The coating is prepared in the following manner:
1.
Mix 5 g Apiezon Type L grease in 200 ml reagent grade Toluene and let stand in a tightly capped bottle for 24 h. The mixture will become cloudy.
2.
After 24 h, stir or shake the mixture well, mix 1 part with 2 parts reagent grade Toluene and place in a tightly capped bottle. This latter solution is used to coat the filters, but must be checked to assure that evaporation does not raise the solution strength above 2:1.