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    Hardened Ashless Filter Papers

    These wet strengthened hard filter papers are manufactured from refined pulp and linters and have a low ash content of <0.01%.

    Johnson Test Papers offers three grades of hardened ashless quantitative cellulose filter papers. These specially treated grades are available for critical quantitative analytical techniques requiring increased wet-strength and handling capacity.

    These high purity filter papers have a tough, smooth surface free of loose fibres and are ideal for a range of critical filtration procedures such as collecting wet precipitates in pressure filtrations or in Buchner funnels in gravimetric analysis of samples. The smooth surface of the filter allows the recovery of most precipitates without the fibers adhering to them. Due to their high mechanical strength in wet conditions they are particularly suited for applications, where the residue is removed from the filter e.g. with a spatula or a jet of water. Each grade offers a convenient combination of pore size and filtration speed.

    Johnson Test Papers hardened ashless quantitative filter papers are acid-hardened and are generally used because of their high chemical resistance in their moist state to strong acid and alkali with extremely low ash content. They are available in different filter sizes, from small circle formats to large size sheets. We can also make custom-sized filters to meet your specific needs.


    Click on a Grade to find out more...

    Grade 371

    - Slow
    Application :

    Used for difficult and finely grained filtration, barium sulphate, metastannic acids, cuprous oxide, analysis of acid solutions

    Grade 372

    - Medium
    Application :

    Used when the filtration speed is not important, analysis of acid solutions.

    Grade 373

    - Fast
    Application :

    Used for coarse and voluminous precipitates, iron, cobalt and chromium hydroxides as well as bismuth sulphides, analysis of acid solutions

    Available Grades
    Grade Whatman Equivalent Speed Thickness (mm) Pore Size (μM) Weight (g/m²) Filtration Speed (sec*) Burst Strength (kg/cm²)
    Grade: 371 Whatman Equivalent: = No.50 Speed: Slow Thicness (mm): 0.14 Pore size: 2-3 Weight: 84 Filtration speed (sec*): 180 Burst strength (kg/cm²): >0.3
    Grade: 372 Whatman Equivalent: = No.52 Speed: Medium Thicness (mm): 0.15 Pore size: 5-8 Weight: 84 Filtration speed (sec*): 50 Burst strength (kg/cm²): >0.3
    Grade: 373 Whatman Equivalent: = No.54 Speed: Fast Thicness (mm): 0.18 Pore size: 12-15 Weight: 84 Filtration speed (sec*): 10 Burst strength (kg/cm²): >0.3