Test apparatus

An apparatus for carrying out chemical reactions simultaneously on a number of samples under identical pressure conditions comprises a plurality of upwardly open pressure vessels 1 mounted on a lower plate 2 and a plurality of vessel closure means 10 mounted on an upper plate 15 such that the plurality of vessel closure means 10 can be applied to the plurality of pressure vessels 1 simultaneously in order to hermetically seal said vessels 1, each vessel closure means 10 having a passage 19 communicating the interior of an associated pressure vessel 1 with a common manifold 22. A plurality of retaining posts 6 extend upwardly from the lower plate 2 and pass through apertures 27 in the upper plate 15. A locking ring 34 has a plurality of keyhole apertures therein having a wider portion allowing each retaining post 6 to pass through the locking ring 34 when the locking ring 34 is in an unlocked position and a narrower portion that engages a peripheral groove 7 adjacent the upper end of each retaining post 6 when the locking ring 34 is in a locked position.