376 IRON IRON-CLAD SHIPS KINDS. Ultimata breaking strain in 11*. per >q. inch. Elonga- tion for cent. Strain applied in lb. per ]. inch. Difference in maximum and minimum. No. of applications before fracture. Orlg. rt. Fract'd are*. Maximum. Minimum.
21.400
25,080
37.450
Wroapht iron, Phoenix company, I
Ih37 f
47,080
109,675
66,126
135,997
H-8-j
12-1-
51,360
88,520
47,030
47,080
85,600
49.220
85,600
17,050
10,700
51, SCO
88.520
25,680
21,400
65.600
49,220
48.150
17.050
10,700
800
480,852
2,373,424
4,000,000 not broken.
18,741
13.200.000 not broken.
12,000.000 not broken.
8,140
7,600,000 not broken.
Piece of cast-Jron cylinder, Stettin.
The effect of vibration on fibrous iron, it has
been generally supposed, is to make it crystal-
line. Experimental evidence is however lack-
ing on this point. Iron subjected to vibratory
shocks may become weak and break from " fa-
tigue," or by reason of poor material or bad
working ; but there are no facts to prove that
weakening is the result of a passage from the
fibrous to the crystalline condition. Prof.
Robert H. Thurston has investigated the effect
of unintermitted static stress on wrought iron
and steel strained beyond the limit of elastici-
ty, and has found that they do not lose their
power of resistance or yield in the slightest de-
gree. He has further determined that iron
and steel, if strained beyond the limit of elas-
ticity, and left under the action of the distort-
ing force which has been found just capable
of equilibrating their power of resistance, gain
resisting power to a degree which has a limit
in amount approximating closely, if not coin-
ciding with, the ultimate resistance of the ma-
terial, and which had a limit as to time in ex-
periments hitherto made of three or four days.
Releasing the piece entirely and again submit-
ting it to the same force immediately does not
produce this strengthening effect. The pro-
duction of iron and steel in the United States
in 1872 was as follows, in tons of 2,000 Ibs. :
Iron and steel rails 941,992
Other rolled and hammered iron 1,000,000
Forges and bloomaries 58,000
Cast Bteel 82,000
Bessemer steel 110,500
Martin steel 8,000
Tig iron 2,830,070
The following is the production of England.
Prussia, and Sweden for 1871, and France for
1872:
COUNTRIES.
Fig iron.
Wrought Iron.
Steel.
6,627,179
1,827.934
1,299,890
292,850
5,56<
897,273
971,889
188,989
>,175
211,867
152.409
84,388
Prussia
IRON. I. A S. E. county of Missouri, drain-
ed by affluents of the St. Francois and Big Black
rivers; area, about 500 sq. m. ; pop. in 1870,
6,278, of whom 352 were colored. Iron moun-
tain arid Pilot Knob are on the N. E. border.
The surface is hilly and mountainous. There
are large forests of oak, hickory, pine, and ce-
dar. Iron ore is abundant, and other metals
are found. The St. Louis and Iron Mountain
railroad crosses the county. The chief produc-
tions in 1870 were 12,221 bushels of wheat,
90,385 of Indian corn, and 28,141 of oats.
There were 690 horses, 919 milch cows, 1,703
other cattle, 3,178 sheep, and 4,714 swine; 5
manufactories of carriages, 1 of charcoal, 1 of
pig iron, and 5 saw mills. Capital, Ironton.
II. A S. county of Utah, extending from Col-
orado on the E. to Nevada on the W. ; area,
9,200 sq. m. ; pop. in 1870, 2,277. It is inter-
sected in the E. by the Colorado river, and
crossed in the W. by the Wasatch mountains.
Iron ore is found in this range, and at its base
is some land suitable for agriculture, but much
of the county is unavailable. The chief pro-
ductions in 1870 were 8,917 bushels of wheat,
2,857 of Indian corn, 21,276 of potatoes, 17,968
Ibs. of wool, 21,355 of butter, and 736 tons of
hay. There were 732 horses, 2,114cattle, 4,502
sheep, and 3 saw mills. Capital, Parowan.
IRON-CLAD SHIPS, or Armored Ships, vessels
covered or plated with iron for the purpose of
rendering them impenetrable to the fire of ar-
tillery. The idea of strengthening the sides of
ships so as to enable them to resist attack is
nearly as old as the art of navigation itself.
From the time of the Norman freebooters,
who protected themselves by ranging their
bucklers along the sides of their vessels, down
to the battle between the Kearsarge and the
Alabama in 1864, in which the sides of the
former were protected by hanging chains over
the bulwarks, and from the time of the Ro-
mans, who built their triremes with castellated
prows, to the English, who have covered their
frigates with plates of solid iron, all nations
have sought by means more or less perfect to
make their ships impenetrable, and to render
them invincible in battle. The first attempts
at making iron-clad vessels were made by the
Normans in the 12th century, who put an ar-
mature or belt of iron around their vessels,
just above the water line ; this belt terminated
in front by a spur. In some instances this ar-
mature was converted into a curtain of iron or
brass reaching above the bulwarks for the pro-
tection of the combatants. The crusaders of
the 12th and 13th centuries protected their
ships in a similar manner. Pedro of Aragon
in 1354 ordered the sides of his ships to be
covered with leather or raw hide to protect
them against incendiary compounds. Andrea
Doria, who commanded in the expedition
