C. GENERAL PHYSICS. 149 



EXPERIMENTS UPON NON-LUMINOUS FLAMES. 



The experiments by Knapp, and the subsequent ones of 

 Blochmaun, in which a luminous gas flame was rendered 

 non-luminous by the introduction of gases indifferent to 

 combustion, in place of air, have been modified by Wibel 

 in such a way as to permit the heating of the mixed gases 

 at the moment of combustion. The diluting gas was intro- 

 duced through a glass tube, soldered into one of the draught- 

 holes of the ordinary Bunsen burner, the others being closed, 

 and the mixed gases were burned from a platinum tube, read- 

 ily formed by rolling a piece of thin platinum foil spirally, 

 slipped into the top of the burner. Two opposite horizon- 

 tal Bunsen burners were arrano-ed for heatinsf this tube. 

 Upon heating it when the flame was rendered non-luminous 

 by air, as in the ordinary Bunsen burner, or by carbonic acid, 

 nitrogen, or hydrogen, Wibel noticed the immediate forma- 

 tion of a luminous cone in the interior of the flame, which 

 gradually disappeared when the heating burners were re- 

 moved. The temperature required was not very high, es- 

 pecially if the gases were mixed in the proper proportions. 

 The flame did not strike down, and in all respects resembled 

 an ordinary luminous flame, affording soot, and also a con- 

 tinuous spectrum. Very slight decomposition took place in 

 the hot tube with nitrogen and carbonic acid, as ascertained 

 by analysis of gas taken from the flame by aspiration, as well 

 as from the exceedingly slight deposit of carbon in the tube. 

 A sheet-iron plate, perforated so as to fit the burner, prevent- 

 ed the products of combustion from the heating burners from 

 coating the flame. It was also found that when the flames of 

 two good Bunsen burners were brought in contact with the 

 exterior mantle of flame, rendered non-luminous by carbon- 

 ic acid, an interior luminous cone was formed, which disap- 

 peared immediately on their removal. He concludes from 

 his experiments that the non-luminous character of the flame 

 in Knapp's experiment is not due to dilution of the burning 

 gas, according to the views of Frankland and of Blochmann, 

 but rather to a cooling of the interior of the flame by the gas 

 introduced a view that is supported by the peculiarities of 

 the flame when oxygen is the diluting gas. The luminosity 

 of the flame of a substance containin<r carbon, other thinsjs 



