. Practical methods of organic chemistry . Fig. 36. Fig. 37. Fig. 38. Similar to the Biichner funnel in its construction and action isthe so-called Nutsch filter. This consists of a shallow dish witha perforated bottom, which isfitted to the cover of a tubu-lated cylinder by means of arubber ring, the joint beingair-tight. This apparatus isespecially adapted to the filtra-tion of larger quantities thancan be conveniently treated inthe Biichner funnel (Fig. 39). If the solution to be filteredacts on the filter-paper, filter-cloth may be used in its fine or coarse meshed clothis selected
. Practical methods of organic chemistry . Fig. 36. Fig. 37. Fig. 38. Similar to the Biichner funnel in its construction and action isthe so-called Nutsch filter. This consists of a shallow dish witha perforated bottom, which isfitted to the cover of a tubu-lated cylinder by means of arubber ring, the joint beingair-tight. This apparatus isespecially adapted to the filtra-tion of larger quantities thancan be conveniently treated inthe Biichner funnel (Fig. 39). If the solution to be filteredacts on the filter-paper, filter-cloth may be used in its fine or coarse meshed clothis selected, according to thenature of the precipitate; it ismoistened before the nitration If this is also attacked, nitrocellulose cloth may be used ; it ismade by treating a cloth woven from plant fibres with a mixture of. 54 GENERAL PART nitric and sulphuric acids. Concentrated sulphuric acid may befiltered through it. Such cloth and other substances containingnitrocellulose must always be preserved under water, on accountof their explosiveness. In cases of this kind the precipitate is retained by using glasswool, or better, long fibrous asbestos, with which the bottom of thefunnel, containing in this case a platinum cone, is filled, or it isspread out in thin layers over a filtering plate, or on the surface ofa Buchner funnel. Under these conditions, the suction is appliedgently at the beginning of the filtration ; as soon as a large quantityof the precipitate has accumulated, the suction is increased. Verycoarse-grained precipitates can be filtered without the use of a filterby placing in the point of an ordinary glass funnel a sphere of glass (amarble) ; this is surrounded by glass wool, or asbestos, if Cells. — For the filtration of precipitates, like calciumsulphate, barium sulp
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