Sentence:  The reactants for the <WSD>gas</WSD> phase experiments were first frozen out in a side arm attached to the manifold and then allowed to distill slowly into the manifold of pre-cooled reaction cells before sealing off . 
Meaning of the word marked with <WSD> tags:  the state of matter distinguished from the solid and liquid states by: relatively low density and viscosity; relatively great expansion and contraction with changes in pressure and temperature; the ability to diffuse readily; and the spontaneous tendency to become distributed uniformly throughout any container