82 Prof. R. Bunsen on Flame Reactions. 



C. The luminous pointy ab a, not seen when the lamp is burn- 

 ing with the draught-holes open, but obtained of the size required 

 for the reactions by closing these holes up to a certain point. 



The following six points in the flame are used in the re- 

 actions : — 



(1) The base of the flame lies at «; its temperature is compa- 

 ratively very low, as here the burning gas is cooled by the up- 

 ward current of cold air, and much heat is absorbed by the cold 

 end of the metal tube. If mixtures of flame-colouring substances 

 are held in this part of the flame, it is often possible to vaporize 

 the most volatile constituent, and thus in the first few moments 

 to obtain tints which cannot be observed at higher temperatures, 

 because they then become masked by colours produced by the 

 volatilization of the remaining substances. 



(2) The zone of fusion lies at /3, somewhat above the first third 

 of the flame in height, and midway between the inner aud outer 

 limits of the mantle at the point where the flame is thickest. 

 This is the point in the flame which possesses the highest tem- 

 perature, and it is therefore used in testing substances as regards 

 their melting-point, their volatility, emissive power, as well as 

 for all processes of fusion at high temperatures. 



(3) The lower oxidizing flame lies at 7, in the outer margin of 

 the zone of fusion, and is especially suitable for the oxidation of 

 substances dissolved in beads of fused salts. 



(4) The upper oxidizing flame at e is formed by the highest 

 point of the non-luminous flame, and acts most powerfully when 

 the draught-holes of the lamp are wide open. This flame is 

 suited for the oxidation of larger portions of substance, for roasting 

 off volatile oxidation-products, and generally for all those cases of 

 oxidation in which an excessively high temperature is not needed. 



(5) The lower reducing flame lies at S, on the interior edge of 

 the mantle next to the dark central zone. As the reducing gases 

 at this point are mixed with unburnt atmospheric oxygen, many 

 substances remain here unaltered which become deoxidizedon 

 exposure to the upper reducing flame. This point of the flame 

 gives, therefore, very valuable reactions which cannot be obtained 

 with the blowpipe. It is especially available for reductions on 

 charcoal, and in beads of fused salts. 



(6) The upper reducing flame is formed by the luminous point 77, 

 produced over the dark zone when the admission of air is lessened 

 by the gradual closing of the draught-holes (fig. 1, a). If this 

 luminous point is made too large, it will be found that a test- 

 tube filled with cold water becomes covered with a film of lamp- 

 black : this never ought to occur. This flame contains no free 

 oxygen, is rich in finely divided incandescent carbon, and hence 

 it possesses far more powerful reducing-powers than the lower 



