THE ROYAL ARTILLERY INSTITUTION. 
105 
There is some improvement in the pressures,, but evidently not much in the 
velocity. The experiment was again repeated with charcoal more highly 
charred—a well-recognised method of reducing the violence of gunpowder. 
The samples were pressed 15f ins., and stoved as in the last case :— 
Stoving. 
Density. 
Moisture. 
1 
. Pebbles 
Experiments. 
M.Y. 
Pressures. 
to 1 lb. 
Date. 
No. 
A. 
B. 
C. 
8. 2. 73 Ao 
1-759 
1-1 
78 
19- 2. 73 
313 
1539 
25*5 
24-5 
22-4 
« b: 
1-759 
1-08 
76 
11 
314 
1533 
21-7 
21-2 
20-7 
n C 2 
1-759 
1-3 
78 
n 
315 
1507 
19-7 
18-5 
18-1 
11 L>2 
1-759 
•9 
76 
a 
316 
1541 
24-4 
23-3 
22-6 
Evidently there is no improvement yet, but four other samples were tried 
made with ordinary charcoal, pressed still more—15 \ ins.—and stoved only 
24 hours at 125°, with the following results :— 
Stoving. 
Density. 
Moisture. 
Pebbles 
to 1 lb. 
Experiment. 
M. Y. 
Pressures. 
Date. 
No. 
A. 
B. 
C. 
6. 3. 73 A, 
1-795 
1-26 
80 
14. 3. 73 
413 
1405 
14-4 
14-3 
14-6 
„ B^ 
1-790 
1-22 
80 
n 
414 
1408 
14-2 
14-8 
12-7 
„ C, 
1-790 
1-30 
70 
a 
415 
1393 
13-2 
13-2 - 
13-0 
a d 3 
1-788 
1-22 
74 
11 
416 
1383 
11-7 
11-6 
12-0 
These samples are given at some length, because it was now that the author 
fancied he saw into the secret recesses of pebble-powder and its mode of 
action. The whole question seems to lie in the porosity of the grains. The 
more porous the grains, the more violent will be the action. It is a case 
exactly similar to that of large interstices in large charges. If the grains be 
large it matters little if they be porous, for the pressure of the gas in the 
powder-chamber will force the flame into the very heart of the grains; and 
hence the very violent action of 2A 4 powder. Now, it follows that anything 
which adds to, or takes from, the porosity of the grains during manufacture 
will have a corresponding effect at proof. It is a very remarkable fact that, 
as summer advances, the tendency, both with large and small-grain powders, 
is for the density to increase. The presses have to be continually altered so 
as to press less and less in order to give, the required density. No doubt this 
is due to the fact that the incorporating or milling is more perfect in summer 
than in winter—a fact w'ell known to manufacturers. 
The more milling the powder receives, the more pasty it becomes—so much 
so, that with fine-grain powder, where long milling is used, the powder on 
the beds of the mills has a tendency to adhere to the runners. This pastiness 
has the effect of rendering the powder more compact and easily pressed. The 
opposite effect, of course, takes place with shorter milled powder. It will 
not press so close together, and will be less dense and more porous than 
powder longer milled* This accounts for the low densities of the 3. 1. 73 
* The author has quite recently been informed by Mr. Haycraft, of Messrs. Hall and Son’s, that he 
has lately had a remarkable confirmation of the truth of the statement made in the text. As the 
summer advanced, he found it constantly necessary to press the powder less and less, and even by so 
doing he failed to bring down the density. It was only by reducing the milling that he succeeded 
in restoring equilibrium. 
