Abstract: An improved apparatus for gas curing foundry cores includes an instrument system for attachment to a source of curing gas such as a gas generator. The system includes a signal generating section for providing a plurality of first signals. These signals represent the instantaneous mass flow rate of gas flowing to the core box. A counter/controller section is coupled to the signal generating section and totalizes the first signals. A valve device is coupled to the counter/controller section, opened to initiate the flow of gas to the core box and closed to terminate the flow of gas. The valve is opened upon receipt of a signal initiating the curing process and closed when the total of the first signals reaches a value representing a predetermined total mass of gas which has flowed to the core box. The improved method includes initiating flow of a gas to a core box containing raw cores to be cured. The gas includes a curing constituent, either in substantially pure form or mixed with a carrier gas.