51 
Sir H. Davy's researches on flame. 
upper part of the tube till the glass began to soften, and 
passed the spark, when a feeble flash was observed not reach- 
ing far into the tube, the heated gases only appearing to enter 
into inflammation. This last experiment requires consider- 
able care. If the exhaustion is much greater, or if the heat is 
raised very slowly,* it does not succeed ; and if the heat is 
raised so high as to make the glass luminous, the flash of 
light, which is extremely feeble, is not visible : it is difficult 
to procure the proper degree of exhaustion, and to give the 
exact degree of heat ; I have, however, succeeded three times 
in obtaining the results, and in one instance it was witnessed 
by Mr. Brande. 
To" elucidate the enquiry still farther, I made a series of 
experiments on the heat produced by some of the inflammable 
gases in combustion. In comparing the heat communicated to 
wires of platinum by flames of the same size, it was evident, 
that hydrogene and olefiant gas in oxygene, and hydrogene 
in chlorine, produced a much greater intensity of heat in 
combustion, than the other gaseous substances I have named 
burned in oxygene : but no regular scale could be formed 
from observations of this kind. I endeavoured to gain some 
approximations on the subject by burning equal quantities of 
different gases under the same circumstances, and applying 
the heat to an apparatus by which it could be measured. 
For this purpose a mercurial gas holder was furnished with 
a system of stop cocks, terminating in a strong tube of plati- 
num having a minute aperture. Above this was fixed a copper 
cup filled with olive oil, in which a thermometer was placed. 
The oil was heated to 212 0 to prevent any differences in the 
communication of heat by the condensation of aqueous vapour; 
# The reason will be obvious from what is stated in page 55. 
H 2 
