236 Mr. G. A. Hemsalech on the Line Spectrum of 



have not been appreciably increased by the extra oxygen. 

 There is, indeed, no trace o£ the quartet at 4376. The 

 enhanced chemical activity is further demonstrated by the 

 appearance of the Swan spectrum. 



The results of the observations made on the relative be- 

 haviour of various groups of iron lines in the last three 

 experiments (§§ 8, 9, 10) are summarized in the following 

 table : — 







Air 



in 

 Coal Gas. 



Air-coal Gas 



in 



Coal Gas. 



Air-coal Gas 



in 



Oxygen. 



Class I. . 

 Class 11. . 



f Quartet at 4376 

 •• [Triplet at 3860 



f Triplet at 4046 

 .. \ Triplet at 4384 



absent 

 present 



absent 

 absent 



present 

 present 



absent 

 trace of head 



absent, 

 partly present 



present, 

 present. 



bands 



absent 



line only 

 absent 



present. 



From the results of these experiments, we may infer that 

 the presence of oxygen in the medium surrounding an air- 

 coal gas flame is essential for bringing about the formation 

 of iron nitride in the explosion region. 



§ 11. Experiments with a Nitrogen-coal Gas Flame. 



A stable flame was obtained with a burner consisting 

 of a brass tube of -f-inch bore. The flame is composed of a 

 large non-luminous pale blue cone, enveloped by a pale 

 green mantle. The latter passes at the summit into a bundle 

 of pale red streamers. The green coloration of the mantle 

 is perhaps due to copper vapour carried over by the nitrogen, 

 which was produced by passing air over red-hot copper. 

 When the nitrogen is charged with perchioride of iron 

 spray the mantle becomes feebly luminous, but no change 

 is observed in the appearance of the cone. The luminosity 

 of the mantle was, however, so feeble that no photograph of 

 its spectrum could be secured. This experiment is, however, 

 instructive in demonstrating the absolute necessity of the 

 admixture of oxygen to the combustible gas mixture, in 

 addition to its presence in the surrounding atmosphere, 

 in order to start chemical activity in the cone. 



§ 12. Effect of Heating and Cooling an Air-coal 

 Gas Flame. 



A graphite rod (fig. 2) of semicircular section, 5 milli- 

 metres in diameter and 15 centimetres in length, is placed 

 in the mantle just above the explosion region of a flame 



