THE BUN SEN LAMP. 383 



" non-luminous." This effect can not be caused by cooling, for the 

 greater supply of oxygen makes the flame hotter, nor by dilution, for 

 nothing is diluted. Evidently it must be caused by the greater supply 

 of oxygen. The air contains four volumes of nitrogen-gas for every 

 one volume of oxygen. When a substance burns in air, the particles 

 of oxygen are hindered in getting at the combustible by the particles 

 of nitrogen, which are four times as numerous. When the substance 

 burns in pure oxygen there is no trouble of this sort, and the combus- 

 tion takes place much more rapidly and energetically. Such is the 

 case in our experiment. The oxygen-particles are no longer hindered 

 in getting at the carbon by the inert nitrogen, and therefore seize on 

 it so promptly as to leave none to make the flame luminous. If we 

 allow the carbonic-acid gas, resulting from the burning, to accumulate 

 in the jar, this gas will perform the function of the nitrogen of the air. 

 At first a very bright spot appears in the center of the flame where the 

 least oxygen penetrates. It is brighter than a gas-flame in air, because 

 the more rapid combustion makes the flame hotter, and consequently 

 the little particles of carbon glow more intensely. As the carbonic- 

 acid gas accumulates, it becomes more and more difficult for the oxy- 

 gen to get at the flame. When four fifths of the gas in the jar are 

 carbonic acid, the flame burns as it does in the air. As the carbonic 

 acid still goes on accumulating we get another effect, viz., that of dilu- 

 tion, and the flame becomes " non-luminous " again. In this experiment 

 are illustrated all three of the causes which render luminous gas-flames 

 " non-luminous." At first we observe that the combustion is so rapid 

 that no carbon is separated. At the close of the experiment we see the 

 flame become "non-luminous" again on account of the dilution of the 

 air with inert gas and the attendant cooling of the flame. 



If we try this same experiment with a flame which owes its lumi- 

 nosity to incombustible solid particles, or to vapors, we shall get only 

 the effect of the greater heat of the flame. For example, hydrogen-gas 

 containing a small proportion of the vapor of chromyl chloride burns 

 with a luminous flame, the light being due to the separation in the 

 flame of particles of solid oxide of chromium. If this flame be placed 

 in pure oxygen it becomes of an almost dazzling brilliancy. The 

 particles of oxide of chromium are incombustible, and therefore the 

 greater heat of the flame only makes them glow the more brightly. 

 This experiment shows that a flame becomes hotter in pure oxygen 

 than in the diluted oxygen of the air, and furnishes an indirect proof 

 that the reason why a gas-flame is made "non-luminous" in oxygen 

 is because its carbon is burned up so quickly. 



We distinguish, then, two effects produced on a luminous gas-flame 

 by pure oxygen. First, it makes the flame hotter, and consequently 

 tends to make it brighter ; and, second, if the supply of oxygen is rela- 

 tively large, it burns up the carbon of an ordinary flame at once, and 

 thus renders the flame " non-luminous." 



