4 Some new Researches on Flame. 
I. On the Effect of Rarefaction by partly removing the Pressure 
of the Atmosphere upon Flame and Explosion, 
The earlier experimenters upon the Boylean vacuum observed 
that flame ceased in highly rarefied air; but the degree of rare- 
faction necessary for this effect has been differently stated. 
Amongst late experimenters, M. de Grotthus has examined this 
subject. He has asserted that a mixture of oxygen and hydro- 
gen ceases to be explosive by the electrical spark when rarefied 
sixteen times, and that a mixture of chlorine and hydrogen can- 
not be exploded when rarefied only six times, and he generalizes 
by supposing that rarefaction, whether produced by removing 
pressure or by heat, has the same effect. 
I shall not begin by discussing the experiments of this inge- 
uious author. My own results and conclusions are very different 
from his; and the cause of this difference will I think be ob- 
vious in the course of these inquiries. 1 shall proceed in stating 
the observations which guided my researches. 
When hydrogen gas slowly produced from a proper mixture 
was inflamed at a fine orifice of a glass tube, as in the experi- 
ment called the philosophical candle, so as to ake a jet of 
flame of about 1-6th of an inch in height, and introduced under 
the receiver of an air-pump containing from 200 to 300 cubical 
inches of air, the flame enlarged as the receiver became ex- 
hausted ; and, when the gauge indicated a pressure between four 
and five times less than that of the atmosphere, was at its maxi- 
mum of size: it then gradually diminished below, but burned 
above, till the pressure was between seven and eight times less, 
when it became extinguished. , 
To ascertain whether the effect depended upon the deficiency 
of oxygen, I used a larger jet with the same apparatus, when 
the flame to my surprise burned longer, and when the atmosphere 
was rarefied ten times, and this in repeated trials. ,When the 
larger jet was used, the point of the glass tube became white hot, 
and continued red hot till the flame was extinguished. It im- 
mediately occurred to me, that the heat communicated to the 
gas by this tube, was the cause that the combustion continued 
longer in the last trials when the larger flame was used; and 
the following experiments confirmed the conclusion, A piece 
of wire of platinum was coiled round the top of the tube, so as to 
reach into and above the flame. The jet of gas of 1-6th of an 
inch in height was lighted and the exhaustion made; the wire 
of platinum soon became white hot in the centre of the flame, 
and a small point of wire near the top fused: it continued white 
hot till the pressure was six times less, when it was ten times it 
continued red hot at the upper part, and, as long as it was dull 
red, 
