NATURAL PHILOSOPHY. 175 



CONVENIENT METHOD OF ASCERTAINING THE CONSTITUTION OF 



FLAMES. BY M. L. DUFOUR. 



M. L. Dufour recommends the following process for demon- 

 strating, for instance, that the flame of a candle is formed of a 

 hollow cone, luminous on the outside only, and dark in the inte- 

 rior. For this purpose it is necessary to cut the flame ; the most 

 preferable method of doing this is by means of a sheet of water 

 or air. The arrangement is as follows : A caoutchouc tube has, 

 at one of its extremities, a gas-jet, such as is used for common 

 gas flames; this jet has an almost semi-circular slit of OA m.m. 

 in depth. The other end of the tube communicates with a reser- 

 voir of water placed at a convenient height. Upon a suitable 

 pressure, the water flows out by the slit in the jet, producing a 

 clear sheet capable of preserving, for a sufficient length of time, 

 an invariable form and size. The slit is placed in such a manner 

 that the sheet presents a horizontal surface ; and this will easily 

 cut the flame of a candle showing a jDcrfect section. The hot 

 gases and carbonaceous f)^^i'ticles are carried off by the water. 

 On placing the e3'e above the hollow cone, the luminous wall, 

 etc., can be distinctly seen. Sections may easily be made near 

 the wick or near the point; nothing hinders observation, which 

 may be j^rolonged at pleasure, and a lens may be used if desired. 

 A flame of gas may be cut and examined in the same manner, 

 but the current of gas must not be strong enough to traverse the 

 sheet of water. If a current of air be caused to come out of the 

 slit by bellows, an invisible sheet of air is formed, which is, also, 

 very convenient for making a section of flame. Close observa- 

 tion is quite possible ; for the aerial current prevents the heated 

 gases from reaching the eyes, and a lens may be used; as in the 

 former case, the flame forms a cone, whose luminous walls are 

 extremely thin, and their interior can be plainly seen. A platinum 

 wire may be introduced across the section ; and, on being plunged 

 as far as the wick, it will remain unreddened in the dark interior 

 of the cone. 



A jet of gas issuing from a circular opening, of from one to 

 two millimetres in diameter, may also be cut very conveniently 

 by the sheet of air. It will be seen to consist of a cone whose 

 walls are brilliant and extremely thin. Upon bringing the sheet 

 of air close to the aperture whence the gas escapes, the flame 

 will be divided at its base and will reappear a little higher. By 

 this means the entire length of the luminous cone, its thin walls, 

 and their interior may be examined. 



If a jet of gas produced by a fan-tail burner be cut, the lumi- 

 nous fan will be found to consist of two brilliant blades, between 

 which there is a narrow, obscure space. The blades are at a 

 greater distance apart, and the dark space is wider towards the 

 end of the fan-tails; and, by assuming a suitable position, it is 

 easy to see through the section of flame into the dark space 

 which separates the brilliant walls, and at the end of this will be 

 seen the slit by which the gas escapes. 



