8, 9, and 10 are the topaz, sapphire, and
diamond respectively, and as these and minerals of similar hardness will
probably not be found in any of the localities of which I make mention,
we need not become accustomed to them for the present. 7 is of
sufficient hardness to scratch glass, and is also not to be cut with the
file before mentioned, which is used for these determinations. 6 is
of the hardness of ordinary French glass. 5 is about the hardness of
horse-shoe or similar iron; 4 of the brown stone (sandstone) of which
the fronts of many city buildings, etc., are built; 3 of marble; 2 of
alabaster; and 1 as French chalk, or so soft as to be readily cut with
the finger nail. The method of using and applying these comparisons is
by having the above matters at hand, and compare them by the relative
ease with which they can be cut by running the edge of the file over
their surface. One will soon become familiar with the scale, and it
may of course then be discarded. As it is one of the most important
characteristics of some of the minerals, it should be carefully
executed, and the result carefully considered. It is of course
inapplicable under those conditions with minerals that are in very small
crystals or in a fibrous condition.
_Action of Hot Acids_.--This very important test is never, like the
above, applicable upon the field, but applied when home is reached.
From the body of the mineral as pure and clean as possible a portion is
chipped, about the size of a small pea; this is wrapped in a piece of
stiff wrapping paper, and after placing it in contact with a solid body,
crushed finally by a blow from the hammer.
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