Ahlstrom's qualitative grades of filter paper are, by definition, recommended for use in analytical methods, which determine or identify particulate constituents of a mixture irrespective of the amount present. Qualitative filter papers are often used in routine separation work that still requires high purity and consistent performance. Ahlstrom offers a complete range of low ash filter papers for general laboratory work that provides you with the correct combination of particle retention, filtration speed, loading capacity and wet-strength. All our qualitative grades consist of greater than 95 percent super refined a-cellulose and linter fibers. This grade has finer particle retention than Ahlstrom 601 but with slightly lower filtration speed. Ahlstrom 642 also has higher absorption than Ahlstrom 601. It is used in general laboratory applications to retain particles above 2 micrometer in size. Ahlstrom 642 is also found in agricultural and environmental laboratories for plant growth trials, soil testing, and air analysis for monitoring specific contaminants and in the filtration of organic and sulfide precipitates. 229 sec/100mls Filtration speed herzberg. 30 mls/min Filtration speed rapidity. Medium loading capacity.