INSTRUMENTS AND CHEMICAL TESTS 



517 



thin, in fact, that it will not hold its shape and is very liable to 

 split or crack with but little use, and become worthless. The 

 tip A should be thick at the very end, with a smoothly drilled 

 hole of 0.5 mm. diameter. The tip should always be kept dean 

 of dust and when in use yield a 

 well-pointed symmetrical flame at 

 ri^ht angles to the shaft, and should 

 under no circumstances be used as a 

 pn>l>e to stir or turn the assay. 



Burner. As the fuel used in labo- 

 ratories and under ordinary circum- 

 stances is gas, the Bunsen burner 

 will be used. It is constructed as 

 in Fig. 525, stands 13 cm. high, with 

 an orifice a, near the base of the tube, 

 to admit air, which mixes with the 

 gas entering at b ; this mixture passes 

 up through the tube c to be burned 

 at the top. When the orifice a is open 

 the flame should be nearly colorless, 

 and should not deposit soot upon any 

 object held in the upper portion of the 

 flame. This colorless or light blue 

 flame is used to boil test tubes, heat glass tubes, for fusion with 

 the fluxes, or for any experiment where a moderate heat only 



is required. The sub- 

 stance being heated 

 should be held near 

 the top of the flame, 

 which is by far the hot- 

 test portion, and not 

 near the top of the 

 burner tube, as the 

 beginner is always in- 

 clined to do. When 

 the orifice a is closed 

 and no air is allowed 

 to enter and mix with 

 the gas as it passes up, 

 the flame will be yellow and yield a thick deposit of soot 

 upon any object that may be held in it; while this flame is useless 



Fio. 625. The Bunsen Burner. 



FIG. 526. The Blowpipe Burner. 



