Whatman No. 42

Of the ashless grades, this is the most retentive. Ideal for filtration of fine crystalline precipitates (less than 2.5 µm). 240 seconds is the initial filtration speed. Loading capacity is normal. Recommended for critical gravimetric analysis. Used extensively for precipitates with tendencies toward colloidal dispersion. Suitable for low suction or gravity filtration. 0.12 mg ash content per 12.5 cm circle. (For cost savings, see Ahlstrom equivalent, 445-800-02 Series)