550 MINERALOGY 



is rough, or the draft has been directed against the cap of the 

 burner. All of these must be looked to, until all irregularities 

 of flame are corrected. The length of the flame may be regulated 

 by the position of the platinum tip. If a short flame is required, 

 the tip is pushed a little farther over the slot, and when a long flame 

 is needed the tip is withdrawn, when the flame will shorten or 

 lengthen as the case may be. 



The O. F. is used to oxidize substances ; for this use the object is 

 held beyond the tip of the blue cone. It must be remembered that 

 the blue cone is formed by burning carbon monoxide, which is reduc- 

 ing, therefore the blue cone must not come in contact, with the 

 substance being oxidized. The O. F. is used for testing the fusi- 

 bility of minerals, testing for flame colorations, and, as it is the 

 hottest flame, in general where a high temperature is required. 



To test the temperature of the 0. F. take a piece of platinum 

 wire 0.1 mm. in diameter, bend 5 mm. of the end at right angles ; 

 holding the wire in the forceps, place it in the flame just so that the 

 extremity touches the tip of the blue cone, with the bent portion 

 parallel to the draft and pointing in the direction of the blowpipe. 

 If the conditions are right, the wire will be seen to shorten and a 

 small globule of fused platinum form on the end. Platinum fuses 

 at a temperature of 1755 C. This temperature must have been 

 reached in the small flame or the globule could not have formed. 

 It will also be seen that it is not the largest flame, but a small well- 

 pointed flame which fuses the wire the more quickly. 



The reducing flame, R. F. It is only necessary to turn the gas 

 up somewhat and withdraw the blowpipe tip until the point is 

 just over the edge of the burner and somewhat higher than when 

 blowing the 0. F. The entire flame will be deflected by the draft 

 to the left and a little below the horizontal. 



The R. F. is composed of burning hydrocarbons and carbon 

 monoxide and colored with particles of glowing carbon, all of which 

 are reducing agents. The R. F. will reduce many oxides to a lower 

 state of oxidation. If red oxide of iron, Fe 2 0s, be held in it for only a 

 short time it will be reduced to the protoxide, FeO, thus Fe 2 3 + 

 CO = 2 FeO + C0 2 ; one third of the oxygen will be taken up by 

 the R. F. If the FeO be held in a pure O. F. it will pass back to 

 Fe 2 Os. In all such cases a portion of the oxygen is at the com- 

 mand of the operator ; it can be taken away or added to the sub- 

 stance according to the flame used. 



Another class of oxides when treated in the R. F. is reduced di- 



