Mean hydrostatic pressures up to 50,000 kg/${\mathrm{cm}}^2$ combined with shearing stresses up to the plastic flow point are produced in thin disks confined between hardened steel parts so mounted that they may be subjected to normal pressure and torque simultaneously. Qualitative and quantitative studies are made of the effects of such stresses. Among the qualitative effects it is found that many substances normally stable become unstable and may detonate, and conversely combinations of substances normally inert to each other may be made to combine explosively. Quantitatively, the shearing stress at the plastic flow point may be measured as a function of pressure. The shearing stress at plastic flow may rise to the order of 10 or more times greater at 50,000 kg/${\mathrm{cm}}^2$ than it is normally at atmospheric pressure; this is contrary to the usually accepted results in a narrower range of pressure. If the substance undergoes a polymorphic transition under these conditions of stress, there may be a break in the curve of shearing stress vs. pressure. This gives a very convenient tool for the detection of transitions. 57 elements have been explored in this way, and a number of new polymorphic transitions found.

• Received 3 September 1935

DOI:https://doi.org/10.1103/PhysRev.48.825