18 Dr. Karl Heumann's Contributions to 



this fact might be sought for in the presence of unburned and 

 comparatively cold gas, which afterwards becomes heated 

 at the expense of the lowest name-mantle. It has been 

 already shown that the distance between the flame and any 

 object in contact with it is increased so soon as the temperature 

 of the flame is decreased by the admission of indifferent gas. 

 The cold unburned gas in the ordinary flame plays the same 

 part, in reference to the lowest part of the flame, as the indif- 

 ferent gas in the above-cited example did towards the burning 

 gas in general. That the action of this cold gas in increasing 

 the space between flame and burner is not, however, very great, 

 is evident from the fact that, in an ordinary burner the vacant 

 space alluded to is no greater, or not much greater, than that 

 noticed between the flame and a metallic rod held in the upper 

 part of the burning gas. 



The foregoing observations are only applicable in the case 

 of flames which burn under moderate pressures, as the flames 

 of our ordinary lighting apparatuses — gas-burners, oil and 

 petroleum lamps, candles, &c. If abnormal pressures are em- 

 ployed, the phenomena presented by the flames are greatly 

 altered: in place of a space measuring scarcely 2 millims. from 

 burner to flame, there is noticed a distance of very varying 

 magnitude, generally to be measured in decimetres, the pro- 

 duction of which is to be ascribed to quite other causes than 

 those operative in ordinary flames. 



An experiment has long been known in which spirit of wine 

 is confined in a strong brass vessel furnished with an exit-tube 

 and stopcock, and is then boiled until, when the stopcock is 

 opened, the spirit rises towards the ceiling of the room : on 

 bringing a flame near the exit-tube, the spirit burns with a 

 luminous flame only near the ceiling, the stream of issuing 

 liquid appearing non-luminous. 



By boiling spirit of wine in a copper vessel, and causing the 

 vapour to issue through a glass tube drawn to a fine opening 

 about 3 millims. in width, a long flame is obtained the base of 

 which is separated by a distance of 10 or 12 centims. from the 

 orifice of the glass tube. This distance is diminished by warm- 

 ing the exit-tube, or by holding a small rod in the issuing 

 vapour and thereby decreasing its velocity. A small drop of 

 alcohol soon gathers at the opening of the glass tube ; if this 

 be ignited by bringing a source of heat near it, or by causing 

 the flame of the burning vapour to rush back by means of a 

 rod held in the vapour, a small flame is produced which mo- 

 mentarily diminishes the distance between flame and burner ; 

 but so soon as the little drop of alcohol is burned, the original 

 distance is again assumed. According to a recent investiga- 



