84 . CHEMICAL PROPERTIES OF MINERALS. 
To ascertain the fusibility of a mineral, the fragment for the 
platinum forceps should not be larger than the head of a pin, 
and, if possible, should be thin and ablong, so that the extrem- 
ity may project beyond the platinum. The fusible metals alloy 
readily with platinum. Hence compounds of lead, arsenic, an- 
timony, etc, must be guarded against. ‘These compounds are 
tested on charcoal. The forceps should not be used with the 
fluxes, but instead either charcoal or the platinum wire or foil. 
The charcoal should be firm and well burnt; that of soft 
wood is the best. It is employed especially for the reduction 
of oxides, in which the presence of carbon is often necessary, 
and also for observing any substances which may pass cff and 
be deposited on the charcoal around the assay. These coatings 
are usually oxides of the metals, which are formed by the oxi- 
dation of the volatile metals as they issue from the veduction 
flame. 
The platinum wire is employed in order to observe the ac- 
tion of the fluxes on the mineral, and the colors which the 
oxides impart to the fluxes when dissolv ed in them. ‘The wire 
used is No. 27. This is cut into pieces about three inches long, 
and the end is bent into a small loop, in which the flux is fused. 
This makes what is called a bead. When the experiment is 
complete the beads are removed by uncoiling the loop and draw- 
ing the wire through the finger nails. After use for awhile the 
end breaks off, because platinum is acted upon by the soda, and 
then a new loop has to be made. Dilute sulphuric acid will 
remove any of the flux that may remain upon it after a trial 
has been made. 
Glass tube is employed 6% various purposes. It should be 
from a line to a fourth of an inchin bore. It is cut into pieces 
four to six inches long, and used in some cases with both ends 
open, in others with one end closed. In the closed tube, either 
heated directly over the Bunsen burner, or with the aid of the 
blowpipe, volatile substances in the assay are vaporized and 
condensed in the upper colder part of the tube, where they 
may be examined by a lens if necessary, or by further heating. 
The odor given off may also be noted, and the acidity of any 
fumes by inserting a small strip of litmus paper in the mouth 
of the tube. ‘The closed tube is used to observe all the effects 
that may take place when a substance is heated out of contact: 
with the air. In the open tube the atmosphere passes through 
the tube in the heating, and so modifies the result. The assay 
is placed an inch or an inch and a quarter from the lower end 
of the tube; the tube should be held nearly horizontally, to 
