Bridgman seal

A Bridgman seal, named after Percy Williams Bridgman, seals a high pressure volume by the use of a three part mechanism. A viscous material such as rubber, copper or soap stone is set so that it stretches longitudinally against a hard steel ring, followed by a softer steel ring and horizontally against a steel piston. This arrangement ensured that higher pressures created tighter seals.

This seal allowed for pressure increases from 400 MPa to 40,000 MPa. These are typical pressures expected in the Earth's internal structure. For Bridgman a whole universe of possibility had opened. Everything he squeezed did something interesting and unexpected. Water froze into strange phases. Salts changed colour. Conductivities changed unpredictably. A new science world became explorable.