Durand, Loyal, Jr. (ed.) / Transactions of the Wisconsin Academy of Sciences, Arts and Letters
volume XXXI (1938)
James, Harry Raymond; Birge, Edward A.
A laboratory study of the absorption of light by lake waters, pp. -154 PDF (46.6 MB)
James & Birge—La/ce Waters and Light 19 kets at the ends of the tubes and they are held tightly in position by a heavy brass ring, which in turn is held by screws passing through the ring and into the collar at the end of the tube. The rubber gaskets are soaked for a time in hot ceresin wax to coat them, so that water cannot come in contact with the rubber, from which it might become contaminated. It was found necessary to place several gaskets under one of the end-plates, making a spongy mounting, so that the position of the plate could be shifted slightly with the screws to bring it parallel with the other end-plate and perpendicular to the axis of the tube. This arrangement was necessary to prevent the long tube of water from acting as a prism and deviating the beam. In working with distilled water, this end mounting was much modified (p. 29). The short tube, T-2, shown in Figs. 1 and 2, is empty except for the comparison cell mounted at one end; the tube is used only for convenience in holding the cell in position. The comparison cell is made from two plate glass~ discs cut from the same stock as that used in making the end plates for the water tubes; the absorption of light in each of these was found to be the same as in the others. The discs in this cell are separated by a film of water about 0.02 mm. thick. Thus, when light passes through the glass of the comparison cell, it suffers the same losses from reflection and absorption as in passing through those of the long water tube, and the only difference is the absorption due to the longer column of water in the long tube. It was necessary to boil the distilled water used in the comparison cell so that air bubbles would not form within the cell after being assembled. Thermo pile The thermopile is the single junction compensated type designed according to the theory given by Dr. C. H. Cartwright, (1930). The elements are of bismuth and tellurium and the receiver is a piece of silver foil 5 mm. long and 1.50 mm. wide, coated with platinum black. The junctions are mounted in a brass case, with a quartz window, arranged to be evacuated. A high vacuum is maintained by means of cocoanut charcoal cooled by liquid air. The tellurium used for the junctions was first annealed by heating it slightly above the transition temperature between the alpha and beta forms of the crystal (360 degrees)
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