A sliding retort including an outer section and complimentary inner section the outer section and the inner section overlap proximate a receiver end and an insert end, wherein the inner section insert fits into an outer section receiver so that an insert wall and a receiver wall overlap to form a gas tight barrier; and a retort cavity formed within the compact sliding retort responsive to the outer section and the inner section being coupled, wherein a first load rod orifice and a second load rod orifice are configured to receive a load train of a uniaxial test rig and a test specimen coupled within the load train, such that the test specimen is surrounded with a gas forming a predetermined non-standard atmosphere within the retort cavity, whereby the load train can move axially with the sliding retort and maintain the non-standard atmosphere.