through the tube 11 the coating thickness of the coated filament where it enters the exit passage 21 is typically 5 10 times the diameter of the filament for this reason the diameter of the exit passage 21 is correspondingly larger than that of the entrance passage 20 apart from having a larger exit passage 21 the configuration and operation of the exit electrode 16 is identical to that already described with reference to the entrance electrode 14 the coated filament has a variety of uses dependant on the composition of the coating for instance the fabrication of high performance metal matrix composites the use of mercury has several disadvantages due to its toxicity operators of such known filament coating apparatus could come into physical contact with mercury vapour and or liquid mercury droplets should they fail to follow appropriate health and safety guidelines some of the mercury is transferred to the surface of the filament and to the coated filament by the liquid mercury in the reservoirs 23 and any mercury leaking into the tube 11 may become incorporated in the filament coating and or be entrained in the waste gas exiting through the gas outlet 26 thereby necessitating precautions in its disposal traces of mercury on or in the coated filament are a potential hazard to users of the coated filament and could also adversely affect the physical properties of the coating its adherence to the filament and particularly its adherence to the metal in a metal matrix composite attempts have been made to replace the mercury with a variety of low melting point eutectic alloys but these all incur the release of associated toxins and suffer from equivalent disadvantages fig3 4 and 5 use the.