130 
NATURE 
[ Dec. 15, 1870 

But there are two objections to its use for heavy 
artillery that are decisive against it :—It is very expensive. 
The respective cost of guns of the several materials 
treated of in this paper may be takea in general as stated 
in the following table :— 
Cast-ironguns . . £21 per ton weight of gun, 
Armstrong wrought-iron £ 100 + #3 
” J ( - 
Fraser construction ( £65 2 2 
Steel on Krupp’s or } £17 
Whitworth’s plan . § #17° ¥ 23 
(Gun-metal) a) othe eucatoo % ” 

Fic. 1 
But a still more fatal objection to gun-metal for heavy 
pieces of artillery is its softness, and the rapidity with 
which it becomes heated. It is therefore quite unfit for 
the large charges of powder and immense rifled shot, 
with its severe friction on the bore, which are used in 
armour-piercing guns. Even small bronze guns, when 
fired repeatedly, exhibit the curious phenomenon of 
“drooping at the muzzle.” This has been very inte‘est- 
ingly explained by Mr. Mallet in the valuable work be- 
fore referred to, and shown to arise chiefly from the 
rapidity with which that metal takes up heat. For large 
guns it is a material out of the question. 
The last material to be spoken of is a far more for- 
midable rival to wrought-iron, namely, steel. Of this 
Krupp’s guns and Sir Joseph Whitworth’s guns are con- 
structed. The latter are made in a series of cylinders 
| like the Armstrong coils, and which fit very tightly one 
over the other, and are forced on each other by hydraulic 
pressure. The former are bored out of huge solid ingots, 
which have been hammered to give them a fibrous cha- 
racter. Now steel has some admirable qualities as a 
material for heavy guns. It is very hard; and this makes 
it very suitable for the grooves of a rifled gun which have 
to bear such sevére friction from the shot. For this 
reason all our wrought-iron guns are provided with an 
inner tube of steel. Moreover, it is very strong; the 
average breaking weight of a bar of steel of an inch sec- 
tional area is thirty-one tons, against twenty-five tons for 
| a similar bar of wrought-iron (in the direction of its fibre) 
and ten tons for cast-iron; and when toughened by being 
tempered in oil the breaking weight rises as high as forty- 
| five tons to the square inch. The reason why steel is so 
| much stronger when tempered in oil instead of water, is, 
| 

| that the boiling point of oil is so high (600° F.) that it 
withdraws the heat very slowly from the red-hot mass 
| plunged into it, compared with water, which is turned into 
| vapour at 212° F, The steel for the tubes of the Wool- 
| wich guns is always thus tempered. But though steel has 
| these admirable qualities as a material for heavy artillery, 
| there are very grave objections to its use, and, on the whole, 
| good reasons for preferring the wrought-iron guns to 
any steel ones that have yet been made. One is the 
greater cost, as shown in the table given above. 
| A much stronger reason is, that though steel bears a 
| gradual pressure so well, such as that of a testing 
| machine for the breaking weight, it is brittle under 
| a very severe dynamic strain or blow. When a steel 
gun bursts, it does so explosively without previous 
indications of yielding, and breaks up into fragments like 
| a cast-iron gun. Another objection, and one perhaps 
even still more weighty, is that it is very difficult to make 
steel in large masses homogeneous throughout, and free 
from flaws. It is very much a chance whether it is so or 
not; and in the case of a gun, this is determined by the 
| fact of its not bursting in service, but cannot be settled 
| by a few proof shots beforehand. A good steel gun is a 
weapon of wonderful power and very great endurance. 
But one apparently exactly the same, and made in the 
very same way, in fact a twin gun, may burst before the 
hundredth round, or even at the first or second. From 
time to time, inventions of some process to make steel 
cheaply and of a homogeneous texture are announced. 
When some such announcement passes into realisation, 
it will be time for our Government to abandon a system 
which arms the country with guns at a moderate price, of 
a power which weight for weight is not surpassed by those 
made on any other system, and whose endurance may 
after proof be relied upon. Our gunners have no reason 
to be afraid of their own guns. Many of the continental 
Governments have been supplied with Krupp’s steel guns, 
but very frequently they have burst in an unceremonious 
and unsatisfactory manner. On one occasion, the director 
of the Artillery Depot at Tegel, near Berlin, was killed by 
the unexpected bursting of a steel 4-pounder gun, The 
manner of manufacture shows that steel is not calculated 
to bear a high dynamic strain. At the great gun factory 
at Essen the steel is hammered with steel hammers 
of immense weight, as much as 50 tons; but they 
are single action hammers, lifted up by steam, and 
allowed to fall by their own weight.* The 12-ton ham- 
mer used for forging our wrought-iron guns, which is 
* The greatest achievement of Krupp’s Guh Factoty is a fifty-ton gun to 
fire a rcolb shot, which he presented to the King of Prussia ; a fitting present 
tomake a monarch. It cost nearly 10,o00/., and occupied ten months of 
labour, night and day, in its manufacture. It was exhibited at Paris in 1867. 
Alas, that it should now return there under far different circumstances! but 
the manner of its construction cannot claim the merit of high scientific prin- 
ciples. A steel tube was formed sufficiently strong to resist the discharge ; 
but as this would be so light that the recoil would hurl it into the air, like the 
toy cannons of our boyhood, it had shrunk round it enormous cast-iron rings 
or tubes. This was metal used for weight and not for strength. Whereas, the 
scientific principle very fairly laid down by the late Captain Blakely, R.A., is 
that ‘*a gun should, if possible, be constructed in such a manner that each 
parc of its mass would do its due proportion of work at the instant of firing.” 

