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grain, however, maximum rapidity of burning and 
evolution of gas takes place at first, owing to the 
ignition spreading over the whole surface of the cubes, 
and instead of the gas coming off with more and 
more rapidity as the space in the gun became larger, 
the evolution rapidly diminished with the decrease of 
surface caused by the burning away of the powder. 
In order, so far as possible, to avoid this defect, 
built-up charges were resorted to, and it was General 
Rodman, of the American Service, who first tried to 
overcome the difficulty by building up the charge of 
solid slabs perforated with holes, from the interior of 
which the combustion was started, so as to expose 
the minimum surface of powder at first, whilst the 
enlarging holes produced a greater and greater sur- 
face. of powder as the space behind the projectile 
increased. 
Large perforated cakes, however, are always liable 
to break, and cannot be made of uniform density, so 
that it was found far better to mould the powder into 
hexagonal prisms with a central core through them, 
which could be built up into a charge, the prisms 
being made with such exactitude that when the charge 
was fired by a layer of fine grain powder at the base 
of the cartridge the combustion started from the 
central cores, and as the powder burnt away a greater 
and greater surface for combustion was continually 
formed until the whole of the charge was spent. 
With the continued growth, however, in the size of 
the guns employed other changes became necessary, 
as even when using the black prism powder for buiit- 
up charges the pressure given began to throw too 
severe a strain upon the breech of the gun, even when 
the cartridges were made up in such a way as to 
leave air spaces at the seat of the charge. In order 
to relieve the initial pressure so far as possible, and 
to secure further modifications, alterations in the com- 
position of the powder became necessary, so that by 
the time the 80- and r10-ton guns were introduced 
into the Naval Service prism powder containing an 
increased percentage of potassium nitrate and char- 
coal with a smaller proportion of sulphur were in use. 
This fitting of the powders to the guns enabled 
perfect ballistics to besobtained, and really converted 
the explosive into what Sir Frederick Nathan was 
fond of calling these -_powders— propellants.” These 
powders had one characteristic, however, in common 
with the old grain powder, and that was that they 
gave volumes of smoke, and when rapid-firing guns 
were introduced so dense was the cloud produced that 
after the first few rounds nothing could be seen, and 
the guns became useless until the smoke had cleared. 
This rendered a-smokeless powder a necessity, and 
the history of the inception of the smokeless powders 
of to-day is full of interest. 
In any successful explosive certain conditions have 
to be fulfilled; one must be able to concentrate in a 
small space bodies which will act upon each other 
independent of the air with enormous rapidity, form- 
ing the largest possible volumes of gas, which, ex- 
panded by the heat of the action and having to find a 
way for itself, gives the explosive effect. If this 
change takes an appreciable time, the body can be 
used as a “propellant” in a gun, and gunpowder is 
of this character. When, however, the change tales 
place practically instantaneously, it cannot be used in 
a gun, and is used in high-explosive shells, bombs, 
torpedoes, and mines; and such bodies we call “high 
explosives,” nitroglycerin being an example of this 
class. 
When during the formation of the gas from the 
solid in explosion other solid compounds are formed 
as well, these solids are blown out in a fused form as 
fine particles and form a cloud-smoke, but; if only 
gases are produced, the explosion is smokeless. Gun- 
NO. 2387, VOL. 95] 
NATURE 
| 

[JuLy 29, 1975 
powder on being fired gives nearly half its weight as 
solids and theretore forms clouds of smoke; guncotton 
is resolved entirely into gases and gives no smoke. 
When the necessity for a smokeless powder became 
urgent, it was naturally to nitro-cotton, discovered by 
Schonbein in 1845, that attention was most largely 
turned, but all attempts to convert it from an “explo- 
sive” to a “propellant” failed until it was discovered 
that its rate of combustion could be slowed 
down sufficiently to make an - excellent  pro- 
pellant by destroying the original cotton — struc- 
ture that still existed in the nitro-cotton by gelatinising 
it with alcohol and ether, so forming a grain that can 
only burn from the exterior. lf cotton fibre is 
examined under the microscope it is found to consist 
of very minute tubes, and in the process of converting 
the cotton into ‘ guncotton,” by soaking it in a mix- 
ture of the strongest nitric and sulphuric acids, wash- 
ing out all acid and drying, this structure remains. 
If the guncotton were used as a charge in a big 
gun, no matter how much it was compressed, the 
flame of the combustion would be driven back into 
these tubes and so accelerate the burning as to give 
almost instantaneous explosion, straining the gun and 
giving very low velocity to the projectile. 
Nitroglycerin is an even more rapid explosive than 
guncotton, and if used in a gun would burst it, prob- 
ably without driving out the projectile at all. Nobel, 
however, in 1875 discovered that if a low form of gun- 
cotton was macerated in nitroglycerin the guncotton 
was gelatinised, all structure disappeared, and both 
explosives became so tamed in their action that they 
were converted into a perfect blasting explosive; and 
in 1888 the mixture was made the basis of a smoke- 
less propellant far superior to gunpowder. This idea 
was improved upon by Sir Frederick Abel and Sir 
James Dewar, who found that the highest form of 
guncotton, which is unacted upon by nitroglycerin, 
could be got into a gelatinised mass with nitro. 
glycerin if a common solvent, such as acetone, was 
used to blend them, and afterwards ‘evaporated out, 
and this blend with 5 per cent. of vaseline to increase 
the stability and lubricate the gun forms our modern 
‘propellant’ cordite, so named from the fact that it 
is cast into sticks, rods, or cords, according to the 
size of the gun in which it is to be used. 
The ‘*Mark I” cordite first made contained 68 per 
cent. of nitroglycerin, and the heat of its combustion 
| in the guns gave rise to a troublesome form of erosion, 
which in the South African war shortened the lives 
of the field guns, which had to be re-lined after a 
certain number of rounds had been fired, and this led 
to an alteration in the proportion of the ingredients 
in the MD cordite now used in all arms, from the 
15-in. guns of our super-Dreadnoughts to the Service 
rifles. 
Our Allies and enemies alike use smokeless pow- 
ders of a somewhat different type, made by gelatinis- 
ing nitro-cotton without any nitroglycerin for their 
field artillery and rifles, but in the German and Aus- 
trian naval guns nitroglycerin powders of much the 
same kind as our ‘‘cordite” are used, as a larger 
charge of nitro-cotton powder has to be employed 
than of-a nitroglycerin powder, and this means larger 
chambers in the guns and larger magazines to carry 
the necessary amount of explosive. 
As may be imagined, the introduction of smokeless 
powder made an immediate change in gun construc- 
tion, as much smaller chambers were needed, and the 
possibility of throwing the pressures further forward 
in the gun enabled them to be made lighter, and as a 
result our biggest naval guns are only 35 in. as 
against the 16-25-in. tro-ton guns in use in 1886, and 
the charge of MD cordite only 4oo Ib. as against the 
960 Ib. of prism powder, but the muzzle velocity has 
