the invention provides a new method and apparatus for the detection of non - conductive particulates in molten metals , such as aluminum , gallium , zinc and lead , that can be liquified and drawn into a suitable refractory container . the passage into the container is of very small diameter and it forms part of a current path between two electrodes carrying a current of about 1 to 500 amperes . the path is surrounded by liquid metal which forms an effective faraday cage screening the path , enabling the passage of a particulate of about 15 micrometers or larger to produce a voltage pulse between the electrodes of greater than 5 microvolts , which is detectable above the inevitable background noise , which is of about that value . the size of the pulse gives an indication of the particle size and appropriate measurement and sampling electronically of the pulses gives a rapid evaluation of the particle size distribution , giving the operator an opportunity of deciding immediately whether or not further cleansing of the metal is required .