674 BEPOET— 1892. 



2. On the Luminosity of Hydrocarbon Flames. J5i/ Vivian B. Lewes, 

 Hoyal Naval College, Greenwich. 



In the year 1816, while engaged upon those historical researches which cul- 

 minated in the discovery of the miner's safety-lamp, Sir Humphry Davy noticed 

 certain facts which led him to work out and propound his theory of the causes 

 which lead to luminosity in flame — a theory which is generally stated as being 

 that the presence of solid particles in the flame is essential to its luminosity. This 

 theory remained unquestioned until 1868, when Professor E. Frankland, in his 

 celebrated communication to the Royal Society, showed that, although incan- 

 descent solid matter in a flame renders it luminous, luminosity is also in many 

 cases produced when the flame contains very dense vapours at a sufficiently high 

 temperature, and also that a non-luminous flame may be rendered luminous by 

 increasing the pressure. 



More recent researches, however, seem to point conclusively to the luminosity 

 of all flames containing hydrocarbons, being due to the presence of incandescent 

 particles of carbon, and the author has made an exhaustive series of experiments 

 as to the causes which lead to their production in an ordinary coal-gas flame. 



Coal gas is a mi.xture of hydrocarbons with hydrogen and small quantities of 

 carbon monoxide ; and it also contains traces of carbon dioxide, nitrogen, and 

 oxygen. 



The unsaturated hydrocarbons consist of ethylene, benzene, butylene, and 

 acetylene, and probably also traces of crotonj'lene and others ; while the saturated 

 hydrocarbons consist chiefly of methane, with traces of ethane, propane, and butane. 



As the gas leaves the jet the hydrogen rapidly diffuses to the outer edge of 

 the flame and burns, the methane doing the same but rather more slowly. The 

 combustion of these gases raises the temperature 500° C. in the first half-inch ; 

 while before another half-inch has been traversed 1,000° C. is reached, and chemical 

 changes in the hydrocarbons are progressing rapidly, the unsaturated hydro- 

 carbons and higher members of the saturated hydrocarbons being rapidly converted 

 into acetylene. If the temperature of the flame were not allowed to rise above 

 1,000° C. this acetylene would be nearly all polymerised into benzene, naphthalene, 

 diphenyl, and other more complex bodies, which would be slowly burnt up with- 

 out liberation of carbon, and a non-luminous flame would result. This may be 

 shown by holding a platinum dish against a luminous flat flame, when luminosity 

 disappears; but it may be reproduced by heating the interior of the dish. In the 

 case of a gas flame, however, instead of remaining at 1,000° C, the temperature 

 rapidly rises to 1,200° C, with the result that, instead of polymerising into more 

 complex bodies, the acetylene formed at once splits up into carbon and hydrogen, 

 and the former, lieated to incandescence by combustion, gives the luminosity. It 

 is the attainment of this temperature that marks the limit of the non-luminous 

 zone. If this were the only action, however, the luminous zone would be very 

 short. But the bodies formed from the acetylene before 1,200° C. was reached, 

 and the methane, of which some still remains unburnt, are converted into acety- 

 lene at a still higher temperature, i.e., 1,300° C. ; and this being reached near the 

 top of the luminous zone yields a fresh supply of carbon, and so increases the 

 height of the light-yielding portion of the flame. 



3. Experiments on Flame. By Professor Aethue Smithells, B.Sc. 



The author described four distinct regions of an ordinary luminous flame, the 

 existence of which he thought could not be doubted by any impartial observer. 

 His experimeijts had arisen from a desire to understand more fully the chemical 

 changes which determined this peculiar structure, and especially the twofold 

 character of the outer sheath. 



He described the construction and demonstrated the use of his apparatus for 

 separating the two cones of combustion in non-luminous flames, and gave a sum- 

 mary of the results he had obtained with it. He considered these results to 

 furnish fresh protff that when a hydrocarbon is starved of oxygen, the carbon will 



