INSTRUMENTS AND (II KM KM. TESTS 553 



:il. Mini the roaMing continued. The assay is stirred from time 

 to time iir turned over with the spatula until :dl parts an- brought in 

 contact with the ll;ime Mild :iir. If sulpliMtes Mild ar>enal< 

 present, the O. F. and R. F. should le u>ed alternately. When 

 white fumes no longer escape or the odor of sulphur dioxide i> no 

 longer perceptible, the roasting is completed; the residue remain- 

 ini:. generally .-peaking, is MII oxide, MIK! is in condition for UH- 

 in subsequent 1)CM(1 or reduction tests with the fluxes. 



Illustration. Spread finely ground pyrite. 1 '. S ... in a thin layer 

 over M shallow cavity on coal, heat gently in the O. F., but not hot 

 enough to fuse it. Bluish fumes of SO 2 , identified by the odor, will 

 ari-e MS the result of oxidation; the assay will blacken from the 

 formation of the magnetic oxide of iron, Fe 3 O 4 , which may be 

 proven with the magnet. If the roasting is completed and the 

 oxidation continued, the final product will be the red oxide of iron, 

 I * ),, which is not magnetic. 



Platinum wire, .4 mm. in diameter, is used to support fine pow- 

 der in testing for flame colorations, for fusing silicates with soda 

 iNaaCOs), but especially as a support for the borax and 

 salt of phosphorus beads, in testing for the bead colora- 

 tions, so characteristic of many oxides. For this purpose 

 the wire is held in the platinum wire holder, Fig. 530, 

 the free end is bent in a loop as nearly circular as pos- 

 silile 1 mm. in diameter. To make the borax bead, heat 

 the loop of wire in the O. F. ; while hot touch it to the 

 powdered borax, or to a grain of borax of suitable size, 

 then fuse it in the O. F. until all bubbles have dis- 

 appeared, and the bead is clear and colorless when cold. 

 Sufficient borax should be used to fill the loop and form 

 a spherical bead when cold. Oxides are dissolved in 

 the borax bead by touching the hot bead to the oxide, 

 when some of it will stick to it. It is then heated once 

 more in the O. F. until all the little particles seen floating 

 in the fused borax have disappeared and the bead is 

 clear and transparent. If oxide of manganese is used, 

 the bead when cold will be colored violet-red. In viewing a 

 bead it should be held up to the light of a window, or with a 

 white l)Mckground; never hold it between the eye and the 

 yellow flame of the burner. If the bead is dark and opaque, 

 an .excess of oxide has been dissolved, and the color will appear 

 only after it has been flattened with a gentle pressure with 



