70 Modern Cannon Powder. [January, 
uneven surface it is a quick-lighting powder: the whole 
charge (if of the proper form) is quickly and uniformly 
lighted, and the maximum pressure in the powder chamber 
is consequently even throughout its surface, while with 
powders which are both quick lighting and quick burning, 
like the old L.G. and R.L.G., intense local pressures, 
varying in different parts of the chamber, are produced. 
As an example of this the following results obtained in the 
10-inch gun its smooth bore state are given. 
Pressure per square inch by 
Crusher Gauge at 
ane 
= a 
ve B. C. 
Powder and Renae Muzzle Axisof Centreof Front of 
Charge. * Velocity. Bore. Charge. Charge. 
Feet. Tons. Tons. Tons. 
12G.200dbS.y j24 16 1273 49 28 29 
Pellet 64 lbs... 43 1377 21d Zan 21 
Pebble 70 lbs. . 6 1435 22 22 23 
The explanation of these local pressures caused by quick 
burning powders is very clearly stated by Captain A. Noble, 
in a paper read at the Royal Institution, on the “ Tension of 
Fired Gunpowder,” and may be expressed briefly as follows :— 
The products of combustion of the first portion of the 
powder inflamed, in travelling from one end of the chamber 
to the other, attain a very high velocity before meeting with 
any resistance, and the re-conversion of the wis viva thus 
acquired into pressure at the base of the shot and the end 
of the bore; gives rise to the intense local pressures at those 
points, while the rapidity of combustion of the powder at 
that part of the charge is probably enormously accelerated 
by the tension under which it is exploded. ‘The time 
during which these abnormal pressures are kept up must 
be exceedingly minute, even when compared with the in- 
finitesimal times we are considering ; for we find the chrono- 
scope pressure, which may be regarded as representing 
the mean of pressures of a violent oscillatory character, 
hardly altered at all, even although the local pressures are 
increased 50 per cent.” 
At Plate III. a representation is given of the pressure 
curves calculated from the chronoscope observations, and in 
the following table the pressures in tons shown by the crusher 
gauge are compared with those obtained by the chronoscope 
in the 10-inch gun. 
