Year: 1876

Popularity speaking, the firing of a


gun is an instantaneous process; the ig-


milton oil the charge and the movement


OF the bullet being to all appearance


simultaneous. But slthough a large


mass of gunpOwder in close cavity is


infiamed with amazing rapidity, this


Inflammation is not instantaneous. We
know that there are other explosive


substances, such as gun-cOtton, nitro
glycerine, and various Illuminating


powders. which fire much more rapid
/ ly than yunpOwder; but it would be
WRONG To say that the rapidity of their
combustion WAS more instantaneous


than gunpovder, because instantane-


Ousnt IS can admit OF 40 degrees.


Looking at the question, therefore,


from this point of view, We are forced


to ackuOa ledge that there must be


some duration of time in the burning


of the charge. The length Of that du-


ration may be 80 small that we can
scarcely conceive il. Scientifically
| speaking, however, there is a very ap-


preciable duration of time between the
| first ignition of charge of gunpOwder


and the conversion of the whole mass


into gas; moreover, this duration is
NOhi etCdICI less QQQeT


different conditions. When, on the
discharge of a gun, the fire reaches the


charge from the teuch-hole, the near
est grains OF powder are kindled; the


heated gas evolved permeates through


the charge, successively igniting each


grain, and the grains burn until con-


sumed. Thus we have-first, the igni-


tion of small portion of the charge;


next the excessively rapid, altho' not


Instantaneous, ignition of every grain;


and, lastly, the consumption of these


grains. All this process requires time,


although, as celebrated engineer put


it, it may be II task for our conception


TO grasp these events, following one an.


other in distinct succession, each hav-


ing its beginning, middle, and end ,and


ali being comprised in the period of


less than the one hundredth part of a
serond. But if we can master this in


imagination it will not be difficult to


understand how the action of gunpow-
der can be controlled and how the mon
ster guns have become possible. 1t is
apparent that on the ignition of the
charge each grain in its turn becomes
intiamed over the whole surface, and
continues Burning until it is consumed.
II is also evident that, as q large grain
will take longer time to burn than a
small grain, all other conditions being
the same, charge composed of large
grains will take longer to burn than
the sams weight of charge made up uf
smaller grains. Thus, the larger the
grain the less the rapidity of combus-
ton. But the size of the grain also af-
fects the rapidity of ignition, as it is ca
ser for the gas first evolved to perme-
ate through the interstices of mass of
large grains. Moreover any cause
which hinders or impedes regularity of
ignition, particularly in lagre and long
charges, is liable to give rise to oscilla-
tiOns in the gas by which the pressure
in the bore of the gun may be locally
intensified without the velocity of the |
shot being i:.c easad. We can see,
therefore, that large grains will burn |
slowly and ignite rapidly, and that in |
a charge composed of large grains,
the combustion will be slow and
regular. 1t follows from this that the
explosion Ofsuch charge will be at
tended by gradually increasing and
uniformly applied pressure until at
length the maximum strain is arrived
at We are thus enabled to cOmmuni-
cate sufficiently high velocity to the
shot without overstraining the gun, or,
as sir William Armstrong puts it, by
a Slower burning powder, less heat and
pressure are evolved at first, and the
WASTE OF heat in the stage of initial
pressure being less, more heat remains
Tor expansive action. Hence the slow
er burning powder is weaker at first,
r ut stronger afterwards and althOuUh |
the total quantity of gas may be only
the same, and the pressure not so great
at any point, yet the aggregate pres
sure throughout The bore may equal
that of the more energetic and more
dangerous powder. We are thus led
to increase the size of common powder
from small grains to large Jumps. A
buy OF onion seed would fairly repre-
sent the charge of the sixty-eight-
FOUNDER of 1855, while sack of pOts-
toes would not be II bad parallel to sug-
sest the size of the charge of the eigb-
ty-one-t0n gun of 1875.