548 MINERALOGY 



for ordinary purposes, it is the flame always used with the 

 blowpipe. It is better to have two burners, one the Bunsen 

 burner as just described, and another, a modified burner, as in 

 Fig. 526. This burner is fitted with a special cap a which flattens 

 the flame in the direction of the blast. This cap simply pushes on 

 the top of the burner tube and is easily removed, when the burner 

 may be used in the ordinary way. For convenience in use and ease 

 in blowing, this modified burner should stand not more than 8 cm. 

 high. 



Where gas is not to be had, as in field work and prospecting, the 

 paraffine candle will take the place of the blowpipe burner, or a 

 kerosene oil lamp, with a flat wick, will furnish more heat and larger 

 charges may be used. For heating test tubes the alcohol lamp is 

 easily carried and yields a hot, colorless flame, which deposits no 

 soot. 



Before testing substances in the blowpipe flame it is necessary 

 to thoroughly understand the difference between the oxidizing flame, 

 always designated the O. F., and' the reducing flame, designated 

 the R. F. The student must practice blowing these two flames 

 until a pure flame is obtained in each case, which can be kept con- 

 stant and can be continued for some time with ease and without 

 exertion. 



Structure of the flames. Light the Bunsen burner, open the 

 orifice and admit air to mix with the gas, have the cock opened 

 ,11, until the flame stands about 7 cm. high. Immediately 

 above the tube of the burner will be seen a conical-shaped 

 area, a, Fig. 527. This cone is formed by the upward 

 pressure of the gas. Here the flame is hollow, the gas has 

 not yet ignited, and there is little or no heat. If a plati- 

 num wire be pushed quickly across this cone, it will become 

 red-hot on either side of this area and in the center will re- 

 main dark for some little time. Surrounding this area 

 like a mantle is the inner blue cone b, Fig. 527, where the 

 ignited gas is being decomposed ; here it contains a large 

 proportion of carbon monoxide, which burning to carbon 

 dioxide colors the flame blue. Carbon monoxide has a 

 strong affinity for oxygen ; thus this blue mantle will re- 

 duce a large number of compounds when held in it. The 

 FIG. 527. mogt e ff ect i ve reducing portion of the blue cone is just 

 below the tip ; the substance to be reduced is held so as to be 

 completely surrounded by the blue flame. 



