Abstract: A device for sampling heats of molten metal includes a mold cavity which has an inlet which may be in the form of a tube projecting outwardly therefrom with the open end of the tube being closed and sealed prior to the sampling step by a metallic cap which will melt in the molten metal heat. The sealed end of the tube is enclosed within a diffusion chamber having an inlet closed with a cap which will be melted or vaporized by the metal heat and which normally retains a quantity of a suitable oxygen-fixing agent such as aluminum or titanium, for example, within the chamber. Molten metal entering the diffusion chamber immediately melts the fixing agent which is quickly dissolved by and thoroughly diffused through the molten metal in the chamber before the metal cap on the end of the tube melts to permit the molten metal with the oxygen-fixing agent diffused therethrough to flow into the sample-forming mold cavity.