524 
On Water and Air. 
[August, 
piston P descends to its original position. The principle of 
the hydraulic press is simply the forcing of water from a 
narrow cylinder into a wide one. We have here a small 
sample of the hydraulic press. It is the pressure of that 
which we have been working here which has converted the 
carbonic acid gas into the liquid form, and that without the 
exercise of very particular force by the human arm. 
Now I want to try whether we cannot break a bar of iron 
by the hydraulic press. You have here no creation of 
power, but you have the means of applying power. You 
have the means of adding power to power, until, by the 
addition of small fractions of power, you are able to break 
that bar. We will place the arrangement for breaking this 
thick iron bar between the fixed plate A and the movable 
table B, and work the lever h as before described ; the 
piston P rises, and now I have half a ton of pressure upon 
that bar, and you see it has snapped asunder. It has been 
placed across two supports, and a point pressed upon the 
centre ; and by certainly not a very inordinate amount of 
effort on my part, I have been able to snap that thick bar 
asunder. 
Now I wish to bring before you a most striking example 
perhaps the most striking application of the hydraulic 
press that has been made in our time. The world is 
indebted to that illustrious engineer Sir William Armstrong 
for the introduction of the hydraulic press into a variety of 
engineering operations. This occurred to Sir Joseph Whit- 
worth some years ago, and I had an opportunity of talking 
to him at the time, and I saw that the problem that he had 
placed before him was enormously difficult. Here I have a 
number of specimens of steel. This specimen has been 
cast as steel used to be formerly cast. It has been cut 
across, and you see that it is honeycombed, — full of bubbles 
of air, so that you never could trust steel of that kind. It 
might be very hard, very strong, but still you never could 
trust to it, because you never knew where these bubbles 
might not exist in the steel. Here is another sample of 
steel which is perfectly close, without the trace of a bubble. 
There is not a bubble large enough to admit a pin’s head or 
a pin’s point. It is perfectly compact. Now the problem 
which Sir Joseph Whitworth set before him was to convert 
steel of the old kind into steel of this close compact cha- 
racter. And how did he do it? He devised a mould of a 
certain quality, — a mould that would not allow the molten 
metal to pass through it, but would allow all these gases to 
pass through, — and he brought enormous pressure to bear 
