General Cleaning
A new fritted filter should be washed by suction with hot hydrochloric acid and then rinsed with water before it is used. This treatment will remove loose particles of foreign matter such as dust. It is advisable to clean all Pyrex® brand fritted filters as soon as possible after use. This will prolong their life.
Many precipitates can be removed from the filter surface simply by rinsing from the reverse side with water under pressure not exceeding 15 lbs/square inch. Drawing water through the filter from the reverse side with a vacuum pump is also effective. Some precipitates tend to clog the pores of a fritted filter. Treatment here must be by chemical means.
A few suggestions found generally useful follow:
Material Cleaning solution
Fatty materials - Carbon tetrachloride
Organic matter* - Hot concentrated cleaning solution, or hot concentrated sulfuric acid plus a few drops of sodium or potassium nitrite
Albumen - Hot ammonia or hot hydrochloric acid
Glucose - Hot mixed acid: H2SO4 + HNO3
Copper or iron oxides - Hot hydrochloric acid plus potassium chlorate
Mercury residue - Hot nitric acid
Silver chloride - Ammonia or sodium hyposulfite
Viscose - 5 to 10% NaOH, followed by cleaning solution
Aluminous and siliceous residues - 2% hydrofluoric acid (EDIT: Hydroflouric acid is very dangrous, newbees take care)followed by concentrated sulfuric acid; rinse immediately with distilled water followed by a few mL of acetone. Repeat rinsing until all traces of acid are removed.
*Cleaning solution containing bichromate will tend to permanently stain fritted ware. This is undesirable for biochemical or pharmaceutical work, and hence the sulfuric-nitrite solution is suggested.
Operating Pressures
Fritted glassware is designed primarily for vacuum filtration or for gas flow at relatively low pressures. If used for pressure work, the MAXIMUM differential on the disc should not exceed 15 pounds per square inch. Care should be taken when preparing sample solutions to avoid trapping air. If dissolved air is present, the flow rate may be reduced by up to 50%
Thermal Limitations
The resistance to thermal shock of fritted ware is less than that of non-porous Pyrex brand labware. Therefore, articles of fritted ware should not be subjected to excessive temperature changes or to direct flame.
Dry fritted crucibles at room temperature may be placed into a drying oven operating at 150°C (302°F).
Fritted ware may be safely heated in a furnace to 500°C (932°F) without ill effect, provided that the cycle of heating and cooling is gradual.