. Fresh-water biology. Freshwater biology. 82 FRESH-WATER BIOLOGY tacea. Smaller organisms escape in variable quantity and the smallest are not caught at all. When the pump is used a known volume of water is drawn from a known source and all of this is filtered, so that the source of error arising from a varying and uncertain net coefficient is ehminated. The leakage error remains uncorrected so long as a net is used to separate the plankton from the water. The plankton obtained by nets whether directly or by aid of the pump may be treated quantitatively by the following methods: (a) The volum
. Fresh-water biology. Freshwater biology. 82 FRESH-WATER BIOLOGY tacea. Smaller organisms escape in variable quantity and the smallest are not caught at all. When the pump is used a known volume of water is drawn from a known source and all of this is filtered, so that the source of error arising from a varying and uncertain net coefficient is ehminated. The leakage error remains uncorrected so long as a net is used to separate the plankton from the water. The plankton obtained by nets whether directly or by aid of the pump may be treated quantitatively by the following methods: (a) The volume may be obtained by allowing the alcohoUc material to stand for 24 hours in gradu- ated tubes (carbon tubes of the chemist) until it has settled, when the volume may be read off. There is thus obtained in cubic centimeters the volume of one catch and from this may be calculated the vol- ume per cubic meter or under one square meter of the original water. (&) The approximate weight may be obtained by. Fig, Piston pipette n- designed by Hen- sen. A, glass vessel wliich contains di- luted plankton. B, strong glass tube. In- side the tube is a pis- ton made of alternate layers of metal i and , , cork h. held together drying the Sample on filter paper and weighing it. by screws: wi, spool- ./ o ir ± a *-> kj shaped metal piece at- tached to the piston. gksstublaccurate'y^ of the filter paper, and from this the number of spindifand'thlglis grams of plaukton per cubic meter of water or under «ube is of known vol- ^ ^ , iij_j ume; /, piston-rod One square meter of surface may be calculated. with handle; K, cover of vessel. (From Ap- steia, after Hensen.) The net weight is obtained by deducting the weight (c) Chemical analyses may be made of the dried material and from these the quantities of the various constituents: ash, organic material, silica, etc., may be calculated per cubic meter of water or per square meter of surface. {d) The organisms may he counted in the Sedgwick-
Size: 1032px × 2421px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectfreshwa, bookyear1918
