Abstract: An apparatus for acetone clearing of cellulose or nitrate membrane filters includes an elongated electric heater element with tubing for transporting acetone coiled around said heater element and in contact therewith. Liquid acetone is introduced to said tubing wherein it is heated by said heater element and acetone vapor is discharged from said tubing. The temperature of the coiled tubing is thermostatically controlled. Acetone vapor is removed from said tubing and passed over a glass slide having an exposed filter containing particulars, such as asbestos fibers. The vapors clear the filter to render it translucent for examination in optical microscopy.