ROCK SALT 267 
Chip off a piece of the specimen and observe the 
fracture, which in most cases is conchoidal or shell-like 
(see page). Break up the specimen still further and 
observe its cleavage. Notice the shape of the fragments, 
which generally take the form of cubes: 2.¢, its cleavage 
is cubical. Observe closely its form and make out 
whether this is crystalline or non-crystalline. If it shows 
cubical cleavage, its structure is crystalline. 
Scratch the surface of the specimen with a file or knife- 
blade, and notice that it is easily cut into. Compare its 
hardness with Coal and other substances, and find out 
its place in the scale of hardness: i.¢., its hardness com- 
pared with that of other substances examined. 
Its taste is easily determined—but pupils should be 
required to distinguish between the saline taste of Rock- 
Salt, the sour taste of a lemon, and the bitter taste of 
quinine, and the acid taste of vinegar. 
Before determining its specific gravity, cover the 
surface of the fragment to be operated on with a thin coat 
of varnish to prevent solution. The varnish, should, of 
course, be allowed to dry before the mineral is immersed. 
The increase in volume owing to the presence of the 
varnish will be so small as not appreciably to affect the 
result of the experiment. For an account of the method 
of finding specific gravity see page 260. 
Chemical Properties, Reduce a small portion of the 
specimen to powder, and heat this in a crucible over a hot 
flame. If the flame be hot enough, notice that the mineral 
does not burn, but gradually melts or fuses together 
into a mass which becomes compact and hard on cooling 
—it is, therefore, fusible. 
Place some of the powdered mineral in a beaker con- 
taining cold water and stir well. Notice that it soon dis- 
appears—the water has dissolved it-—it is, therefore, 
