30 
COMBUSTIBILITY OF GASES. 
VI. 
A Memoir upon the Limits of Combustibility of Gaseous In- 
flammable Mixtures diminishing in Density, and upon the 
Colours of the Electrical Spark in different Mediums, by 
M. Grotthuss.* 
Rarefied gases 
jjot combusti- 
ble. 
Remarkable 
difference be- 
tween the 
combustibility 
of expanded 
compounds of 
oximuriatic 
gas, and those 
The former, 
I N the ninth volume of Gehlen’s Journal, I shewed how 
much the influence of the pressure of the air is of 
importance in the combustion of bodies, particularly with re- 
gard to the gaseous mixtures. I proved, that at the height of 
about 35,000 feet, all combustion in the atmosphere must 
cease. From my experiments of that time it may be con- 
cluded, that the combustibility of a gas, comports itself as the 
degree of dilatation at which it ceases to be inflammable. If 
we lay down this principle for measuring the combustion of 
inflammable; gaseous mixtures, we shall find anomalies which 
are interesting, but difficult to be explained. 
II. It is generally admitted, that most combustible bodies are 
more easily inflamed at the ordinary pressure of the atmos- 
phere in oximuriatic gas, than in oxigen gas. The oximuriatic 
gas produces a sudden inflammation by simple contact of 
phosphorus with different metals, and with certain gases 5 an 
inflammation which does not take place with oxigen gas, ex- 
cept when it has obtained a maximum of compression, which 
may happen, as I have shewn, from the united action of ex- 
pansion and resistance. A mixture of oximuriatic gas and 
hydrogen gas inflames, by a slight heSt externally applied, even 
by the solar rays ; and from this fact it was to be presumed, 
that a gas so easily inflammable, would require a much more 
considerable dilatation to deprive it of the property of inflaming, 
than the denotating gas, composed of two measures of hydro- 
gen, and one of oxigen, gas. This would be a consequence, 
however, which is contradicted by the following fact. 
III. I filled a tube, (of which the internal part of its upper 
* From a Translation of Vogel of the original Schweigger’s Che- 
mical Journal, iii, 219. 
extremity 
