OF CENTRAL CANADA PART I. 17 



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 thread (about four inches in length) furnished at its 

 free end with a " slip-knot " or running noose to hold the specimen 

 whilst this 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. 



As an application of specific gravity, apart from the employment 

 of the character in the determination of minerals, it may be observed 

 that the weight of masses of rock, heaps of ore, etc., may be readily 

 ascertained by reference to this property. The length, breadth, and 

 depth of the body being taken in feet and decimal parts of a foot, 

 and these dimensions being multiplied together, we get the contents 

 of the body in cubic feet. This value is then multiplied by 62.32, 

 the weight in Ibs. of a cubic foot of water. This gives the weight of 

 an equal bulk of water, which must finally be multiplied by the 

 average sp. gr. of the body. The weight of the latter is thus obtained 

 in Ibs. This weight divided by 2,000 gives the weight in American 

 or Canadian tons; and by dividing it by 2,240, we get the weight 

 in British tons. 



Relative Malleability. Some few minerals, as native gold, native 

 silver, sulphide of silver, native copper, &c., are malleable or ductile, 

 flattening out when struck, instead of breaking. A few other 

 minerals, as talc, serpentine, &c., are sectile, or admit of being cut by 

 a knife ; whilst the majority of minerals are brittle, or incapable of 

 being cut or beaten out without breaking. In testing the relative 

 malleability of a mineral, a small fragment should be placed on a 

 little anvil, or -block of steel polished on one of its faces, and struck 

 once or twice by a light hammer. To prevent the fragment from 

 flying off when struck, it may be covered by a strip of thin paper, 

 held down by the forefinger and thumb of the left hand. Thus 

 treated, malleable bodies flatten into discs or spangles, whilst brittle 

 substances break into powder. 



Magnetism. Few minerals attract the magnet in their natural 



condition, although many do so after exposure to the blowpipe. 



(See below.) In trying if a mineral be magnetic, we chip off a small 



fragment, and apply to it a little horse-shoe magnet, such as may be 



3 



