1872.] Modern Cannon Powder. 59 
for use in the rifled breech-loading guns introduced about 
twelve years ago, and a modified kind was therefore 
adopted, on the recommendation of Sir William Armstrong. 
The modification consisted in making the powder much 
larger* in the grain, and in addition, coating it with a thin 
film of graphite, so as further to retard its combustion and 
thus to reduce the strain upon the breech-closing mechanism 
of the gun. 
This new powder was at first called “‘A,,” but its name 
was afterwads changed to ‘‘R.L.G.,” or ‘‘ Rifle Large Grain” 
powder, when its use was extended to both muzzle-loading 
and breech-loading rifled guns. Now at the time of the in- 
troduction of this modified powder, the means of testing the 
action of the charge in the bore of a gun were very imperfect, 
and the change then made was founded almost entirely 
upon theoretical considerations. In order to understand 
these, and also the results of more modern experiments, it 
will be necessary to say a few words on the subject of the 
combustion of gunpowder. 
In the first place it must be borne in mind that gunpowder, 
unlike nitro-glycerine, fulminate of mercury, and other 
detonating substances, is not a chemical compound, but only 
a mechanical mixture. By the incorporating process during 
manufacture the three substances of which powder is com- 
posed—saltpetre, sulphur, and charcoal—are so intimately 
mingled that the eye cannot detect the presence of any one 
of them in a free state. They are notwithstanding only 
mixed, and the saltpetre can be readily dissolved out by 
water, or the sulphur sublimed, in the form of vapour, by 
the application of a moderate heat, leaving in either case 
the other two ingredients chemically unchanged. The 
more intimate the mixture, the more nearly does gunpowder 
approach to a chemical compound, and the more violent is 
its combustion; but there always must remain a vast differ- 
ence between the most complete mechanical mixture and the 
most unstable chemical compound. 
For this reason the combustion of gunpowder is only very 
rapidly progressive, and not instantaneous as is the case with 
the violent explosives mentioned above. It is this difference 
that renders gunpowder so valuable as a propelling agent, 
for, were it not for its comparatively mild action, no gun 
could be made sufficiently strong to resist its force. The 
_* The size of grain in “ L.G.” powder is such that it will pass through a 
sieve of 8 meshes to the inch and be retained on one with 16 meshes, while 
the limits of “ R.L.G.” or “A,” powder are between a 4-mesh and an 8-mesh 
sieve. 
