Some new Researches on Flame. 7 
 T rarefied a mixture of oxygen and hydrogen by the air-pump 
to about eighteen times, when it could not be inflamed by the 
electric spark. I then heated strongly the upper part of the 
tube till the glass began to soften, and passed the spark, when 
a feeble flash was observed not reaching far into the tube, the 
heated gases only appearing to enter into infiammation. This 
last experiment requires considerable 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 vi- 
sible: it is difficult to procure the proper degree of exhaustion, 
and to give the exact degree of heat; I have, however, suc- 
ceeded three times in obtaining the results, and in one instance 
it was witnessed by Mr. Brande. 
To elucidate the inquiry still further, I made a series of ex- 
periments 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 
hydrogen and olefiant gas in oxygen, and hydrogen in chlorine, 
produced a much greater intensity of heat in combustion, than 
the other gaseous substances I have named burned in oxygen: 
but no regular scale could be formed from observations of this 
kind. I endeavoured to gain some approximations on the sub- 
ject 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 platinum having a minute aperture. Above this 
was fixed a copper cup filled with olive oil, in which a thermo- 
meter was placed. The oil was heated to 212° to prevent any 
differences in the communication of heat by the condensation of 
aqueous vapour; the pressure was the same for the different 
gases, and they were consumed as nearly as possible in the same 
time, and the flame applied to the same point of the copper cup, 
the bottom of which was wiped after each experiment. 
The results were as follows : 
The flame from olefiant gas raised the thermometer to 270° 
—— hydrogen .. ie av 288 
—————  sulphuretted hydrogen oe oo) 282 
—— coal gas .. . ee .- 236 
— gaseous oxide of carbon’. «: fo.218 
The quantities of oxygen cousumed (that absorbed by the hy- 
drogen being taken as one) would be, supposing the combustion 
perfect, for the olefiant gas six, for the sulphuretted hydrogen 
* The reason will be obvious from what is stated in page 9. 
A4 three, 
