OF CENTRAL CANADA PART I. 29 



Difficultly fusible substances become vitrified only on the surface, or 

 rounded on the extreme edges ; whilst infusible bodies, though often 

 changing colour, or exhibiting other reactions, preserve the sharpness 

 of their point and edges intact. 



The more characteristic phenomena exhibited by mineral bodies 

 when exposed to this treatment, are enumerated in the following 

 table : 



(a) The test-fragment may " decrepitate " or fly to pieces. Example : most 

 specimens of galena, heavy spar, &c. In this case a larger fragment must be 

 heated in a test-tube over a small spirit lamp, and after decrepitation has 

 taken place, one of the resulting fragments can be exposed to the blowpipe 

 flame as directed above. Decrepitation may sometimes be prevented if the 

 operator expose the test-fragment cautiously and gradually to the full action 

 of the flame. 



(b) The test-fragment may change colour (with or without fusing) and 

 become attractable by the magnet. Example, carbonate of iron. This becomes 

 first red, then black, and attracts the magnet, but does not fuse. Iron pyrites, 

 on the other hand, becomes black and magnetic, but fuses also. , 



(c) The test-fragment may colour the flame. Thus, most copper compounds 

 impart a rich green colour to the flame ; compounds containing baryta and 

 many phosphates and borates, with the mineral molybdenite, colour the flame 

 pale green ; sulphur, selenium, lead and chloride of copper colour the flame 

 blue of different degrees of intensity ; compounds containing strontia and 

 lithia impart a crimson colour to the flame ; some lime compounds impart to it 

 a pale red colour ; soda compounds, a deep yellow colour ; and potash com- 

 pounds, a violet tint. 



(d) The test-fragment may become caustic. Example, carbonate of lime. 

 The carbonic acid is burned off, and caustic lime remains. This restores the 

 blue colour of reddened litmus paper. It also imparts, if moistened, a burning 

 sensation to the back of the hand. 



(e) The test-fragment may take fire and burn. Example, native sulphur ; 

 common bituminous coal, &c. 



(f) The test-fragment may be volatilized or dissipated in fumes, either 

 wholly or partially, and with or without an accompanying odor. Thus, grey 

 antimony ore volatilizes with dense white fumes ; arsenical pyrites volatilizes 

 in part, with a strong odor of garlic ; common iron pyrites yields an odor of 

 brimstone, and so forth. In many cases the volatilized matter becomes in 

 great part deposited in an oxidized condition on the charcoal. Antimonial 

 minerals form a white deposit or incrustation of this kind. Zinc compounds, 

 a deposit which is lemon-yellow whilst hot, and white when cold. Lead and 

 bismuth are indicated by sulphur-yellow or orange-yellow deposits. Cadmium 

 by a reddish-brown incrustation. 



