1872.) Modern Cannon Powder. 69 
reaching the piston. It consists of a screw-plug of steel, 
having a movable base which admits of the insertion of a 
small copper cylinder, B. One end of this cylinder rests 
against an anvil, A, while the other is acted upon by a 
movable piston, c, which is kept tight against the cylinder by 
the spring, z. The cylinder is retained in the centre of the 
chamber, c¢, d, e, f, by a small watch-spring. A gas-check, 
D, is inserted against the lower extremity of the piston, and 
should any gas get past this there are passages by which it 
can escape into the open air. Upon the explosion of the 
charge the gas, acting on the area of the piston, crushes the . 
copper against the anvil, and, the amount of pressure re- 
quired to produce a definite amount of compression of the 
copper having been determined by previous experiments, the 
pressure on the piston is at once ascertained. The area of 
the copper cylinders used in the 8-inch gun was 1-12th of a 
square inch, and that of the piston 1-6th of a square inch. 
We have stated that four varieties of powders were 
chosen out of a large number for further experiment: these 
were—R.L.G. service powder, pellet service powder, Russian 
prismatic powder, and ‘‘pebble” powder No. 5. When 
fired from the 8-inch gun, in charges which best suited each 
kind of powder, the following results were obtained :— 
Nature of Powder. Charge. ve poe ee 
Lbs. Feet. Tons. 
eG. 5 eek, > 30 1324 29°8 
Russian prismatic. 32 1366 20°5 
metvice, pelleh . 5 30 1338 17°4 
Pebble No.5 =. « 35 1374 15°4 
From this table it is evident that the Service R.L.G. is 
far inferior to all the others, while the pebble is manifestly 
the best. 
“* Pebble” powder, so called from its resemblance to small 
black pebbles, was first tried in Belgium, but the powder 
which gave the above satisfactory results is an improvement 
on the foreign powder, being more uniform in size and 
density. It consists of irregular cubes, having edges, from 
5-8ths to 4-8ths inch in length, made by cutting up the 
““press-cake”” into the required form; the powder is as 
usual glazed in a revolving barrel, which operation removes 
the sharp edges. Its manufacture is therefore very simple, 
little or no new machinery is required for its produ¢tion, and 
it is cheaper than any of the other descriptions. Its density 
is high, about 1°8, but owing toits large size and comparatively 
