48 
POPULAR SCIENCE REVIEW. 
the side of the block, and as soon as the press-box has been 
forced up to the required point, the catch is liberated by 
coming in contact with it, and rings a bell in the pump-room. 
The pumps are then stopped, the ram falls by its own weight, 
and the box is unloaded, the gunpowder being taken out in 
large cakes the size of the metal plates, and as hard as slate. It 
is in the pressing of the gunpowder that the most serious explo- 
sions occur, for if by any chance the pressure becomes too 
severe, and the powder explodes in the box, its force is much 
greater than if it were ignited in the open air. Seven men were 
killed by an explosion in the press-house at Waltham Abbey in 
1843, and by a similar accident on June 16, 1870, five were 
killed and seven injured. 
The question of the density given to gunpowder by pressing and 
its effects is one which is only now being worked out. Formerly 
the density of the powder was roughly ascertained by weighing 
a cubic foot of it, and then its quality was tested by observing 
to what distance it would fire a shell from a mortar. These 
primitive methods are now superseded by a testing apparatus, 
which gives scientifically accurate results. The density is de- 
termined by reducing a small quantity of the powder to dust in 
a mortar, and then placing it in a glass globe provided with 
stopcocks, one of them connected with an air-pump, and the 
other with a tube dipping into a vessel of mercury. On ex- 
hausting the air, closing the first cock and opening the second, 
the mercury is forced into the globe, and completely fills it. It 
is then weighed in a delicate balance, and, its weight when filled 
with mercury only being known, it is easy to calculate the 
density of the gunpowder. 
Its force is ascertained by observing the initial velocities 
which it will give to a shot fired from a cannon. These veloci- 
ties are measured with Bashforth’s Chronograph, as explained 
in a former article in the Popular Science Keview ; * and with 
the Noble Chronoscope, the invention of Captain A. Noble, of 
the Elswick Works, by means of which we are enabled to ascer- 
tain what takes place in the bore of the gun on the explosion of 
the charge, and what is the velocity of the shot, not only in the 
whole length of its course within the gun, but also in each 
portion of that short distance, thus determining the velocity 
within very small limits both of time and space, and this with 
the most perfect accuracy. 
It is difficult to describe the chronoscope without a diagram, 
but it is easy to indicate the general principles of its action in 
a few words, and this will be sufficient for our purpose. A gun 
* “ On the Striking Velocity of Shot.” By W. Royston Pigott, M.D., 
P. S. R. ; Jan. 1871. 
