Iron Vapour in Air-Coal Gas Flame. 235 



than its neighbour 4376 of the quartet, and the relative 

 appearance of these two lines is very similar to that ob- 

 served in the mantle of the air-coal gas flame burning in 

 air. For this reason it seems to me probable that the 

 presence o£ the line 4384 does not, in this case, point to 

 the formation of a nitride in this flame, but rather to thermal 

 actions slightly more energetic than those prevailing in the 

 air flame burning in coal gas. This conclusion is in harmony 

 also with the slight increase in the number of Class I. lines 

 observed. 



§ 10. Spectrum of Iron emitted by an Air-coal Gas 

 Flame burning in an Atmosphere of Oxygen. 



The general arrangement for producing this flame was the 

 same as described in § 8, but only two 2 millimetre holes of 

 the burner were used and a constant stream of oxygen was 

 passed through the lamp chimney. 



The combustion of the gases is accompanied in this cnse 

 by a singing flame which, in a revolving mirror, can be split 

 up into a great number of individual streamers. In fact, the 

 flame can be regulated by the pitch of the sound-note given 

 out, and kept constant with the help of it. 



The general aspect of this flame is rather curious, in that 

 the sharp outline of the Bunsen cone is absent and its charac- 

 teristic blue coloration is visible only near the base. When 

 charged with iron vapour the flame is considerably brighter 

 than one burning in air, but the visible spectrum of the 

 luminous flame seems to be chiefly continuous. The in- 

 tensified chemical actions due to the excess of oxygen were 

 rendered apparent by a thick deposit of red oxide of iron 

 on the inner wall of the lamp-chimney at the end of an 

 experiment. 



The spectrum obtained with a one hour's exposure shows 

 only three lines of Class L, namely, W 3860, 3886, and 3930. 

 On the other hand, the Class II. triplets at 4046 and 4384 

 are brought out completely, the head lines being quite as 

 intense as the line 3886. Thus, it seems that the formation 

 of nitrides will take place under these conditions. This may 

 be accounted for either by the absence of hydrogen in the 

 surrounding atmosphere or also by the presence of increased 

 chemical actions of a different nature due to the excess of 

 oxygen. But the reaction between the nitrogen and iron 

 can only be of a very restricted nature in this case because 

 no Class III. line is emitted. The thermal actions, to judge 

 by the imperfect development of the temperature spectrum, 



