1817.] Royal Society. 151 
and employed in France, though afterwards abandoned But he 
allows that Mr. Seppings has introduced so many improvements, 
and has so happily got over the difficulties to be overcome, as to 
have made his method in a great measuré his own. 
On Thursday, Jan. 9, 1817, part of a paper by Sir Humphry 
Davy on Flame was read. The author divided his subject under 
four heads :—1. On the effect produced by rarefaction by means of 
the air-pump oh the inflammation of gases. A small jet of hydrogen 
#as from a glass tube was extinguished when the air was rarefied six 
times. But when the jet was larger it was not extinguished till the 
rarefaction amounted to 10 times. In the second case the point of 
the tube frorn which the gas proceeded was white hot, and the gas 
continued to burn till the tube ceased to be visibly red. It imme- 
diately occurred to the author that the cause of the extinction was 
not the deficiency of oxygen; but the want of sufficient heat. 
Hence it followed that those bodies which produce most heat, and 
which requiré the least for combustion, would burn tlic longest ; and 
a set of experiments made on purpose confirmed these ideas. 
Hydrogen burned till the atmosphere was rarefied 10 times ; 
olefianit gas, till the rarefaction was neatly as great; carbonic oxide 
was éxtinguished when the rarefaction amounted to five times ; and 
carbureted hydrogen when it was only four times. Sulphur con- 
tinued to burn till the rarefaction was 30; phosphoras, till it was 
60; and phosphureted hydrogen gas burned in the best vacuum 
which he could form by means of his air-pump. 
The heat produced by the different gases when burning was found 
to follow the same order as the rarefaction in which they would burn: 
Hydrogen prodaces most heat, olefiant gas the next, then sulphu- 
feted hydrogen and carbureted hydrogen, and earbonie oxide the 
least of all. Carbonic oxide, being combustible at a much lower 
temperature than carbureted hydrogen, burns in an atmosphere 
more rarefied. 
A mixture of oxygen and hydrogen gases does not explode by 
electricity when rarefied 18 times; but a mixtufe of chlorine and 
hydrogen still burns, though very feebly, when rarefied 24 times, 
When the rarefied mixture of oxygen and hydrogen is strongly 
heatéd, it then becomes capable of exploding by electricity; but 
only the heated portion burns. 
2. On the effect of rarefaction by heat on the combustibility of 
the gasés. Grotthus has stated that, when gaseous mixtures aré 
rarefied four times by heat, they cease to explode. Our author was 
able only to produce an expansion of 2} times. It was produced by 
a cherry-red heat ; which of course indicates a heat of about 1032°. 
The result of his experiments is precisely the reverse of that of 
Grotthus. He found that rarefaction by heat increases the explo- 
dability of gaseous mixtures. He infers, likewise, from his expe- 
timents, that the hypothesis of Dr. Higgins, Berthollet, &c., that 
the reason why gaseous bodies explode by electricity is the com- 
pression occasioned by the sudden expansion of the heated portion 
5 
