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Art. III. — A description of an Improvement in Bramah's Hy- 
dro-mechanical Press , with its application to Oil Mills. By 
John Tredgold, Esq., Civil Engineer, and Honoray Mem- 
ber of the Institution of Civil Engineers, London. Com- 
municated by the Author. 
The powerful instrument called Bramah's Press is so well 
known, that we need not enter into a particular description of 
its construction. Next to the steam-engine, it has proved the 
most generally useful mechanical invention of modern times. It 
is applied, and is applicable, in all cases where intense pressure 
or great power is required. In our manufactories it is used for 
discharging colours, for pressing paper, gunpowder, &c. for 
packing cotton and other light goods, for expressing oils ; and, 
in bleaching, for expressing water instead of wringing. The 
press is also used for drawing up piles, for rooting up trees, and 
for cranes for loading and unloading goods. 
But, valuable as this instrument is, it has an imperfection 
when applied in the ordinary manner to certain purposes, such, 
for example, as packing cotton, discharging dyes, and expres- 
sing oils. The imperfection consists in the great variation in 
the power necessary to work the press at different periods of the 
operation, in consequence of the variable resistance of the mate- 
rials under pressure at the different states of compression ; which 
not only causes loss of time, but also, when the pumps are worked 
by an invariable power (as they must be when driven by inanimate 
power) it renders the stress on the first mover irregular. 
Several methods had been tried to remedy this inconvenience, 
but none of them succeeded in doing more than diminishing the 
variations in a small degree; but the invention we are [now 
about to describe effects the purpose, and by a contrivance so 
simple, ingenious, and beautiful, that we are assured our me- 
chanical readers will be interested by its description. 
The effect in Bramah’s press is produced by pumping a cer- 
tain quantity of water into the press cylinder at each stroke of 
the pump ; and if, with an invariable power, only one pump be 
employed, the quantity injected at one stroke must not be 
greater than can be forced in when the press is exerting its 
