A device for maintaining a constant temperature for chemical analysis performed with slides having at least one layer adapted to absorb a substance to be analyzed. The slides are conveyed upon a lower conveying belt which may have projections or recesses formed therein for receiving the slides. The upper portions of the slides are sealed by a sealing guide belt which has a surface disposed parallel to and adjacent the conveying belt with the slides passing therebetween. A heater may be provided within the conveying belt and the guide member provided within the sealing guide belt which may itself perform a heating function.