to create a vapor tight enclosure when closed the residue 52 is placed in a suitable tray or similar receptacle 62 and lid 51 is sealably closed a stream of air is passed into enclosure 50 via line 54 line 54 carries a valve 55 so that the flow can be regulated an outflow stream of air exits enclosure 50 via line 61 for conduction to vent scrubber 34 in practice scrubber 34 presents a small negative pressure such as from 0 psig to about 1 psig so that line 61 pulls a small vacuum on enclosure 50 in this setting line 54 can be merely an aperture and valve 55 can be a damper or the like regulating the flow of air drawn into enclosure 50 by means of the vacuum drawn through line 61 the flow of air through enclosure 50 is a gradual flow that is it is not a high velocity flow that drives or knocks solvent from the residue rather it is a flow having an average velocity of less than about 10 feet sec and preferably less than about 1 feet sec more preferably less than about 1 or 2 feet min which relies on simple evaporation to remove solvent enclosure 50 is equipped with a device for varying its internal temperature this device is shown in fig1 as a stream line 56 which passes a controlled flow of steam through regulation 57 to coil 59.