316 ELEMENTARY CHEMICAL MICROSCOPY 
rod 2 to 4 millimeters in diameter. Heat the wire red hot, dip 
into borax (or other substance) and heat until a clear glassy bead 
is obtained of from i to 2 millimeters thick. Cool. Examine 
under the microscope, using a low power to assure the absence of 
crystals. Heat and touch to the powdered material to be studied. 
Then very carefully heat the preparation in the flame of a Bunsen 
burner until the borax or phosphorus salt bead just begins to melt. 
Avoid heating to redness. Cool and examine with a i6-milh- 
meter objective. Heat again, and again place under the micro¬ 
scope, thus following any changes which may take place. Should 
a blast lamp be employed for the heating care must be observed 
to avoid too large and too hot a flame. 
This method can be made to yield good results in testing for 
calcium and magnesium and also for silicon, zirconium, titanium 
and molybdenum. Colored bead reactions are also obtainable, 
as for example in testing for Co, Ni, Cr, Mn, etc. 
The general principle of the method is, however, much broader 
in its scope since it comprehends all cases where a crystalline 
phase will separate from a transparent molten mass which solidi¬ 
fies upon cooling. 
Testing with Hydrofluoric Acid or Silicofluorides. 
These reagents are applied in one of the manners already de¬ 
scribed, usually by Methods I, III, or III A. 
Specific comment is necessary, however, because of the im¬ 
possibility of employing ordinary glass object slides and because 
of the great danger of permanently damaging the objectives 
through the corrosive action of hydrofluoric acid vapors. 
Before undertaking any tests in which hydrofluoric acid vapors 
will probably be present, remove all objectives from the nose- 
piece save the lowest power, and place all microscope accessories 
at such a distance from the preparation as to render them safe. 
Take a small cover glass, carefully add a tiny drop of pure glyc¬ 
erine to its center and bring the drop in contact with the lower 
lens of the objective and press gently until the drop spreads out 
into a thin film, holding the cover glass in place. This is done to 
