These standard ashless grades are high purity filter papers suitable for routine quantitative gravimetric techniques and in the preparation of samples for use in analysis involving instrumental techniques. Ahlstrom 55, 15 µm - Fast Speed. This is a fast filtering grade for gravimetric analysis of coarse particles and gelatinous precipitates (i.e.: aluminum and zirconium hydroxides) in acid and alkali solutions. Ahlstrom 55 is also used in air and foodstuffs analysis and for chloride and phosphorous in cement, coal and coke.