Abstract: A device for measuring metal purity, comprising a receptacle for holding a sample of molten metal, the receptacle being made, at least internally, from an insulating refractory material and having a bottom wall provided with a hole containing a filter element. The bottom wall is substantially impermeable to air except at the hold. An enclosed collection vessel is positioned below the receptacle for collecting molten metal which passes through the filter element from the receptacle, the collection vessel having an opening permitting extraction of gas from within the vessel to enable a vacuum to be generated within the vessel during use of the device. A leak-tight seal is established between the receptacle for molten metal and the collection vessel to permit vacuum generated in the collection vessel to draw molten metal into the collection vessel from the receptacle through the filter.