On Water and A ir. 
525 
1880.] 
y 
upon the steel when it was in a molten condition, and he 
produced what is certainly one of the greatest achievements 
of the time — this compact quality of compressed steel. 
But here I am going to refer to one of the achievements 
of the hydraulic press. Whitworth places his steel under 
pressure and squeezes out every bubble, and he converts the 
steel from a material which is full of holes and unreliable 
into a steel of this compadt charadfer, which can be tho- 
roughly depended upon. Now, thanks to Sir Joseph Whit- 
worth, I am able to show you the manner in which he tests 
this steel. There is a hydraulic press, of very great power, 
invented by Sir Joseph Whitworth himself, and we will 
place a piece of Whitworth iron within the apparatus. The 
reason I wished to bring this before you was that I saw 
some time ago, in Great George Street, a pressure of 40 or 
50, or 60, tons per square inch applied to the cylinder of iron 
that I now hold in my hand, and it was elongated and ulti- 
mately drawn asunder. The hydraulic apparatus is so 
arranged as to work by traction and exert a pull upon this 
cylinder of iron we are testing. This cylinder is exadtly a 
square inch in area, and we will work the press, and exert 
an enormous strain upon it. It is worth while remembering 
what occurs. For a time it will resist the strain, and if we 
release the pressure it will go back again ; but when the 
pressure goes beyond a certain point the iron passes what is 
called its limit of elasticity, and it begins to be elongated, 
and then after a time it snaps asunder. By the continuation 
of the strain on the iron cylinder we have reached a pressure 
of 20 tons to the square inch. This point is the limit of 
elasticity of the iron, and you see the cylinder begins to 
elongate, and is reduced in diameter from one inch to nearly 
d. half inch ; and now the cylinder has broken asunder. 
That has required a force of 32 tons to the square inch. 
The end of this cylinder is a square inch in area, and there- 
fore it is as if you had screwed it up and attached to it a 
weight of 32 tons, which would be just sufficient to break 
the cylinder. That is called the strength of the cylinder; 
and here another point comes into play which is of very 
great importance, and that is the ductility of the cylinder. 
The dudfility is measured in this way : — The power neces- 
sary to break a cylinder is measured by the number of tons 
required to cause it to give way : the ductility is measured 
carefully by placing the two broken halves together, and 
measuring the elongation of those two halves. That gives 
the dudtility. The specimen we have just broken is a very 
dudtile metal, but it is not of great strength. Here, however, 
