ON THE COMBUSTION OF G\S FOR ECONOMIC PtJIlFOSES. 165 
evening’s lecture ; and in order that you may follow me through the various details of 
the inquiry, it will be necessary to pursue it from the beginning. 
The phenomena of visible combustion are always the results of energetic chemical 
action; and the heat and light which characterize it are the consequences of the violent 
collisions and rapid trembling of the combining atoms. When this collision occurs by 
the showering down, as it were, of gaseous atoms upon a solid, as you here see in the 
combustion of carbon and of iron in oxygen gas, and of antimony in chlorine, there may 
be a very intense ignition of the solid, but there is no flame. On the other hand, when 
the conflict is entirely among the particles of gaseous or vaporous matter, or matter in 
a flnely divided and mobile condition, the phenomena are altogether different; for al¬ 
though, as before, the atoms or molecules of the burning body are intensely heated, yet 
from their mobility they give rise to that appearance called flame. 
In all cases, therefore, we must regard flame as gaseous, or vaporous, or very flnely 
divided matter intensely heated. That the particles of the gas or vapour must be them¬ 
selves bodily and intensely heated to produce flame is evident from this—that when I 
burn hydrogen, or coal gas, or the vapour of ether, or alcohol by means of a flnely di¬ 
vided solid, as I do here with a rosette of flne platinum wire, you see how the wire 
glows; but there is no flame, for the combustion is limited to the thin layer of gaseous 
matter which immediately surrounds the metal, and the temperature of the combustion 
is comparatively low. But if I raise it to a higher temperature, as will sometimes 
happen of itself, then the whole mass of escaping gas or vapour is thrown into a state of 
ignition, and it bursts into flame. 
Let us pause for awhile to study the complicated nature of this phenomenon. When¬ 
ever a gas or vapour burns in an atmosphere of another gas or vapour, as we here see in 
the flame of the burning gas and candle, the phenomena are very complicated. At the 
points of contact which are now at the outside of the flame, the collision of the parti¬ 
cles, because of their rapid chemical union, is most violent; and here, therefore, we have 
the highest temperature; but as a portion of the outer atmosphere penetrates for some 
distance into the burning gas, it extends the conflict into the body of the flame, and 
there finding itself in the presence of complex particles, it closes with those whose 
energies are most active. In this manner the hydrogen of the hydrocarbon is burnt first, 
and the liberated carbon, standing for awhile in an ignited state, forms the luminous 
shell of the flame; and within, waiting for the presence of air, or rather passing out to 
take part in the conflict, is the unchanged gas or vapour. Every common flame, there¬ 
fore, consists of at least three parts—the inner layer of unchanged gas or vapour, next 
the shell or cone of luminous matter, and lastly the outer shell of perfect combustion. 
That there is always an inner portion of gas or combustible vapour in every common 
flame may be proved by drawing it out with a glass tube and burning it at the end. 
See how I do it here with the flame of burning ether, and the same may be done with 
all other flamer. 
And now we are prepared to ask why it is that different substances burn with such 
different degrees of luminosity. The answer is clearly to be found in the circumstance 
that different substances contain, or evolve, or produce different amounts of solid particles. 
In all these flames of hydrogen, and sulphur, and carbonic oxide, there are no solid 
particles to be heated; but in this gas, and candle, and paraffin lamp, the particles of 
soot or carbon are very numerous; and if it so happens that the products of the com¬ 
bustion are also solid particles, the intensity of the light is so much the greater. Look 
at the splendid combustion of phosphorus in oxygen, and of magnesium in air. In both 
cases you will notice that the products are a white powder, every particle of which at 
the moment of its fonnation is intensely heated. It follows from this that every cir¬ 
cumstance which increases the number of solid particles, within a reasonable limit, or 
which prolongs the time of their ignition, or which exalts the temperature of it, increases 
the light of the flame, and conversely everything which destroys the particles or lowers 
their temperature will also destroy the light. 
If I throw the solid particles of lime into this almost invisible flame of oxygen and 
hydrogen, you will notice how vividly I bring out the light; and so also if I give the 
vapour of a hydrocarbon as benzole, which is rich in carbon, to the hydrogen by merely 
passing it through a tube packed with tow and moistened with naphtha, you observe 
how brightly the hydrogen burns. In the same way we can increase the illuminating 
power of coal gas by passing it into a chamber containing naphtha; and experiment 
