ON FLOW OF SOLIDS UNDER GREAT PRESSURES. 
137 
ON TRESCA'S REMARKABLE INVESTIGATIONS 
INTO THE FLOW OF SOLIDS UNDER GREAT 
PRESSURES.* 
BY W. P. MARSHALL, M.I.C.E. 
The application of pressure to solid bodies is ordinarily 
looked upon as producing simply consolidation in the body 
under pressure, making it more dense and hard; but this is 
only true within the limits of ordinary pressures, and when 
sufficiently high pressures are applied such bodies become 
plastic and yielding, and with an extremely high pressure 
the harder metals and even steel itself can be squeezed into 
new forms, and made to behave similarly to a lump of clay. 
We are indebted for the knowledge of these facts to the remark¬ 
able investigations of the late M. Tresca, the talented director 
of the “ Conservatoire des Arts et Metiers,” at Paris, who 
made a long series of experiments in many very ingenious 
forms for the investigation of this subject, and carried out 
important practical applications of the results in improvements 
in the mode of making sound iron forgings. 
The first series of these experiments was made upon lead, 
as the softest and most ductile of the metals ; the lead to be 
compressed was placed in a circular metal cylinder, shown in 
Fig. 1, Plate IV., which had a round hole in the centre of the 
bottom, and a circular ram, fitting the cylinder closely, was 
then gradually forced down upon the lead in the cylinder, 
by placing the whole in a hydraulic press, exerting a 
very great pressure uniformly over the upper surface 
of the lead. The lead being rigidly supported by the 
sides and bottom of the cylinder everywhere excepting 
opposite the hole in the bottom, that hole was the only point 
in which it could yield to the pressure; and it was found that 
as the pressure was increased the lead began to bulge out¬ 
wards at the hole, and presently protruded through the hole, 
forming ultimately a continuous cylinder the same diameter as 
the hole, and several times longer than the original mass of 
lead in the cylinder. In fact, the metal was made to floiv 
through the hole by the application of a sufficient amount of 
pressure, forming a solid jet, just as a soft body such as clay 
would flow through the hole under a moderate pressure, or a 
liquid would flow through under the pressure of gravity 
alone. An extreme case that was tried was a set of discs 
* Transactions of tlie Birmingham Natural History and Micro¬ 
scopical Society, June 24th, 1884. 
