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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. [1]-154 PDF (46.6 MB)


Page 19

 James & Birgeā€”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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