54 
Sir H. Davy’s researches on flame. 
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, owing to the 
collapsing of the glass tube 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 absorp- 
tion was scarcely sensible. If M. Gay Lussac’s conclusions 
be taken as the ground work of calculation, and it be sup- 
posed that air expands equally for equal increments of tem- 
perature, it would appear that the temperature of air capable 
of rendering glass luminous must be 1035° Fahrenheit.* 
M. de Grotthus describes an experiment in which atmos- 
pheric air and hydrogene, expanded to four times their bulk 
over mercury 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 inexplosive elastic fluids, prevents combustion when 
mixed in certain quantities with explosive mixtures ; but 
though he seems aware that his gases were not dry, yet he 
draws his general conclusion, that expansion by heat destroys 
the explosive powers of gases, principally from this incon- 
clusive experiment. 
I introduced into a small graduated tube over well boiled 
mercury, a mixture of two parts of hydrogene and one of 
* The mode of ascertaining temperatures as high as the point of fusion of glass by 
the expansion of air, seems more unexceptionable than any other. It gives 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. 
