16 A POPULAR EXPOSITION OF THE 
The acids used in these experiments may be conveniently kept in 
small glass bottles furnished with a long glass stopper, reaching to the 
bottom of the bottle, and with a glass cap to prevent the escape of 
corrosive fumes. For geological purposes (testing calcareous rocks, 
&c.,) strong hydrochloric acid diluted with half its bulk of pure 
water, is principally used. The ‘‘ specimen basket” may be provided 
near its upper edge with a little nest, or wicker-work pocket, for the 
reception of the acid bottle. 
Action of the Blow-pipe.—The blow-pipe in its simplest form is 
merely a narrow tube of brass or other metal, bent round at one 
extremity, and terminating at that end in a point with a very fine 
orifice (a: fig. 21). If we place the pointed end of this instrument 
just within the flame (and a little above 
the wick) of a lamp or common candle, 
and then blow gently down the tube, the 
flame will be deflected into a horizontal 
position, and its heating powers will be 
wonderfully increased. Many minerals 
when held in the form of a thin splinter at 
the point of the blow-pipe flame, melt 
with the greatest ease ; and some are either 
wholiy or partially volatilized. Other minerals, on the contrary, 
remain unaltered; and thus, by the aid of the blow-pipe, we are 
often enabled to distinguish from one another, in a moment, various 
minerals which in external characters may be closely alike.* 
The blow: pipe has, strictly, a three-fold application. It may be 
employed, as just pointed out, to distinguish minerals from one 
another; some of these being fusible, whilst others are infusible ; 
some attracting the magnet after exposure to the blow-pipe, whilst 
others do not exhibit that reaction; some imparting a colour to the . 
flame, others volatilizing, and so forth. Secondly, the blow-pipe 
may be employed to ascertain the general composition of a mineral, 
or the presence or absence of some particular substance in it, as 
copper, lead, iron, cobalt, manganese, sulphur, arsenic, and the like. 
Thirdly, the blow-pipe may be used to determine in certain special 
Fig. 21. 
* More convenient forms of blow-pipe will be found described in special works on the use 
of that instrument, but the common form described above is quite sufficient for the simple 
experiments required in the determination of our ordinary minerals. 
