Some new Researches on Flame. 9 
raised until the tube began to run together; but though this 
heat appeared cherry red, the expansion was not to more than 
2°5, and a part of this might perhaps have been apparent only, 
ewing to the collapsing of the glass tmbe before it actually melted. 
It may be supposed that the oxidation of the fusible metal may 
have had some effect in making the expansion appear less ; but 
in the first experiment the air was gradually brought back to its 
original temperature of boiling water, when the absorption was 
searcely sensible. If M. Gay Lussac’s conclusions be taken as 
the ground-work of calculation, and it be supposed that air ex- 
pands equally for equal increments of temperature, it would ap- 
pear that the temperature of air capable of rendering glass lu- 
minous must be 1055° Fahrenheit*. 
M. de Grotthus describes an experiment in which atmospheric 
air and hydrogen, expanded to four times their bulk over mer- 
cury by heat, would not inflame by the electric spark. It is 
evident, that in this experiment a large quantity of steam or of 
mercurial vapour must have been present, which, like other in- 
' explosive elastic fluids, prevents combustion when mixed in cer- 
tain quantities with explosive mixtures; but though he seems 
aware that his gases were not dry, yet he draws his general con- 
clusion, that expansion by heat destroys the explosive powers of 
gases, principally from this inconclusive experiment. 
I introduced into a small graduated tube over well boiled mer- 
cury, a mixture of two parts of hydrogen and one of oxygen, 
and heated the tube by a large spirit-lamp till the volume of the 
gas was increased from | to 2°5. I then, by means of a blow- 
pipe and another spirit-lamp, made the upper part of the tube 
red hot, when an explosion instantly took place. 
I introduced into a bladder a mixture of oxygen and hydrogen, 
and connected this bladder with a thick glass tube of about 
1-6th of an inch in diameter and three feet long, curved so that 
it could be gradually heated in a charcoal furnace ; two spirit- 
lamps were placed under the tube where it entered the charcoal 
fire, and the mixture was very slowly pressed through: an ex- 
plosion took place before the tube was red hot. 
This experiment shows that expansion by heat, instead of di- 
minishing the combustibility of gases, on the contrary, enables 
them to explode apparently at a lower temperature, which seems 
perfectly reasonable, as a part of the heat communicated by any 
ignited body must be lost in gradually raising the temperature, 
* The mode of ascertaining temperatures as high as tbe point of fusion 
of glass by the expansion of air, seems more unexceptionable than any 
other [t yives for the point of visible ignition nearly the same degree as 
that deduced by Newton from the times of the cooling of ignited metal in 
the atmosphere, 
I mate 
