The supports F F can be made of rather heavy walled glass tubing, about 1 cm. outside diameter.The mirrors are made of a good grade of looking glass, the lower and top edges blackened, and cemented to the ground ends of the glass tubes with Canada balsam, after which the backs are coated with paraffin. Paraffin answers well as a coating for a large number of colorimetric solutions. In case a liquid is to be used which attacks paraffin, a substitute must be employed which is unaffected by the liquid in question. It will be found necessary to replace the mirrors from time to time, as it is not possible to so protect the silvered surfaces as to prevent the gradual eating in from the edges by the various solutions used.The comparison is made by pouring a solution of known strength into one of the cells. The unknown solution made up to a definite volume, is put into the other. The left-hand cell, is then placed at a convenient point, which should be determined by the depth of color of the solution it contains. The right-hand cell is then moved back and forth till, on looking in the end M of the apparatus, Fig. 1, the two mirrors appear to be of the same shade.The strengths of the two colorimetric solutions being inversely proportional to the thickness of the liquids looked through, by substituting in the following equation the amount of the material to be determined may be found.Let R equal the reading of the cell containing the known solution with a concentration 0, and r the reading of the cell containing the unknown solution, which has a concentration c, then
portions of the solution. was treated with indium hydroxide. in white, easily soluble, hygroscopic crystals. ing results : The solution of pure selenic acid thus obtained Indium selenate crystallized out Analysis gave the follow-Theory for Inz(SeO&. xoH20. Per cent. Found. Per cent.
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