26 Dr. Karl Heumann's Contributions to 



the velocity of the gaseous mixture is increased or diminished. 

 The same phenomenon may be well shown by passing carbon 

 dioxide through ether contained in a vessel surrounded with 

 warm water, and igniting the issuing mixture. The distance 

 between flame and burner may, in this experiment, be altered 

 either by altering the velocity of the stream of carbon dioxide, 

 or by warming or cooling the vessel containing the ether. 



Or the mixed gases may be caused to issue from a small 

 balloon furnished with an exit-tube and stopcock: by slightly 

 altering the pressure by means of the hand, the flame may be 

 caused to move backwards or forwards ; or it may be main- 

 tained in a constant position. If the exit-tube be of platinum, 

 the flame may be caused to rest upon the orifice of this tube 

 by heating the tube with a Bunsen's burner. Such flames 

 then behave in a manner exactly analogous with that observed 

 in the case of rapid streams of gas; and the explanations 

 already given of the observed distance between flame and 

 burner can be predicated of these flames, although diluted 

 with carbon dioxide <fcc. ; for the decrease in velocity of the 

 gas is compensated for by the increase in the proportion of 

 indifferent gases. The temperature of the flame is therefore 

 low, and the withdrawal of heat by the indifferent gases con- 

 siderable. The second explanation given of the distance 

 between flame and burner, depending upon the different 

 velocities of the gaseous stream and of the propagation of 

 ignition, holds good in the case of these flames. 



One might be disposed to raise the objection that in these 

 experiments the gaseous mixture was not strongly compressed, 

 and therefore did not issue with any great velocity. But it 

 has been shown that the greater distance between flame and 

 burner is a function of the difference of velocities of the 

 gaseous stream and the propagation of ignition ; and in the 

 foregoing cases the latter must be very small, because the 

 temperature of the flame is very low, and the molecules of 

 carbon dioxide interspersed between the molecules of the com- 

 bustible gas must carry away heat from the latter. In these 

 flames, for the reasons just stated, the rate of propagation of 

 ignition is small and is easily exceeded by the velocity of a 

 comparatively slowly moving gas-stream, whence results the 

 great distance between flame and burner. This explanation 

 is rendered more probable by considering that experiment in 

 which the distance spoken of was diminished by warming the 

 ether through which carbon dioxide was passed. 



Inasmuch as the volume of diluting gas was here propor- 

 tionally diminished, the temperature of the flame was in- 

 creased ; the rate of propagation of ignition was also increased, 



