CHEMICAL COMPOSITION OF MINERALS. 83 
_y immersion in an acid. The screw at 6 is for the purpose of 
shortening the tube one-half so as to make it more convenient 
for the pocket of the field mineralogist. It is un- 
screwed for this purpose, and the smaller part put 
within the larger. 
In using the blowpipe it is necessary to breathe 
and blow at the same time, that the operator may 
not interrupt the flame in order to take breath. 
Though seemingly absurd, the necessary tact may 
easily be acquired. Let the student first breathe a 
few times through his nostrils while his cheeks are 
inflated and his mouth closed. After this practice 
let him put the blowpipe to his mouth and he will 
find no difficulty in breathing as before while the 
muscles of the inflated cheeks are throwing the air 
they contain through the blowpipe. When the air 
is nearly exhausted the mouth may again be filled 
through the nose without interrupting the process 
of blowing. 
The flame of a candie, or a lamp with a large l_ia 
wick may be used, and when so it should be bent 
in the direction the flame is to be blown. But it is far better, 
when gas can be had, to use a Bunsen’s burner. 
The flame has the form of a cone, yellow without and blue 
within. The heat is most intense just beyond the extremity of 
the blue flame. In some trials it is necessary that the air 
should not be excluded from the mineval during the experiment, 
and when this is the case the outer flame is used. The outer is 
called the oxidizing flame (because oxygen, one of the consti- 
tuents of the atmosphere, combines in many cases with some 
parts of the assay, or substance under experiment), and the in- 
ner the reducing flame. In the latter the carbon and hydrogen 
of the flame, which are in a high state of ignition, and which are 
enclosed from the atmosphere by the outer flame, tend to unite 
with the oxygen of any substance that is inserted init. Hence 
substances are reduced in it. 
The mineral is supported in the flame either on charcoal; or 
by means of steel forceps (as in the annexed figure) with plati- 








































num extremities (a 6), opened by pressing on the pins pp; or 
on platinum wire or foil. 
