Abstract: A monitoring technique is disclosed for determining when the end point has been achieved in the evaporation of the constituents from an alloy such as a tin lead alloy. An optical pyrometer or other temperature sensing device, is focused on a crucible in which both tin and lead is being heated. Since, under vacuum conditions, lead evaporates at a lower boiling point than does tin, the temperature of the crucible will achieve a first temperature plateau while the lead is being evaporated. After the lead has been depleted in the crucible, the temperature of the crucible will rise to a higher temperature plateau at which the tin will evaporate. The output of the optical pyrometer is digitized and is applied to a microcomputer which periodically samples the temperature of the crucible.