Filtering paper renders valuable service, and it should indeed be more extensively employed for the purification of water, as it far surpasses sand in its power of retention. It is important that the paper itself shall be clean and have no loose particles, for which it should be carefully examined. In time, and owing to the continuous softening, small fibrous particles will become detached from the filter paper, and it should, therefore, be covered on both sides with closely woven muslin, especially on the sides from which the filtrate runs. Holding the paper firmly compressed during the filtration also contributes to its preservation and prevents the separation of loose fibres. Filtering-paper for filtering purposes in the laboratory, for purifying wine, cider, etc., will do excellently, and there are indeed some filters which contain filtering-paper as their principal filter medium. It will also do very well for clarifying water by retaining suspended impurities, but will not act chemically in case such impurities are present. It is natural that the filtering-paper has also frequently to be renewed. For larger establishments, where an immense amount of water has to be purified daily, both mechanically and chemically, it will not do.