I.NSTKrMKXTS AM) CIIKMICAL Tl 8TS 



519 



The third :iiv:i c, :i large purplish com- inclosing the blue mantle, 

 is formed l>\ the heated products of eombu.-t ion mixed with air, 

 which rushes into the llanir from all sides. Area c \s oxidizing, as 

 substances held in it are raised to a high temperature and while 

 heated come in contact with the oxygen of the air. The hottest 

 portion is immediately outside the blue mantle. In heating test 

 tubes and other large objects they should always be held above the 

 blue cone and never down near the tube of the burner. 



The areas of the O. F. as produced with the blowpipe are very 

 similar to those of the Bunsen burner. To produce the O. F. grasp 

 the blowpipe in the right hand with the first and second fingers 

 above, the third and fourth fingers below the shaft of the instru- 

 ment, with the thumb braced up toward the mouthpiece. In this 

 position a firm pressure may be applied to the mouthpiece, a very 

 material aid in keeping the flow of air constant, and at the same 

 time the blowpipe will not slip through the hand. With the hand 

 in the position described, place the lips against the mouthpiece, 

 fill the cheeks with air from the lungs ; while the air from the cheeks 

 is passing slowly through the blowpipe take another breath through 

 the nose. With each breath taken keep the tension on the cheek 

 muscles as nearly constant as possible. With a little practice the 

 constant draft through the blowpipe can be continued almost 

 indefinitely with but little exertion. 



Having practiced the breathing as described, place the forearm, 

 about halfway from the elbow, against the edge of the desk. The 

 lighted burner should be placed to 

 suit this position and with the nar- 

 row slot in the cap parallel to the 

 ed-e of the desk, slanting down 

 to the left. Place the tip of the 

 blowpipe over the slot, covering 

 half of it, and 5 mm. above the 

 cap. Blow a strong constant draft 

 through the blowpipe parallel to 

 the slot. The flame will be di- 

 rected down and to the left, by the draft, as in Fig. 528. It should 

 be about 3 cm. long, sharp-pointed, with a well-defined inner blue 

 cone a corresponding to the- blue mantle of the Bunsen burner 

 flame. It should burn steadily without sputtering or hissing, and 

 should contain no yellow stripes. If it is irregular, forked, or hisses, 

 the tip is probably imperfect, contains particles of dust, the orifice 



FIG. 528. The O.F. 



