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4.1.1 Samples of known volume can be obtained from a precise depth.

4.1.2 A quantitative sample is obtained. Nanno- and ultraplankton are not lost from the sampling device.

4.1.3 A sampler of almost any desired volume or construction material can be obtained.

4.1.4 The sampler is light-weight and can be used without auxiliary equipment.

4.1.5 There is a free flow of water through the cylinder of the sampler when it is being lowered.

4.1.6 Samplers can be arranged serially to facilitate sampling at several depths almost simultaneously.

4.1.7 The sampler can be used in most depths of water.

4.2.1 Samples are obtained from only discrete depths; they cannot be obtained from horizontal or vertical strata of water.

4.2.2 The samplers cannot be used satisfactorily in fast-flowing water.

4.3.1 The samplers should be protected from damage, which commonly results in leakage.

4.3.2 Following use, the samplers should be hung open in a horizontal position to allow for thorough drying.

4.3.3 The end stoppers should be inspected periodically for signs of wear or deterioration and replaced as necessary (Fig. 1a, b, c).

FIG. 1 Water-Sampling Bottles (a) Kemmerer (b) Van Dorn (c) Nansen (d) Fjarlie (Illustration by J. W. Steiner and W. G. Hester, U.S. Geological Survey, Doraville, GA)