Whatman No. 41 is the fastest ashless filter paper, recommended for analytical procedures involving coarse particles or gelatinous precipitates (e.g., iron or aluminum hydroxides). Retention is 20 to 25 µm. Also used in quantitative air pollution analysis as a paper tape for impregnation when determining gaseous compounds at high flow rates. This filter is also available in the Whatman Disposable Filter Funnel. This is a convenient, disposable 47mm filter funnel with a 250mL capacity. The 47mm Grade 41 filter can be easily removed for further analysis or culturing. 100 circles/box.