428 
MINUTES OE PROCEEDINGS OF 
By the empirical formula I have derived from Kumforcfis experiments put 
in the form of— 
y 
20 + P 
G +1 ) 
I deduce the respective proportions of each of those powders which are 
consumed at the time of the maximum pressure to be: B.L.G. 60 per cent,, 
prismatic 57 per cent., and pebble 43 per cent. 
The comparison of the prismatic and pebble curves is most suggestive; 
for though the prismatic charge is only 32 lbs. while the pebble is 35, and 
though the prismatic begins to burn more slowly than the pebble, yet not 
only does the prismatic very nearly maintain its velocity, but actually shows 
a greater pressure than the pebble, and that too at a point further forward 
in the gun. 
It does not follow from this that at any point as regards time more 
prismatic than pebble is consumed, as will be evident by a reference to the 
time curves given in Big. 10; but, as regards space moved by the shot, it 
does. It may to a great extent be due to the shape of the grain, which 
allows of greater acceleration of combustion. The fact that at the time it 
occurs the shot is moving less rapidly may also have something to do with 
it. But it is not to be left out of consideration that it may be due to 
another cause; for the low initial pressure would be favourable to ignition, 
and thus in the case of the prismatic, the whole charge may become more 
thoroughly ignited than in the case of the pebble, and though the combustion 
be less rapid at first, it may proceed with greater intensity afterwards. The 
greater velocity and less pressure of the pellet as compared with the B.L.G. 
may be similarly accounted for. 
That there is room for an increased acceleration of combustion, is evident 
from the moderate amount of powder consumed at the time of the maximum. 
This supposition would also appear to explain the unaccountable fact of 
unconsumed grains being blown out of the gun when large charges are used, 
for the truth of which I can vouch. It is probable that the violent com¬ 
motion set up in the chamber on first ignition of the charge is such that, 
more especially in long charges, portions are driven to the extremities and 
become so packed together by the enormous pressure, as to prevent thorough 
ignition of some of the grains.* 
* In the discussion which follows, Professor Abel explains that the unburnt grains, when expelled 
from the gun, are in a state of combustion, and are afterwards extinguished by the expansion of the 
gas. This fact is in accordance with the view put forward in the text, on the supposition that the 
ignition of some of the grains is delayed in the manner suggested. An experiment will be familiar 
to many, especially to those who have attended Professor Bloxam’s lectures at the Royal Military 
Academy. A charge of 5 grs. F.G. is put in a miniature cannon with a projectile consisting of 
a cylinder of press cake V x *25". The latter seems to leave the muzzle of the gun unignited, 
and may be caught in a box; but if a paper target be placed over the box to show where the 
projectile hits, it not uncommonly happens that the press cake ignites in going through the paper 
screen, perhaps from the heat resulting from the arrest of its motion, since it must have a very 
high temperature when it leaves the gun, and requires little more to raise it to the igniting point. 
The size of the grain is not the only cause of unburnt grains being blown out, for the same effect 
is produced with R.L.G. when large charges are used. It is probable that, in some cases, the 
passage of the flame is either prevented, or at least so filtered and cooled down in passing through 
