THE ROYAL ARTILLERY INSTITUTION. 
429 
I am aware that it is usual to consider that the amount of powder con¬ 
sumed depends on the burning of each grain from the surface towards the 
centre, and that most of these curves might be explained in this way. 
Sir William Armstrong we have seen explains the anomaly of the pellet 
maintaining its velocity against R.L.G., by the loss of heat which the latter 
sustains during the initial stage of combustion. There are, however, as we 
shall see, other points not so easily explained on the theory usually adopted. 
Whatever be the cause, the pebble is undoubtedly a better curve than the 
prismatic, and shows some advantages in addition to its less maximum; for 
the maximum pressure of the pebble takes place before that of the prismatic, 
and also there is less appearance of suddenness in the former than in the 
latter. The prismatic gets up the pressure very slowly at first, but, when 
about to reach the maximum, it takes a sudden rise, which may possibly be 
rapid enough to produce partially the effect of a sudden pressure. Its 
maximum is 20’5 tons; but suppose the pressure rises slowly up to 12 tons, 
and then suddenly becomes 20, we should have a pressure of 20 tons met 
by a resistance of 12, 13, 14,—20 tons in succession, during which time 
the walls of the gun have acquired a velocity outwards, requiring a resist¬ 
ance of 20, 21, 22—28 tons in succession to bring them to rest. The 
walls would again vibrate back to 12 tons, and out to 28 tons, increasing 
the injurious effects on the gun. 
With the 10-inch gun, 
<e The principal average results, in various series of six rounds each, are shown 
in the following abstract, the pressure given being the highest as indicated by the 
crusher gauge.* * 
Nature of powder. 
Density. 
Charge. 
Velocity. 
Pressure. 
Remarks. 
lbs. 
f.s. 
r 1-742 
60 
1318 
51 
R.L.Gr. 
\ 1-733 
60 
1321 
48 
(.1*67 
60 
1313 
53 
Pellet ... 
1-677 
64 
1364 
25 
Prismatic Russian . 
1-66 
<61 
) 68 
1335 
1425 
19 
29 
One round. 
Prismatic Ritter. 
1-66 
5 61 
?70 
1349 
1416 
21 * 
24 
One round. 
fl-732 
70 
1474 
29 
Uniform grain. 
Pebble . 
> 1-782 
70 
1432 
21 
1 1-732 
60 
1359 
21 
One round. 
U-782 
60 
1298 
15 
One rotind. 
We here see the remarkable fertility of the subject, the initial velocity 
being increased by more than 150 f.s. when pebble powder is used, while 
the strain is very much reduced. The great importance of density is also 
the spaces between the grains, that the portions at the extremities are not ignited at the same time 
as the bulk of the charge. On the other hand, should the extremities become ignited before the 
maximum jamming action takes place, then the crushing up of the grains will make their com* 
bustion very much more rapid. The uncertainty of this action may thus account for the very irregular 
results which are obtained, both as regards pressure and velocity* when large charges are used. 
* Memorandum, 12th July, 1870, Committee on Explosives. 
