268 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 16-milli- 

 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. 



XV. Testing with ^Hydrofluoric Acid or Silico fluorides . 



These reagents are applied in one of the manners already de- 

 scribed, usually by Methods /, ///, or /// 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 



