14 
MINUTES OF PROCEEDINGS OF 
ON THE INFLUENCE OF ATMOSPHERIC PRESSURE UPON SOME OF THE 
PHENOMENA OF COMBUSTION. 
By Dr EDWARD ERANKLAKD, E.R.S. 
Although the rate of burning of candles and other similar combustibles, 
whose flames depend upon the volatilization and ignition of combustible 
matter in contact with atmospheric air, is not perceptibly affected by the 
pressure of the supporting medium, yet this is not true of all combustibles. 
The rate of burning of self-supporting combustibles, like the time-fuzes of 
shells, depends essentially upon the pressure of the medium in which they 
are deflagrated. Attention was first called to this fact by Quarter-master 
Mitchell,* who found that the fuzes of shells burnt longer at elevated 
stations than when ignited near the level of the sea. The results of the 
author's experiments with six-inch or thirty-seconds fuzes burnt in artificially 
rarefied air are embodied in the following table :— 
Average 
pressure of air 
in inches 
of mercury. 
Average time 
of deflagration 
of 6-in. fuze. 
Increase of 
time of burning 
over preceding 
observations. 
Reduction of 
pressure 
corresponding 
with increase 
of time. 
Increase of 
time of each 
diminution of 
1-in. pressure. 
seconds. 
seconds. 
inches. 
seconds. 
30-40 
30-33 
28-25 
32-25 
1-92 
2-15 
•893 
25-70 
34-75 
2-50 
2-55 
•980 
22-45 
34-75 
3-00 
3*25 
•925 
19-65 
41-50 
3-75 
2-80 
1*339 
15-95 
45-50 
4-00 
3-70 
1-081 
There are here evident indications of the rate of retardation being some¬ 
what greater at low than at comparatively high pressures; but, neglecting 
these indications, the above numbers give 1*043 second as the average 
retardation in a six-inch or thirty-seconds fuze for each inch of mercurial 
pressure removed. This result agrees closely with that obtained by. 
Quarter-master Mitchell, if we except those fuzes which he burnt at the 
greatest altitude; and in reference to which some error must obviously have 
crept in. The following table shews Mr Mitchell's results uniformly with 
those in the last table. The fuzes which he employed were fifteen-seconds 
or three-inch ones, and their times of combustion have therefore been 
* Proceedings Royal Society, Vol. XI. p. 137. 
