1864. | Mining, Mineralogy, and Metallurgy. 153 
This has been most strikingly shown in the application of mechanical 
engineering to several branches of iron manufacture. 
There are few things which illustrate the giant power of machinery 
more entirely than the manufacture of armour-plates. A number of 
scientific men, and some of the Lords of the Admiralty, witnessed 
recently a great experiment with some new Rolling Mills belonging 
to John Brown of Sheffield. These rolls have a first foundation of 
no less than 60 tons of solid iron, resting on masonry carried far 
below the earth. The rollers themselves are 32 inches in diameter, 
and 8 feet wide, and are turned by an engine of 400-horse power. 
A powerful screw, applying its force through compound levers, 
allows the distance between the rollers to be adjusted to the frac- 
tion of an inch, so that the plate which on its first rolling, is 
forced through an interval of—for instance—12 inches apart is, on 
its next, wound through one of ten inches, next through one of 
8 inches, and so on until the required thickness has been carefully 
and equally attained by compression through every part of the metal. 
When the enormous mass of iron to be rolled was first taken from 
the heating furnace, and brought to the rollers, it was found that they 
did not bite directly the mass came to them, and when they did, the 
engine was almost brought to a stand-still by the tremendous strain 
upon it; but at last the soft plate yielded, and the rollers wound it 
slowly in, squeezing out jets of melted iron, that shot about as the 
pile was compressed from 19 inches to 17 inches by the force of the 
rollers. From the time the mass had once passed through the mill, 
it was kept rolling backwards and forwards, the workmen sweeping 
from its face the scales of oxide that gathered fast upon it. Every 
time the plate was passed through, the rollers were squeezed closer 
and closer together, until at the end of a quarter of an hour from leaving 
the furnace, an almost melted mass, it was passed through the rolls for 
the last time, and came out a finished armour-plate, weighing 20 tons, 
19 feet long, nearly 4 feet wide, and exactly 12 inches thick through- 
out from end to end. 
Attention has been directed by Lieut-Colonel H. Clerk, R.A., to 
a matter of some engineering importance, “‘The Change of Form 
assumed by Wrought Iron and other Metals when Heated and then 
Cooled by partial Immersion in Water.” The experiments recorded 
in a communication made by Colonel Clerk to the Royal Society 
originated in this way :— 
“A short time ago, when about to shoe a wheel with a hoop tire, 
to which it was necessary to give a bevel of about $th of an inch, one 
of the workmen suggested that the bevel could be given by heating the 
tire red hot, and then immersing it one-half its depth in cold water. 
This was tried and found to answer perfectly, that portion of the tire 
which was out of the water being reduced in diameter.” These experi- 
ments have an important bearing on many engineering problems; the 
general result appears to prove that metals heated to redness, and 
partially cooled, by having one portion only placed in cold water, 
contract about one inch above the water line, and that this is the same, 
whether the metal be immersed one-half or two thirds of its depth. 
