are not perceptibly rounded, as has been 
obferved in the ruby. The only effect of simple heat is, to dissipate 
some foulnesses which sometimes taint its purity, or water, as it is 
called by the jewellers ; but it makes no change in its texture, if 
the diamond has been free from previous cracks or flaws. 
Nor does the utmost violence of fimple heat volatilize the dia 
mond. If it be protected from the action of the air, it fuffers no 
diminution of its weight by the longest continuance in the fire. But 
if it be fubjected to intense heat, and to a current of free air, it will
	        
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