MINERALS AND GEOLOGY OF CANADA. 13 
acters. Where, in the above scale, two terms of comparison are 
employed, both must of course be attended to in the determination 
of the hardness. 
Specific Gravity.—This is also a character of great value in the 
determination of minerals. The specific gravity of a body is its 
weight compared with the weight of an equal bulk of pure water. 
In order io ascertain the specific gravity of a mineral we weigh the 
specimen first in air and then in water. The loss of weight in the 
latter case exactly equals the weight of the displaced water, or, in 
other words, of a volume of water equal to the volume of the mine- 
ral, Now, the specific gravity of pure water, at a temperature of 
about 62°, being assumed to equal 1, or unity, it follows that the 
specific gravity of a mineral is obtained by dividing its weight in air 
by its loss of weight in water. Thus, if a = the weight in air, and 
w = the weight in water, G, or sp. gr. = anh 
Ezample.—. piece of calcareous spar weighs 66 grs. in air, and 
42/ers. when immersed in rain or distilled water. Hence its sp. gr. 
66 66 
——__ = — = 2.75.* 
i 662242 94 2.75 
The weight of the mineral may be ascertained most conveniently 
and with sufficient exactness for general purposes, by a pair of small 
scales such as are commonly called “ apothecaries’ scales.’ These 
may be purchased for a couple of dollars, or even less. A small hole 
must be made in the centre of one of the pans for the passage of a 
horse-hair or silken fibre, about four inches in length, and fur- 
nished at its free end with a “slip-knot”’ or running noose, to hold 
the specimen whilst it is being weighed in water. The strings of the 
perforated pan may also be somewhat shortened, but the balance 
must in this case be brought into equilibrium by a few strokes of a 
file on the under side of the other pan, or by attaching thinner 
strings to it. If grain weights be used with this balance, the follow- 
ing will be required : 50 grs., 30, 20, 10, 5, 3, 2, 1, 0.5, 0.3, 0.2, G.1. 
The ‘specific gravity bottle often recommended in mineralogical 
works, is too heavy to be carried by the scales described above. 
Bottles of the smallest capacity, weigh, when filled with water, at 
least 500 grains; and these scales will not carry more than 200, or 
250 grains at the most. They are not very sensitive, indeed, when 
* This is the maximum specific gravity of calcareous spar. 
