18 A POPULAR EXPOSITION OF THE 
must be heated in a test-tube over a small spirit lamp, and after 
decrepitation has taken place, one of the resulting fragments may 
be exposed to the blow-pipe flame as already explained. 
(6) The test-fragment may change colour (with or without fusing) 
and become attractable by a 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 mag- 
netic, but fuses also. 
(c) The test-fragment may colour the flame. Thus, most copper 
compounds impart a rich green colour to the flame; compounds con- 
taining 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 paler 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 or 
other sensitive part. 
(ec) The test-fragment may take fire and burn. Example, native 
sulphur ; common bituminous coal, &e. 
(f)The test-fragment may “ volatilize,’ or dissipate 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; com- 
mon iron pyrites yields an odour of brimstene, and so forth. 
(g) The test-fragment may fuse, either wholly, or only at the point 
and edges; and the fusion may take place quietly, or with bubbling, 
and with or without a previous “ intumescence” or expansion of the 
fragment. Most of the so-called zeolites, for example, (minerals 
abundant in Trap rocks), swell or cur} up on exposure to the blow- 
pipe, and then fuse quietly. Lepidolite fuses with great bubbling, 
and colours the flame red. Feldspar only melts on the edges, at 
least, in ordinary cases. 
(h) The test-fragment may remain unchanged. Example, Quartz, 
and various other infusible minerals. 
