44 MINERALOGY. 
chemistry, which in its system must, summarily at least, treat of all the 
combinations of matter, and consequently of all minerals, we must consider 
the analytical portion of the latter science as the instrument by which we 
construct the former on a sure basis. This indeed is the view which we 
have taken in the following pages. 
1. Testinc or Mineraus, AND THE Apparatus NEcESSARY. 
The chemical analysis of a mineral is indispensable to a proper knowledge 
of it. This analysis once performed, however, it is not necessary to repeat 
it in every case; all that is needed being to determine, with certainty, one 
or more constituents. The blowpipe (pl. 32, fig. 1) serves this purpose. 
It consists of a tube through which air is blown from the mouth into an 
expansion of the instrument, where it is somewhat condensed; thence to 
emerge with some force, through a small aperture at the extremity of a fine 
lateral tube. On bringing this aperture of the blowpipe over the burning 
wick of a spirit or oil lamp, the fine current produced as just described, 
causes the flame to run out into an attenuated point (jig. 2) of extraordi- 
nary intensity of heat; this flame is the agent employed in conducting the 
investigations. Mineral bodies, to be tested by means of the blowpipe, 
are placed in very small quantity on a piece of charcoal or clay, or else 
held in a platinum spoon or forceps (fig. 3), and thus submitted to the 
flame. This consists of two cones, one within the other ; the former being 
blue, the latter yellow. The greatest intensity of heat is found just beyond 
the end of the blue flame. The blue flame is called the flame of reduction, 
bodies being deoxydized in it; the yellow is the oxydizing flame, causing, 
in many cases, the combination of oxygen with the bodies in question. 
Thus we may learn the melting point of bodies, or their relation to heat ; 
we may reduce an oxydized body to its base in the blue flame, and oxydize 
it, if at all possible, in the yellow. By the application of such acids as 
phosphoric or boracic, capable of resisting the decomposing action of the 
flame, we dissolve a small portion of the mineral in the flame, and thus 
ascertain the color of its various salts. Another construction of the blow- 
pipe is given in pl. 32, fig. 4. Here it is screwed to a post with an 
attached stand, and can be set higher or lower along the post, for the sake 
of allowing a proper position with reference to the accompanying lamp. It 
thus permits the free use of both hands. 
A physical examination must frequently be combined with the chemical 
in the determination of a mineral. Thus the knowledge of its specific 
gravity is of great importance. In addition to the ordinary methods which 
may be employed, Nicholson’s areometer (pl. 82, fig. 5) is often used to 
great advantage. This consists essentially of the funnel a, the cylinder 8, 
the rod cm, and the table or plate d. The instrument is so arranged that 
when set in distilled water, and a definite weight laid upon d, it will sink to 
a mark, m, made on the rod. To determine the specific gravity of a 
mineral it is laid on the plate d, when it will, of course, depress the 
474 
